Integrating Biological Control into Farming Systems(l) Douglas A. Landis Department of Entomology and Pesticide Research Center Michigan State University, East, Lansing, MI 48824 Can biological control be successfully integrated into Midwest agriculture? While the ultimate answer involves many social and economic factors and is therefore very complex, the scientific evidence is clear; biological control is already successfully integrated into many farming systems and can be further utilized if producers desire to do so. What is biological control? What practices are included and which ones are most likely to be integrated into our current and future farming systems? Biological control is the planned manipulation of predators, parasites or diseases to reduce the damaging impact of crop pests. Biological control can be used against any type of pest; weeds, diseases, vertebrates or insects, although in this paper I will concentrate on biological control of field crop insects. All organisms have natural enemies in their environment that limit their populations. Disease and parasites may weaken or directly kill individuals and predators remove the inexperienced, the sick or the old from a population. In general, these checks and balances on populations are positive and serve to maintain a healthy equilibrium. We term these natural checks on pest numbers "natural control." While natural control occurs in agricultural systems, frequently the balance is tipped in favor of the pest. This may be due to the way in which we grow the crop (ex. monocultures) or due to a lack of natural enemies (ex. imported pests). Producers can improve on natural control by purposefully manipulating natural enemies to reduce pest populations. There are three main types of biological control; importation, augmentation and conservation. Importation refers to the process where an exotic pest is controlled by natural enemies which are imported from the pests country of origin. This is typically initiated by university, state or federal scientists. Imported natural enemies must go through a quarantine procedure to assure that no new pests or hyperparasites (i.e. parasites of beneficial parasites) are introduced. This is followed by establishing the new natural enemy on the target pest population. Importation is also called "classical" biological control and can (and in many cases has) provided remarkable control of pest populations (ex. alfalfa weevil, cereal leaf beetle). In addition, it is self-perpetuating and may be permanent. Augmentation is used where populations of a natural enemy either cannot be permanently established, or where their population cannot respond quickly enough to the pest population. Augmentation may involve either inoculative or inundative releases. For example, in areas where a particular parasite cannot overwinter, an inoculative release each spring may allow the population to establish and adequately control a pest. Inundative releases involve the release of large numbers of a natural enemy such that their population completely overwhelms that of the pest. Conservation of natural enemies involves any action that serves to maintain or increase the population of the beneficial species. This may be as simple as leaving unsprayed strips as a refuge or source of hosts for the natural enemy population. Providing alternate prey, or other resources such as overwintering sites or food for adult parasites are other examples of conservation techniques. Levels of Integration Natural enemies can be integrated into farming systems at several levels. The most basic level is to understand and utilize the benefits of natural control to your advantage. This requires no specific actions by the producer beyond an appreciation for what Mother Nature is doing. An important example in the Midwest is the impact of the potato leafhopper disease, Zoophthora radicans. This fungus is present throughout the upper Midwest. When a leafhopper becomes infected it will die in 2-3 days. Under the right conditions (cool and moist) the fungus then goes on to produce thousands of conidia capable of infecting other leafhoppers. As the disease spreads through the population, leafhopper numbers can drop rapidly. In Michigan, we have detected outbreaks of this disease (epizootic) every year since 1989. Typically they occur in late July or August in conjunction with a cool, wet period. Dry bean and alfalfa producers frequently find no need for further leafhopper control after an epizootic occurs. Taking advantage of other forms of biological control may require some modification of farming practices. In particular, restricting insecticide use is necessary to enjoy the full benefit of many insect predators and parasites. In alfalfa systems, using harvesting rather than insecticides to manage alfalfa weevil during first cutting allows native and introduced natural enemies to survive and continue to suppress weevil and other pest populations. In no-till corn, studies in Ohio have shown that predators, primarily ground beetles, are effective in removing black cutworm larvae and preventing cutting of plants (Brust et al 1985). However, certain soil insecticides kill the natural enemies without reducing cutworm populations and thus, result in more plant damage than where no insecticides were used. Other biological controls can be used directly as an intervention against pest populations, however, this generally requires some special knowledge or information about their use. One example is the microbial pesticides based on Bacillus thuringiensis (Bt). For European corn borers, these products must be applied against young larvae to be effective. In some cases, this may require special scouting to determine if susceptible host stages are present. Augmentative release of Trichogramma egg parasites will require an accurate knowledge of the pest's life cycle as well as that of the parasite. Trichogramma are tiny wasps about the size of the period at the end of this sentence. They seek out and lay their eggs inside the eggs of many types of caterpillar pests. The pest egg is killed and instead of a caterpillar, one or more Trichogramma wasps are produced. Various species of Trichogramma are in widespread use around the world. A promising application of Trichogramma in the Midwest is to help manage the European corn borer (ECB). Degree-day models are used to predict the development of ECB pupae and adults. At the proper time, the Trichogramma are brought out of cold storage where they are in a state of diapause (hibernation) and released into the field to develop in concert with ECB. The idea is have an abundance of wasps present in the field for the entire period during which corn borers are laying eggs. In trials in the Midwest, Trichogramma have been as effective as insecticides in reducing ECB damage in field corn. Using Trichogramma will not be as simple as spraying a pesticide, however, the ultimate advantages of a zero-pesticide technique for