FILE: <bc-34.htm> Pooled References GENERAL INDEX [Navigate to MAIN MENU ]
BIOLOGICAL CONTROL IN FORESTS
(Contacts)
----CLICK on desired underlined
categories [to search for Subject Matter,
depress Ctrl/F ]:
|
|
|
Overview Some unique
ecological attributes are present in relatively complex forest environments
including a diversity of species, ages, intraspecific genetic composition,
spacing and stocking levels (Dahlsten & Mills 1999). Intensively managed
forests, even-aged stands, plantations of single and mixed species and seed
orchards resemble agriculture, but even these usually exist in a variety of
different conditions. It is important to look at some of these ecological
attributes in detail as the opportunities for biological control vary
depending on the environment and species involved. In addition
to timber production, forests serve as wildlife refuges, recreation,
watershed and grazing areas. Where in agriculture the goal of management is
to harvest a commodity one or more times a year, in forestry pest management
is further complicated by multiple goals and competing interests, including
sportsmen, environmentalists, bird watchers, hikers, cattlemen, woodcutters
and the Army Corps of Engineers. Forests tend to be extremely large
continuous areas with gradual boundaries, thus quantitative evaluation of
controls becomes very difficult and expensive. Control strategy in forests is
also affected by the length of time to harvest, which may be 20 to 30 years
or more in warm temperate areas to 50 to 100 years in colder areas. Compared
to agricultural ecosystems, forests are much more complex ecologically.
Forests vary from single species plantations to multistoried stands and plant
diversity is greater than in an agricultural field even in the simplest
forest stand. Researchers must often deal with stands trees exceeding 70 m in
height, a mixture of age and size classes, a mixture of tree species,
numerous canopy levels including herbaceous plants and different stocking
levels or spacing.. In view of the ecological attributes of
forest ecosystems, the choice and evaluation of biological control tactics
may vary. The influence on the classical approach to biological control has
been analyzed by Pschorn-Walcher (1977). The vast, diverse, relatively less
disturbed, long-lived and highly stable in space and time ecosystem confers
both advantages and disadvantages for biological control. Diversity confers
an advantage for foreign exploration as a large complex of natural enemies is
available from which to choose (Pschorn-Walcher 1977). However, this could
also make it more difficult for colonization of new species of natural
enemies. There would be expected to be a greater chance for the introduced
natural enemies to be in competition with related native natural enemies
since there is a high probability that relatives would be present in the rich
forest fauna. The vastness and diversity create sampling and evaluation
problems but less disturbance allows long term evaluations to be more exact. The collector of natural enemies has an
advantage in the relatively uniform forested regions because only minor
regional differences are usually exhibited (Pschorn-Walcher 1977). However,
any widely distributed pest or a pest introduced in a number of locations in
a large forest region would make any colonization program long in term.
Pschorn-Walcher (1977) maintains that the great differences between forest
and agroecosystems dictate a different approach to biological control in
forestry from agriculture. The approach to biological control in agriculture,
where there is much less predictability because of continuous disturbance,
can be faster using trial and error releases until the best natural enemy is
found. With forest insects preintroduction studies are desirable in order to
understand the interrelationships of the various natural enemies and finally
to select the most likely natural enemies for success. Natural enemy
complexes of forest insects can be chosen with a higher degree of
predictability for successful introductions and therefore preintroduction
studies are justified (Pschorn-Walcher 1977). Studying the parasitoid complex
in detail provides information on those species that might be good
colonizers, those that would operate at low or high population levels, those
that were monophagous or polyphagous, those attacking early or late life
stages, those that could adapt to some degree of inbreeding and could then
withstand initial low number colonization, or prolonged laboratory rearing,
and those that were cleptoparasitoids and then could be selected out . Strategies
in Forest Biological Control A variety of approaches in biological control including importation,
augmentation and conservation have been used. The major efforts have been in
North America (Canada and the United States) and the classical approach of
importation has been the most commonly used. Undoubtedly this is because the
highest proportion of introduced forest pests occur in North America
(Pschorn-Walcher 1977). The majority of insects are lepidopteran and
hymenopteran defoliators (sawflies). Since these insects are relatively large
hosts it may explain why 9 of the 15 tachinid flies established in biological
control attempts were used in forests. It seems that Lepidoptera and
Hymenoptera are more commonly pests in the less disturbed, contiguous forest
regions. Also forests are not as intensively managed as agricultural
ecosystems and it may explain why Homoptera, which are common subjects for
biological control in agriculture, are not as common as forest pests. Importation of Natural
Enemies For Introduced Pests.--The most common approach in forestry has been the
importation of natural enemies against introduced pests (Turnock et al. 1976,
Pschorn-Walcher 1977). This has usually involved colonizing and establishing
a relatively small number of natural enemies for control of an exotic pest
through direct inoculative releases of newly imported parasitoids. With a few
exceptions, parasitoids have been the preferred natural enemies introduced in
forestry. Dahlsten & Mills (1999) gave some estimates of the numbers of
importations of parasitoids and predators and their success of establishment
and control. The data show that 78% of importations involved parasitoids
(Hymenoptera or Tachinidae). Only homopteran pests have attracted substantial
importations of predators and while the overall rates of establishment of
these two groups of natural enemies are equal, the parasitoids have on
average been more than twice as successful in achieving some degree of
control of the target forest pests. About 40 species predators were introduced
against the balsam woolly aphid, Adelges
piceae (Tatz) in an
unsuccessful colonization program (Clark et al. 1971), there being no known
parasitoids of this species. Attempts to introduce predators against bark
beetles have been made on several occasions. Hopkins tried to introduce the
clerid, Thanasimus formicarius (L.) from Germany
to West Virginia for control of the southern pine beetle, Dendroctonus frontalis Zimm. in 1892-93.
Although a complete failure, it was the first attempt to import a natural
enemy of a forest insect into the United States (Dowden 1962). Other
unsuccessful attempts have been made using Rhizophagus spp. from Britain both in Quebec, Canada in
1933-34 with one species against the Eastern spruce beetle, D. obesus (Menn.) and in New Zealand in 1933 with three
species against the European bark beetle, Hylastes
ater (Payk) (Clausen 1978).
Success was reported in the Soviet Union with Rhizophagus grandis
Gyll. against the European spruce beetle, D.
micans Kugelann (Kobakhidze
1965, Grégoire et al. 1987). Both predator and host are native and this is a
good example of augmentation through periodic inoculation. There are also
recent projects in Britain and France with R. grandis
against D. micans (Evans & King 1987,
Grégoire et al. 1987). Several species of carabid beetles have been imported
for control of the gypsy moth, Lymantria
dispar (L.), with one
species in particular, Calosoma
sycophanta (L.) becoming
well established (Clausen 1978). Red wood ants were imported in North America
on a few occasions (Finnegan & Smirnoff 1981). Formica lugubris
Zett. was imported from Italy in 1971 and 1973 for forests in Quebec
(Finnegan 1975), and Formica
obscuripes Forel was moved
from Manitoba to Quebec in Canada in 1971 and 1972 (Finnegan 1977). The 15
species in the Formica rufa L. complex in North
America are not well known but F.
obscuripes appeared to have
potential and did not occur in the east (Finnegan 1977). The effectiveness of
these introductions against defoliators such as the Swaine jack pine sawfly
and the spruce budworm is unknown as yet, but the ant populations are still
encouraged so that eventually they will be well established in a wide area.
