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Commercial Production of Entomophagus Insects
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Commercial Production of Entomophagus Insects and Their Successful Use in Agriculture

 

by E. J. DIETRICK Published in: BIOLOGICAL CONTROL IN CROP PRODUCTION (BARC Symposium number 5–George C. Papavizas. ed.) Allanheld, Osm

 

ABSTRACT

The commercial insectary is defined as a free enterprise business offering live predatory and parasitic insects (parasitoids) over the counter. Emphasis is on their commercial marketing and successful use in agriculture, rather than any particular mass production techniques applicable to the entomophagus arthropods offered for sale. Conclusions are based on the author's 35 years of personal experiences: 15 years of employment in classical biological control research at the University of California, Riverside, and more than 20 years in management of a commercial insectary. Rincon Vitova Insectaries, Inc., P. 0. Box 1555, Ventura, California 93002.

 

INTRODUCTION

The commercial insectary, financially supported by sales of entomophagus arthropods beneficial to agriculture, has grown from humble beginnings into the somewhat sophisticated business enterprise of insect farming and marketing. The business has advanced from harvesting hibernating ladybird beetles to using labor-intensive, mass production techniques, which keep all stages of each species of carnivorous predators and the substitute host used as food in continuous production. Like farming, the growing of many different species has great complexity peculiar to each species, and there may be several equally effective ways to mass culture any one of them. Therefore, I have chosen not to dwell on rearing methods. There are excellent comprehensive publications available on insectary facilities, equipment, and methods useful in the culturing of entomophagus insects (DeBach 1974; DeBach and Schlinger 1964; Fisher 1963; Huffaker and Messenger 1976; Leppla and Ashley 1978; Ridgeway and Vinson 1977; Smith 1966).

 

Evolution of the commercial insectary and its marketing techniques are outlined from inception to a modern practical alternative to the count-and-spray programs of pest management that are advocated by chemical company sales propaganda. Problems facing further advancement of the insectary as a business are discussed. A favorable assessment is given for the future expansion of many small businesses composed of pest control advisors working independently for individuals or groups of farmers. They may or may not own insectary facilities, but they will be applying cost-effective biological controls wherever and whenever it is practical in integrated pest management programs. Finally, an assessment is made of the existing situation, with suggestions that would help this kind of business to develop.

 

For the purposes of this discussion, biological control will mean the use of mass-cultured and/or field-harvested predators, parasites (parasitoids), and various naturally occurring microorganisms that cause epizootics of arthropod populations and can often be harvested and stored for future use. I exclude from my concept of biological control such expanded meanings as third-generation pesticides or those microbial pesticides that have been registered. The natural enemy complex refers to the full range of organisms, minor pests, decomposers, competitors, and antagonists that are recognizable in biologically balanced, field situations, i. e., the untreated, commercially clean field that produces marketable products.

 

INSECTARIES THAT DEPEND ON FIELD-HARVESTED SOURCES

Among the many reasons for culturing entomophagus insects, probably the most straightforward one is that it is common sense to promote biological control. Most of us who have gardened have seen ladybird beetles feeding on aphids. Why wouldn't one wish to help this natural enemy of a garden pest? Probably the first farmers in history were aware of the more-obvious insect predators that were observed feeding on phytophagous insect pests. This urge to help the "good" insects is still strong among farmers. In spite of considerable efforts to discredit the practice, the mountain-collected ladybird beetle, Hippodamia convergens Guerin, is still the most-marketable product sold by commercial insectaries. Egg cases of the praying mantids are also harvested, although to a lesser extent than the thousands of gallons of ladybird beetles. Market demand for both of these species far surpasses the supply in most years, even though neither of these beneficial insects is likely to reduce substantially the populations of any particular target pest.The major problem associated with marketing field-harvested products is their limited availability. It is economical to harvest only when large populations occur in limited space. Also, the product usually has aged or is ready to enter an aggregation or diapause state in its development. Other problems that are common to all products offered by commercial insectaries and that limit the marketing of field-harvested predators are as follows: (a) the desired species must be separated from chaff and living plant material; (b) refrigerated storage is required to slow the activity sufficiently to facilitate separation of the desired species and prevent exposure losses; and (c)the harvest must take place under conditions that prevent loss of quality, e.g. air conditioning. Many of these products are extremely tiny, fragile, and require special packaging for containment on the way to market. Finally, such beneficial insects are poorly understood by most potential customers and by entomologists.

