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OCR for page 55
Report of the
Research Bneftug Panel on
Biological Control
in Managed Ecosystems
OCR for page 56
Research Beefing Panel on
Biological Control
in Managed Ecosystems
R. lames Cook (Chairman), Reseach Leader,
Root Disease and Biological Control
Research Unit, USDA-ARS-
Washington State University, Pullman
Lloyd Andres, Research Entomologist,
USDA-ARS, Albany, Calif.
Gustaaf A. de Zoeten, Professor of Plant
Pathology, University of Wisconsin,
Madison
Charles Doane, Director of Research anct
Development, Scentry, Inc., Buckeye,
Ariz.
l
Robert W. Gwadz, Scientist Director,
USPHS, and Head, Meclical Entomology
Unit, NATD/N1[H, Bethesda, Md.
Ralph W. F. Hardy, President, Boyce
Thompson Institute for Plant Research,
Ithaca, N.Y.
Bruce Hemming, Research Specialist, Plant
Microbiology, Monsanto Life Sciences
Research Center, St. Louis, Mo.
Joseph Kuc, Professor of Plant
Microbiology, University of Kentucky,
Lexington
Reinhold Mankau, Professor of
Nematology, University of California,
Riverside
56
David Miller, Staff Scientist, Genetics
Institute, Tnc., Cambridge, Mass.
Clarence A. Ryan, Jr., Professor of
Biochemistry, Institute of Biological
Chemistry, Washington State University,
Pullman
M. Scott Smith, Associate Professor of Cell
Microbiology, University of Kentucky,
Lexington
Staff
Clifford l. Gabriel, StaffOff~cer, Board on
Basic Biology, Commission on Life
~ .
sciences
AlIan R. Hoffman, Executive Director,
Committee on Science, Engineering, and
Public Policy
Sandra Anagnostakis, Consultant,
Connecticut Agricultural Experiment
Station, New Haven
Edward Michelson, Consultant, Uniformed
Services University of the Health
Sciences, Bethesda, McI.
George Templeton, Consultant, University
of Arkansas, Fayetteville
OCR for page 57
Report of the
Research Bnefing Panel on
Biological Control
in Managed Ecosystems
Biological control is the use of natural or
modified organisms, genes, or gene prod-
ucts to reduce the effects of undesirable or-
ganisms (pests), and to favor desirable or-
ganisms such as crops, trees, animals, and
beneficial insects and microorganisms. Man-
aged ecosystems are environments managed
for human benefit. They include farmland,
rangeland, forests, lakes, and urban and res-
idential areas. Biological control in managed
ecosystems includes the manipulation and
strategic introduction of organisms, genes,
or gene products to influence the outcome of
otherwise natural biological interactions in a
manner favorable to humans. Major target
pests of biological control are insects, mites,
weeds, parasitic nematodes, rodents, and
pathogens and their vectors. Achieving suc-
cessful levels of biological control is depen-
dent on fundamental knowledge of biologi-
cal interactions at the molecular, cellular, or-
ganismal, and ecosystem levels.
Biological control has provided the under-
pinning of agriculture since ancient times
through practices such as crop rotation, in-
tercropping, soil flooding, and tillage. Fortu-
nately, most pests are still suppressed by
natural biological controls such as that pro-
vided by antagonists (natural enemies) and
57
self-defense mechanisms (e.g., resistance to
pests) that have evolved through long asso-
ciations between the host plant or animal
and its pests. The era of modern biological
control began about 100 years ago with the
highly successful introduction of the vedalia
beetle from Australia into California to con-
trol the cottony-cushion scale insect pest of
citrus. Nearly 90 years ago, shortly after the
rediscovery of Mendel's laws of genetic in-
heritance, studies of resistance to wheat
stem rust provided the first indication that
genes for disease resistance in plants could
be transferred by conventional breeding.
Because of economic forces and the lack of
adequate knowledge about biological con-
trols, many managed ecosystems have be-
come heavily dependent on chemical pesti-
cides. A "spray it" attitude developed, and
even today some scientists responsible for
research and extension programs tend to
think of chemical controls first and of alter-
native biological controls second. Thus, bio-
logical control remains relatively unexplored
as an active area of research. in the United
States, public and private support for re-
search and development applied to biologi-
cal control is less than 20 percent of that for
chemical control. On a global basis, of the es
OCR for page 58
timated $16 billion spent annually on pest
control, less than ~ percent is spent for bio-
logical control agents.
WHY BIOLOGICAL CONTROL?