These ants have been observed feeding on spruce budworm and other forest
insects (McNeil et al. 1978). One species of vertebrate, the masked shrew,
Sorex cinereus Kerr, was colonized in Newfoundland for control
of the larch sawfly, Pristiphora
erichsonii (Hartig). In a
rather unique situation there were no insectivores and few small fossorial
animals on the island. These shrews were transported from northern New
Brunswick, Canada in 1958 and subsequently released. Shrews also feed on
other insects and it is believed that the importation was successful even
though there was some public opposition to the operation (Turnock &
Muldrew 1971). Classical biological control using pathogens
has not been common in forestry. However, two exceptions are the accidental
introduction of a nuclear polyhedrosis virus of the spruce sawfly, Gilpinia hercyniae (Htg.) into eastern Canada (McGugan & Coppel
1962). One nematode, Deladenus
siricidicola Bedding was
imported for control of the woodwasp, Sirex
noctilio F. in Australia
(Bedding & Akhurst 1974). Dahlsten & Mills (1999) noted four cases
where mass rearing and release programs were performed in the biological control
of forest insects: (1) propagation of 882 million Dahlbominus fuscipennis
(Zett.) at Belleville, Canada for Gilpinia
hercyniae control (McGugan
& Coppel 1962); (2) release of 200 million D. fuscipennis
by the Maine Forest Service in the United States against G. hercyniae
(Clausen 1978); (3) mass rearing and release of several parasitoids of the
gypsy moth, Lymantria dispar, in the eastern United
States (Leonard 1974); and (40 the use of a nematode, Deladenus siricidicola
against Sirex noctilio in Australia (Bedding
& Akhurst 1974). Importation of Natural
Enemies For Native Pests.--As mentioned earlier in other sections, exotic natural
enemies may be used effectively against native organisms, even though the
procedure is sometimes controversial. This approach was evaluated by Hokkanen
& Pimentel (1984) who concluded that it ought to be the preferred
approach in biological control. It stems from the idea that through genetic
feedback mechanisms host-parasitoid systems evolve toward homeostasis and
because of this coevolved equilibrium parasitoids would be limited in their
effectiveness as biological control agents (Pimentel 1961, 1963). Generalists
would probably be preferable to specialists in the selection of candidate agents.
This approach must be done with extreme caution because the Pimentel genetic
feedback concept is not wholly acceptable (Huffaker et al. 1971) as it is
believed that natural enemies may become better adapted through time in controlling their hosts. To
support this are examples of long standing and effective introduced natural
enemies such as Rodolia cardinalis and Cryptochetum for control of
cottony cushion scale and many others. Nevertheless, the Hokkanen & Pimentel
(1984) analysis concluded that success in biological control was about 75%
higher for the new associations. These conclusions were disputed by Goeden
& Kok (1986) using biological control examples. They explain that the
data used included cacti, which are not representative of target weeds, and
that there were inaccuracies with some other examples. Dahlsten &
Whitmore (1987) analyzing the 286 examples of successful biological control
used by Hokkanen & Pimentel (1984) showed that there was a significant
advantage for old associations in terms of complete versus intermediate
versus partial success. The use of new associations as the preferred method
for biological control is also contradicted by the analyses of Hall &
Ehler (1979) and Hall et al. (1980), who found that the establishment rate of
natural enemies was significantly higher for introduced pests, the complete
success of importations against introduced pests was higher but not
statistically significant and the general rate of success for introduced
pests higher than for native pests. There appear to be some other
misinterpretations in the data of Hokkanen & Pimentel (1984) who used the
reference by Clausen (1978) for much of their information. These include the
case of the elm leaf beetle, Xanthogaleruca
luteola (Müller) and some
native Neodiprion sawflies
that were controlled by natural enemies in new associations (see Clausen
1956, McGugan & Coppel 1962, DeBach 1964b, Bird 1971, McLeod &
Smirnoff 1971, Cunningham & DeGroot 1981, Finnegan & Smirnoff 1981,
Laing & Hamai 1976, Clair et al. 1987). It is encouraging that there are examples of
successful introductions of natural enemies for control of both exotic and
native pests. Each approach has merit depending on the ecological
circumstances. They state that the sawfly examples of efforts against native
species are good examples of what can be done. Also the extremely successful
project using a parasitoid from a host in a different genus in North America
against a native geometric moth, Oxydia
trychiata (Guenée), Colombia
is a good case. Biological control efforts against native species through the
importation of exotic natural enemies or by periodic inoculation of native
natural enemies have merit according to Carl (1982). Several ongoing (1996)
examples of careful evaluations for Canada are the Douglas-fir tussock moth, Orgyia pseudotsugata (McDunn) (Mills & Schoenberg 1985), the
spruce budworm, Choristoneura
fumiferana (Clemens) (Mills
1983a) and bark beetles (Mills 1983b, Moeck & Safranyik 1984). Augmentation of Natural
Enemies.--As discussed in
an earlier section, the effects of natural enemies can be enhanced by various
manipulations of the organisms themselves or by alteration of their
environment, such approaches being extremely promising for native pests.
Although augmentation and conservation can be distinguished theoretically, it
is difficult to distinguish them in practice (Rabb et al. 1976). The two
tactics were defined by DeBach (1964c) as to manipulation of natural enemies
themselves (augmentation) or their habitat (conservation). Neither approach
has been used extensively in forestry, most literature being from agriculture
(DeBach & Hagen 1964, van den Bosch & Telford 1964, Rabb et al. 1976,
Stern et al. 1976, Ridgway et al. 1977). Augmentation is either by periodic
colonization or inoculation, development of adapted strains by artificial
selection or inundation (DeBach & Hagen 1964). The tactic may involve
either entomopathogens, parasitoids or predators. Attempts have been made with inoculation of
several parasitoids against forest pests in Europe and South America (Turnock
et al. 1976). Inoculations were made of Rhizophagus
against D. micans in Russia, France and
Britain and of the nematode Deladenus
against S. notilio in Australia. Red wood
ants (Formica spp.) have
been moved and relocated in Europe where they are considered to be effective
predators on a number of forest pests. Otto (1967) reviewed a number of the
programs and concluded that good results were obtained primarily in pin
forests against dipterous and lepidopterous larvae. Ants are less effective
against sawflies and ineffective against beetles. Effective protection of
coniferous forests using ants has been achieved against five lepidopterans
and three sawfly pests in Germany, Switzerland, Italy, Russia, Poland and
Czechoslovakia (Otto 1967, Turnock et al. 1976). Three to eight species in
the Formica rufa complex in Europe are
considered to be good biological control agents, with identified species
being F. polyctena Forst, F. lugubris, and F.
aquilonia Yarrow. Some examples of parasitoid inundation
include Trichogramma minutum Riley against the
brown-tail moth, Euproctis chrysorrhea L. in North America
(DeBach 1964c, Howard & Fiske 1911); Trichogramma
spp. for control of various forest defoliators in Germany and Russia, and Telenomus verticillatus Kieff. against the lasiocampid, Dendrolimus pini (L.) in the Soviet Union
(DeBach 1964c). In China inundative releases of Trichogramma spp. are made routinely against various
forest defoliators, which is facilitated by a large and economic labor force
(McFadden et al. 1981). Diprion pini (L.)
has been successfully controlled in Spain by the collection of sawfly cocoons
which were then either placed directly in special emergence cages or exposed
to Dahlbominus fuscipennis in the laboratory
before return to the field. Parasitoid emergence from these cages contributed
about 3 million additional D.
fuscipennis and
ichneumonids, Exenterus oriolus Htg to the forests,
producing about 65% parasitism (DeBach 1964c, Ceballos & Zarko 1952). Various pheromones and kairomones have been
identified for hosts and natural enemies that are considered for
implementation in natural enemy release programs to enhance their performance
(Haynes & Birch 1985, Borden 1982, 1985, Vinson 1984). Mills (1983b)
suggested the use of Dendroctonus
aggregation pheromones as a way of selecting useful European bark beetle egg
predators for introduction into Canada. Miller et al. (1987) have shown Thanasimus
undulatus Say to exhibit
cross-attraction in field tests to other bark beetle pheromones and Rhizophagus grandis to be attracted to the
frass of three North American Dendroctonus
species in the laboratory. Moeck & Safranik (1984) concluded that
inundative releases of native clerid beetles against low levels of D. ponderosae offered a good potential. Bird encouragement programs have been used extensively in Europe by
providing nesting boxes in forests for cavity nesting spots (Bruns 1960). In
California, Dahlsten & Copper (1979) demonstrated that populations of the
mountain chickadee can be
increased two to three fold with nesting boxes. It is speculated that bires
operate in an inverse density-dependent manner and their importance would be
in preventing outbreaks of forest pests rather than in suppressing them. Since 1980 entomopathogens have begun to
play a dominant role in forest biological control. The principal
entomopathogens used are the bacterium Bacillus
thuringiensis Berl., and
baculoviruses. These agents have been tested against a wide variety of forest
defoliators in the form of inundative treatments and have the advantage of
reduced impact on other groups of natural enemies and non target organisms.
Morris et al. (1986) point out that microbial insecticides are likely to
receive as wide an application in forestry as in agriculture for several
reasons. Forest protection is of much greater concern to the general public
due to the more extensive areas covered by forest pests. Forest pest problems
also tend to involve only single target species rather than a complex of
pests, which requires the development of only a single microbial product. The
forest crop is also better able to withstand the slower action of microbial
treatments in comparison with agricultural crops. The spruce budworm, Choristoneura fumiferana in North America and
the gypsy moth both in Europe and North America have been the main targets of
extensive development of Bacillus
thuringiensis as a means of
inundative biological control. More consistent success has been attained
against the spruce budworm and guidelines have been formulated (Morris et al.
