Principles of Insect Parasitism Analyzed From New Perspectives Practical Implications for ...

348 Pages·2010·5.04 MB·English

Principles of Insect
Parasitism Analyzed
From New Perspectives
Practical Implications for
Regulating Insect Populations
by Biological Means

W * * K -m^
■

' -m. - * " , • ^
■ ■ ■
^¡^ United States
Agricultural
Agriculture
È) Department of
Research
Handbook
Agriculture
Service
Number 693
Principles of Insect
Parasitism Analyzed
From New Perspectives
Practical Implications for
Regulating Insect Populations
by Biological Means
E.F. Knipling
United States Agricultural Agriculture
Department of Research Handbook
Agriculture Service Number 693
Abstract
E.F. Knipling. 1992. Principles of Insect Parasitism Analyzed From
New Perspectives: Practical Implications for Regulating Insect
Populations by Biological Means. U.S. Department of Agriculture.
Agriculture Handbook No. 693, 349 pp.
This publication presents the results of a theoretical study on the
roles that parasitic insects can and cannot play against populations
of their insect-pest hosts under natural conditions More impor-
tantly, the feasibility of managing major insect-pest problems
through highly augmentative releases of parasites in the host
ecosystems is critically examined by theoretical deductive proce-
dures.
Ke3rwords: augmentation release, beneficial insect, biological agent,
biological control, entomophagous insect, host insect, insect, insect
management, insect pest, insect suppression, integrated pest
management, parasitic insect, pest control, pest management,
predator insect, prey insect.
While supplies last, single copies of this publication may be ob-
tained free of charge from USDA-ARS, Information Staff, 6303 Ivy
Lane, Room 400, Greenbelt, MD 20770.
The United States Department of Agriculture (USDA) prohibits
discrimination in its programs on the basis of race, color, national
origin, sex, religion, age, disability, political beliefs, and marital or
familial status. (Not all prohibited bases apply to all programs.)
Persons with disabilities who require alternative means for commu-
nication of program information (Braille, large print, audiotape, etc.)
should contact the USDA Office of Communications at (202) 720-
5881 (voice) or [phone] (TDD).
To file a complaint, write the Secretaiy of Agriculture, U.S. Depart-
ment of Agriculture, Washington, DC 20250, or call [phone]
(voice) or [phone] (TDD). USDA is an equal employment
opportunity employer.
June 1995
This publication slightly revises Principles of Insect Parasitism
Analyzed From New Perspectives: Practical Implications for
Regulating Insect Populations by Biological Means, issued April
1992.
Foreword
The improved use of parasitoids as biological control agents is at
the forefront of our quest for more effective, lasting, and environ-
mentally safe technology for pest management. Various avenues
are available for utilizing parasitoids, including the importation of
new species, mass-propagation and release of parasitoids, and
habitat management techniques to increase the abundance and
performance of feral and released individuals. Our limited under-
standing of parasitoid/host interactions and other factors affecting
their efficacy is a central barrier to consistently effective use of
parasitoids with all of these approaches. The author herein pre-
sents an analysis that is of major value in our endeavor to under-
stand host/parasitoid interactions.
Dr. Knipling has for many years advocated the need to seek envi-
ronmentally compatible and lasting solutions to our major pest
problems versus the more conventional, reactive measures and has
continually stressed the importance of approaching these pest
problems from a total-population perspective. He further has
envisioned parasitoids as potentially invaluable weapons in our
pest management arsenal and sought ways to develop that poten-
tial. This treatise is the fruit from his years of diligent pursuit
toward a fundamental understanding of parasitoid/host interac-
tions at the total-population level, and it presents the results that
could be derived by the mass-release of parasitoids over a major
area of the pest ecosystem.
He has assembled the key information on the variety of factors that
are known to affect parasitoid-host coexistence patterns and used it
in a thorough analysis of the population dynamics of several
parasitoid-host examples, each species having certain unique
characteristics. The results derived from these analyses and
especially the conclusions as to certain common principles govern-
ing parasitoid populations and their efficacy offer a truly new and
important perspective. The author's highly significant central
conclusion is that the rate of parasitism (at the total-population
level) is primarily a function of the ratio of parasitoid numbers to
host numbers—^with host density, of itself, being of little conse-
quence. A major supporting premise for this conclusion is reported
research which demonstrates that parasitoids have highly sophisti-
cated host-detection mechanisms and, thereby, waste very little
time searching in spaces other than the immediate sites of host
infestation.