The use of chemical pesticides has pro-
duced an increasing number of negative and
nontarget effects, and pesticide residues are
being found in groundwater and food. Bio-
logical controls, however, have resulted in
no known or only limited negative effects on
the environment. Also, many pests are cle-
veloping resistance to once-effective pesti-
cides, making it necessary to develop new
chemicals or to find effective combinations of
chemicals. It is becoming increasingly more
difficult and expensive to discover effective
chemical pesticides. Although some pests
have genetically overcome certain genes for
resistance introduced in crop plants, thus far
there are no examples of pests becoming re-
sistant to natural enemies, pheromones, or
microbial pesticides. Furthermore, many
chemicals applied to control pests also de-
stroy beneficial organisms and some create
temporary, vacant biological niches that may
then provide an opportunity for a new pest
or a resurgence of the original uneasy. in con-
trast, biological controls are nearly always
targeted for specific pests and are therefore
less likely to upset the balance among inter-
acting populations.
Biological control can be achieved by regu-
lar or repeated applications of a control agent
(e.g., a microbial pesticide) that is specific for
a target pest, by a one-time or occasional in-
troduction of a control agent (or genetically
resistant crop cultivar) with the ability to es-
tablish and keep the target pest in a state of
suppression, and by enhancing the effects of
indigenous natural enemies (antagonists) of
the target pest or maximizing host-plant re-
sistance to the pest through the use of cul-
tural practices (e.g., crop rotation). Some of
these biological controls may be initially less
effective than many chemical controls, but
58
they are generally more stable and longer
lasting. By their nature, biological controls
tend to be less dependent than chemical pes-
ticides on fossil energy, and many (e.g.,
those that achieve control in a single or only
occasional application) are self-sustaining.
There are many economically important
pests, notably the soilborne pests and insect-
vectored pathogens, for which chemical con-
trols are either nonexistent or impractical.
Moreover, the modern trend in agriculture
toward less or no tilIage (for soil conserva-
tion) and shorter or no crop rotation has fa-
vored increased damage from soilborne
pests. Unfortunately, the use of high-energy
production inputs such as fertilizer and irri-
gation are commonly increased to compen-
sate for inadequate pest control or to attain
greater crop yields despite the pest damage.
Biological control achieved through greater
knowledge of ecology and strategic intro-
ductions of beneficial organisms or genetic
resistance in the crop may offer the only
means of stably and effectively controlling
these intractable pest problems. Any gain in
control over these pests is a gain for produc-
tion efficiency, since yields are increased
without requiring more fertilizer or water.
Thus, biological control is not only an alter-
native to chemical control, it also greatly
helps industries such as agriculture conserve
resources and become more sustainable and
efficient with fewer negative effects on the
environment (Table I).
The development of recombinant DNA
technology is unquestionably the most sig-
nificant advance thus far for biological con-
trol research. Recombinant DNA techniques
enable scientists to understand the mecha-
nisms of biological control at the molecular
level in ways previously not possible. Un-
derstanding the genes and gene products
important to biological control opens the
way for the genetic alteration of the agents
carrying these genes, for the production of
more useful transgenic biological control
agents, and for deriving improved practices
to enhance biological control.
OCR for page 59
BIOLOGICAL CONTROL IN MANAGED ECOSYSTEMS
TABLE 1 Potential Benefits from Biological Control Research
F.
armmg
Improved pro-
duction effi
Agribusiness
Input
New high-value
products for
ciency leading national and
to a more fa- international
vorable com- markets
Food
Processing
Decreased levels
of agrichemi-
cal residues in
commodities
for food
Consumer Society International
petitive stand
. . .
1ng In aomes-
tic and export
markets
Reduced health
risk from agri-
chemicals
Plant protection
for new or
modified
crops
Low-cost food
Increased qual-
ity (healthful-
ness) of food
Cleaner, safer Improved com
environment petitiveness
COMPONENTS OF
BIOLOGICAL CONTROL
The components of biological control (Ta-
ble 2) can include a pest agent used against
itself (e.g., pheromones and sterile mates of
insect pests), a host plant or animal we seek
to protect whose defense mechanisms have
been enhanced through management or ge-
netic manipulation, and the pest's natural
enemies and antagonists (the classic biologi-
cal control agents). These components and
the approaches to their management cro-
vide the basis for three major biological con-
tro} strategies:
1. Regulation of the pest population: biologi-
cal control agents are used to regulate the
pest population at or below an acceptable
threshold.
2. Exclusionary systems of protection: benefi-
cial microorganisms are used as a living bar-
rier that excludes infection or cleters pest
attack.
3. Self-defense: resistance mechanisms in
the plant or animal host itself prevent or sup-
press disease or pest damage.
59
All of these strategies can be demonstrated
by the multiple uses of the Bacillus thuringien-
sis (Bt) toxin, a protein lethal to certain in-
sects. The bacterium B. thuringiensis has long
been marketed throughout the worIct as a
highly effective and safe microbial pesticide
for use against some insect pests. With the
tools of recombinant DNA technology, the
Bt toxin gene has now been transferred to,
and expressed in, both the common soil bac-
terium Pseudomonas fluorescent and tobacco
plants. Therefore, when the toxin gene is ex-
pressecl in its native B. thuringiensis, it can
regulate the pest population (Strategy I).
