FILE: <museum5.htm> [Use Landscape orientation to print] <Navigate
to COMMUNITY INSTRUCTION>
ECONOMIC
GAINS & ANALYSIS OF SUCCESSES IN BIOLOGICAL
PEST CONTROL Dr. E. F. Legner, University of California, Riverside (Contacts)
Economic Gains Abundant
empirical evidence shows that Biological Pest Control, as practiced by
professionals is among the most cost effective methods of pest control. Because of its highly positive social and
economic benefits, biological control should be among the first pest control
tactics to be explored. Biological
control workers must not be indiscriminate in introducing exotic organisms,
however. Biological control is a
serious endeavor for professionals:
it cannot become a panacea for enthusiasts having little of the formal
training and understanding of the basis of this discipline. In pest control the rights of society and
the environment are increasingly in conflict with private profit. Classical biological control and other
forms of natural control, plus other environmentally and economically sound
methods must fill the gap. Biological
control has the best pest control record and remains a considerable untapped
future resource (Gutierrez et al. 1992). It is
difficult to make an analysis of costs and benefits for biological control
because the definition "biological control" has been given various
meanings (Caltagirone & Huffaker 1980, NAS 1987, Garcia et al. 1988,
Gutierrez et al. 1992). Perhaps it is
appropriate to distinguish classical and naturally occurring biological
control from other methods such as the use of pesticides derived from
biological organisms (e.g., Bacillus
thuringiensis toxins, ryania,
pyrethrum, etc.), the use of sterile males, etc.). Gutierrez
et al. (1991) consider periodic colonization of natural enemies
(inundative and inoculative) as an extension of biological control. It is a mistake to call biological control
any procedure of pest control that involves the use or manipulation of a
biological organism or its products as was done by Reichelderfer (1979, 1981,
1985). Reichelderfer's contribution
has been to show how economic theory applies to an analysis of the economic
benefits of augmentative releases of biological control agents, and in this
sense the arguments are similar to those for estimating the benefits of using
pesticides or any other control method.
In this
discussion of economic gains, the discipline of biological control as an
applied activity, concerns itself with the introduction and conservation of
natural enemies that become, or are essential components of self-generating
systems in which the interacting populations (principally predator/prey or
parasitoid/host) are regulated. In
biological control of pests the manipulated organisms include predators,
parasitoids, pathogens and competitors.
No judgments are made concerning the value of other procedures, except
to note those which encourage environmentally safe and economically sound
approaches. Biological control of
pests has been implemented worldwide, in environments that are climatically,
economically and technologically diverse (Clausen 1978). The net benefits derived from this tactic
as a whole are difficult to quantify with any degree of accuracy. However, the considerable number of cases
that were successful, and continue to be so, and the fact that no
environmental damage has been detected in the great majority of them make
this tactic a very desirable one.
Nevertheless, the classical biological control approach (introduction
of exotic natural enemies) has been challenged on the basis of possible
negative effect on native organisms.
For example, Howarth (1983) proposed that in Hawaii the introduction
of some natural enemies has adversely affected the native fauna, and that to
restore the ecological situation by removal of these organisms is nearly
impossible. This points to the vexing
aspect of possible environmental risk in using exotic biological control
agents (Legner 1986a,b). It has been
accepted that these organisms, when introduced according to restrictions
established by regulatory agencies (Animal and Plant Health Inspection
Service in the United States) are considered to pose no environmental
hazard. Routinely, risk is recognized
when considering candidate natural enemies to control weeds. A comprehensive discussion on this aspect
of biological control is given by Turner (1985), and Legner (1986a,b). The
biological impact of exotic biological control agents on target pests is
difficult to assess and few cases have been thoroughly documented (Luck et
al. 1988), making economic analysis difficult. Even more demanding would be to include in the equation the
monetary value of the side effects as referred to by Howarth (1983) and the
positive ones (e.g., the benefit that society derives from the reduction in
or the elimination of the use of objectionable pesticides) as a result of the
introduction of an effective natural enemy. Biological Control From Naturally Occurring
Organisms
The
economic benefits of naturally occurring biological control have been
repeatedly demonstrated in those cases where secondary pests became
unmanageable as a result of overuse of chemical pesticides to control primary
pests. DeBach (1974) clearly showed
the effect of DDT in the disruptions of pests in many crops. The rice brown plant hopper, Nilaparvata lugens, in southeastern Asia
continued to be a pest as a result of it overcoming the new varieties'
resistance and the use of pesticides to control it. Host plant
resistance may be overcome by natural selection of new biotypes of
phytophages in the field in less than seven years (Gould 1986). Kenmore (1980) and Kenmore et al. (1986)
showed that the rice brown planthopper is a product of the green revolution
wherein the increased prophylactic use of pesticide destroyed its natural
enemies and caused the secondary outbreak of this pest. Recognition of this problem recently led
to the banning of many pesticides in rice in Indonesia (Gutierrez et al.
1992). This prohibition has resulted
in no losses in rice yields. Most of
the pests in cotton in the San Joaquin Valley of California (Burrows et al.
1982, Ehler et al. 1973, 1974; Eveleens et al. 1973, Falcon et al. 1971), the
Cañete and other valleys in Peru (Lamas 1980), Australia (Room et al. 1981),
Mexico (Adkisson 1972), Sudan (von Arx et al. 1983) and other areas are
pesticide induced. This often causes
these pests to become more important than the original target pests. These examples substantiate the benefits
of naturally occurring natural enemies in controlling pests. Furthermore, these benefits are largely
free of cost, unless special procedures are required to either augment or
reintroduce them (Gutierrez et al. 1992). Estimation of Benefits & Costs of
Classical Biological Control
The costs
of a classical biological control project (C) may be calculated easily. One simply sums the cost of the base line
research, the cost of foreign exploration, shipping, quarantine processing,
mass rearing, field releases and post release evaluation. The last cost must be evaluated
judiciously as pursuing academic interests may push these costs beyond those
required by the practical problem at hand.