 

Those commercial ventures that depend on field-harvested sources for their products have certainly helped to keep alive the concept of biological control throughout an age of massive reliance on chemical pesticides. The red ladybird beetle collected each winter and marketed the next spring has been the symbol representing the "good bug" that has exposed as a myth the chemical company advertising slogan "the only good bug is a dead bug."

 

Many farmers buy these beetles every year because their experience with them has been good. It is very difficult to convince them that many other species of predators might be responsible for their good fortune or that the insects they bought probably flew away. Nevertheless this receptive response or urge to believe in the benefits of utilizing natural enemies has made it possible for pest control advisors to communicate with farmer clients about biological control and thereby develop a market for other, more-useful species.

 

PEST MANAGEMENT WITH NATURAL ENEMIES

My experiences in classical biological control research, while employed at the University of California, gave me a strong appreciation for the full, natural enemy complex that can exist on farms not exposed to the adverse effects of pesticides. Most of my time was spent in citrus, cotton, and alfalfa fields, comparing various predator and parasite exclusion methods on small plots in unsprayed farms (DeBach, Dietrick, and Fleschner 1949). We measured the effects of pesticides on various species of beneficial insects that controlled certain pests. We developed methods with the use of pesticides and other habitat-disturbance techniques, e. g. DDT checks, dust checks, and ant checks, to encourage the buildup of pest populations by selectively destroying the natural enemies. We subsequently observed the return of biological control organisms in these plots and monitored the biological suppression and cleanup of these deliberately created pest infestations. We also experimented in fields with pest problems created by ant and excessive dust interference to natural enemies, and then obtained pest control by the elimination of these interferences. Various harmful effects of pesticides were investigated in many different crops, and the results were similar to the pest population outbreaks created by our interference experiments. Such procedures for fostering pests (DeBach 1974) by the elimination or even selective suppression of natural enemy populations without affecting similar control of the pests showed the value of natural enemies in pest management programs.

 

These experiences helped us to identify the reasons why there was such a difference of opinion among entomologists about biological control. Chemical control advocates generally ran their test plots in fields where the target species flourished. It was logical that they seek those fields in order to obtain the data needed about the effects of pesticides on those pest species. These fields were high in pests and low in predators and parasites. Conversely, entomologists interested in biological controls ran their studies in fields that had relatively large populations of predators and parasites compared to pests. Their experimental requirements needed fields free from pesticide and other habitat interferences to explore the effects of natural enemies and specific biological control agents on their host populations.Clearly, these were two different kinds of field situations. The former was deficient in predators and parasites. Even those natural enemies present were destroyed under the small plot experimental design. Pesticide drift and interplot migration of the more-mobile predators and parasites adversely affected the biological control that was present. The latter biological control experimental field situations were isolated from effects of pesticides, and the full range of natural enemies were present. Large experimental plots were used to minimize the drift effects from any pesticides used.

 

There is little wonder that there exists such a divided opinion among entomologists regarding biological controls. It is difficult to form a good opinion about natural enemies if there are none in the fields chosen for studies.The devastating interpretation of this situation occurred when the untreated check plots in the small plot pesticide screening experiments were referred to as being representative of biological control failures. Instead of measuring the ineffectiveness of the natural enemies (or lack of them) these entomologists demonstrated the detrimental effects of pesticides on those few predators and parasites that were attracted to these check plots in search of their prey. These checks were pesticide interference plots.

 

Conclusions on economic thresholds were derived from such fields that were deficient in natural enemies. The lack of any biological control suppression on the pest populations led to the setting of pest density levels that were far too low for fields where natural enemies were allowed to help suppress the pests. Pest management with natural enemies can flourish where population monitoring allows for minor pest spots to appear in fields in order to attract and multiply the natural enemy complex that will predictably control the pests and result in a marketable harvest.

 

Pest control advisors face three kinds of fields each time they check the farms of their clients. Clean fields are quickly identified and little time is spent in them. Dirty fields full of pests with few natural enemies are also quickly managed by making the proper pesticide recommendation. Most of the advisors' time is spent monitoring the insect populations in the borderline fields, which are not clean of pest species but have a moderately high level of natural enemies. There is time to watch and wait, because the pest populations do not Increase as quickly where natural enemy suppression is occurring. Some of these develop sufficient natural enemies for the pests to be biologically controlled and the use of pesticides can be avoided.