When B. thuringiensis is applied as a micro-
bial pesticide on plants or when the toxin
gene is expressed in P. fluorescent, which
grows on corn roots, it protects against insect
attack by operating as an exclusionary sys-
tem on the plant host (Strategy 2~. Finally,
when the gene is expressed in tobacco
leaves, it limits pest damage by functioning
as a self-defense system within the plant
host (Strategy 3~. Undoubtedly the flexibility
made possible by recombinant DNA tech
OCR for page 60
TABLE 2 Selected Examples of Biological Controls
Component
Strategy
Regulation of the
Pest Population
Pheromone gossypol to
control pink bollworm
in cotton in Egypt,
South America, and the
United States
Sterile males to control
Exclusionary Systems
of Protection
Self-Defense
Pest agent used against
itself
Natural enemies and an-
tagonists (classic biolog-
ical control agents)
Host plant or animal
screw worm in the
United States
Mosquitoes genetically in-
capable of vectoring the
malaria agent used to
displace capable typesa
Wasps for control of the
alfalfa weevil in the
United States
Predatory snail for control
of snail vector of schisto-
somiasis agent in Puerto
Rico
Puccinia rust for control of
skeleton weed in Aus-
tralia and the United
States
Bacillus thuringiensis for
control of certain cater-
pillars-used worldwide
Crotalaria grown as a trap
plant; root-knot nema-
tode infects this plant
but does not repro-
duce-minor use in the
United States
Avirulent strain K-84 of
Agrobacterium for control
of crown gall on fruit
trees and ornamental
plants in several
countries
Ice-minus strains of
Pseudomonas syringae to
exclude ice-nucleation-
active strains from
leaves of frost-sensitive
plantsa
Phlebia 8igantea applied to
pine stumps to exclude
the pine root-rot fungus
Heterobasidion annosum
Nonpathogenic Lactobacil-
lus strains used to ex-
clude Escherichia cold
from the intestinal lining
and protect piglets
against neonatal scoursa
Toxin gene from B. thurin-
giensis expressed in
Pseudomonas on corn
roots for protection
against certain soil
insectsa
Dense sowings of cereal-
grain crops to preempt
the establishment of
weeds-used world-
wide
Mild strains of citrus tris
teza virus to protect cit-
rus against virulent
strains of the virus in
Australia and Brazil
Resistance to tobacco mo-
saic virus (TMV) in to-
bacco plants genetically
engineered to express
the coat-protein gene of
TMva
"Immunization" (in-
duced resistance) of cu-
cumbers and other plant
species against Colletot-
richum (anthracnose) by
inoculating their leaves
with tobacco necrosis
virusa
Toxin gene from B. thurin-
giensis expressed in to-
bacco leaves for control
of certain leaf-feeding
caterpillarsa
Genetic resistance to
southern corn leaf blight
in corn in the United
States
Genetic resistance to Hes-
sian fly in wheat in the
United States
aExperimental stage only.
nology will provide other new uses for other
traditional biological control agents.
For managed ecosystems, integrated mul-
tiple biological controls are common and
tend to be more effective than single-shot
tactics. This may account for the relatively
stable nature of biological control. A system
60
is generally developed first by using cultural
practices, such as crop rotation and tillage,
that maximize the effect of the natural (indig-
enous) biological controls and then by intro-
ducing specific controls, such as certain
genes for resistance to pests, exotic enemies
of naturalized pests, or inundative applica
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BIOLOGICAL CONTROL IN MANAGED ECOSYSTEMS
lions of biological control agents in cases in
which the natural populations are too small
to be effective.
SUCCESSFUL BIOLOGICAL CONTROLS
REGULATION OF THE
PE ST POPULATION ~ STRATEGY 1)
Many (probably most) pests do not be-
come economically important until they es-
cape their own natural enemies or until other
constraints on the pest population are eased.
This generally happens when the pest is in-
advertently introduced into a new environ-
ment. The great majority of economically
important pests in the United States, for ex-
ample, were accidently introduced as a
result of commerce. It has been estimated
that 11 new insect pests are inadvertently in-
troducec! into the United States each year.
For some of these pests, successful control
has been achieved by tracking down their
original source and then finding and intro-
clucing one or more of their natural enemies.
A classic example of this is the control for the
past 50 years of the Opuntia cactus in Austra-
lia, following the introduction from South
America of a moth (CactobZastis cactorum) that
feeds on that cactus. In the United States,
more than 70 candidate plant-feeding insects
and plant pathogens (all fungi) have been in-
troduced to control target weed species.
These organisms were first selected because
they are specifically adapted to feed on or
parasitize the target weeds. About 14 weed
species are now partly or completely con-
trolled in the United States in this way. Al-
most five times this number of naturalized
insect pests have been controlled in the
United States through the introduction of
exotic parasites, predators, or pathogens.