Harris (1979) proposed that costs be measured in scientist years (SY),
with one SY being the administrative and technical support costs for one
scientist for one year. For example,
the U. S. Department of Agriculture estimated that one SY in biological
control cost $80,000 in 1976 (Andrés 1977). DeBach
(1974) gave a rough estimate of the cost of importing natural enemies at the
University of California. He
commented that he had imported several natural enemies into various countries
with resulting impressive practical successes where the cost had been less
than $100 per species. In other cases
the cost may run much higher, but he believed not more than a few thousand
dollars per entomophagous species at most.
These tentative costs suggest that some classical biological control
projects may be very inexpensive, but others may cost more because of the
biological and other complexities encountered. Also, the efficiency of the organization involved may cause
costs to vary considerably, and the cost of the biological control efforts on
a per organization, per country, or worldwide basis must include the cost of
fruitless efforts. Like any other
tactic, biological control must record not only its successes but also
failures (Ehler & Andrés 1983). A
monetary loss due to a failure may still provide a scientific gain in
knowledge which is usually unmeasurable.
Such knowledge may be applied positively in future efforts with a
consequent savings of cost. Once establishment
and dispersal in the new environment is obtained in classical biological
control, no further costs for this natural enemy are incurred unless new
biotypes are introduced. Other uses
of natural enemies may involve repeated releases of natural enemies in the
field or glasshouse. These costs are
analogous to the cost of pesticide applications. The release of Aphytis
in California orange orchards (DeBach et al. 1950), Pediobius foveolatus
against Mexican bean beetle on soybean (Reichelderfer 1979), Trichogramma spp. in many crops
worldwide (Hassan 1982, Li 1982, Pak 1988), Encarsia formosa
against whiteflies in glasshouses (Hussey 1970, 1985, Stenseth 1985a),
phytoseiid mite predators in
strawberries (Huffaker & Kennett 1953), almonds (Hoy et al. 1982, 1984),
and glasshouses (Stenseth 1985b) are examples in which costs of manipulation
of natural enemies are incurred periodically. The use of sterile males in campaigns against screwworm,
Mediterranean fruit fly or pink bollworm was aimed at eradication rather than
regulation of the pest. Under these
circumstances it is assumed that much higher costs can be tolerated. The
environmental costs of biological control derived from the possible
suppression or eradication of native species by introduced exotic natural
enemies (Howarth 1983, Turner 1985) could be included in a benefit/cost
analysis if some monetary value could be placed on them. More often than not such factors cannot be
accurately priced in much the same way that increased cancer risks due to the
use of some pesticides cannot be priced. Biological Control Benefit Computation
is a more difficult task. One of the
most successful, and historically the first, case of biological control in
California was the control of the cottony cushion scale, Icerya purchasi,
by the imported natural enemies Rodolia
cardinalis and Cryptochaetum iceryae. In 1889-1889, when these natural enemies
were imported to California at the cost of a few hundred dollars, the young
citrus industry was at the verge of collapse because of the scale. One year later shipments of oranges from
Los Angeles County had increased three-fold (Doutt 1964). What figures should we use to determine
the benefits of such a program?
Obviously the benefits continue to accrue to the present. In 1889 there was no other effective way
to control the scale even though it is possible that some of the modern
chemical pesticides could control it today.
So is the yearly benefit the full net value of the citrus crop
(assuming the uncontrolled pest could destroy all of the crop and many of the
trees as well), or the total cost of using an effective pesticide? Should we include the benefits of
introducing these natural enemies from California to 26 other countries, in
23 of which the scale was completely controlled? Whichever method is chosen, the benefits of this project are
vast but undocumented. Much more
difficult are those cases were partial noneconomic control occurs: the natural enemy becomes established,
regulates the population of the target species to a lower level, but not low
enough as to have economic significance.
It is conceivable that in cases like these the natural enemies may
make it easier to implement a more effective, complementary control tactic
(e.g., IPM). The effects of
biological interactions are complex and they are often influenced by other
factors including weather, and the beneficial effects of the natural enemy
may not be obvious. When the results
of biological control are clear-cut, increased production and increased land
values may be only part of the equation, as enhanced environmental and health
effects may also occur but may go undocumented. The basis for a comparison between the situation prior and
after establishment of biological control must further consider the changing
real value of money over time, changing markets for the commodity involved,
and the dynamics of land use.
Enhanced yield may be due to reduced pest injury, but also to
reduction in diseases the pest may vector. Benefits
which are easiest to estimate are those to the agricultural sector. Because of the permanent nature of
biological control, the net benefits (II) [i.e., benefit (B) - costs (C)]
corrected for the present value of money using the discount rate (1 + @)-1
accrue over t years (i = 1,...,t).