1984). Baculoviruses, which include the nuclear
polyhedrosis viruses (NPV) and granulosis viruses (GV), have been widely
tested in field trials against forest insects (Cunningham 1982). They show a
marked degree of specificity for their phytophagous hosts and have no impact
on non-target organisms. Natural epizootics of NPV are often responsible for
the termination of outbreaks of major forest insect pests, particularly among
the Diprionidae and Lymantriidae. The diprionid sawflies provide some of the
most striking examples of the use of NPVs in biological control (Cunningham
& Entwistle 1981). The virulence of the diprionid NPVs is appreciably
greater than that of other host groups (Entwistle 1983) and the gregarious
habit of the diprionid larvae promotes the spread of virus through the larval
population. Virus production cannot be achieved on
artificial media and for sawflies, in contrast to Lepidoptera which can be
reared on artificial diets, foliage fed host larvae are required for mass
production of the virus. Host larvae must either be collected from the field
for infection in the laboratory (Rollinson et al. 1970) or a heavily infested
plantation may be sprayed with virus and the infected larvae harvested as
they die (Cunningham & DeGroot 1981). The periodic inundation of the
virus can be carried out either by distribution of host cocoons containing
infected eonymphs in forest stands or by more conventional aerial or ground
spraying machinery. The former methods has potential for Neodiprion swainei
(Smirnoff 1962) which has an NPV that spreads rapidly from epicenters, while
the latter has been widely used for N.
lecontei and N. sertifer (Geoff.) (Cunningham & Entwistle 1981). The
NPV of N. sertifer has been successfully
used in 12 countries and is the most operationally used of the sawfly NPVs.
One factor that contributes to this success is the more synchronous hatching
of the larvae of N. sertifer, as a result of
overwintering as eggs rather than as eonymphs, which facilitates the timing
of spraying to infect the younger more susceptible larval instars. Conservation of Natural
Enemies.--Conservation of natural enemies should be considered a part
of all silvicultural systems and treatments. In addition there are measures
that can be taken directly to conserve natural enemies. However, studies of existent predators are
few (see Legner & Moore 1977 ). There has been much more done in agriculture to conserve
natural enemies (van den Bosch & Telford 1964), including strip
harvesting and habitat diversification (Stern et al. 1976). Pesticide
disturbances should be avoided as much as possible, which includes the forest
floor where Syme (1977) has shown that a parasitoid of the European pine
shoot moth, Rhyacionia buoliana (Schiff.) requires the
flowers of small herbaceous plants for nourishment. The judicious use of
chemical insecticides is important for conserving natural enemies. There are
undoubtedly many naturally occurring biological controls in forests where
often the importance of a natural enemy is not known until their effect on
the host is disrupted (Hagen et al. 1971). Secondary outbreaks have been
known in forestry, but an extensive outbreak of the spruce spider mite, Oligonychus ununguis (Jacobi) following the
application of DDT for western budworm control in Montana and Idaho has been
documented (Johnson 1958). Outbreaks of the pine needle scale, Chionaspis pinifoliae (Fitch) occurred in California on Jeffrey and
lodgepole pines near Lake Tahoe when an area was fogged with Malathion to
control adult mosquitoes (Luck & Dahlsten 1975). The importance of
natural enemies was shown in this study as the collapse of the scale
population after spraying was halted, occurred over a three-year period and
was shown to be due to a small complex of predators and parasitoids. Other
insecticide-induced outbreaks have been reported for the target insects. The
elimination of parasitoids and virus diseases of the European spruce sawfly, Gilpinia hercyniae, after three years of spraying with DDT in New
Brunswick, Canada, resulted in an outbreak of the sawfly (Neilson et al.
1971). In Texas an increase in an infestation of southern pine beetle, Dendroctonus frontalis, was attributed to
the deleterious effects of chemical insecticides on the natural enemies
(Williamson & Vité 1971). Swezey & Dahlsten (1983) have documented
the effects of lindane on the emergence of natural enemies of the western
pine beetle, D. brevicornis (LeConte). The physical environment in forests may be
changed to favor natural enemies. Parasitoids and predators can be benefitted
by encouraging specific plants for food, shelter and protection from their
natural enemies (Bucklner 1971, Sailer 1971). The effectiveness of natural
enemies in Poland in 1958 was increased by applying fertilizers, planting
deciduous trees and shrubs and providing nectar plants (Burzynski 1970,
Koehler 1970). The presence of wild carrot, Daucus carota
L., in pine plantations in Canada increases control of the European pine
shoot moth, Rhyacionia buoliana (Syme 1981). Longevity
and fecundity of the most effective introduced parasitoid, Orgilus obscurator (Nees), was increased due to its feeding on the
nectar of several flowers (Syme 1977). In efforts to conserve natural enemies of
bark beetles, Bedard (1933) recommended examination of infested trees for
high degrees of parasitism prior to control in order to conserve parasitoids.
The disruption of old infestations of mountain pine beetle in lodgepole pine
should be avoided since the braconid Coeloides
rufovariegatus (Prov.) is
very abundant in old infestations (DeLeon 1935). Wind thrown western white
pines should not be disturbed because of the high populations of mountain
pine beetle parasitoids (Bedard 1933). Because the parasitoid Coeloides vancouverensis (D.T) is more abundant in small diameter
Douglas fir infested with the beetle D.
pseudotsugae, such trees
ought to be left in place (Ryan & Rudinsky 1962). Clerid predators of the
western pine beetle eventually move to the lower portions of the bole of
infested trees and thus the lower sections of trees should not be treated
with insecticide during control projects (Berryman 1967). Clerids associated
with the southern pine beetle emerged later than the bark beetles and it was
urged that infested trees not be removed until after clerid emergence (Moore
1972). Biological
Control Organizations in Forestry There are various world organizations devoted to biological
control of forest pests. They indicate that activity has been most prevalent
in temperate and Mediterranean regions, but that there are no organizations
devoted solely to the biological control of forest insects. References
pertaining to organization are Clausen (1956), Beirne (1973), Greathead
(1980), Taylor (1981), Embree & Pendrel (1986), Detailed
Examples of Biological Control of Forest Pests Dahlsten & Mills (1999) provide detailed case histories of
biological control projects in forest environments; the following being for
the most part from their account: LARCH CASE BEARER, Coleophora laricella
Hübner--Coleophoridae The larch casebearer is native to central Europe
and is relatively innocuous in the alpine area on its normal host, Larix decidua Mill. (Jagsch 1973). A fairly rich complex of
parasitoids is thought to maintain the casebearer at lower densities in its
endemic region (Ryan et al. 1987). It is a defoliator of Larix species and becomes a pest in Europe and Asia
wherever larch is planted. This insect was probably introduced on nursery
stock into North America from Europe and was first found at Northampton,
Massachusetts in 1896 and in Canada at Ottawa in 1905 (Otvos & Quednau
1981). They spread rapidly on tamarack, Larix
laricina (Du Roi) K. Koch,
in eastern Canada so that by 1947 it was in Newfoundland, the Maritimes, and
Ontario and in the United States, Maine, Michigan and Wisconsin (McGugan
& Coppel 1962). It is currently widely distributed in the eastern United
States and Canada. In 1957 the casebearer was discovered on western larch, Larix occidentalis Nutt, in Idaho (Denton 1958) and in 1966 in
British Columbia (Moinar et al. 1967). It is now widely distributed over the
range of western larch including British Columbia, Montana, Idaho, Washington
and Oregon (Clausen 1978). The casebearer has one generation per year.
The adults begin appearing in late May and lay eggs on either side of the
needles. The larvae hatch and burrow directly down into the needles. In the
late summer the larvae emerge from the mined needles and form overwintering
cases. They feed for a while and then move to branches and twigs to pass the
winter. In the early spring the larvae with their cases move and begin
feeding on the young buds and foliage. Pupation occurs within the enlarge
case, which is commonly attached to a branch on a leaf whorl. The larval
feeding, when extensive, causes a loss of growth that is its greatest impact
on larch (Ryan et al. 1987). The biological control program had its
beginning in 1928 in western Canada with a request to the Farnham House
Laboratory of CIBC for information on the parasitoid complex of the
casebearer in Europe (McGugan & Coppel 1962). Importation and field
releases of 5 species of parasitoids occurred in eastern Canada between 1931
and 1939 as follows: 1,037 Agathis
pumila (Ratz.)--Braconidae,
29,664 Chrysocharis laricinellae
(Ratz.)--Eulophidae, 506 Cirrospilus
pictus (Nees)--Eulophidae,
3,283 Dicladocerus westwoodii Steph.--Eulophidae,
and 97 Diadegma laricinellum
(Strobl)--Ichneumonidae (Clausen 1978). All species were subsequently
recovered at release sites in Ontario but only two became well established
and spread rapidly, A. pumila and C. laricinellae.