Tracking down the source of the pest can
be difficult, especially if its origin is not read-
ily accessible, such as in the People's Repub-
lic of China,* the Middle East, or the USSR,
*Henceforth referred to as "China."
61
all of which are sources of major U.S. pests.
Moreover, in testing biological control
agents to be used against weeds, the number
of plant species that must be examined is in-
creasing because of growing concern that the
agent may also attack nontarget plant spe-
cies. Once released, the biological control
agent must be monitored for several years
within the ecosystems in which the releases
were made as well as within adjacent ecosys-
tems. Thus far, no insect or microorganism
introduced for pest control in the United
States has itself become a pest.
EXCLUSIONARY SYSTEMS OF
PROTECTION (STRATEGY 2)
A method discovered in Australia for bio-
logical control of crown gall on ornamental
shrubs and orchard trees is based on an ex-
clusionary system that prevents the crown-
gall pathogen from infecting the plant. The
pathogen population may then decline
through attrition, but this is secondary to
keeping the plant healthy. Crown gall is
caused by Agrobacterium tumefaciens, a soil
bacterium that infects roots and stems
through wounds such as those that occur
during transplanting. In the biological con-
tro} system, an avirulent Agrobacterium is
used to protect wounds against the virulent
Agrobacterium. This biological control agent
(known as strain K-84) lacks the genetic
means to incite gall formation and produces
a substance that inhibits the pathogen. Bare-
root transplants dipped in a cell suspension
of K-84 are protected for most or all of their
life.
In another exclusionary type of biological
control, which was developed in England, a
nonpathogenic fungus is used to protect
pines against root rot. This biological control
agent and K-84 were the first two agents reg-
istered by the Environmental Protection
Agency (EPA) for use in the United States
against plant cliseases. It took 10-15 years to
develop each system, both of which are now
used in many countries.
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Another control aimed at exclusion has the
potential for protecting livestock against cer-
tain pathogens. A U.S. company has devel-
oped a product consisting of live cells of a
nonpathogenic 7actobaciZIus fermentum,
which occupies attachment sites on the in-
testinal lining when introduced into new-
born piglets. This preempts the attachment
to the lining of the strain of Escherichia cold re-
sponsible for neonatal scours.
SYSTEMS OF SEEF-DEFENsE
(STRATEGY 3)
Plants and animals have evolved many ef-
fective defense mechanisms that are subject
to improvement by conventional breeding
and by genetic engineering. For example,
the last major epidemic of wheat stem rust in
the Great Plains of the United States oc-
curred over 30 years ago; this success is due
to the introduction of genes for resistance as
necessary according to results of annual sur-
veys for virulence genes in the pathogen
population. Although they are not within
the scope of this report, vaccines have been
the most successful biological control of dis-
eases of humans and livestock. Plants have
no immune system comparable to that of ani-
mals, but they can be effectively protected
against disease agents by inoculation with
avirulent strains related to the pathogen or
with a microorganism that is pathogenic to
another plant. For example, the citrus tris-
teza virus from Africa was introduced into
South America in the 1920s anc! nearly deci-
mated the citrus industries of Argentina,
Brazil, and Uruguay until biological control
was developed. In 1951, mild strains of the
tristeza virus complex in Brazil were found to
protect trees against severe strains. Com-
mercial testing of these strains was begun in
196S, and by 1980, ~ million trees were pro-
tected in Brazil by deliberate inoculation of
seedlings with a mild strain. The same
method is also used in Australia. Thus far,
there is no evidence that the control is likely
to break down or cause any detrimental non-
target effects.
RECENT ADVANCES IN RESEARCH
ON BIOLOGICAL CONTROL
NEW APPROACHES TO THE
REGULATION OF PEST POPULATIONS
Scientists are continuing to discover natu-
ral enemies of pests and to find better ways
to track and favor these beneficial organ-
isms. Microbial pesticides are a particularly
promising aspect of this classic approach
and are becoming recognized by both estab-
lished and start-up industries as opportuni-
ties for commercial development.
At least four baculoviruses are now regis-
tered by the EPA for use as microbial insecti-
cides, but none are commercially available in
the United States. Baculoviruses are expen-
sive to mass produce for large-scale distribu-
tion and are slow to kill target insects. Spe-
cial processes are being clesigned to decrease
the cost of production, and attempts to accel-
erate the kill speect are being made by genetic
manipulation of the bacuTovirus genome
(chromosome). For example, a toxin gene
can be substituted for or inserted into a non-
essential virus gene, so that the toxin is pro-
duced on ingestion by the insect and kills it
more quickly than the viral infection would.
Microbial herbicides can rapidly and selec-
tively eliminate weeds from managed eco-
systems with an effectiveness similar to that
of chemical herbicides. Two microbial herbi-
cides are now commercially available in the
United States for control of relatively minor
weeds. These microbial herbicides are for-
mulations of living, host-specific fungal
pathogens, and were discovered around
1970. Their commerical development re-
sulted from the effective collaboration of the
public and the private sectors. No hazards to
human health or other nontarget effects
have been observed for either of these micro-
bial herbicides.