Note that @ is the interest rate or price of money. t II = Z (Bi - Ci) / (1 + @)i 1=1 [ Z =
summation sign] Gross
revenue (B) to the grower equals P (Y-DN(1-E)) with P being price, Y the
maximum possible yield, D the damage rate per pest N, and E the efficacy of
the biological control. In reality, D
is a function of N (i.e., D(N(1-E))), but for simplicity we assume that D is
a constant. In fact, the benefit of
biological control for the ith year is Bi = PDNiE, and
in the extreme may equal PY. DeBach (1971, 1974), van den Bosch et al. (1982) and
Clausen (1978) summarized several classical biological control projects
worldwide. A few of them are reviewed
also in Gutierrez et al. 1992), who note their benefit/cost ratios
(B/C). This ratio is however
dimensionless and tells nothing about the total gain, rather it is a useful
measure of the rate of return per dollar invested. Some projects, such as control of the Klamath weed and the Citrophilus mealybug have B/C
ratios in the thousands, while the ratios for most of the others are in the
hundreds. These estimates are, at
best, rough approximations for the reasons stated previously. But even if they overestimate the benefit
by 50% the B/C ratios will overwhelmingly favor the use of classical
biological control. In fact the
estimates of benefits are conservative and the errors are in the opposite
direction. There are
many other examples of the benefits of biological control. Tassan et al. (1982) showed that the introduced natural
enemies of two scale pests of ice plant, an ornamental used in California to
landscape freeways, potentially saved the California Department of Transportation
ca. $20 million dollars in replanting costs (on 2,428 ha.). Chemical control at a cost of $185/ha., or
$450,000 annually, did not prove satisfactory. Therefore, if suitable biological control agents did not exist
the minimum long term benefit would appear to be the replacement cost. The total cost of the project was $190,000
for a one year B/C ratio of 105. This
was certainly a cost effective biological control project. The control
of cassava mealybug by the introduced parasitoid Epidinocarsis lopezi over parts of the vast cassava belt in
Africa was a monumental undertaking.
Successful control of the mealybug enabled the continued cultivation
of this basic staple by subsistence growers, thus potentially helping to
reduce hunger for 200 million inhabitants in an area of Africa larger than
the United States and Europe combined.
What monetary value could be assigned to this biological control
success? How is the reduction or
prevention of human misery priced?
This project has been characterized as the most expensive biological
control project ever ($16 million to 1991) by some of its critics, but all
things being relative, the costs of this program since its inception in 1982
are less than those of the failed attempt to eradicate pink bollworm from the
southwestern United States, or roughly about the cost of a fighter plane
bought by many of these countries.
The per capita cost of the project amounts to eight cents per person
affected in the region, which contrasted to average yield increases in the
Savannah zones of west Africa of 2.5 metric tons per cultivated hectare would
appear to be a good return on the investment (Neuenschwander et al.
1991). Finally, the project has been
diligent in documenting nearly all phases of the work (Herren et al. 1987,
Gutierrez et al. 1988a,b,c; Neuenschwander et al. 1991), and satisfying as
much as possible the concerns of Howarth (1983). There are
also recent cases of successful biological control where the benefits are
just as impressive but an economic analysis has not been conducted. The control of three Palearctic cereal
aphids over the wheat growing regions of South America reduced the pesticide
load on the environment causing direct enhancement of yields. New wheat varieties were being developed
at the time, but their yield potential had not been stabilized. Thus it is not possible to assess the
maximum contribution of the biological control effort. But if as a result of the establishment of
natural enemies there was a saving of one application of pesticide per annum
the total savings in Argentina, Brazil and Uruguay on 8,996,000 ha. of wheat
alone (FAO 1987) would be substantial, especially if it is contrasted with
the cost of the biological control component, which has been estimated at
less than $300,000 (Gutierrez et al. 1992). Gutierrez et al. (1991)
compare the economic benefits of several successful classical biological
control projects and compare them with the use of inundative releases of
natural enemies in soybean for control of Mexican bean beetle and for
greenhouse pests, and the well known sterile male eradication program. The release of resistant predatory mites
in almonds gave a B/C ratio of 100 (Headley & Hoy 1987), and the screwworm
eradication project is estimated to have given a ratio of 10. Although impressive, these B/C ratios on
the average are still not as high as those achieved using classical
biological control which is self sustaining. In
augmentative release and especially eradication programs, the cost of starting
and maintaining them may be very high.
In some cases a particular pest may be understood to be of such
damaging nature and effective natural control may not be available that the
high costs of eradication may be deemed necessary. However, eradication programs are not without risks. For example, an economic analysis of the
proposed eradication of the boll weevil from the southern United States
predicted that the eradication of the pest would cause the displacement of
cotton from the area (Taylor & Lacewell 1977). In this scenario increased cotton production due to eradication
of the pest would cause prices to fall forcing production to move to the west
where it is more efficient. In the
case of the ill fated pink bollworm eradication effort in the desert regions
of southern California, early termination of the crop was available as an
alternative, but it is not favored by growers because they did not pay for
the full cost of the eradication program or the environmental costs of high
pesticide use, and yields were lower.
Only resistance to insecticides in pesticide induced pests made them
reconsider alternatives such as short season cotton varieties and
conservation of natural control agents. Justification of Need for Biological
Control
The question
is then why do we feel the need to make economic justifications for
biological control? Why hasn't
biological control been more widely supported worldwide? Economists would call this a market
failure, because the users of pesticides do not pay for long term
consequences of pesticide use and hence may ignore environmentally safer
alternatives (Regev 1984). But there
are also problems of perception, for as Day (1981) assessed in his review of
the acceptance of biological control as an alternative for control of alfalfa
weevil in the northeastern United States:
"At first, the general opinion was that biological insect control
was outmoded, because it had not been effective in the east in decades, and
it was not likely to be competitive with synthetic insecticides or the newer
synthetic chemicals such as pheromones, chemosterilants, attractants and
hormones." Thus, biological
control was not appreciated as competitive with newer technologies and it was
not considered modern. The recent
over selling of bioengineering solutions for crop protection can also be
added to the list of reasons why classical biological control is not
currently strongly supported. Often the
damage of important pests may not be obvious to funding agencies, or grower
groups may not be sufficiently organized to provide the funding. For example, a related weevil species, the
Egyptian alfalfa weevil in California is a very serious pest not only in
alfalfa, but more important in pasture lands where it depletes the nitrogen
fixing plants. In 1974 feeding damage
resulted in $2.40 - $9.59 reduction in fat lamb production (or $5.00
reduction in beef production) and $1.00 - $1.50 reduction in fixed nitrogen
per acre per year, in addition to spraying costs of $2.50/acre/year plus
materials (Gutierrez et al. 1992).