 

Farmers who buy biological control products try to help the natural enemies in these borderline fields. This commonsense idea of periodic augmentation of insectary products in infested fields to help the natural enemy suppression of the pests is the foundation for the use of such biological controls in agriculture. Such pest management is based on principles of ecology, the recognition that 100% mortality of all pests is not desirable, and on attempts to avoid as much as possible the impact of pesticides and other habitat disturbances on beneficial insects (DeBach 1969, 1974; Dietrick 1972; Kilgore and Doutt 1967).

 

EVOLUTION OF THE FREE ENTERPRISE INSECTARY

Rincon Vitova Insectaries, Inc., began as a part-time partnership, Rincon, growing "Crypts'," a mealybug-destroying coccinellid named Cryptolaemus montrouzieri Mulsant. This Australian predator had been mass-cultured for many years by county government insectaries, individual farmer-owned insectaries, and farmer association insectaries (Fisher 1963). The county effort, which had used tax money for support but gave the insects to farmers free of charge, was discontinued for budgetary economy and other reasons. A ready market for rearing and selling these beetles thus became available. It quickly became clear to us that this potential market would not develop. The weak endorsement for these inoculative-type releases from nearly all agricultural researchers, coupled with the euphoria for chemical pesticides, almost completely stopped the use of this product. Crypts are still used today by our insectary, and at least one citrus farmer cooperative insectary continues to grow several millions of these beetles each year, as it has for nearly 50 years. The lesson that Rincon Insectary learned was that farmers would not necessarily buy products that were previously obtained free of charge.Rincon Insectary then found a market for "Trichos," a trichogrammatid parasite of eggs of the cotton bollworm moth, Heliothis zea Boddie (now Heliocoverpa zea), that were being cultured by a farmer in west Texas. The potential market for these Trichogramma spp. was larger than the supply. Costs for production were greater and less reliable in Texas than in Rincon' s coastal climate, and an agreement was reached for Rincon Insectary to grow the insects and the Texas partners to market them. In spite of the controversy that had raged over inundative releases of Trichogramma spp. (DeBach and Hagen 1964), the farmers were eager to acquire and use the product. Rearing methods first proposed in the early twenties were resurrected (Flanders l930, l934). The farmers bought Trichos for the same reason that they bought ladybird beetles: the results were satisfactory, and it was commonsense to help the existing natural controls. This west Texas cotton-growing area was blessed with large populations of natural enemies, and the use of ladybird beetles, Trichos, or any other species of insects known to help suppress bollworm populations would have satisfied the customers. These products were more economical than pesticides and their use lessened the farmers' worry when cotton bollworm moths were reported to be flying. They provided the pest control advisors a logical alternative product to counteract the fear generated in the farmers by the unrealistic economic thresholds set for bollworms. The recommendation to treat for bollworms, when 4 out of 100 cotton plants were infested with eggs of bollworm moths, was clearly set too low for fields that had natural enemies that were destroying these eggs. The Trichos released to help attack the populations of bollworm eggs was a commonsense approach. The results were generally favorable in fields that had not received earlier applications of pesticides for such minor pests as thrips, aphids, and mites. The natural enemies in these untreated fields had been allowed to increase their populations on these minor pest problems, thus controlling them biologically. (The questionable recommendation to "clean up these early pests so biological controls could work" had not yet reached these farmers.)

 

With the natural enemy complex capable of control, many farmers experienced good results solely with releases of Trichos. With the use of D-Vac (trade name for sampling equipment manufactured by D-Vac Company, P. 0. Box 2095, Riverside, CA 92516) vacuum insect sampling equipment, we were able to show customers that most bollworm eggs were destroyed and that the few one-day-old worms that did emerge were victims of predators before they grew to be three to four days old (Dietrick 1961; Dietrick, Schlinger, and van den Bosch 1959). The low survival rate of these eggs and small worms was shown to be a measure of the effectiveness of biological control. These observations eventually resulted in economic thresholds being raised for untreated cotton fields. The 1973 cotton pest and disease control guide of the Division of Agricultural Sciences, University of California, states: "In fields not previously treated for insect control, insecticide treatment (for bollworms) is indicated when 20 small worms per 100 plants are found." This economic threshold was compatible with the use of insectary products.

