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I. Early
explorers wrote in considerable detail their experiences abroad. Such experiences are also common to modern-
day
explorers
II. The
importation of beneficial insects today remains the most widely practiced and
potentially most rewarding
approach to biological control.
The reasons given for the practice of importation have remained
essentially
unchanged. It is assumed that
exotic insects are pests as a result of their having escaped regulation by
their natural
enemies after their accidental introduction into new regions. Importation is done to restore the natural
balance,
so to
speak.
III. Guidelines in Foreign Exploration
A.
Certain concepts have arisen over the years as a result of accumulated
experience on natural enemy
importations. These concepts
serve, for better or worse, to guide foreign exploration. Exceptions exist,
of
course, as with any generalizations; yet the concepts function as useful
guidelines.
B.
Experience suggests that exotic pests offer better prospects for
successful biological control than
native pests. This discrepancy
probably reflects the greater amount of work that has been done with
foreign pests. Biological
control efforts against native pest have been few compared to alien pests.
1. the lack of attention to native pests is
though to be due to the fact that they are already attacked
by
a complex of natural enemies, and that their rise to pest status has resulted
primarily from factors
other than a lack of parasitoids and predators.
2. for example, the establishment of vast crop
monocultures greatly expanded the habitats of these
native
pests, disrupting the formerly effective natural controls.
3. success begets success; thus, we find that
many biological control projects have followed and will
continue to follow the lead of previously successful projects. Hence, experience suggests that considerable
future foreign exploration work will involve scale insects, white flies,
mealybugs, aphids and probably
Lepidoptera.
C. An
important concept relative to foreign exploration is that natural enemies of an
alien pest are best
sought in its native home.
1. this is still held to be the logical initial
approach to foreign exploration, because it is in the native
home of a pest that the long standing host/natural enemy complexes are
to be found. These furnish natural
enemy species capable of locating and regulating their hosts at low host
densities.
2. it is generally believed that the first
choice ought to be the dominant species occurring at low host
densities.
D. It is
not conceded that the search for natural enemies should also extend to areas of
similar climate
containing close relatives of the pest.
IV. Procedures in Planning
and Preparation For
Explorations
A. The
first step is to insure the proper identification of the pest species. Once correctly identified, the
host-plant
affinities and the probable country of origin can be ascertained. Such relationships are learned
from the literature, museum collections, and from consultation with
world specialists.
B.
Misidentification can result in wasted time and effort. Examples are:
1. Circulifer
tenellus, the beet leafhopper,
first came into prominence as a pest in the United States around
1905.
This insect spreads the destructive "curly top" virus of sugar
beets, tomatoes, melons and a number
of
other crops:
A
first this species was placed in the genus Eutettix
and was thought to be native to the southwestern
United States.
In 1917-18 two expeditions to Australia failed to uncover any effective
natural enemies. In
1928, acting on a misidentification recorded in
the literature, an expedition was sent to Argentina, but also
failed to
find either the leafhopper or natural enemies.
In
1936, Dr. Paul Oman called attention to a close resemblance between the beet
leafhopper and a species
described
from Israel. He concluded that C. tenellus was incorrectly placed in the genus Eutettix, and
ought to belong to the genus Circulifer, which contained a number of species native to
the arid regions of
the Mediterranean and Central Asia. Foreign exploration was redirected to these
areas where the beet
leafhopper and its natural enemies were
found. Although several parasitoids
were introduced into California,
they were not economically effective, however.
2. The fern weevil, Syagrius fulvitarsus,
was once a destructive pest of indigenous tree ferns in Hawaii.
When biological control was contemplated in the 1920's, no clue as to
its country of origin was forthcoming.
While examining a private insect collection in Sydney, Australia, a
noted Hawaiian entomologist, Pemberton,
discovered a single specimen of the fern weevil which had been collected
in Australia in 1857. Subsequent
search of the area from which the specimen had been collected produced a
braconid larval parasitoid of the
fern weevil. Successful
biological control was achieved when the braconid was introduced into
Hawaii.
Thus, the data borne on a collecting label attached to a single insect
specimen in Australia contributed
directly to the successful biological control of the fern weevil in
Hawaii some 65 years later!
C. The
third step, following identification and location of the native home of the
pest, is to choose the
appropriate season for the exploration.
Timing of collection is also somewhat dictated by the periods
most
suited to domestic culture and colonization efforts. Ideally, foreign exploration is undertaken during
the
period of greatest seasonal availability of natural enemies.
V. Foreign
exploration for natural enemies has been greatly simplified nowadays with the
advent of rapid air
transportation. In the past,
foreign collecting often involved arduous work in rearing, with a relatively
small part
of
the collector's time being spent on detection and collecting.
A. Some
of the early accounts of foreign exploration explain the various hardships of
the collector. For
example, Albert Koebele <PHOTO> who played an important role in the
cottony-cushion scale project,
spent the last six months of 1902 in Central Mexico collecting natural
enemies of the weed, Lantana camara.