These losses averaged over the vast expanse of grazing land in
California and other western states make an enormous sum. Despite the economic significance of this
pest, funding for a project has proved elusive, thereby greatly hindering
biological control efforts. In
contrast, funding for the biological control of the ice plant scales in
California was rapid because damage was readily visible along the freeways,
and the California Department of Transportation, which funded the project,
had ready access to funds from fuel taxes. The
technologically advanced countries the advocates of biological control,
compared to those promoting predominantly the use of chemical pesticides, are
much fewer in number, generally have sparser resources and have a more
difficult educational task. It
requires great educational skills, financial resources and personal
dedication to effectively convey the necessary information in order to enable
growers to make educated decisions about pest control. The processes of biological control are
not visible to the majority of agriculturists, and with rare exception its
benefits become part of the complicated biology that is absorbed in the
business of crop production, and is quickly forgotten by old and new clients
alike. On rare occasions the
biological and economic success was so dramatic, as occurred with Klamath
weed in California, that the generations four decades later is aware of the
history of the control. The problem
is also increasing in developing countries as modern agrotechnology displaces
traditional methods, and they too become dependent on pesticides for the
control of pests. To combat this
problem the United Nations sponsored project on rice in southeastern Asia
headed by P. E. Kenmore has set as its goal the training of millions of rice
farmers on how to recognize the organisms responsible for the natural control
of rice pests. Thus, perceptions of
the seriousness of a pest control problem often determine whether an
environmentally sound alternative is selected. Biological Control &
Pesticide Use
In a free
market economy individual growers make their own pest control decisions, and
purveyors of alternatives such as pesticides have the right to market them in
accordance with state laws. Under such
a system, the perceptions of the problem by growers and the marketing skills
of those proposing alternative solutions often dictate how well biological
control is adopted in the field. In
evaluating the effectiveness of chemical control or augmentative release of
natural enemies, economists traditionally look at the balance of revenues
(B(x)) = the value of the increase in yield attributable to using x units of
the control measure (e.g., pesticide or augmentation) minus the out-of-pocket
cost (C(x)) of causing x units of the control measure. Only infrequently are the social costs
(S(x)) associated with the control measure included. For augmentative releases of natural enemies
and biological control, S(x) is usually zero. The benefit function is usually assumed to be concave from
below and the cost per unit of x constant.
The net benefit (II) function should be: II = B(x) -
C(x) The optimal solution to this
function occurs when dB/dx = dC/dx, hence the optimal quantity of x to use is
x1 when S(x) is excluded, but is x2 when included? If the cost per unit of x used increases
with x, costs rise rapidly and less pesticide (x3) is
optimal. Unfortunately, the social or
external costs of pesticides in terms of pollution, health and environmental
effects are seldom included in the grower's calculations because there is no
economic incentive to do so. In
contrast, augmentative releases of natural enemies also engender ongoing
costs, but they are environmentally safe and may be more economical than
pesticide use. Prime examples of the
successful use of this method are the highly satisfactory control of pests in
sugarcane in Latin America (Bennett 1969), and in citrus orchards in the
Filmore District of southwestern California (van den Bosch et al. 1982). Conservation
of natural enemies for control of pests such as Lygus bugs on cotton in the San Joaquin Valley in
California and in other crops elsewhere (DeBach 1974) often yields superior
economic benefits than does insecticidal control (Falcon et al. 1971). In such cases the ill advised use of
chemical pesticides (x) may induce damage resulting in additional pest
control costs and, at times, lower yields (Gutierrez et al. 1979). With naturally occurring biological
control and economically viable classical biological control (BC), the costs
of other pest control tactics and social costs often become zero, and the
whole of society obtains the maximum benefits: the natural and biological controls supplant other methods of
control and may solve the problem permanently. In such cases biological control should be favored as the
equation for profit becomes, B(BC) -
C(BC) > B(x) - C(x) >
B(x) - C(x) - S(x). Even with the presence of effective
natural control, growers may still visualize a high positive risk of pest
outbreak and may apply cheap pesticides as insurance against risk of pests
such as Lygus in cotton, but
in paying the premium they may become stuck in a treadmill of pesticide use
as described by van den Bosch (1978).
DeBach (1974) named pesticides "ecological narcotics"
because of their effect of suppressing problems temporarily, but causing
addiction to their continued use.
Regev (1984) also referred to the addiction to pesticides, and
concluded that generally the root of the problem is that pesticides are
preferred because the social costs are not paid by the users. Two ideas
appear in an analysis of the reliance of growers on pesticides: one is a measure of the mean and variance
of profits and the other is the perception of risk (Gutierrez et al.
1992). If there is effective natural
control (e.g., San Joaquin Valley cotton), growers who do not wish to take
risks still consider the distribution of profits with and without pesticides. Obviously if such growers think that
despite the same average profit, the variation in profit is lowest using
pesticides they will undoubtedly choose to control pests by using them. If growers are more informed about all the
issues, they may still judge the distribution more favorable using pesticides
(2B) because they have no incentive to assume responsibility for social
costs. The decision might not be so
certain in the latter cases, if increases in pesticide costs cause a
significant shift in the perception of risk involved in the various control alternatives. A desirable outcome might be that natural
controls are increasingly preferred.