 

The door was open to begin talking to more and more cotton farmers about biological control. We showed them fields where effective populations of predators and parasites destroyed bollworm eggs overnight. We also were able to explain to the farmers that, in those field situations where nearly all bollworm eggs hatched and grew into full-grown worms, there was no buffering natural enemy complex to suppress these pest populations and much cotton was destroyed as a result.

 

About that time Rincon learned another lesson about the insectary business. The marketing partner in Texas decided to build his own insectary with funds collected from farmers and owed to Rincon. As a result, we lost over 80% of our business and gained a bad debt as well. This was only the first of many such experiences. The method of payment for insects came long after harvest and the delivery of our products, but the insectary borrowed the money to set the cultures six months in advance of the market. The live insect products were grown, delivered, and released on the farms throughout the growing season. Usually, only after the farmer sold the crop, did he pay the insectary. Since biological controls were not considered pest controls, they could not be included in the bank loans set aside for chemical pesticides and other production financing. Some farmers simply never paid; after all there was no proof that releasing Trichos had helped. The problems of late payment and bad debts are enough to make most potential investors shy away from this business.

 

Fortunately, there was sufficient financial support to keep us in the struggle. We found new markets, diversified our product line, and broadened the areas where we sold these products. One such market developed in citrus with the use of the golden chalcid parasites, Aphytis lingnanensis Compere and A. melinus DeBach. These species attack the number one pest of citrus, California red scale, Aonidiella aurantii Maskell (DeBach 1969). One of the farmer cooperative insectaries contracted with Rincon to buy 5 million of the red scale parasites. At the same time, we borrowed a program from these farmer cooperatives and began contracting with individual farmers for pest management advice and beneficial insect colonizations wherever they might be located. We insisted that the advice services include releases of our insectary grown products. Trichos were for cotton and the crypts and Aphytis spp. were used as periodic inoculative releases in citrus. The charge per ha set by the farmer cooperative insectaries was increased to cover the additional travel costs, the costs of field monitoring advice, and the insectary products. This seasonal contracted market gave our business some stability and provided compensation for all the extra insect products that we grew, but could not sell over-the-counter. The only real difference between our operation and the farmer cooperatives was the voluntary participation on the part of our clients. My observation about these farmer cooperatives is that it is difficult to please continually all of the individual member farmers.

 

This voluntary, professional-client relationship gave our effort considerable freedom for direction. We simply had to please enough farmer clients in order to pay our expenses. Profits could come from the over-the-counter sales of insect products. Some farmers wanted to believe in sophisticated pest control advice, and we convinced them to buy the insects. Other farmers wanted to believe in the augmentative releases of predators and parasites, so we sold them the insect products and tried to follow up with advice where possible. We contacted other independent pest control advisors and found a few of them willing to use our products as part of their advice programs. Even competing insectaries have on occasion purchased our products to help fill their market needs.

 

These professional-client contracts were more like verbal agreements, but they provided enough cash flow to keep the business going. Even the late-paying customers provided a winter income when the payments finally came in. We avoided any business ties that would obligate us to any particular market or dealerships. We grew as many insects as possible with the resources available and used them in our pest management or sold them as the market developed. We had solved the problem of how to be compensated for all the insects that flowed daily from the production units, at least during the summer growing season.

 

The arrival of the pink bollworm, Pectinophora gossypiella Saund., as a new pest species in our cotton marketing area, triggered an eradication effort by state and federal authorities. The blanket pesticide applications required by this effort immediately created another shock to our struggling insectary business. Adequate natural enemies for this pest were not available, and the eradication procedures advocated for its control were not compatible with our biological pest management programs. The effect on our Tricho sales was devastating.

 

One group of farmer clients, the Coachella Valley Growers Gin, had been our customers continuously since 1961. These farmers chose not to apply the pesticides in the eradication effort, and thus the federal authorities substituted the sterile moth releases as an eradication procedure. This program allowed for biological controls to be used early in the season even though chemical pesticides had to be resorted to in late season. We were thus able to continue our programs with these farmers.The business lesson we learned from this experience was how to be adaptable. We then adjusted our programs to the sterile moth eradication experiment. We found new markets to replace the lost ones in other cotton-growing areas. We helped ourselves by helping cotton farmers in Mexico and Central America to further their insectary efforts. We also lengthened our marketing season by delivering our products to Nicaragua. We began a new line of parasites that helped biological control of pestiferous flies associated with manure accumulations on poultry farms (Legner and Dietrick 1972). These business-diversifying actions again created enough income to keep us going. During this time we added production facilities by purchasing another insectary known as Vitova (a contraction for the Latin vita ova meaning live eggs).Research has benefited our insectary a great deal. The existence of a commercial insectary challenged researchers to investigate some of the programs that we intuitively advocated, doing what seemed obvious from our field observations. Influential farmer clients asked questions in important places, and research money flowed from various commodity groups for university and government researchers involved in such biological control efforts. Our insectary supported research and encouraged customers to fund such research (E. J. Dietrick, unpublished). The fallout of useful knowledge that comes from such ecological experimentation far surpasses any possible effects that any negative findings would have on our business. The problem still lies in finding the funds to study the Implementation of biological controls.