Between 1942 and 1947 large-scale redistribution releases were made at a
number of sites in eastern Canada. The parasitoids were obtained at
established colony sites at Millbridge, Ontario (Clausen 1978). By 1948
populations of the casebearer were low on the original release sites. The
parasitoids followed the spread of the casebearer to the west assisted by
occasional releases (Ryan et al. 1987). This can be cited as an example of a
successful biological control program (Webb & Quednau 1971). A separate, extensive parasitoid importation
program was also conducted between 1932 and 1936 in the eastern United States
in New England and New York (Clausen 1978). Four of the same parasitoids as
released in Canada were used in the U.S. (Clausen 1978) as follows: 8,141 A. pumila, 24,671 C.
laricinellae, 231 D. westwoodii, and 3,580 D.
laricinellum (Strobl).
Although there is little information to go on, the results were apparently
the same in the eastern United States with the establishment of A. pumila and C.
laricinellae followed by
high parasitization rates particularly by A.
pumila (Dowden 1962).
Releases of the two established parasitoids were also made in 1937, 1950 and
1952 in Michigan and Wisconsin. In the western United States, the first
releases of A. pumila were made in 1960 with
2,360 adult parasitoids that were collected in Rhode Island (Clausen 1978).
These were released at 5 locations in Idaho. Recoveries were made at 3 sites
in 1962. Between 1964 and 1969 field rearing of A. pumila
in whole tree cloth cages permitted the release of this parasitoid at 400
sites in Idaho, Montana, Washington and British Columbia (Ryan et al. 1987).
The parasitoid became established and built up at some sites but at other
sites it either didn't become established or it didn't build up. In addition,
significant defoliation still occurred throughout much of the area by 1970
and the program was rated as a failure (Turnock et al. 1976, Ryan et al.
1987). Between 1971 and 1983 a new strategy was
used as C. laricinellae and five other
species of parasitoids from Europe and Japan were released over a period of
several years. C. laricinellae became widely
established but the other species don't appear to be very important for
control of the casebearer though isolated recoveries have been made (Ryan et
al. 1987). In an effort to properly evaluate the effect of the parasitoids,
the larch casebearer was sampled at sites in Oregon where the casebearer had
recently invaded. The populations were followed to the point of severe
defoliation from 1972 to 1978 and then parasitoids were released between 1979
and 1985 (Ryan 1983, 1986; Ryan et al. 1987). The first parasitoid to be
released was C. laricinellae followed by A. pumila. Parasitoids increased and the casebearer steadily
declined and this trend has continued in all plots through 1987 (R. B. Ryan,
personal communication). Although the prospects are good for a complete
success, Ryan et al. (1987) feel it is too soon to make the claim. In British Columbia the larch casebearer
biological control program was reviewed in 1974 due to the successes in
eastern Canada (Otvos & Quednau 1981). Four parasitoids have been
released: A. pumila, C. larcinellae,
Diadegma laricinellum, and Dicladocerus japonicus Yshm. The story is
much the same as with the other release programs--A. pumila
and C. laricinellae have become well established and the other
two have not been recovered. It is too early to evaluate the effects of the
two parasitoids but C. laricinellae is fairly common
in British Columbia and may be responsible for the reduction of larch
casebearer and less tree mortality (Otvos & Quednau 1981). The larch casebearer is a successful
biological control program in eastern Canada and may shortly be successful in
the northwestern United States. It is an example of a classic introduction
program with the subsequent redistribution of the parasitoids from areas of
establishment to new areas. It is interesting because the two parasitoids
complement one another in their action against the casebearer. Agathis is extrinsically
superior at low host densities and Chrysocharis
is effective at high host densities. Quednau (1970) hypothesized that Agathis can only give partial
control on its own and that success is only possible through cooperative
interaction with Chrysocharis.
Ryan (1985) hypothesizes that Agathis
may not be detected in successive samples since parasitized larvae commonly
descend to understory vegetation. Samples could be biased toward Chrysocharis due to the absence
of Agathis in the foliate
that is sampled. There has been no success in establishing other parasitoid
species. This program also is an example of one where there was a rigorous
attempt to evaluate efficacy of the parasitoids (Ryan 1986, Ryan et al.
1987). WINTER MOTH, Operophtera brumata
(L.)--Geometridae This polyphagous defoliator of hardwoods is
native to most of Europe and parts of Asia, where it is particularly frequent
on fruit trees and oak. It was first recognized as an accidental introduction
on the south shore of Nova Scotia in 1949 and eventually extended its range
to the whole of this region together with small isolated parts of New
Brunswick and Price Edward Island by 1958. In the first few years after its appearance
in Nova Scotia, damage was evident in apple orchards, shade trees and oak
forests. However, at this time hardwoods were not commercially exploited in
the Province and so the winter moth was not considered a serious pest (Embree
1971). Consequently it was possible to initiate a biological control program
rather than a program of insecticide eradication. The general research policy
in the early 1950's was directed towards population dynamics of forest insect
populations and thus the biological control program was initiated in 1954
with a view to population studies of the host and introduced parasitoids. Prior to the introduction of parasitoids
from Europe, the winter moth fluctuated erratically at high population
densities. These fluctuations resulted from the coincidence of hatching of
the overwintering eggs and bud burst in early spring (Embree 1965). This same
key mortality factor was also found to be responsible for changes in
population levels of winter moth in Britain (Varley & Gradwell 1968). Three tachinid and three ichneumonid
parasitoids were obtained in sufficient quantity for introduction into Nova
Scotia from Europe. The parasitoids were collected and shipped to Canada by
staff of the Belleville Laboratory and the CIBC and field releases were made
during the period 1954-62. These included releases of over 22,000 individuals
of the tachinid Cyzenis albicans (Falk.) and a total of
2,261 individuals of the ichneumonid, Agrypon
flaveolatum (Grav.), the
only two species that became established. C.
albicans is very fecund and
oviposits microtype eggs around the edge of damaged foliage where they are
ingested by late-instar host larvae. The egg hatch in the midgut of the host
and the larvae bore through the gut wall to develop rapidly after the host
has pupated. The tachinid pupates and overwinters within the host pupal case
in the ground. The biology of A.
flaveolatum is similar but
its oviposits directly into the host larvae and has larger eggs and much
lower fecundity. Following the establishment of these two
parasitoids, parasitism by C.
albicans increased rapidly
to 50% in 1960 and life table data showed that a considerable increase in
prepupal mortality was responsible for the collapse of the winter moth
population in the main study site (Embree 1965). Parasitism by A. flaveolatum increased only following the initial decline
of the host outbreak and while it may have enhanced the depression of the
winter moth density, population models indicate that the efficiency of C. albicans alone is sufficient to account for successful
biological control (Hassell 1980). However, a more recent analysis of the
life table data from Nova Scotia and Britain (Roland, pers. comm.) indicates
that the increased pupal mortality may have arisen only indirectly from the
introduction of C. albicans. Increased parasitism
by C. albicans is closely followed by an increase in the
activity of soil predators, perhaps sustained on overwintering C. albicans puparia through late summer and early spring when
prey are generally more scarce. Thus predation rather than parasitism may be
more directly responsible for the observed increase in winter moth pupal
mortality. Recent unpublished work in British Columbia indicates that
staphylinid predators are especially important in regulation and that C. albicans puparia are avoided because they are too large
for the predators. More recently, between 1976 and 1978, winter
moth has been noted in Oregon, Washington and British Columbia on various hardwood
and fruit trees. Both C. albicans and A. flaveolatum were relocated to these areas between 1979 and
1982 and recoveries were made in many regions (Kimberling et al. 1986).