If resistance occurs, growers soon learn that preserving natural
enemies in the field is an option to bankruptcy. In cases of complete biological control, the mean profits may
be greatly increased because pesticides would no longer be required, yields
would be near maximum and the variance of yield narrowed. It is
therefore important how a grower understands risk which determines how much
he will be willing to pay for pest control to minimize that risk. Adding the social cost of pesticide use to
the cost of pesticides narrows the gap between unrealistically perceived risk
and the real risk to profits. Taxing
pesticide users to fund biological control efforts would be a socially
responsible way to fund permanent solutions for pest problems (Gutierrez et
al. 1992). The most
thorough resume of biological control efforts and successes may be found in
Clausen (1978). Another publication
will be released later in 1991 by the University of California Press that
discusses in great detail some of the outstanding contributions to pest
control employing the biological control method. The
so-called Island Theory seems to be borne out in thee results, because a
substantial portion of the more striking successes in biological control have
occurred on such islands as Hawaii, Fiji and Mauritius, and ecological
islands such as portions of California.
One reason is that biological control work began early in such places,
and a disproportionate amount of research and importation was undertaken
there in comparison to continents (excepting California). However, the present record shows that
about 60% of all the complete successes have occurred on continents; thus,
the island theory is no longer fully acceptable. Parasitoids
have been argued to be better than predators as biological control
agents. Because a predaceous larva
consumes many host individuals during its lifetime and a parasitoid but one
host, it might appear that a predator is inherently more destructive and thus
makes a better biological control agent.
However, analysis of the 139 species of entomophagous insects imported
and established in the United States as of 1967 showed that 113 were parasitoids
and 26 predators. This ratio has
remained similar into the 1990's.
Roughly twice as many successes in biological control have resulted
from parasitoid introduction in the United States. However, about four times as many on the world scene. The
apparent superiority of parasitoids is the subject of contemporary debate and
research. This may only reflect the
fact that parasitoids have received the greatest amount of attention in terms
of the number of species introduced and the number subjected to field
analyses. Multiple as Opposed to "The Best" Species The
question has arisen whether multiple importation of different natural enemy
species attacking a given host and the resulting interspecific competition
among them produces a greater or lesser total host mortality than would be
the importation of the so-called "best" species allowed to act
alone. Analysis of past successes
suggests that multiple species importation, whether made simultaneously or
sequentially, have nearly always resulted in enhanced biological control. Multiple
introductions provide a series of natural enemies that can attack a sequence
of host stages in any one habitat.
Here environmental changes may adversely affect one natural enemy yet
favor another, so that the latter natural enemy may tend to compensate for
the reduced efficiency of the former.
Howard and Fiske made these points
the basis of their so-called sequence theory of multiple importations. When several natural enemy species are established
on a common host, they are more likely to parasitize that host over a greater
geographic range than a single species of natural enemy. Multiple introductions increase the
chances of obtaining a species of natural enemy that can use alternate hosts
to overcome difficulties associated with seasonal fluctuation in pest
abundance. Multiple importations
favor the chance of establishing a truly superior species of natural enemy. Clausen's 3-Host Generation / 3-Year Rule A good exception to the Clausen rule is provided by the
mymarid egg parasitoid, Patasson
nitens imported from
Australia into South Africa in 1926.
Complete biological control of the eucalyptus weevil was achieved
within the required three years in southern and southeastern parts of the
country. However, in the northeastern
highlands where conditions were less favorable to both host and parasitoid,
several additional years were required for the parasitoid to bring about
substantial control of the eucalyptus weevil. This example also nullifies the generalization that egg
parasitoids alone would not prove capable of biological control. Single Larval Parasitoid Importations A good example of a single larval parasitoid working
successful biological control is the tachinid, Ptychomyia remota,
introduced into Fiji from Malaya in 1925, which resulted in the complete
control of the coconut moth. This
also illustrates a case where an area other than the native home of a pest
produced a useful biological control agent, since Ptychomyia's natural host in Malaya was a related, but
innocuous species of native moth. Single Pupal Parasitoid The imported cabbage worm controlled in New Zealand by Pteromalus puparum introduced from North America in 1933 is a notable
example. Other Generalizations Such generalizations as biological control being more
likely to succeed against pests of perennial rather than short-lived annuals,
against sessile or nonmotile pests, or against alien rather than native pests,
must also be qualified. As with any
generalization, there are exceptions to the rule. Analyses of the results of past efforts can provide useful
guidelines. It will probably continue to hold that the number of successes
attained in biological control in any one country is directly proportional to
the amount of research and importation work carried out there. Hawaii, California, the rest of the United
States, New Zealand and Australia, as well as the former Commonwealth
Institute of Biological Control, currently lead in the number of cases of
successful biological control of insect pests and weeds brought about by
imported natural enemies. This
reflects the proportionately greater amount of biological control programs
instituted by each of those countries where early impetus was provided by the
proportionately greater losses that those countries have suffered from
introduced pests. There are
of course many other countries reporting successful cases of biological
control. Many of these are
represented by only one or two successes that resulted largely from
trans-shipments of biological control agents of proven value following their
initial successful employment in other countries. Four insect pests that have been controlled in this manner in
various countries are: A. Cottony-cushion scale controlled by the Rodolia (Vedalia) beetle in 55
countries following its initial success in California. B. Woolly apple aphid controlled by Aphelinus mali in 42 of 51 countries into which it was introduced
following its initial success in New Zealand. C. White peach scale controlled by Prospaltella berlesei in 5 countries
following its initial success in Italy. D.