managing ECB may make it as popular in this country as it currently is in Europe and China Designing Farming Systems for Successful Biological Control. Up until now we have been asking the question, which examples of biological control fit the way I currently farm? The ultimate integration of biological control comes when we begin to ask the question, how can I alter my farming system to take full advantage of the potential of biological control? At the core of this question is a philosophical choice. Do I use the management tools available to me to react to pest problems when they develop, or do I use my management skills to prevent pest problems from ever occurring? This alternative model of insect management has been likened to preventative health care. In preventative pest management, a series of practices are put into place that serve to prevent the pest from ever reaching damaging (i.e. threshold) levels and thus, reduce the need for intervention. The concept of Integrated Pest Management (IPM) was originally conceived as just such a strategy. By integrating biological and cultural controls, IPM systems would prevent most pests from reaching threshold levels, however, if they did, scouting would detect them and the least disruptive option could be used to bring the pest under control. Unfortunately, we have too often forgotten about the importance of cultural and biological controls and placed the emphasis solely on pest detection and chemical control. Until there is a commitment to prevention of pest problems vs. reaction to pest problems, the full potential of biological control will never be realized. An example of designing farming systems to take full advantage of biological controls involves Eriborus terebrans, a parasite of European corn borer (ECB) larvae. Eriborus was one of 24 parasite species imported from Europe and the Orient during 1920-1938 to assist in controlling the corn borer. In early publications it was cited as being one of the most promising of the ECB natural enemies and observed to kill up to 56% of the larvae in a given field (Baker et al. 1949). However, in the Midwest, this wasp currently parasitizes an average of only 2.4 - 7.8% of the ECB (Lewis 1982, Hill et al. 1978). Why is a parasite with such great potential currently so limited in it's effectiveness? Our studies have shown that the female wasps are very sensitive to heat and die rapidly when temperatures exceed 90¡ F. In addition, they require a source of sugar, either from the nectar of flowering plants (ex. wild carrot) or from aphid honeydew (ex. bean aphids on lambsquarters) on a daily basis or they will die. Given these requirements, most current Midwest corn production systems are a difficult if not outright hostile environment for Eriborus. Prior to canopy closure, during the first generation of ECB, afternoon temperatures within corn fields frequently exceed 90¡ F. Since the wasps cannot exist there, they must seek more sheltered locations. In addition, there are no sources of sugar (nectar or honeydew) in these fields at this time. In Michigan, the wasps respond by retreating to the nearby shade of wooded fencerows and woodlots where they find reduced temperatures, increased relative humidity and sources of food. ECB larvae in parts of the corn field near these types of habitats are parasitized at two to three times the rate of those in field interiors. In one field with several wooded edges, we have observed up to 40% parasitism by Eriborus (Landis and Haas, 1992). Our research is aimed at determining if we can modify corn production systems to provide more of the proper resources for natural enemies in a way which is compatible with modern farming systems. Strip cropping and other fairly simple modifications of the agricultural landscape may be a potential solution. Guidelines for managing natural enemies in farming systems have been proposed by various authors, they typically include providing habitats to maintain or increase: 1) availability of alternate hosts, 2) availability of food resources for adult natural enemies, 3) availability of overwintering habitats, 4) a succession of hosts (constant food supply), 5) availability of appropriate microclimates (Debach and Rosen 1991, van Emden 1965, van Emden 1990, Powell 1986, Rabb et al. 1976). In addition, recent ecological theory proposes that the arrangement (spatial distribution) of these resources in the landscape is critical to the functioning of these species. Our studies suggest that management of insect natural enemies should be guided by practical combinations of the principles listed in Table 1. Applications of biological control techniques have great potential to make Midwest farming systems more efficient, profitable and sustainable. Opportunities exist for easily integrating certain aspects of biological control into existing farming systems, while others techniques will require significant modification of current systems. It is clear that as the ultimate integrators of agricultural technologies, farmer innovation in these areas is critically needed. Table 1. Guidelines for managing populations of insect predators and parasites in Midwest farming systems Create refuges in or next to fields that contain: ¥ overwintering habitats for natural enemies ¥ within season habitat (may be different than overwintering) ¥ early season hosts for natural enemies ¥ an abundance of alternate hosts ¥ moderated microclimates (shade, high relative humidity) ¥ food resources for adult parasites (nectar, pollen, aphid honeydew) (1) Reprinted from: Summary of Presentations. 1994 Illinois Agricultural Pesticides Conference, January 5-6, 1994. Urbana, L. University of Illinois at Champaign-Urbana, College of Agriculture, Cooperative Extension Service. Reference Cited: Baker, W. A., W. G. Bradley & C. C. Clark. 1949. Biological control of the European corn borer in the United States. USDA Tech. Bull. 983. Brust, G. E. B. R. Stinner and D. A. McCartney. 1985. Tillage and soil insecticide effects on predator-black cutworm (Lepidoptera: Noctuidae) interactions in corn agroecosystems. J. Econ. Entomol. 78: 1389-1392. Debach, P. and D. Rosen. 1991. Biological Control By Natural Enemies. Cambridge Univ. Press. Hill, R. E., D. P. Carpino & Z. B. Mayo. 1978. Insect Parasites of the European corn borer Ostrinia nubilalis in Nebraska from 1948-1976. Environ. Entomol. 7: 249-253. Lewis, L. C. 1982. Present status of introduced parasitoids of the European corn borer, Ostrinia nubilalis (Hubner), in Iowa. Iowa State J. of Res. 56: 429-436. Landis, D. A., and M. Haas. 1992. Influence of Landscape Structure on Abundance and Within-Field Distribution of Ostrinia nubilalis Hubner (Lepidoptera: Pyralidae) Larval Parasitoids in Michigan. Environ. Entomol. 21: 409-416. Powell, W. 1986. Enhancing parasitoid activity in crops. In. J. Wagae ed. Insect Parasitoids. Rabb, R.L. RE. Stinner and R. van den Bosch. 1976. 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