 

PROBLEMS FACING THE COMMERCIAL INSECTARY

Problems encountered by commercial insectaries can best be solved in the free market place. Farmers will discontinue acquiring and using pesticides when they are convinced that alternative pest management is cost-effective. Rising costs for petroleum-based farm chemicals and fuels and narrowing profit margins are forcing farmers to look for more economical solutions than those presently available. Farmers presently spend millions of dollars every year for chemical pest controls that may not provide any permanent solutions to the problems. When farmers buy chemical pesticides, their support goes to further the development of more chemicals. Perhaps a financially viable biological control industry can also influence further research and development in classical biological control. Biological control importation projects are the main source of beneficial predators and parasites that can be developed as products by commercial insectaries.

 

Increasing energy costs are also influencing insectaries that serve the farmers. The appropriate ate size firm seems to be one which is small enough to adjust its products and services to) meet local needs. Maximum use of habitat management techniques that are capable of trapping pests and increasing the populations of predators and parasites can then be used (Schlinger and Dietrick 1960). Insect-harvesting equipment can be employed to move the surplus natural enemies from fields where pest populations have been destroyed to fields deficient in predators and parasites (E. J. Dietrick, unpublished; Stern 1969; Stern et al. 1964, 1965; van den Bosch l969). The local insectary can become abase for pest control advisors for such operations along with mass-culturing of certain parasites that can be more economically grown than harvested.

 

Probably the single most-prevalent problem facing the commercial insectary is the low visibility of biological controls. It would greatly help if extension efforts could provide farmers with biological control information with color pictures of the key predators and parasites associated with each crop. There are few bulletins that provide "do-it-yourself" assessments of key natural enemies (Bethell 1978; van den Bosch and Hagen 1966). Perhaps a periodic newsletter identifying the "good bugs'' and their relationship to pest management would enhance the visibility of biological controls. Unfortunately, the usual endorsement from the entomological establishment, including many researchers in biological control, is reduced to) such statements as ''It won't do any harm to use them." Some of the more-optimistic statements are that "we do not have sufficient information to recommend for or against the use of Trichogramma, chrysopids, praying mantids, ladybird beetles or any other parasites or predators in the manner proposed for controlling agricultural pests" (U. S. Department of Agriculture 1968). Such position papers, presumably based on adequate information, make it very difficult to sell biological control products. Weak statements that call for conservation of natural enemies without identifying the species involved, or without specifying which pesticide to use to conserve the predators, are also nonproductive.

 

There seems to be a strong effort to regulate biological control practices as if they were a threat to society similar to the poisons in our pesticides. Certainly, no harm can result from predators and parasites known to attack pests and already established in the area. One major justification for the commercial insectary is to help with the further spread of newly established, exotic species and/or races when the limited research funds for such dispersal to all farms are inadequate. This free market allows a free choice to farmers who want to improve their complex of species of predators and parasites by purchasing new strains of biological control products. Marketing strains that are known to mate with indigenous strains may increase the genetic capability of certain biological control agents (Bartlett and van den Bosch 1964).

 

Other issues that need to be resolved in order to help the commercial insectary industry have to do with financing. The insectary is a farming venture without any of the advantages of a farm (production credit, etc.). The products are perishable, adaptable to agricultural production systems, and as other beneficial farm animals, should not be considered for sales tax: they help the farmer just as any other work animals that are given tax exemptions.

 

THE COMMERCIAL INSECTARY AND THE FUTURE

Like most businesses marketing products with little shelf life, the insectary needs a steady market to survive; free enterprise insectaries cannot sustain many poor market years. Beneficial insect products must be sold once they are grown. All other insectaries operate from other financial bases, but the commercial insectary will be out of business if the farmer clients cannot pay. Other pest control products can be kept in readiness for problems to develop, but the insectary must arrange for an orderly delivery of its products as they emerge daily from the production cages. Whenever possible, we must find enough farmer clients to buy the insectary products as part of a regular inoculative release program.