Several genetic traits are known to render
62
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BIOLOGICAL CONTROL IN MANAGED ECOSYSTEMS
mosquitoes refractory to the transmission of
the malaria parasite Plasmodium falciparum.
In a novel approach to malaria control, it has
been proposed that genetic manipulation
could be used to transfer genes to mos-
quitoes rendering them incapable of trans-
mitting the parasite. These mosquitoes
would be expected to compete with and re-
place indigenous vector types. This ap-
proach might be extended to vectors of plant
viruses, but we must first amass a great deal
more fundamental information, including
information on vector specificity for patho-
gen strains, pathogen reservoirs, and the ge-
netics of virulence and transmission.
MANAGEMENT OF BENEFICIAL
PEANT-MICROBE ASSOCIATIONS
Plants support large populations of mi-
crobes (bacteria and fungi) as indigenous
cosmopolitan inhabitants of their leaves,
stems, and roots. These microbes may well
provide the first level of defense of plants
against pests. Some of the more beneficial
plant-microbe associations include mycor-
rhizal fungi that help the plant take in nutri-
ents and water while providing some protec-
tion against root disease, fungi within plant
tissues (endophytes) that produce sub-
stances that inhibit or are obnoxious to insect
pests, and microorganisms on the leaves and
roots (epiphytes) that compete with and in-
hibit pathogens even before they enter the
plant. These types of potential biological
control agents can be applied to seeds or
other planting material and therefore repre-
sent significant opportunities for commer-
cial development.
Recent studies conducted in Australia,
Canada, China, the Netherlands, and the
United States reveal the potential of root-col-
onizing microorganisms to inhibit or dis-
place pathogens at the root-soil interface
and thereby protect the root health of peren-
nial and annual plants. These microorgan-
isms inhibit root pathogens by producing
antibiotics siderophores (compounds that
63
chelate biologically available iron), and pos-
sibly substances that stimulate plant growth.
One such biological control is the use of bac-
terial strains of Pseudomonas fluorescens and
P. putida (root-colonizing bacteria) to protect
wheat roots against the soilborne fungus
Gaeumannomyces graminis var. tritici. This
fungus incites an important disease of wheat
called "take-all. " Take-all is enhanced by the
current trend toward less crop rotation and
less tillage and has become the most eco-
nomically important root disease of wheat
worldwide. The benefical bacteria were dis-
covered during basic research on the natural
history of a spontaneous decrease in severity
of take-all a natural biological control that
sometimes follows two or three outbreaks of
the disease and the continued monoculture
of wheat. The bacteria thrive on wheat roots
infected with G. graminis and are believed to
provide this natural biological control. The
most effective strains produce phenazine-
type antibiotics that are strong inhibitors of
G. graminis. The effective strains tested on
crop plants so far occur naturally, but the
genes for phenazine production are being
isolated and will be available in the future to
improve strains by genetic engineering.
ADVANCES THROUGH UNDERSTANDING THE
MOLECULAR BIOLOGY OF SEEF-DEFENsE
Rapid advances are being macle in re-
search on the use of natural defense systems
of plants in biological control. Most if not all
plants are thought to have the genetic poten-
tial to protect themselves from infectious
agents and from most insect and nematode
pests. Damage results when the pest agent
somehow circumvents or suppresses this
defense mechanism by its own genetically
controlled mechanisms. In addition to ge-
netic improvement of resistance in plants,
these defense mechanisms can be induced
by inoculating the host plant with avirulent
pathogens.
Induced resistance in plants occurs in re-
sponse to all categories of plant pathogens
OCR for page 64
and to certain insect pests. For example,
beans, cucumbers, watermelons, and musk-
melons can be systemically protected against
diseases caused by fungi, bacteria, or viruses
by prior inoculation with agents that are ca-
pable of causing only restricted infections.
This protection persists for essentially the
entire crop season. When certain chewing
insects begin to feed on the leaves of pota-
toes or tomatoes, a systemic signal triggered
by small fragments of plant cell-wall material
activates genes in distant leaves for synthe-
sis of protease inhibitors. Insects acquire the
protease inhibitors while feeding on these
leaves. The insects' own digestion, physiol-
ogy, and growth are then inhibited, and they
cease feeding on that plant. This provides an
advantage to the plant and the predators that
feed on the insect pest. Investigators are now
trying to transfer these genes for insect-in-
duced synthesis of protease inhibitors to
those plants without them.
Studies of plant virus infection indicate
that virus coat protein protects the plant cells
against subsequent infection by a closely
related strain of the virus a type of cross-
protection. On the basis of these studies, to-
bacco plants resistant to tobacco mosaic vi-
rus (TMV) were produced by recombinant
DNA technology. The TMV gene for coat
protein was transferred to and expressed in
tobacco and tomato plants, resulting in
cross-protection without inoculating plants
with the protecting virus strain. This method
has also been extendecT to alfalfa mosaic vi-
rus control. This approach to virus control is
a major advance ant! avoids any potential
risks associated with the use of mild virus
strains in the field.