Citrus blackfly controlled by Eretomocerus
serius in 9 countries
following its initial success in Cuba. Pest Groups Further
analysis reveals that 55% of the 107 pest species brought under some measure
of biological control through 1960 belong to the Homoptera, nearly 40% of
which are scale insects. 20% of the
pests are Lepidoptera; 17% are Coleoptera, while 8% belong to other taxa. Natural Enemy Groups Because a majority of successes have involved coccids, it
follows that a large proportion of the natural enemies involved in biological
control success have been natural enemies of scale insects: Hymenoptera-- Encyrtidae & Aphelinidae; Coleoptera-- Coccinellidae This grouping will probably change
as more emphasis is given to non-homopterous pests. For weed control, Homoptera-Hemiptera,
Thysanoptera, Coleoptera, Lepidoptera, Diptera and Hymenoptera. It is suggested that biological
weed control has registered a proportionately greater measure of success than
biological control of insect pests.
Only during the last few years has the method been used against weeds
other than those infesting relatively stable, undisturbed rangelands. Weeds engage in intense competition for
space, water and nutrients with other plants, and the competitive advantage
of these other plants may be strongly favored by further additional insect
injury to the weeds. Plant injury by
weed-feeding insects may be attended and intensified by the action of plant
pathogens. The work has been
necessarily restricted to promising prospective biological control agents. Unlike
insect hosts, plants do not always die from the attack of a single
insect. The greater numbers of
natural enemies that are thus generated at low host densities makes for a
greater searching effectiveness on the part of biological weed control
agents. Other texts and files in this series may be viewed by CLICKING on
the following: Secrets of
Science <museum1.htm> History of Biological Control
<museum2.htm> Introduction and Scope of Biological Control <museum3.htm> National and International Organizations Active in Biological
Control <museum4.htm> Economic Gains and Analysis of Successes in Biological
Control <museum5.htm> Trends and Future Possibilities in Biological Control <museum6.htm> Beneficial Insects <museum7.htm> Case Histories of Salient Biological Control Projects <detailed,htm> Guide to Identifying Predatory and Parasitic Insects <NEGUIDE.1>, <NEGUIDE.2>...
etc. Insect
Natural Enemy Photos
<NE-2ba.PCX>, <NE-2bb.PCX>... <NE-247ba.PCX>... etc. Meal Worm Project <project.3.htm> Ladybird Beetles <ladybird.htm> Fruit Flies in California <fruitfly.htm> Killer Bees <killer.htm> Monarch & Viceroy Butterflies
<31aug95.mus.htm> Everywhere is Home <9feb98.mus.htm> Familiar Butterflies of the
United States & Canada <butterfl.htm> References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Anonymous.
1992. Principles and
Application of Biological Control.
University of California Press, Berkeley, CA. (in press). Adkisson, P. L. 1972. The integrated
control of insect pests of cotton.
Proc. Tall Timbers Conf. Ecol. Anim.
Control Habitat Mngmt., Tallahassee, Florida 4: 175-88. Andrés, L.
A. 1977.
The economics of biological control of weeds. Aquatic Botany. 3: 111-23. Bennett, F. D.
1969. Tachinid flies as
biological control agents for sugarcane moth borers, p. 117-18. In: J. R. Williams, J. R. Metcalfe, R. W.
Mungomery & R. Mathes (eds.), Pests of Sugar Cane. Elsevier Publ., New York. 568 p. Burrows, T. M., V. Sevacherian, H. Browning
& J. Baritelle. 1982. History and cost of the pink bollworm
(Lepidoptera: Gelechiidae) in the Imperial Valley. Bull. Ent. Soc. Amer. 28:
286-90. Caltagirone, L. E. & C. B. Huffaker. 1980.
Benefits and risks of using predators and parasites for controlling pests. Ecol. Bull. (Stolkholm) 31: 103-09. Clausen, C. P.
(ed.). 1978. Introduced
Parasites and Predators of Arthropod Pests:
A World Review. U. S. Dept. of
Agriculture, Agric. Handbk. No. 480., Washington, D.C. 545 p. Cullen, J.
M. 1985.
Bringing the cost benefit analysis of biological control of Chondrilla juncea up to date, p. 142-5. In: E. S. DelFosse (ed.), Proc. 6th Internal.
Symp. Biol. Contr. Weeds, 19-25 Aug, 1984.
Vancouver, Canada. Agric.
Canada. Day, W. H.
1981. Biological control of
alfalfa weevil in northeastern United States, p. 361-74. In: G. C. Papavizas (ed.), Biological Control
in Crop Production. BARC Symp. No. 5,
Allenheld, Osmun, Totowa, New Jersey.
461 p. Dean, H. A., M. F. Schuster, J. C. Bolling
& P. T. Riherd. 1979. Complete biological control of Antonina graminis in Texas with Neodusmetia
sangwani (a classic
example). Bull. Ent. Soc. Amer. 25(4):
262-67. DeBach,
P. 1971.
The use of imported natural enemies in insect pest management. Proc. Tall Timbers Conf. Ecol. Anim.
Control Habitat Mngmnt., Tallahassee, Florida 3: 211-32. DeBach, P.
1974. Biological Control by
Natural Enemies. Cambridge Univ.
Press, London. 323 p. DeBach, P., E. J. Dietrick, C. A. Fleschner
& T. W. Fisher. 1950. Periodic colonization of Aphytis for control of the
California red scale. Preliminary
tests, 1949. J. Econ. Ent. 43: 783-802. Doutt, R. L.
1964. The historical
development of biological control, p. 21-42.
In: P. DeBach (ed.), Biological Control of
Insect Pests & Weeds. Reinhold
Publ, New York. 844 p. Ehler, L. E.