However, it is too early to determine the success of these releases. But in contrast
to the earlier program in Nova Scotia, the western program has been conducted
at a time when research policy has moved away from population dynamics toward
practical application of pest control and thus no detailed monitoring of the
winter moth before and after parasitoid release has been made. This program is often considered a good
example of biological control in which, in contrast to earlier multiple
introduction programs, selective introduction were made. These led to the
establishment of a high host density specialist (Cyzenis), with high fecundity to bring about the collapse
of an outbreak, and a low host density specialist (Agrypon), that has good searching ability to maintain the
collapsed population at a low level of abundance. However, the main reason
for the release of a smaller number of parasitoid species was the relatively
meager size of collections in Europe, where winter moth abundance was not
high at the time. Thus the only conscious selection process was of parasitoid
species obtained in sufficient quantity for meaningful release (Mesnil 1967),
although once the two established parasitoids were becoming effective in the
early 1960's a decision was made to curtail releases of other species (Embree
1966). The end results was the successful establishment of two particularly
suitable parasitoids and the program provides one of the best examples of the
detailed evaluation of a biological control project. Also as was pointed out
in earlier sections, the development of a detailed model in England prior to
the importations tended to show very little regulatory impact by Cyzenis, which might have
precluded its importation into North America. COLOMBIAN DEFOLIATOR, Oxydia trychiata
(Guenée)--Geometridae A successful example of the use of an exotic
parasitoid to control a native forest pest was the importation of the egg
parasitoid, Telenomus alsophilae Viereck, from North
America to Colombia in South America against a geometrid defoliator (Bustillo
& Drooz 1977, Drooz et al. 1977). There are a number of interesting
facets to the program since the normal geometrid host of the parasitoid in
North America, the fall cankerworm, Alsophila
pometaria (Harris), is in a
different subfamily and genus than the target pest, Oxydia trychiata,
in South America. The Colombian geometrid, O. trychiata,
has a wide distribution extending from Costa Rica to most of the countries in
South America. The moth has 3 generations per year and apparently is capable
of normal development on introduced tree species (citrus, coffee, pine and
cypress). There has been an attempt to establish exotic conifer species in
Colombia for the production of pulp and paper. This previously unimportant
insect became a pest in these pine and cypress plantations (Drooz et al.
1977). The egg parasitoid, T. alsophilae
(Scelionidae) has several biological attributes that are well worth noting
since they may have influenced this unique cross genus introduction. First,
its normal host, the fall cankerworm, feeds on several broad leaved trees but
its host in South America feeds on conifers. This indicates that host plant
odors or other differences between conifers and broad leaved trees are
unimportant in host egg finding. There may have been a clue to this because
the fall cankerworm feeds on several genera of deciduous hardwoods. The
parasitoid is apparently easily to handle as changes in photoperiod and lack
of cold in the winter did not interfere with development (Drooz et al. 1977).
The climate at the origin of the parasitoid in Virginia (30° N. Lat., el. 370
m, mean winter temperature 2°C and mean summer temperature 24°C) compared to
that of the release site in Colombia (6° N. Lat., 2340 m, temperature range
6° - 26°C with annual mean of 16°C) shows a shift from a temperate to a
tropical climate although the extremes are about the same. The rainfall
patterns in the two regions also differ. The ecological plasticity of this
parasitoid is thus demonstrated, and in addition it is long-lived (>6
months) (Drooz et al. 1977). The parasitoid may be easily reared, which
is important to a biological control project (Drooz et al. 1977), and eggs of
another species of geometrid, Abbottana
clemataria (J. E. Smith) are
used because it could be propagated on artificial diet. Around 18,000
parasitoids were sent to and released in a pine plantation in Colombia
between October and December in 1975 (Bustillo & Drooz 1977, Drooz et al.
1977). Parasitization rates on O.
trychiata eggs were very
high and by the time the parasitoid had undergone three generations in April
of 1976 few adults could be found at normal emergence time. Only 13 egg
masses of O. trychiata could be found and
these were 99% parasitized. By May the outbreak was controlled when larvae
could not be found in the area (Drooz et al. 1977). It is speculated that the
parasitoid maintains itself on any of the four species of Oxydia or other geometrids in
Colombia. EUROPEAN PINE SHOOT MOTH, Rhyacionia buoliana
(Schiff.)--Tortricidae This species occurs throughout Europe and
parts of Asia where it is a major pest of pine plantations. It was first
discovered in North America at New York in 1914 and was later also found on
imported nursery stock in Canada in 1925. While its distribution extended
throughout the northeastern United States and eastern Provinces of Canada, as
well as in British Columbia and the northwestern United States, it was
considered an important pest only in the red pine plantations in the
northeastern United States and southern Ontario. In 1927, the Commonwealth Institute of
Biological Control was engaged to collect parasitoids in Great Britain for
introduction into Canada and this led to the release of eight species during
the period 1928-43 and an additional five species from material collected in
continental Europe during 1954-58 (McGugan & Coppel 1962). Two additional
species were released during 1968-74, one from Germany and one from Argentina
(Syme 1981). A similar program of parasitoid introductions was carried out in
the New England states from 1931-37 (Dowden 1962). This program is another
example of the multiple introduction approach where emphasis is placed on the
need to provide rapid results without detailed preintroduction studies. Of
the 15 species of parasitoids released in New England and in southern
Ontario, only three larval parasitoids, the braconid Orgilus obscurator
(Nees), and the ichneumonids Eulimneria
rufifemur (Thoms.) and Temelucha interruptor (Grav.), became firmly established. However,
it was not until the early 1960's that T.
interruptor was disclaimed
as a cleptoparasitoid
detrimental to the potential impact of O.
obscurator (Arthur et al.
1964). Orgilus obscurator
is a specific larval parasitoid with a high fecundity and an efficient host finding
ability that permits it to avoid both superparasitism and very low host
density situations (Syme 1977). In contrast, T. interruptor
is a more general parasitoid of Microlepidoptera and while it also has a high
fecundity it is inefficient at host finding and oviposits most successfully
in host larvae previously attacked by O.
obscurator. Both parasitoids
attack young host larvae and only develop further when the host larvae
approach maturity. However, the first instar larva of T. interruptor
is competitively superior to that of O.
obscurator, which is killed
at an early stage to ensure the successful development of the
cleptoparasitoid (Schroeder 1974). Although the biological control program
against pine shoot moth in North America is considered to be unsuccessful,
there are isolated reports of high levels of parasitism by O. obscurator followed by the collapse of shoot moth
populations at Dorcas Bay in Ontario (Syme 1971) and near Quebec City (Béique
1960). The occurrence of wild carrot, Daucus
carota (L.) at Dorcas Bay
where parasitism by O. obscurator reached 92% prompted
further investigations on the influence of this nectar and pollen source on
parasitism in Ontario. Syme (1977) demonstrated the beneficial influence of
flowers on the longevity and fecundity of O.
obscurator and was able to
show increased rates of parasitism and elimination of pine shoot moth
populations when the parasitoid was released into plantations where D. carota was plentiful (Syme 1981). GYPSY MOTH, Lymantria dispar (L.)--Lymantriideae This insect is native to the Palearctic
region where it is a pest of broadleaf forests in eastern and southern
Europe. It was brought to North America and accidentally released in
Massachusetts in 1868. Since then it has become a serious pest of hardwoods
throughout the northeastern United States and has a continually expanding
range which currently extends into Ontario, Quebec and southward into
Virginia with isolated infestations in Minnesota, Oregon and occasionally
California. A biological control project was organized
by the U. S. Department of Agriculture, Bureau of Entomology in 1905 and
extensive foreign exploration for parasitoids and predators was carried out
in Europe, Japan, North Africa and Asia at various intervals since that time
(Doane & McManus 1981). This was the first major classical biological
control project against a forest insect. The gypsy moth project has revealed
that (1) insect disease was recognized as an important biological control
factor, (2) the sequence theory of natural enemies was introduced by W. F.