RESEARCH OPPORTUNITIES
The diversity of natural systems provides a
wealth of potential biological control agents,
including viruses, bacteria, and fungi. Al-
though many collections of these organisms
exist, adclitional research is needed to col-
lect, characterize, and select the most prom
. .
Sing agents. In many cases, such as the ba-
cuToviruses for insect control, more efficient
and less costly production processes need to
be cleveloped. Stabilization of biological ac-
tivity during formulation and delivery is an-
other need for many biological control
agents. This complex field will require the in-
tegration of biological and engineering
skills. Biotechnology is expected to provide a
means for cleveloping a more complete un-
derstancling of biological interactions and for
expanding genetic manipulations of organ-
isms to make biological control practical on a
broader scale.
Opportunities for research to develop new
or improved methods of biological control
are virtually unTimitect. For example, my-
coviruses (viruses of fungi) are associated
with Toss of fungal virulence (hypoviruTence)
in the fungi responsible for chestnut blight
and Dutch elm disease. In France, chestnut
trees are recovering where virus-infectecl
(less virulent) strains of the chestnut blight
fungus were introduced. The introduction of
virus-infected strains has not worked in the
United States, because "mating" of fungus
strains must occur for the virus to be trans-
mitted and there are many incompatible
mating groups among the chestnut blight
fungi within the country. Nevertheless, re-
search on these viruses and other similar
fungal pathogens deserve increased atten-
tion.
Opportunities for the biological control of
viral diseases will be gained mainly through
molecular approaches, such as genetic engi-
neering to introduce resistance genes into
plants, inhibiting virus multiplication with
antisense viral RNA (viral RNA that is com-
plementary to the messenger-sense RNA),
and building on the molecular basis for
cross-protection. As knowledge of how vi-
ruses infect, multiply, and affect their hosts
increases, so does our ability to control viral
diseases.
For root diseases, greater study is needecl
of the pathogen-suppressive soils those
sods with unique microbiological properties
64
OCR for page 65
BIOLOGICAL CONTROL IN MANAGED ECOSYSTEMS
that prevent pathogens from becoming es-
tablished or from causing disease. Such soils
have also been reported for certain soil-in-
habiting insect pests. Knowledge of the
mechanisms of suppression is providing
useful new information on the ecology of
such pests and is leading to the discovery of
new biological control agents.
There are almost unlimited opportunities
to be explored in the biological control of
nematodes. The pathogenic bacterium Pas-
teuria penetrans is one possible biological con-
tro! agent for several economically important
nematodes, but as for so many other poten-
tial biological control agents, there is no eco-
nomic means to produce it on a large scale.
Another, but less efficient biological control
of nematodes is the use of plants, such as
Crotalaria spectabilis, that prevent the nema-
tode from reproducing. These plants might
be macle to provide more efficient nematode
control or could perhaps be used in insect
control if they could be genetically engi-
neerect to produce attractants or phero-
mones.
Funclamental to all areas of biological con-
tro! is basic research on interspecific and in-
traspecific communications, such as, how
insect pests find their host plants, how
plants repel insects, how natural enemies
find their prey, or how individuals within
the mating population of a species find or
avoid one another so that the population be-
comes inbred or genetically more diverse.
information on local and systemic signals
transmitted within plants when they are
wounded or challenged by a pest will help us
understand the mechanisms of recognition
and defense that are important to biological
control applications. Basic research in popu-
l a t i o n b i o l o g y , o r g a n i s m - e n v i r o n m e n t i n t e r -
actions, physiological ecology, and other
areas is essential to the discovery, conserva-
tion, and enhancement of future biological
controls.
Solving these problems in basic and ap-
plied research in biological control will re-
quire the continuation of traditional single
65
investigator projects; however, problems
involving such complex matters as under-
standing and improving mechanisms of
biological control, testing and integrating
systems in the field, and tracking specific or-
ganisms in the ecosystem can be efficiently
solved only by multidisciplinary teams of
well-trainecT scientists. Such teams should
include geneticists, biochemists, molecular
biologists, microbiologists, physiologists,
plant pathologists, entomologists, and ecol-
ogists. Mathematicians should work with
ecologists in modeling the complex interac-
tions that occur in biological control to help
provide a basis for prediction. Economists
and sociologists must become involved to
help guide projects from the standpoint of
feasibility, acceptability, and integration
with established practices. The commerciali-
zation of biological control products will also
require extensive research in mass produc-
tion, formulation, and clelivery of these
agents.
WORLD STATUS OF U.S.