& L. A. Andrés. 1983. Biological control: exotic natural enemies to control exotic
pests, p. 295-418. In: C. L. Wilson & C. L. Graham (eds.), Ecotic Plant Pests and
North American Agriculture. Academic
Press, New York. 522 p. Ehler, L. E.
& R. van den Bosch. 1974. An analysis of the natural biological
control of Trichoplusia ni (Lepidoptera: Noctuidae) on
cotton in California. Canad. Ent. 106:
1067-73. Ehler, L. E.,
K. G. Eveleens & R. van den Bosch.
1973. An evaluation of
some natural enemies of cabbage looper in cotton in California. Environ. Ent.
2: 1009-15. Eveleens, K.
G., R. van den Bosch & L. E. Ehler.
1973. Secondary outbreak
induction of beet armyworm by experimental insecticide application in cotton
in California. Environ. Ent. 2: 497-503. Falcon, L. A., R. van den Bosch, J. Gallagher
& A. Davidson. 1971. Investigation on the pest status of Lygus hesperus in cotton in central California. J. Econ.
Ent. 64: 56-61. FAO.
1987. Production Yearbook
1986. United Nations, FAO, Rome. Vol.
40. 306 p. Garcia, R.,
L. E. Caltagirone & A. P. Gutierrez.
1988. Comments on a
redefinition of biological control.
Roundtable. Bioscience
38: 692-94. Gould, F.
1986. Simulation models for
predicting durability of insect-resistant germ plasm: a deterministic diploid, two-locus model. Environ. Ent. 15:
1-10. Gutierrez, A.
P., Y. Wang & U. Regev. 1979. An optimization model for Lygus hesperus (Heteroptera: Miridae) damage in cotton: The economic threshold revisited. Canad. Ent.
111: 41-54. Gutierrez, A.
P., P. Neuenschwander, F. Schulthess, J. U. Baumgaertner, B. Wermelinger, B.
Loehr & C. K. Ellis. 1988a. Analysis of biological control of cassava
pests in Africa. II. Cassava mealybug
Penococcus manihoti. J. Appl. Ecol. 25: 921-40. Gutierrez, A.
P., J. S. Yaninek, B. Wermelinger, H. R. Herren & C. K. Ellis. 1988c.
Analysis of the biological control of cassava pests in Africa. III.
Cassava green mite Mononychellus
tanajoa. J. Appl. Ecol. 25: 941-50. Gutierrez, A.
P., B. Wermelinger, F. Shulthess, J. U. Baumgaertner, H. R. Herren, C. K.
Ellis & J. S. Yaninek. 1988b. Analysis of biological control of cassava
pests in Africa. I. Simulation of
carbon, nitrogen and water dynamics in cassava. J. Appl. Ecol. 25:
901-20. Gutierrez,
A. P., L. E. Caltagirone & W. Meikle.
1992. Economics of
biological control. In: Principles and Application of Biological Control. Univ. of California Press, Berkeley (in press). Harris, P.
1979. Cost of biological
control of weeds by insects in Canada.
Weed Sci. 27(2): 242-50. Hassan, S. A.
1982. Mass production and
utilization of Trichogramma: 3.
Results of some research projects releated to the practical use in the
Federal Republic of Germany. 1st Int.
Symp. Trichogramma, Antibes,
France. Coll. INRA 9: 213-18. Headley, J. C. & M. A. Hoy. 1987.
Benefit/cost analysis on integrated mite management program for
almonds. J. Econ. Ent. 80:
555-59. Herren, H. R.,
P. Neuenschwander, R. D. Hennessey, & W. N. O. Hammond. 1987.
Introduction and dispersal of Epidinocarsis
lopezi (Hym., Encyrtidae) an
exotic parasitoid of the cassava mealaybug Pehnococcus manihoti
(Hom., Pseudococcidae), in Africa.
Agric. Ecosyst. Environ. 19:
131-34. Howarth, F. G.
1983. Classical
biocontrol: Panacea or Pandora's
box. Proc. Hawaiian Ent. Soc. 24: 239-44. Hoy, M. A., W. W. Barnett, W. D. Rell, D.
Castro, D. Cahn, L. C. Hendricks, R. Coviello & W. J. Bentley. 1982.
Large scale releases of pesticide-resistant spider mite
predators. Calif. Agric. 36: 8-10. Hoy, M. A., W. W. Barnett, L. C. Hendricks, D.
Castro, D. Cahn, & W. J. Bentley.
1984. Managing spider mites in
almodns with pesticide-resistant predators.
Calif. Agric. 38: 18-20. Huffaker, C. B. & L. E. Caltagirone. 1986.
The impact of biological control on the development of the
Pacific. Agric. Ecosyst. Environ.
15: 95-107. Huffaker, C. B. & C. E. Kennett. 1953.
Developments toward biolgocial control of cyclamen mite on
strawberries in California. J. Econ. Ent. 46:
802-12. Huffaker, C.
B. & C. E. Kennett. 1966. Biological control of Parlatoria oleae
(Colvee) through the compensatory action of two introduced parasites. Hilgardia 37(9): 283-335. Huffaker, C. B., F. J. Simmonds & J. E.
Laing. 1976. Theoretical and empirical basis of
biological control, p. 41-78. In: C. B. Huffaker & P. S. Messenger (eds.), Theory &
Practice of Biological Control.
Academic Press, New York. 788
p. Hussey, N. W.
1970. Some economic
considerations in the future development of biological control, p.
109-18. In: Soc. Chem.
Industry, Monograph 36, Technological Economics of Crop Protection and Pest
Control. SCI, London. Hussey, N. W.