Fiske, (3) a number of future important contributors to biological control
were trained on the project (H. S. Smith, W. R. Thompson and W. D. Tothill),
(4) sleeve cages were invented as well as other equipment and techniques that
are still in use today and (5) L. O. Howard and W. F. Fiske were the first to
clearly distinguish between those causes of mortality that act in relation to
the density of the population and those that do not. L. O. Howard also
stimulated the Canadian interest in biological control in the early 1900's by
making available facilities and scientific assistance from the Melrose
Highlands Parasite Laboratory of the U. S. Bureau of Entomology. Early importations of natural enemies
occurred between 1905-14 and again between 1922-33. While some collections
were made in Japan, attention focused on Europe where temporary field
laboratories were placed wherever gypsy moth outbreaks were sufficient to
permit the rearing of parasitoids from a large number of hosts. Frequent
shipments of parasitoids and predators were made to the gypsy moth laboratory
at Melrose Highlands, Massachusetts and this resulted in the liberation of
>690,000 living insects of more than 45 species during this period (Dowden
1962). The enormous importation and multiple release program enabled two
larval/pupal predators, two egg parasitoids, six larval parasitoids and one
pupal parasitoid to become established in the New England states. The two egg
parasitoids were also subject to either large scale rearing releases in the
case of Ooencyrtus kuwanae (How.), or to
large-scale relocation releases in the case of Anastatus disparis
Ruschka. Most of the establishments occurred rapidly after the initial field
releases but the tachinids Parasetigena
silvestris (R.-D.) and Exorista larvarum (L.) were not recovered until 1937 and 1940
respectively and the chalcidid Brachymeria
intermedia (Nees) was only
recovered in 1965. Biological control by established
parasitoids and predators in New England was limited and large scale aerial
applications of DDT were used until the early 1960's. Since 1960 renewed
interest in the search for additional natural enemies has extended
explorations in Europe, Japan, Morocco, India, Iran and Korea (Doane & McManus
1981). Since 1963 the USDA Agricultural Research Service Beneficial Insects
Research Laboratory has continued to receive gypsy moth natural enemies in
their quarantine facilities and have been able to distribute more than
200,000 individuals of about 60 species to other State and Federal facilities
for culture, study and field release. From 1966 until 1971, the Gypsy Moth
Methods Improvement Laboratory at Otis Air Force Base in Massachusetts was
charged with the development of rearing procedures for the imported natural
enemies. From 1963-71 in conjunction with the New Jersey Department of
Agriculture about 7 million parasitoids of 17 species were reared and
released in the forests of New Jersey and Pennsylvania. Then from 1971-77 a
Gypsy Moth Parasite Distribution Program was established in which the New
Jersey Dept. of Agriculture and the University of Maryland reared and
released an additional two million parasitoids of 18 species throughout the
New England states. Since the late 1970's more new parasitoids and a predator
from Japan and Korea and from the Indian gypsy moth, Lymantria obfuscata
Walk., have been imported (Coulson et al. 1986). More than 100,000
individuals of nine new species or strains have been released in the field in
Delaware, Massachusetts and Pennsylvania. Although much knowledge of the biology and
rearing methods of the imported parasitoids was gained during this massive
program of importation, propagation and release, it has resulted in the
addition of only a single pupal parasitoid, Coccygomimus disparis
(Vier.) to the complex of 10 species established during the initial
importation program. This has prompted Tallamy (1983) to compare the
establishment of gypsy moth parasitoids with island biogeography theory,
suggesting that a dynamic equilibrium now exists between further
introductions and the extinction of established parasitoids. In the last 30
years two of the parasitoids that were initially established, Anastatus disparis and Exorista
larvarum have become very rare,
while two pupal parasitoids Brachymeria
intermedia and C. disparis have become established. However, the main
reasons for the failure to establish additional parasitoids in recent years
are the parasitoids' requirements for suitable alternative overwintering
hosts for their second generation each year and the fact that several of the
parasitoid species released during the 1960's were not closely associated
with gypsy moth as a principal host in their areas of origin. The failure of the established natural
enemies to control expanding outbreaks of the gypsy moth encouraged attempts
during the 1970's to augment the impact of previously established species.
Through inundative releases of Cotesia
melanoscelus (Ratz.), Weseloh
& Anderson (1975) were able to show significantly increased rates of
parasitism but this had little influence on foliage protection or egg mass
counts for the following generation. On the other and several other
inundative releases of this and other species failed to provide any evidence
of increased parasitism in comparison to control plots (Doane & McManus
1981). The combined release of parasitoids and pathogens has been used as a
method of augmentation. Wollam & Yendol (1976) were able to show a synergistic
effect of the release of C. melanoscelus in plots treated
with a double application of low concentration Bacillus thuringiensis
over plots treated with each of these natural enemies alone. The resultant
reduction in defoliation and subsequent egg mass densities has more recently
been attributed to the retarding effect of B. thuringiensis
on host larval growth which exposes the younger larvae to parasitism for a
longer period of time (Weseloh et al. 1983). A similar effect of C. melanoscelus in conjunction with viral treatments is
unlikely to occur since this parasitoid avoids oviposition in moribund host
larvae (Versoi & Yendol 1982). Augmentation through use of microbial
pathogens has been of considerable importance against gypsy moth with
significant advances in recent years. Early trials with B. thuringiensis
in the 1960's were not effective in providing foliage protection; but the
discovery of improved strains (Dubois 1985b) and successive improvements in
formulation and application technology during the late 1970's and early
1980's led to greater success. The results of aerial applications during the
1970's remained highly variable but a recommendation of double application of
low concentrations was developed and used operationally for the first time on
a large scale in 1980. This also met with limited success but further
experimental work in the early 1980's (Dubois 1985a) indicated that the use
of higher concentrations and acrylamide stickers could provide not only good
foliage protection but also could reduce subsequent egg mass densities
significantly with a single application. This development reduced the cost of
B. thuringiensis applications and has been used operationally
with success on 40-70% of the 1.3-1.5 million ha. of hardwood forest treated
since 1983. Many field trials have been conducted with
virus sprays against gypsy moth both in North America and Europe (Cunningham
1982). An NPV virus strain (Hamden standard) isolated from a natural
epizootic in Connecticut in 1967 forms the basis for the commercially
produced "Gypchek" that was registered for use against gypsy moth
in North America in 1978. However, early trials of the baculovirus produced
erratic results and while continued improvements in formulation and
application have produced more positive results, it has never been accepted
for operational use (Podgwaite 1985). Reasons for this are the relatively low
virulence of the virus, its rapid degradation on foliage in the field and the
more recent successes with the use of B.
thuringiensis. The gypsy moth program has been spectacular
in both the scale and the continued enthusiasm with which it has been
conducted, but that the results have been disappointing and serve as a good
example of the failure of classical biological control in situations where
the introduced pest is also severe in its region of origin. Therefore the
search for natural enemies in areas where gypsy moth is not a pest, in
non-outbreak populations or from related non-pest Lymantria species may prove to be a better strategy. HYMENOPTERA:
SYMPHYTA EUROPEAN SPRUCE SAWFLY, Gilpinia hercyniae
(Hartig)--Diprionidae A spruce (Picea spp.) feeding insect native to most of Europe, the
European spruce sawfly was first noted as an accidental introduction in
Canada in 1922. By 1930 a severe outbreak was causing concern in the Gaspe
Peninsula and by 1936 the sawfly threatened to devastate the spruce forests
of eastern Canada by extending its range across all eastern Provinces and
adjacent United States and causing severe damage over an area of more than
10,000 sq. miles (McGugan & Coppel 1962). One of the most extensive projects
undertaken in classical biological control was begun against European spruce
sawfly in 1933. Gilpinia hercyniae was not at first
distinguished from G. polytomum (Htg.) and the
Farnham House Laboratory in England (now known as CIBC) was engaged to make
large-scale parasitoid collections from the latter species in Europe. Initial
studies revealed that apart from the egg parasitoids, all other parasitoids
develop so as to overwinter in the host cocoon. This simplified parasitoid
collections in Europe to those stages of development. A team of about 30
persons collected >1/2 million cocoons of G. polytomum
in Europe for shipment to Canada during 1932-40. Additionally more >1/2
million eggs and 31 million cocoons of other spruce and pine feeding sawflies
were shipped to supplement the numbers of the less host specific parasitoid
species available for field release (Morris et al. 1973, Finlayson &
Finlayson 1958). There were 96 species of primary and secondary parasitoids
obtained from these cocoon collections at the Belleville Laboratory in Canada
and a multiple introduction program involving two egg parasitoids and 25
larval and cocoon parasitoids was initiated in 1933-51. The importation of a
wide variety of parasitoids from diverse hosts permitted the inclusion of
several sawfly pests as additional targets for some of the releases (McGugan
& Coppel 1962). The addition of an elaborate controlled
environment quarantine building was made at Belleville in 1936 allowed the
mass rearing of several of the imported European parasitoids. Dahlbominus fuscipennis, a gregarious
ectoparasitoid of prepupae, readily attacked cocoons in the laboratory and
was selected along with several other species for a massive program of mass
rearing for release. The mass-rearing peaked in 1940 when a total of 221.5
million D. fuscipennis was released and by
the end of the program in 1951 a total of 890 million directly imported or
laboratory reared parasitoids had been liberated (McGugan & Coppel 1962). Only 5 species of parasitoids out of 27
released became established over more than several generations, although four
additional species were recovered during the years shortly after release.