BIOLOGICAL CONTROL RESEARCH,
DEVELOPMENT, AND APPLICATION
CURRENT U.S. POSITION
The United States leacls the world in the
discovery and reporting of biological phe-
nomena related to biological control. It also
ranks first in the development of recombi-
nant DNA and computer technology, both of
which are needed to understand and im-
prove systems of biological control. How-
ever, except for the conventional breeding of
plants with improved resistance and the re-
lease of exotic enemies of naturalized pests
(classic biological control), the United States
in general is not the leader in the use of bio-
logical control.
Many nations have indicated or demon-
strated a greater commitment to under-
standing biological control and to making it
work. For example, research on biological
OCR for page 66
control of plant viruses is not as extensive in
the United States as it is in the Netherlands.
The United States is a leader in the biological
control of weeds, but Australia, a nation
with only a fraction of the U.S. resources,
has an effort that is almost as great. The first
(and so far only) two biological agents for
controlling plant pathogens registered by
the EPA for use in the United States came
from England ant! Australia. The Federal Re-
public of Germany has a greater total effort
than the United States in the biological con-
troT of plant-parasitic nematodes. The
United States is the leader in research on in-
sect pheromones, but large foreign compa-
nies are increasing their involvement in this
approach to biological control. The United
States along with Western Europe and Can-
ada have the strongest programs in basic re-
search on insect pathogens, but Brazil,
China, and the USSR have the greatest expe-
rience in the use of microbial insecticides.
The Unitec! States has also been less suc-
cessful than many countries in its efforts to
assemble interdisciplinary teams of scien-
tists to focus on biological control. China
identified biological control as a priority in its
seventh 5-year plan and has committed ma-
jor resources to this area of research since
1979 (the year biological control teams were
exchanged between the United States and
China). In China, important pest complexes
have been targeted for biological control,
anc! teams of researchers are now being as-
sembled to conduct the necessary research.
These new Chinese research projects are
based on U.S. technology. Belgium has one
of the largest interclisciplinary teams for con-
ducting mainly basic but also applied re-
search on plant-microbe associations; few if
any existing U.S. groups can compete with
teams such as these. Several countries, in-
cluding Canada and Great Britain, have for-
malized links between public agencies and
private companies as a way to assemble large
enough groups to conduct research on the
application of biotechnology, including bio-
logical control technology.
66
U.S. PROSPECTS
The United States has many advantages
that could make it a world leader in the appli-
cation and marketing of biological controls
while also increasing its contribution of new
scientific information basic to the field. it has
many repositories of biological material with
the raw germplasm to develop superior bio-
logical controls, including those with mar-
ketable components. The way is now clear in
the United States for exclusive licensing of
biological control agents by commercial
firms, including agents developed in and
patented by state or federal laboratories. The
United States has an advantage in the com-
position of its industrial infrastructure,
which ranges from cottage industries and
start-up companies to leading multinational
corporations.
Perhaps the single greatest advantage of
the United States relative to other countries
is the human resource within its network of
academic institutions. No other country can
match the U.S. supply of young people
highly trained in molecular biology, com-
puter technology, ecology, and other sci-
ences fundamental to future research and
development in biological control. However,
competition for limited funding is so intense
that agencies such as the National Science
Foundation, the National Institutes of
Health (NTH), and the U.S. Department of
Agriculture (USDA) with interests in this
area are funding only a small fraction of all
proposals. Funding agencies need to direct
or encourage a portion of these resources to-
ward fundamental and applied studies in bi-
ological control.
Another major U.S. advantage is its Land
Grant University and USDA/State Agricul-
tural Experiment Station system. No other
experiment station system in the world has
the capability or experience in fielc! testing
and in developing the management strate-
gies to integrate biological control into agri-
culture, forestry, and other managed ecosys-
tems. This system can also provide links
OCR for page 67
BIOLOGICAL CONTROL IN MANAGED ECOSYSTEMS
with user communities through education
and demonstrations, and employs econo-
mists who can help determine economic fea-
sibility.
NEEDS AND RECOMMENDATIONS
BASIC RESEARCH
Two types of basic research needs can be
identified. First is the obvious need for more
basic research in areas such as ecology, ge-
netics, physiology, cellbiology, and molecu-
lar biology to provide adequate knowledge
about biological interactions, especially
those that can be modified for biological con-
trol. The second need is more subtle. It con-
cerns the perceptions among researchers
that biological control is a narrow and ap-
plied field of study. AS a result, many people
working in areas fundamental to biological
control have generally not thought of their
research as potentially relevant to biological
control. Practitioners must also adopt a
broacler concept of biological control than
they have in the past.