 

Most fields can be helped with insectary products only during a few months of the growing cycle. The insectary personnel must culture these animals 365 days a year in order to have them available for the few weeks when needed. Out-of-season production costs with little or no off-season sales can take away much of the profits.There are no proprietary protections for insectary products. Anyone can pirate one of our employees, buy our products, and begin his own insectary business at much lower start-up costs than it takes to collect and culture the original colonies obtained from field-collected individuals. This satellite insectary can operate seasonally, closing the rearing operations in the off season. By stopping the rearing process completely, much of the labor costs can be saved. Beginning the rearing process again after a few months to clean up and sanitize the various pests that the insectary attracts is a distinct advantage, provided there is some one of the businesses that can provide the new stocks for the coming season. Such satellite insectaries need not overproduce. Instead, they can buy products from the other insectary to fill in shortages in production or satisfy a particularly good market. Such cooperation among those who culture insects will help to promote the industry in the long run, though the short-term effects can be very frustrating.

 

The economic gap is rapidly closing for biological agriculture versus conventional farming that depends mainly on petroleum-based chemicals. The rising energy costs are likely to bring many changes in the future production of food and fiber. The commercial Insectary is already helping farmers to establish biological and cultural controls as the basis for pest management. Our business has grown out of the failures of existing pesticide-dominated programs that ignore many basic ecological principles. As long as pesticides were inexpensive and the repeated applications ultimately succeeded when the customary one or two failed, the alternatives available to farmers seemed fraught with unacceptable danger. Rising production costs and narrowing profit margins are forcing farmers to look seriously at pest management that is based on natural enemies and the help that commercial production of these entomophagus insects can give. Farmers need biological control because it is safe, permanent, and economical.

 

ACKNOWLEDGMENTS

The manuscript for this paper was reviewed by my colleagues in Rincon Vitova Insectaries, Inc., and friends elsewhere. I am particularly indebted to Drs. T. W. Fisher and Fred Legner for their comments.

LITERATURE CITED

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DeBach, P. t969. Biological control of diaspine scale insects on citrus in California. Proc. 1st Int. Citrus Symp. Vol.2: 801–15

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DeBach, P.; E. J. Dietrick; and C. A. Fleschner. 1949. A new technique for evaluating the efficiency of entomophagus insects in the field. J. Econ. Entomol. 42: 546.

DeBach, P., and K. S. Hagen. 1964. Manipulation of entomophagus Species. Pages 429–58 in P. DeBach and E. t. Seblinger, eds. Biological Control of Insect Pests and Weeds. Reinhold, New York.

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Kilgore, W. W., and R. L. Doutt, eds. 1967. Pest Control–Biological, Physical, and Selected Chemical Methods. Academic Press, New York.

Legner. E. F., and F. 3. Dietrick. 1972. Inundation with parasitic insects to control filth breeding flies in California. Pages 129–30 in Proc. and Papers of 40th Ann. Conf. of California Mosquito Control Assoc.

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Stern, V. M. l969. Interplanting alfalfa in cotton to control lygus bugs and other insect pests. Pages 55–69 in Tall Timbers Conf. on Ecol. Animal Control by Habitat Management, No. 1, Tallahassee, Florida.

Stern, V. M.; F. I. Dietrick; and A. Mueller. 1965. Improvement on self–propelled equipment for collecting, separating, and tagging mass numbers of insects in the field. J. Econ. Entomol. 58:949–53.

Stern, V. M.; R. van den Bosch; and T. F. Leigh. 1964. Strip cutting of alfalfa hay for lygus bug control. Calif. Agric. 18: 5–6.

U. S. Department of Agriculture. 1968. Current status of research on the production and use of biological agents for controlling agricultural insect pests. Entomol. Res. Division, A. R. S., Washington, D. C.

van den Bosch, R. l969. The effect of harvesting practices on insect populations in alfalfa. Pages 47–54 in Tall Timbers Conf. Ecol. Animal Control by Habitat Management, No. 1, Tallahassee, Florida.

van den Bosch, R., and K. S. Hagen. 1966. Predaceous and parasitic arthropods in California cotton fields. Calif. Agric. Exp. Stn. Bull. 820.

 

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