Three of the five species, D.
fuscipennis, Exenterus amictorius (Panz.) and E.
confusus Kerr, were widely
established only during the outbreak and have since not been recovered from G. hercyniae. Although E.
amictorius had little
impact, the other two species achieved variable but appreciable levels of
parasitism and have been credited with the decline of the outbreak in at
least some areas. Two other parasitoids, Exenterus
vellicatus Cush. and Drino bohemica Mesn., never became important until the collapse
of the outbreak but have replaced the three species present during the
outbreak to maintain host population at low, non-damaging densities. The epizootic of European spruce sawfly
began to decline in 1939-40, which coincided in the southern part of the
range with the occurrence of a nuclear polyhedrosis virus, Borrelinavirus hercyniae. This virus is
thought to have been accidentally imported and released in Canada along with
the parasitoid. It spread rapidly to produce virus epizootics throughout most
of the outbreak range and by 1943 host population densities had declined to
very light infestations. Unlike other diprionid sawflies, G. hercyniae larvae are not gregarious and the rapid spread
and subsequent impact of the virus was attributed to its virulence (Bird
& Elgee 1957). More recent studies in the Great Britain, where G. hercyniae was accidentally introduced from the European
continent in 1968, indicate that birds play an important role in virus
transmission (Entwistle 1976). The importance of D. bohemica,
E. vellicatus and the NPV virus in maintaining the spruce
sawfly at low population densities in Canada has been inadvertently
demonstrated through chemical spray treatments aimed against spruce budworm.
Both in the early 1960's and again in the 1970's sawfly population levels
increased immediately following the cessation of a 2-3 year spray treatment,
due to the detrimental effects of the spray on natural enemies, but declined
after several generations as a result of increased parasitism and the
reappearance of the virus (Neilson et al. 1971, Magasi & Syme 1961). There are several interesting features of
this successful biological control program. First the success of the accidental
introduction of the virus provides to date the most outstanding example of
the use of a pathogen in classical biological control. Its ability to control
the sawfly population in the absence of parasitoids has been demonstrated
(Bird & Burk 1961, Entwistle 1976) and in Canada it has persisted in the
forest environment since the initial introduction despite the low host
densities (Magasi & Syme 1981). The multiple introduction programs of
parasitoids resulted in the establishment of the two more effective and
specific species, despite the release of a wide range of potential
competitors. However, the continuous and large scale release of poorly
adapted parasitoids, which were later recovered only from other sawfly hosts,
was successful in inducing significant levels of mortality prior to the
introduction of the virus. LARCH SAWFLY, Pristiphora erichsonii
(Hartig)--Tenthredinidae A comparatively rare insect in Europe, the
larch sawfly was first generally recognized as established in larch forests
throughout the eastern Provinces of Canada in 1884. Several short lived but
severe infestations were observed in 1906-16 in which hugh quantities of
tamarack (Larix laricina) were destroyed
(McGugan & Coppel 1962). Ever since the sawfly has been found throughout
the range of larch in North America but remains more important on tamarack
than on western larches. It is unknown whether the sawfly was a recent
introduction in the late 19th Century or of much older origin in North
America (Ives & Muldrew 1981). But the lack of native parasitoids
prompted a classical biological control program in 1910-13, 1934 and 1961-64. Collections were made in Great Britain
during the early phase of introductions (McGugan & Coppel 1962). They
were shipped to Canada for quarantine, screening and direct release. This led
to the establishment of the specific ichneumonid larval parasitoid Mesoleius tenthredinis Morley, which in Manitoba was found in 20% of
sawfly cocoons in 1960 and had parasitized over 80% of the population by 1927
(Criddle 1928). Subsequently a tachinid Zenillia
nox (Hall), was collected in
Japan in 1934 by the U. S. Dept. of Agriculture and released both in New
Brunswick and British Columbia but failed to establish. The success of
parasitism by M. tenthredinis prompted an
extensive relocation program to distribute this parasitoid throughout
Canadian larch forests. Rapid establishment was reported with subsequent
reductions in sawfly populations and reduced timber losses. This appeared to be another example of the
success of classical biological control in Canada, but in the late 1930's
larch sawfly defoliation again became prevalent in Manitoba. Parasitism by M. tenthredinis appeared to have dropped to low levels, so
75,000 parasitoids were transferred from British Columbia across central
Canada. While the parasitoids' range increased, levels of parasitism remained
low due to the encapsulation of parasitoid eggs by host larvae (Muldrew
1953). The appearance of a resistant European strain of the sawfly, capable
of encapsulating M. tenthredinis eggs, appears to
have resulted from the parasitoid introduction program in 1913, when imported
larch sawfly cocoons were placed directly in the field. The resistant strain
has since spread across Canada and into neighboring states of the United
States, becoming predominant in most regions (Wong 1974). Renewed efforts were made in 1957 to obtain
more parasitoids from Europe and Japan, and long term study plots were chosen
in Manitoba to better evaluate the dynamics of the larch sawfly populations
and the impact of introductions. These studies (Ives 1976) indicated that
mortality in the cocoon and adult stages determined population trends and
that high water tables and predation by small mammals were largely
responsible for the erratic population abundance. The native tachinid, Bessa harveyi (Tns.), considered the most important parasitoid
in the renewed outbreaks, had little impact. The CIBC collected 11 parasitoids in Europe
and Japan and shipped them to Canada between 1959-65. Five of the more
abundant species were selected for release and >200 adult were liberated.
A separate introduction of the masked shrew, Sorex cinereus
Kerr from New Brunswick to the island of Newfoundland was made in 1958 in
order to fill the vacant niche for an insectivore and to increase cocoon
predation. The shrew as successfully established as well as two of the
parasitoids. One of these parasitoids, the ichneumonid Olesicampe benefactor
Hinz., attacks young sawfly larvae, the second, a Bavarian strain of M. tenthredinis, was shown to be only weakly encapsulated by
the resistant sawfly strain and was able to pass its characteristics on to
the progeny of mixed (Britain X Bavarian) crosses (Turnock & Muldrew
1971). Parasitism by M. tenthredinis initially increased
following the release of the Bavarian strain but O. benefactor
became the dominant parasitoid influencing cocoon survival. Parasitism by the
latter at the release point in Manitoba attained levels of ca. 90% between
1967-72 (Ives & Muldrew 1981) and was the dominant factor for the
collapse of the sawfly epizootic (ives 1976). Olesicampe benefactor
was relocated from Manitoba to most other Provinces in Canada (Turnock &
Muldrew 1971) as well as to Maine (Embree & Underwood 1972), Minnesota
(Kulman et al. 1974) and Pennsylvania (Drooz et al. 1985). Effects of the masked shrew on larch sawfly
cocoon survival in Newfoundland have never been adequately estimated.
Predation of cocoons is thought to have increased, but outbreaks have
continued through the 1970's (Ives & Muldrew 1981). Therefore, O. benefactor seems to offer the greatest potential for
controlling larch sawfly in Canada. However in 1966 a hyperparasitoid, Mesochorus globulator Thunb. began to attack this parasitoid in
Manitoba. The polyphagous hyperparasitoid is common in Europe and may also
have been accidentally introduced during the initial 1910-13 introductions.
It has spread throughout the region and into Wisconsin, although it hasn't
been reported from Pennsylvania (Drooz et al. 1985). While hyperparasitism
attained very high levels (80-90%) in Manitoba during 1970's, sawfly
populations continue to remain low in abundance, and thus O. benefactor
despite the occurrence of the hyperparasitoid may achieve control. The larch sawfly program gives further
evidence of the value of the more specific and well adapted parasitoids in
classical biological control. As in the case of the European spruce sawfly,
while a wide range of parasitoids was released, only the more specific
species became established. However, while in the absence of hyperparasitism O. benefactor may have been an ideal control agent, its
competitive superiority over the Bavarian strain of M. tenthredinis
may have prevented the latter from establishing and spreading more widely. This
and the known occurrence of various geographic strains of M. tenthredinis differing in ability to avoid encapsulation
by the host, emphasizes the value of detailed studies of parasitoid biologies
prior to introduction. Also, the accidental introduction of both a parasitoid
resistant strain of the host and probably also a hyperparasitoid indicates
the critical need for quarantine handling of imported material to avoid
unnecessary liberations. EUROPEAN WOOD WASP, Sirex noctilio
F.--Siricidae Biological control attempts against the
woodwasp are one of the very few large projects directed against a wood
boring insect. Woodwasps usually are considered secondary pests and attack
dead or dying trees. Sirex noctillio occurs in Canada and
throughout Europe but is most common in the Mediterranean area. It is
somewhat specific to Pinus
species (Spradbery & Kirk 1978), and is unique among the siricids in
Europe in that it is able to kill standing green trees. Under the right
circumstances, as occurred in New Zealand and Australia, this insect was able
to cause serious losses to Monterey pine, Pinus
radiata D. Don.,
plantations. The pest was first discovered on the North Island of New Zealand
about 1900 but it was not until 1927 that it was abundant enough in exotic pine
plantations for control to begin (Taylor 1981). High mortality occurred in P. radiata plantations between 1940-49 in New Zealand, and S. noctilio reached Australia in southern Tasmania in 1952
and Victoria in 1961 (Taylor 1976). There is a special relationship of S. noctilio to a symbiotic fungus, Amylostereum areolatum
(Fr.) Boidin, that serves as a kairomone for the parasitoids of the woodwasp.
