Ecological aspects of soybean production and pest management in Nicaragua.

Abstract

Integrated pest management (IPM), which emphasizes the use of biological control factors and minimization of chemical insecticides, is a pest management approach particularly appropriate for developing countries which currently import expensive, hazardous pest control chemicals. I review the economic and ecological aspects of agricultural technology in Nicaragua, emphasizing the role of pesticides. The recent introduction of soybeans necessitates the development of IPM techniques for this crop because the dominant pest, Spodoptera exigua (Lepidoptera: Noctuidae) is insecticide-resistant and highly polyphagous. I review the biology of this pest, particularly those aspects that contribute to its status as an agricultural pest. I investigate the potential for IPM in soybeans in Nicaragua in field research on Spodoptera exigua, examining the possible use of weeds as a control agent in contrast to insecticides. Because weeds can reduce pest abundance, but also complete with the crop, I measure the effect of weeds and insecticides on pest abundance and yield of two varieties of soybeans, Cristalina and Tropical. Populations of S. exigua were reduced by weeds in 1987 but not in 1988. The reduced abundance of S. exigua larvae in weedy soybean plots is apparently a consequence of reduced oviposition in weedy plots relative to weed-free plots. Insecticides, in contrast to weeds, did not reduce pest abundance relative to insecticide-free plots, suggesting that these are inseciticide-resistant pest populations. Chrysoperla carnea (Neuroptera: Chrysopidae), an abundant natural enemy in this agroecosystem was not reduced by insecticides, suggesting that it is also insecticide-resistant, and has potential use in programs integrating chemical and biological pest control tactics. Weeds neither significantly reduced total seed yield of either soybean variety, nor affected the number of pods produced, number of seeds per pod, or average weight per seed. Plant height of the Cristalina variety, but not the Tropical variety, was increased by weeds. Insecticides did not affect total seed yield per plant of either variety, but increased average seed weight of the Cristalina variety. Plant height of both the Cristalina and Tropical varieties was increased in insecticide treated plots. The implications of these results for soybean production and pest management in Nicaragua are discussed.