Plagued by
sickness and heat throughout this period, he wrote the following of his
collecting trip:
"Alameda, California, December 26, 1902:
“ I
am still unwell, not yet over my fever, but a rest may help me, and I am only
too glad to be out of Mexico
and rid of the hardest work that I ever
did."
B. Modern
foreign explorers can spend a considerable portion of their time searching for
effective natural
enemies, shipping them by air in almost any stage of development from
practically any corner of the earth,
knowing that the odds favor their arrival within a week's time. Also, modern low weight and breakage
resistant plastics that can be variously screened for aeration offer
ease for natural enemy manipulation
and
shipment.
VI. Recognition of Promising
Natural Enemies Abroad
A. Host
scarcity during optimum seasons of abundance is a good sign. The collection of adequate numbers
of natural
enemies in such areas is difficult with ordinary methods. The host-exposure method can be
employed to alleviate this problem.
B. A
colonial or localized type of host distribution is commonly associated with a
high degree of natural enemy
effectiveness. Under these
conditions, localized host populations increase in number, only to be decimated
following their detection by natural enemies, the result being a
numerically and spatially shifting mosaic of host
population loci.
C. The
appearance of localized outbreaks of the host species associated with pesticide
usage, or differences in
host
abundance on insecticide treated crops versus untreated wild hosts, often
indicates a favorable collecting
area.
D. An
abnormal abundance of the host where it is protected from its natural enemies
by ants, dust, litter, spider
webs, etc., is also a favorable indicator of effective natural control
in the area of search.
VII. Many
foreign collectors often confine their collecting to relatively accessible
areas such as botanic and domestic
gardens, parks, roadsides and empty lots, because host plants of the
insects being sought often become infested at
variable intervals in these isolated situations. This often results in the pest species
temporarily evading detection
by
natural enemies, which results in localized outbreaks and which ultimately
attracts high populations of parasitoids
and
predators.
VIII. Certain
precautions must be taken to insure against the introduction of injurious
organisms, such as
hyperparasitoids, potential insect pests, weeds, and plant pathogens.
A. The
foreign collector has the initial responsibility for excluding potentially
dangerous foreign organisms.
B.
Usually the material is sent only to scientific institutions, which
maintain elaborate quarantine facilities
and
where any injurious organisms that may have escaped the attention of the
foreign collector are carefully
screened out and destroyed.
C. There
is additionally the danger of establishing parasitoids which attack other
beneficial insects, such as
useful predators or phytophagous insects introduced for biological weed
control. Predators being considered
for
importation should either be known to lack parasitoids or be freed from them by
laboratory manipulation
prior to their importation.
REFERENCES:
Compere, H. 1961.
The red scale and its natural enemies.
Hilgardia 31(7): 173-278.
Compere, H. & H. S.
Smith. 1932. The control of the citrophilus mealybug, Pseudococcus gahani,
by Australian parasites.
Hilgardia 6: 585-618.
Legner, E. F. 1986.
Importation of exotic natural enemies, p. 19-30. In: J. M. Franz (ed.), Biological Control of
Plant Pests and
of Vectors of Human and Animal Diseases. Fortschritte der Zool. Bd. 32: 341 p.
Legner, E. F. & R. D.
Goeden. 1987. Larval parasitism of Rhagoletis
completa (Diptera:
Tephritidae) on Juglans microcarpa
(Juglandaceae) in western Texas and southeastern New
Mexico. Proc. Ent. Soc. Wash. 89: 739-43.
Legner, E. F. & C. W.
McCoy. 1966. The housefly, Musca
domestic Linnaeus, as an
exotic species in the Western Hemisphere
incites
biological control studies. Canad. Ent.
98: 243-48.
Legner, E. F. & R. A.
Medved. 1979. Influence of parasitic Hymenoptera on the regulation of pink
bollworm, Pectinophora
gossypiella, on cotton in the lower Colorado
Desert. Environ. Ent. 8: 922-30.
Legner, E. F. & A.
Silveira-Guido. 1983. Establishment of Goniozus emigratus
and Goniozus legneri [Hym: Bethylidae] on
navel orangeworm, Amyelois
transitella [Lep: Phycitidae]
in California and biological control potential. Entomophaga 28: 97-106.
Muir, F., & O. H.
Swezey. 1916. The cane borer beetle in Hawaii and its control by natural
enemies. Rept. Hawaiian Sugar
Planters Expt. Sta. Bull. 13:
102 p.
Perkins, R. C. L. 1906.
Leaf-hoppers and their natural enemies (Introduction). Rept. of the work of the Expt. Sta.,
Hawaiian
Sugar Planters Assoc. Bull. 1: 32 p.
Silvestri, F. 1914.
Report of an expedition to Africa in search of the natural enemies of
fruit flies (Trypaneidae). hawaii Bd.
Agric. & Forestry, Div. of Ent. Bull. 3. 176 p.
Zwölfer, H., M. A. Ghani &
V. P. Rao. 1976. Foreign exploration and importation of
natural enemies, p. 189-207. In: C. B.
Huffaker & P. S. Messenger (eds.), Theory and Practice of
Biological Control. Academic Press, New
York, San Francisco, London.