SOEVING THE COMPLEX PROBLEMS
A major limitation in the United States is
the lack of the sustained, concentrated, and
interdisciplinary effort needed to solve com-
plex problems in both basic and anolied bic~-
logical control research. individual investi-
gators have tended to conduct short-term,
descriptive research on an interesting bio-
logical control phenomenon, publish one or
a few papers, and then move on to another
research topic. The U.S. scientific literature
is replete with isolated reports of biological
control, but few of these reports are actually
followed-up. Because of the inherent diffi-
culty and long-term nature of the work, in-
vestigators lose interest, become discour-
aged, or stop because their funding is too
short term. The United States needs to sup-
port multidisciplinary teams that have the
potential for sustained research in solving
67
the complex problems related to biological
control, while simultaneously continuing to
support individual investigators. Such
groups could be formed across departmental
boundaries within a research or academic in-
stitution, between two or more academic in-
stitutions, or between public and private or-
ganizations. in addition, training grants
could be used to attract and support grad-
uate students or postdoctoral associates in
the more productive or successful laborato-
ries or as members of a multidisciplinary
team working on biological control. Career-
development grants, possibly patterned af-
ter the NTH model, could be used to help sus-
tain young scientists for 5-10 years so that
they coulc! continue their work on specific
projects in biological control.
MOVING RESEARCH OUT OF
THE LAsoRAToRY
Even under the most efficient circum-
stances, the transfer of biological control re-
search from the laboratory to the field is a
slow process. Researchers in public-sup-
ported institutions tend to avoid lengthy
field tests that involve several geographic lo-
cations because they are expensive and be-
cause the chance of obtaining successful
results has been low. The private sector, on
the other hand, has generally been reluctant
to invest in developing products for the nar-
row, specialized markets typical of so many
biological controls. The problems for biologi-
cal control development are compounded by
regulatory issues and questions concerning
the guidelines and protocols that must be
followed, whether conducting basic re-
search or testing biological control agents in
the field. Pharmaceutical products devel-
oped through biotechnology are reaching
the marketplace much faster than products
for biological control, in part because of ac-
celerated regulatory approval by the Food
and Drug Administration.
A special grants program available to both
public and private researchers could be initi
OCR for page 68
ated to support field research. Incentives for
the private sector and more cooperative ties
between the public and private sectors (e.g.,
joint ventures) are also needed to accelerate
research on product development. Several
small companies and three or four of the
larger corporations have begun to invest in
the development of biological control procI-
ucts in the United States, which shows that
interest in commercial development of bio-
logical control is growing in the U. S. private
sector.
Existing state and fecleral programs on pi-
Tot testing of biological control systems and
on obtaining data for registration of minor-
use biological control products are impor-
tant. These programs could play a larger role
in the transfer of technology from the labora-
tory to commercial applications. The devel-
opment of protocols for field research and
testing should take into account the fact that
cluring the 99 years of modern biological con-
trol, there are few, if any, examples of a bio-
logical control agent (i.e., an insect, phero-
mone, microbe, or gene) having a known or
significant negative effect on the environ-
ment after its deliberate introduction. Thus,
the existing regulations of the USDA Animal
and Plant Health Inspection Service for im-
portation and release of potential pests (or
organisms related to pests) seem adequate
for regulation of nonengineered biological
control agents. In acIdition, the guidelines
developed by the NTH Recombinant DNA
Advisory Committee (RAC) for laboratory
research with genetically engineered organ-
isms seem to be an appropriate mode! for the
creation of guiclelines on the field testing of
genetically engineered biological control
agents. Regarding final registration, there is
no evidence that biological control products
developed using recombinant DNA technol-
ogy will require regulation that is any differ-
ent from those products developed via non-
engineering processes. Regulations should
be based on the product's properties and not
on the process used to make it. Field research
with pheromones and nonengineered, non
68
pathogenic microorganisms should require
protocols no different from the traditional
procedures used for fielcT research on non-
engineered nitrogen-fixing bacteria or new
plant cultivars.
CONCLUSIONS
Biological control can and should become
the primary method used in the United
States to ensure the health and productivity
of important plant and animal species. The
need for alternatives to complement or re-
place chemical control dictates placing an
increasing emphasis on biological control re-
search and clevelopment. Chemical pesti-
cides are responsible for a wide array of un-
acceptable negative environmental effects.
For example, they tend to create fluctuating
cycles of pests because they lead to selection
for resistance in the pest population, and
they tend to eliminate beneficial as well as
harmful organisms. in contrast, biological
controls have had no known or significant
negative, nontarget effects; instead, they
maintain the biological balance through ad-
justments in the management of ecosystems
and by the strategic introduction of organ-
isms or their genes to influence the outcome
of natural biological interactions. Advances
in biotechnology greatly facilitate the devel-
opment of successful new biological controls
and the more effective manipulation of natu-
ral forms of biological control. Major factors
preventing greater use of biological controls
include a lack of basic information on ecol-
ogy and biological interactions, an inade-
quate interdisciplinary effort to solve com-
plex problems, and constraints on moving
research from the laboratory to the fielcl. The
development of biological contra! as the
foundation of pest control in the United
States is the most important challenge we
face in making safe and efficient use of our
managed ecosystems.
Representative terms from entire chapter:
biological controls