It is important to emphasize, as does the author, that because of
limited information many of the parameters used in the analyses
were derived by deductive reasoning and may be of limited preci-
sion. However, the author has taken great care to reduce errors in
his assumptions by placing them through rigorous validation trials
with numerous models.
As with any such conceptual work, various aspects of the conclu-
sions are certain to be amended and modified with new data and
further analysis. In fact, some important sources of variation
which have an important bearing on the subject, such as recent
findings on learning by parasitoids, are not analysed. These
factors, which argue for more dynamics in the models, should be
kept in mind as we continue to explore the subject. These consid-
erations do not, however, negate the primary value of the work,
which is in the central conclusions; the new perspective for ap-
praising parasitoid/host interactions; and the practical implications
for augmentative use of parasitoids. The findings show that
augmentation on a total-population scale can be an extremely
powerful tool for pest suppression. In fact, when releases raise the
overall population parasitization much over 50 percent, a very
strong "self-increasing" effect can be set in motion.
Some colleagues may feel that the appraisals and conclusions are
oversimplified and too generalized. Such impressions should not,
in my opinion, be drawn because of the simplicity of the models.
The relatively few parameters used in developing the models are
based on a judicious selection of the factors pertinent to the
questions addressed. My experience in following Dr. Knipling's
various works is that he has a tremendous gift for sorting through
complex matters and bringing the essence to focus. I believe he has
again achieved that end with this major contribution to the science
of biological control.
W. Joe Lewis
Research Entomologist
USDA-ARS
Insect Biology & Population Management
Research Laboratory
Tifton, Georgia 31793
Preface
For many years I have encouraged research and development on
techniques and strategies for insect-pest control that in theory offer
possibilities of being more effective, more economical, and less
environmentally hazardous than those in current use.
The investigation herein described was focused on appraising the
role that certain parasites (parasitoids) play as natural control
agents, and the role they might play for regulating populations of
their pest hosts if the number of parasites in the host ecosystem
were sufficiently increased by artificicil means. The appraisals were
made in the light of (1) important new basic information that insect
behaviorists have obtained during recent years on the highly
efficient mechanisms that biological agents possess for finding their
hosts or prey; (2) reports, by a number of investigators, that for
many parasite species there is no evidence of a positive correlation
between host density and the proportion of the host population
parasitized by the coexisting parasite population; and (3) new, more
general information on the biology and behavior of numerous
parasite species.
The appraisals were made by deductive procedures, and the results
are presented and discussed in detail in this publication. While
theoretical, the results are considered to be entirely consistent with
the principles of insect parasitism, the factors that influence the
dynamics of insect populations, and the basic principles of insect
population suppression.
Many complex biological actions and interactions are involved in
natural parasitism processes. However, pest hosts and their
associated parasites have evolved biological and behavioral charac-
teristics which virtually ensure that the relative numbers of hosts
and parasites in the ecosystem they inhabit and the rates of
parasitism that occur will remain within rather narrow limits. This
is to be expected even though the coexisting populations may
fluctuate by up to 100-fold during a single season or over a period
of several years for cyclic species. The rather close numerical
relationships assumed are entirely consistent with nature's balanc-
ing mechanisms, which permit closely associated organisms to
coexist in reasonable harmony.
Thus in natural populations, the ratios of parasites to their coexist-
ing hosts are not high enough to result in dependable control of
many pest hosts. Without question, however, technology can be
developed to efficiently mass-rear parasites of many species so that
they may be released at strategic times in host ecosystems in
numbers that would result in parasite-to-host ratios high enough to
allow effective control of the host populations. To know how many
parasites of a given species to produce and release for achieving
various rates of parasitism, it would be desirable to have good
information not only on the actual and relative numbers of the
parasites and hosts coexisting in natural ecosystems but also on
the relationship of these numbers to available data on rates of
parasitism. For every parasite and its host, elaborate and costly
research programs would be required to obtain reliable information
on these numbers under the variable conditions existing in natural
populations. In this investigation, therefore, theoretical deductive
procedures were used to make realistic estimates of the normal
numerical relationships between the different parasite-host associa-
tions examined. Extensive use was made of rather simple popula-
tion models, which were developed for each association. To develop
the models, every aspect of parasitism and insect population
dynamics had to be critically analyzed. Many estimates and
assumptions had to be made, based on new theories or the limited
information available. The models presented show the numerical
relationships between the pest host and parasite populations, the
growth rates of these populations, and the parasitism trends over
successive generations in natural ecosystems. The basic models
were then used to estimate how the parasitism trends and the
dynamics of the pest hosts would be affected when the normal
numerical relationship throughout a pest ecosystem is greatly
increased by artificial means in favor of the parasite population. 1
doubt whether most of the conclusions in this investigation could
have been reached without the aid of the models.