1958. Whitefly control by
parasites, p. 104-15. In: N. W. Hussey & N. Scopes (eds.), Biological Control - The
Glasshouse Experience. Cornell Univ.
Press, Ithaca, New York. 24p p. Hussey, N. W. & N. Scopes. 1985.
Biological Pest Control - The Glasshouse Experience. Cornell Univ. Press, Ithaca, New
York. 140 p. Kenmore, P. E.
1980. Ecology and outbreaks of
a tropical insect pest of the green revolution, the rice brown planthopper, Nilaparvata lugens (Stal). Ph.D. Thesis, University of California,
Berkeley, CA. Kenmore, P.
E., F. O. Carino, C. A. Perez, V. A. Dyck & A. P. Gutierrez. 1986.
Population regulation of the rice brown planthopper (Nilaparvata lugens (Stal)) within rice
fields in the Philippines. J.Plant
Prot. Tropics 1: 19-37. Lamas, J.
M. 1980. Control de los insectos- plaga del algodonero en el Peru. Esquema de la planificación de una campaña
de control integrado y sus problemas.
Revista Peruana Ent. 23: 1-6. Legner, E.
F. 1986a.
Risk categories of biological control organisms. Proc. Calif. Mosq. & Vect. Contr.
Assoc., Inc. 53: 79-82. Legner, E.
F. 1986b.
Importation of exotic natural enemies. In: "Biological Control of Plant Pests
and of Vectors of Human and Animal Diseases." Fortschritte der Zool. Bd. 32: 341 pp. Li, Li-Ying.
1982. Trichogramma sp. and their utilization in the Peoples'
Republic of China. 1st Intern. Symp. Trichogramma, Antibes,
France. Coll. INRA 9: 23-9. Luck, R. F., B. M. Shepard & P. E.
Kenmore. 1988. Experimental methods for evaluating
arthropod natural enemies. Ann. Rev.
Ent. 33: 367-91. National Academy of Sciences. 1987.
Report of the research briefing panel on biological control in managed
ecosystems. R. J. Coo, (Chair.). Washington, D. C.. Natl. Acad. Press. 12 p. Neuenschwander,
P., W. N. O. Hammond, A. P. Gutierrez, A. R. Cudjoe, J. U. Baumgaertner, U.
Regev & R. Adjakloe. 1991. Impact assessment of the biological
control of the cassave mealybug, Phenacoccus
manihoti Matile Ferrero
(Hemiptera: Pseudococcidae) by the introduced parasitoid Epidinocarsis lopezi
(DeSamtis) (Hymenoptera: Encyrtidae).
Bull. Ent. Res. Pak, G. A.
1988. Selection of Trichogramma
for inundative control. Ph.D. Thesis,
Agric. Univ., Wageningen, Netherlands. 224 p. Regev, U. 1984.
An economic analysis of man's addiction to pesticides, p. 441-53. In: G. R. Conway (ed.), Pest and Pathogen
Control: Strategic, Tactical &
Policy Models. John Wiley & Sons,
New York. 488 p. Reichelderfer,
K. H. 1979.
Economic feasibility of a biological control technology: using a parasitic wasp, Pediobius foveolatus, to manage Mexican bean beetle on soybean. U. S. Dept. Agric. ESCS, AGric. Econ.
Rept. No. 430. Reichelderfer, K. H. 1981. Economic feasibiligy
of biological control of crop pests, p. 403-17. In: G. C. Papavizas (ed.), Biological Control
in Crop Production. BARC Symnp. No.
5, Allenheld, Osmun, Totowa, New Jersey.
461 p. Reichelderfer,
K. H. 1985.
Factor affecting the economic feasibility of the biological control of
weeds. In E. S. DelFosse
(ed.), Proc. 6th Internatl. Symp. Biol. Control Weeds, 19-25 Aug, 1984. Vancouver, Canada. Room, P. M., K. L. S. Harley, I. W. Forno &
D. P. A. Sands. 1981. Successful biological control of the
floating weed Salvinia. Nature 294: 78-80. Simmonds, F. J. 1967. The economics of
biological control. J. Roy. Soc. Arts
115: 880-98. Stenseth, C.
1985a. Whitefly and its
parasite Encarsia formosa, p. 30-3. In: N. W. Hussey & N. Scopes (eds.),
Biological Pest Control - The Glasshouse Experience. Cornell Univ. Press, Ithaca, New
York. 240 p. Stenseth,
C. 1985b.
Red spider mite control by Phytoseiulus
in northern Europe, p. 119-24. In N. W. Hussey & N. Scopes (eds.), Biological Pest Control -
The Glasshouse Experience. Cornell
Univ. Press, Ithaca, New York. 240 p. Tassan, R. L., K. S. Hagen & D. V.
Cassidy. 1982. Imported natural enemies established
against ice plant scales in California.
Calif. Agric. 36: 16-17. Taylor, C. R. & R. D. Lacewell. 1977.
Boll weevil control strategies:
regional benefits and costs.
Southern J. Agric. Econ. 9:
124-35. Turner, C. E.
1985. Conflicting interests
and biological control of weeds.
Proc. 6th Internatl. Symp. Biol. Control of Weeds, Vancouver, Canada
1984. p. 203-25. van den Bosch,
R. 1978.
The Pesticide Conspiracy.
Doubleday, New York. 226 p. van den Bosch,
R., P. S. Messenger & A. P. Gutierrez.
1982. An Introduction to
Biological Control. Plenum Press, New
York. 247 p. von Arx, R, J.
Baumgaertner & V. Delucci. 1983. A model to simulate the population
dynamics of Bemisia tabaci Genn. (Stern.,
Aleyrodidae) on cotton in the Sudan Gezira.
Z. angew. Ent. 96: 341-63. |