Presentation Summary

Internationally–Where/Why Biopesticides Work

Dale G. Bottrell, Department of Entomology, University of Maryland, College Park, MD 20742-4454/USA email: db40@umail.umd.edu

By the 1970s, research institutions around the world had started major programs to develop new or improved alternatives to conventional pesticides. Optimism was high that future pest control schemes would increasingly incorporate novel methods including biopesticides–preparations of living pathogens that attack pest organisms. The biopesticides seemed ideal for integrated pest management (IPM), which combines different control tactics and succeeds only if the tactics spare the pests’ natural enemies. Unlike most conventional pesticides that act on many organisms, biopesticides are generally narrowly selective and pose few problems to nontarget organisms including natural enemies. Therefore, the trends on global use of pesticides are frustrating to those promoting biopesticides. Except for Bacillus thuringiensis (Bt), the predicted demand for commercial biopesticides has not become real. Estimated world sales of all biopesticides amount to less than 0.5% of the total world pesticide market. More than 90% of the total sales are Bt products (Rodgers 1993).

Bt is now commonly used to control insect pests resistant to conventional insecticides, in glasshouse and urban environments where human exposure is a special concern, and on food crops grown for organic markets (Cannon 1993). Especially attractive markets are the minor (and often high value) food crops in developed countries. Of the high Bt-use crops in the U.S. (a crop is in this category if $30% of its total hectares receive Bt), all but cantaloupe (Cucumis melo) and grape (Vitis vinifera) are minor crops (total ha of a minor crop in U.S. #40,470) (Mellon & Rissler 1998). Except for cantaloupe and grape, total hectares of the other major crops treated with Bt range from less than 1% to 15% for a crop (average <5%). Nevertheless, Bt is a highly important pest control tool for many farmers, orchardists, foresters, and homeowners. About 0.81 million ha of U.S. crops received Bt treatments in 1992 (Mellon & Rissler 1998).

The developing countries have produced some of the best examples involving use of biopesticides. One example involves Brazilian farmers who have obtained exceptional control of the velvetbean caterpillar, Anticarsia gemmatalis, by spraying suspensions of nuclear polyhedrosis virus (NPV) to soybean, Glycine max (Moscardi & Sosa-Gomez 1996). The farmers collect freshly killed caterpillars from virus treated fields and freeze them until the following year. They mix the thawed larvae with water to make NPV suspensions. One NPV application (50 larval equivalents/ha) per cropping season has successfully controlled the insect pest and is as effective as two insecticide applications in a season (Kogan & Turnipseed 1987). Thirty percent of the Brazil’s soybean farmers may use the NPV in IPM programs. Soybean farmers in some areas of Asia have also successfully used biopesticides, deploying Beuveria bassiana to control the soybean pod borer, Leguminivora glycinivorella. Chinese farmers apply B. bassiana to the soil surface to infect larvae dropping from the plants to overwinter (Kogan & Turnipseed 1987). However, neither soybean farmers in Brazil nor China rely entirely on biopesticides to control the target pests. These materials are just one component of IPM.

Plant pathologists have been highly successful using antagonists against some harmful plant pathogens. At least 30 different biological control organisms are presently available as commercial formulations to suppress plant diseases (Lumsden et al. 1995). One of the success stories in several countries involves use of Agrobacterium radiobacter strain K84 to prevent crown gall, a plant tumor caused by a related organism, A. tumefaciens. K84 protects plant wounds against infection partially because it produces the antibiotic agrocin 84, which has specific toxicity against sensitive strains of A. tumefaciens.

The past 20 years have produced an impressive literature on bioherbicides (almost all involving fungi). However, use of the materials has been largely disappointing (Morin 1996). The U.S. has registered only three bioherbicides. The manufacturers subsequently withdrew all three for commercial reasons (Hoagland 1996, Morin 1996). In a recent review on biological control of weeds, McFadyen (1998) concluded that bioherbicides are still unproven as practical, economically viable alternatives to chemical or mechanical weed control. Some weed scientists remain optimistic that deployment of indigenous pathogens has considerable potential in weed IPM programs of developing countries (e.g., Watson et al. 1997).

Biopesticides have not been adequately evaluated in terms of their costs relative to their benefits to farmers and others using them. Just because biopesticides are being used is not proof that they (or other control methods) are actually necessary. Examples from both developed countries (e.g., Benbrook 1996) and developing countries (e.g., Oka 1996) show that farmers commonly reduce insecticide use by 50-100% without any loss in crop yield after switching to IPM. In most cases, the IPM farmers do not deliberately replace the withdrawn insecticides with other control methods–something worth remembering when predicting future tradeoffs to pesticides in IPM schemes.