Also the parasitic nematode, Deladenus
siricidicola Bedding, is
wholly dependent in nature on the woodwasp and the fungus (Bedding 1972).
Adults of S. noctilio emerge from midsummer
to late fall and mate in the upper foliage of trees. Female wood wasps
oviposit by drilling holes through the bark into the sapwood of trees that
are usually predisposed or damaged. At the time of oviposition the symbiotic
fungus is introduced (Taylor 1981). Adults live only a few days in nature.
The eggs hatch when the fungi have invaded the surrounding area and this
occurs when some drying has taken place to favor the fungi. First and second
instar larvae feed exclusively on fungus and third and fourth instars begin
to tunnel into the wood. The larvae turn back toward the bark to about 5 cm
from the bark surface to enter the prepupal stage. Pupation may not occur
until the second or third year after hatching, depending on the weather.
After pupation adults emerge in about three weeks, and each generation
emerges over a period of two to three years with the proportion of
individuals emerging in the first, second and third year varying by site
(Taylor 1981). Biological control was initiated in New
Zealand in 1927 (Taylor 1981). During 1929-32 the ichneumonid, Rhyssa persuasoria L. was introduced but the control was not
satisfactory (Turnock et al. 1976). Then Ibalia
leucospoides (Hochenw.)
(Ibalidae) was colonized in 1954-58, which resulted in improved control
(Zondag 1959). The two parasitoids were then colonized in Tasmania. A
large-scale biological control effort did not begin until 1961 following the
discovery of S. noctilio in Victoria,
Australia. A National Sirex Fund was established, which consisted of a
consortium of federal, state and private agencies, and a committee was formed
to coordinate research and control in Victoria (Taylor 1981). A world wide
search for natural enemies was begun by the Division of Entomology, CSIRO in
1962. The search for parasitoids in the northern hemisphere was completed by
1973, and during the 11-year period 21 species of parasitoids were sent to
Tasmania for culture (Taylor 1976). The plan was to obtain all the available
parasitoids of siricids in conifers and as many strains as possible from
different climatic zones with emphasis on the Mediterranean area. This
included collections of siricids in conifers other than Pinus and from genera and species other than Sirex noctilio. Ten different parasitic species were released in
Tasmania and Victoria, six having become established and one additional
species, the ichneumonid Rhyssa
hoferi Roher, probably
established (Taylor 1981). Of the seven species two are holarctic (R. persuasoria and I.
leucospoides), two are
palearctic (I. rufipes drewseni Borries and the ichneumonid Odontocolon geniculatus
Kreichbaumer) and three are nearctic [the stephanid Schlettererius cinctipes
Cresson and the ichneumonids Megarhyssa
nortoni (Cresson) and R. hoferi]. These species tend to be complementary,
although there might be some competition within the guild attacking larger
larvae. The Ibalia species
attack first or second instar siricid larvae and the two species have different
emergence times so that they do not compete directly. The ichneumonids attack
the more developed larvae of their host and there may be differential
preference based on tree diameter (Taylor 1981). Schlettererius cinctipes
emerges after the peak emergence of the ichneumonids, while the other two are
also complementary as O. geniculatus is small, emerges
in springtime and attacks late hatching larvae that are still closer to the
bark surface. Rhyssa hoferi is adapted to drier areas
and could do well in drier climates (Taylor 1981). A parasitic nematode, Deladenus siricidicola,
was found in New Zealand in 1962 (Zondag 1969). It causes female wood wasps
to lay infertile eggs. Additional nematodes wee sought during 1965-75 without
success (Bedding & Akhurst 1974). Different strains of the nematode have
also been released throughout wood wasp infested areas in Tasmania and
Victoria and it is well established throughout. This nematode also affects
the reproduction of some of the female parasitoids (Bedding 1967), which
apparently does not adversely affect biological control. The nematode is
credited with reductions of wood wasp populations to very low levels in
certain areas. The Sirex
noctilio biological control
program is significant for several reasons. A large group of organizations
cooperated in a well funded, extensive worldwide search for parasitoids as
well as a research program that examined many aspects of the host tree/Sirex/fungus/parasitoid
relationships (Taylor 1981). As with Gilpinia
hercyniae there was a
fortuitous introduction (the nematode). Sirex
noctilio was introduced from
the northern to the southern hemisphere and attacked an exotic host plant Pinus radiata (native to California). The search for parasitoids
in the north was made from S.
noctilio and its host trees
to siricids in other genera and species in Pinus as well as other conifers. The project was well
planned with attention given to colonizing strains of parasitoids suited to
different climatic zones and developmental stages of the host. It is believed that this biological control
project will eventually be completely successful (Turnock et al. 1976). It
has been thought that the combination of parasitoids and nematodes along with
sound forest management should hold S.
noctilio down to the level
where losses are not serious (Taylor 1976). GREATER EUROPEAN
SPRUCE BEETLE, Dendroctonus
micans (Kugelmann)--Scolytidae This bark beetle, probably native to
coniferous forests of eastern Siberia, is one of only two Dendroctonus species occurring
in the palearctic region. Dendroctonus
micans is primarily a pest
of spruce, Picea spp., but
will occasionally attack Pinus
sylvestris L. The beetle has
been expanding its range for many years and is still spreading. About 200,000
ha are currently suffering from epizootics and recently invaded areas include
Great Britain, France, The Georgian S.S.R. and Turkey (Grégoire et al. 1987,
Evans 1985). In the inner parts of its range where the beetle has been
established for a long time populations remain at low densities and it is not
a pest. This bark beetle differs from the more
aggressive North American Dendroctonus
species in that it attacks its host tree in low numbers, killing the bark in
patches. Successive attacks over a period of five to eight years may be
necessary to kill a tree except during beetle outbreaks (Grégoire 1985). The
beetle shows kin-mating,
gregarious larvae and apparently lacks associated pathogenic fungi that are
characteristic of many Scolytidae. Dendroctonus
micans has very few natural
enemies which may be due to its unique biology that seems to protect the
beetles from competitors and generalist natural enemies by the defenses of
its living host (Everaerts et al. 1988). One specific predator Rhizophagus grandis
Gyllenhal is very abundant in areas where the bark beetle has been present
for long periods of time. This rhizophagid beetle is believed to be
responsible for maintaining the low, stable D. micans
population in these areas (Kobakhidzi 1965, Grégoire 1976, Moeck &
Safranyik 1984). A massive biological control project was
initiated against D. micans in Georgia S.S.R. in
1963 (Kobakhidze 1965). The spruce beetle had extended its range into Georgia
following World War II in timber imported from the north. A predator
relocation program was planned as the predator did not follow its host. Rhizophagus grandis was released in large
numbers as larvae and adults on spruce trees infested by D. micans
(Kokakhidze et al. 1968). Effective control apparently has been achieved
(Grégoire et al. 1987). First observed in the Massif Central of France in the early
1970's, D. micans was targeted for
biological control in a program funded by the European Economic Community in
1983. Its main thrust was to establish the predator, R. grandis
(Grégoire et al. 1987). A similar program was initiated in 1983 in Great
Britain (Evans 1985, Evans & King 1987). Evaluations are still in
progress, but knowledge that the predator is attracted to the frass of three
North American Dendroctonus
species (Miller et al. 1987) suggests its possible use against species other
than D. micans. Please refer to: <BC-34.REF> [Additional references may be found at
MELVYL Library ] |