Despite the many unknowns and complex biological actions in-
volved, the theoretical investigation proved to be very fruitful. As
discussed in detail in this publication, the parasite release tech-
nique has certain unique suppressive characteristics not possessed
by any other methods of insect suppression. As we will see, these
characteristics have profound practical implications for managing
total pest populations when the technique is employed alone or
when integrated with other methods of suppression.
Many readers of this publication are likely to question the validity
of some of the conclusions reached. They might particularly
question the conclusion that parasites have the inherent ability to
find hosts readily even when the host population is abnormally low.
They might well ask, Why isn't this ability more evident both from
the vast amount of natural parasitism data that are available and
from the results of the augmentation experiments that have been
conducted in the past?
Most certainly I raised that question—repeatedly—as I analyzed the
proposed coexistence patterns of the parasite-host associations
included in the study. I looked for flaws in the premises on which
the suppression models are based. But when I considered that we
can by artificial means create parasite-to-host ratios that exceed
ratios in natural populations by as much as 10- or even 100-fold, I
gained a great deal of confidence in the theoretical results. As will
also be discussed in various chapters that follow, there are a
number of sound reasons why the full potential of the parasite
release method as a means of regulating total pest populations has
remained largely obscured for such a long time.
Very difficult and costly research will have to be undertaken to
confirm the results and conclusions of this investigation. Without
doubt, the development of the parasite release technique as one of
the primary methods for managing insect pest populations will be a
challenge for pest management scientists every step of the way.
However, given the resources, there should be no other barriers to
eventual success in developing this ecologically acceptable way to
regulate populations of a wide range of the world's most damaging
and formidable insect pests. Current methods for controlling many
of these pests are based on using nonselective insecticides and
therefore cause extensive ecological disruptions. For many para-
site-host associations, I estimate that the costs involved to maintain
the pest populations below economically damaging levels would be
only a fraction of the losses the pests cause to agriculture under
current management procedures. The parasite release technique
offers not only opportunities to avoid environmental hazards but
also the realization of large savings to agriculture. Nature has
made available hundreds of parasite species that would be suitable
candidates for exploiting this biologically sound and environmen-
tally safe means of regulating insect pest populations.
Vll
Acknowledgements
I am indebted to many individuals for information and assistance in
the conduct of these investigations. I received much valuable
information on the biology and behavior of the various parasites
and hosts from my associates with the Agricultural Research
Service, U.S. Department of Agriculture. They include W. Joe
Lewis, Harry R. Gross, William C. Nettles, Edgar G. King, James E.
Gilmore, Tim T. Wong, Sess D. Hensley, William E. Guthrie, Ralph
E. Webb, Alton N. Sparks, John J. Drea, Jack R. Coulson, Thomas
R. Ashley, and Keith R. Hopper. I also appreciate the information
received from Thomas M. Odell, Forest Service, U.S. Department of
Agriculture. In addition, I received valuable information from
colleagues with State institutions, including H.C. Chiang and
Richard L. Jones, University of Minnesota; R.M. Baranowski,
University of Florida; and James R. Gate, Texas A&M University.
Finally, I am deeply indebted to Dee Haley and Frances James for
typing and helping to prepare the manuscript, and to Alice Kunishi
for editorial assistance.
Vlll
Contents
Page
1. Introduction 1
2. Factors influencing the behavior and efficiency of
host-speciñc parasites 11
Host density 11
Parasite density 14
Kairomones 18
Host discrimination 22
Environmental factors 24
Host plants 27
Parasite and host fecundities 29
General discussion 31
Introduction of new parasites 32
3. Basic principles of pest population suppression
by parasite releases 39
Development of parasite-host population models 39
Proposed use of the parasite augmentation
technique 42
Characteristics of the parasite augmentation
technique 44
Relative efficiencies of parasite and sterile insect
releases 48
Influence of the distribution pattern of abnormally
low populations of pest insects on the relative
efficiencies of parasite and sterile insect release 52
Synergistic suppression by parasites and sterile
insects in integrated releases 58
4. Suppression of sugarcane borer populations 63
Overview 63
Natural coexistence pattern of sugarcane borer
and Lixophaga diatraeae populations 71
Influence of Lixophaga diataeae releases 75
5. Suppression of European corn borer populations 89
Natural coexistence pattern of European com borer
and Microcentrus grandii populations 90
Influence of Microcentrus grandii releases 95
6. Suppression of tephritid fruit fly populations 101
Overview 101
Suppression of medfly populations 103
Suppression of oriental fruit fly populations 115