Control of the coconut rhinoceros beetle, Oryctes rhinoceros, on coconut, Cocos nucifera, in Asia and the Pacific Islands is a good example of how entomopathogens have provided well documented benefits. Native to the region, the pest has spread and intensified in many new areas this century, seriously threatening coconut production (Waterhouse & Norris 1987). The affected countries tried many different methods to control the invading pest but eventually adopted baculovirus because of its effectiveness and low expense. The virus naturally infests populations in some areas but does not cause high mortality in beetle populations in newly invaded areas. Therefore, the strategy has been to induce virus epidemics in the recently invaded areas by infecting and liberating beetles with the virus (Jacob 1996, Waterhouse & Norris 1987). Results comparing levels of beetle damage to coconuts before and after virus introductions have been impressive, indicating 80-90% reduction (Pertzsch 1984). Once introduced, the virus seems to maintain itself adequately without additional intervention. However, some countries use various management techniques to complement actions of the virus. An IPM program in Western Samoa has integrated the baculovirus with habitat management (cover crops, destruction of breeding sites, etc.), applications of the entomofungus Metarhizum anisopliae, selective insecticide applications, and beetle trapping (Pertzsch 1984). Applied to the beetle’s breeding sites where the spores live up to 2 years, M. anisopliae infects visiting adults and developing larvae of O. rhinoceros. The disease agent spreads naturally only to a limited extent. Its deployment therefore requires continuous maintenance, which is labor intensive and expensive, precluding widescale use (Pertzsch 1984).

High costs of labor have also slowed advancement of other biopesticides. These high costs, coupled with regulatory constraints and problems with formulations and marketing, have led to serious disappointments with biopesticides. However, the crux of the disappointments often traces to the unrealistic view about their expectation in pest management. To expect a slow acting biological control agent–the essence of a biopesticide–to compete with a powerful fast-acting synthetic chemical is quixotic. Early leaders of IPM expressed this view more than 3 decades ago (Smith & van den Bosch 1967). Despite current reminders that biopesticides do not work like pesticides in IPM schemes (e.g., Fuxa 1987), some still tout them as pesticide mimics. As early IPM leaders also indicated, it is improbable that any pest control tactic used unilaterally will be dependable in all situations. Ecosystems are highly variable and unpredictable, and to assume that either their resident pests or biological control agents will respond constantly over space or time is unrealistic. When farmers report on a biopesticide’s failure or inconsistent performance, they may merely be alluding to the variable nature of their crop ecosystem and not flaws in the biopesticide per se. Biopesticides will continue to provide disappointments if we treat them like conventional pesticides, expect them to perform evenly across a range of situations, and apply them in an ecological abyss.

Furthermore, in most free market environments, a biopesticide or other alternative will not out compete a conventional pesticide that is less expensive and provides effective results. Tilting the competition to favor the alternatives may require government regulations and possibly "incentive" programs. Both measures were necessary to kick off the large-scale highly publicized national IPM program in rice, Oryza sativa, in Indonesia (Oka 1996). This program has reduced national insecticide use on rice by 50% while maintaining and even increasing crop yields–no small accomplishment for the world’s third largest rice producer. To make the program work, the Indonesian government first banned many insecticides available to rice farmers and then halted subsidization of pesticides to the farmers. Pesticide subsidies, which may reduce the retail price farmers pay for the chemicals by as much as 50-90%, invariably undermine any effort to introduce alternatives. Subsidies are widescale in the developing world. As along as they continue, biopesticides and other alternatives will lag.

Examples in this paper indicate that many factors determine whether farmers or others will adopt biopesticides. Obviously, there first must be a potentially effective biopesticide and a reliable structure for ensuring its availability. Its successful deployment will then depend on ecological characteristics of the pests, their economic importance, value of the crop or other resource and its intended market (local market, export), and, most important, how a farmer or other user perceives the biopesticide. If a biopesticide costs more but provides no better results than a conventional pesticide, then farmers and other potential users will not likely adopt it except in special circumstances (e.g., when organic markets are sought, if the government eliminates pesticide subsidies). Biopesticides will always lag if we continue to push them as pesticide mimics without properly integrating them into the targeted farms or other operations. The best prospect for biopesticides is to use them in organized IPM programs that combine other pest control tactics in a manner consistent with local needs and constraints.

References Cited

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