Indirect and Direct Effects in a Tropical Agroecosystem: The Maize‐Pest‐Ant System in Nicaragua

Abstract

This study examines the direct and indirect effects of insecticides in maize—pest—ant system in Nicaragua. Population levels of two herbivores, the fall armyworm, Spodoptera frugiperda J. E. Smith, and the corn leafhopper, Dalbulus maidis De Long, were monitored and compared among four insecticide treatments: (1) carbofuran, a systemic insecticide; (2) chlorpyrifos, a broad—spectrum insecticide; (3) a combination of carbofuran and chlorpyrifos; and (4) a control, where no insecticide was applied. Ant foraging activity also was monitored throughout the season for all four insecticide treatments. Predation of S. frugiperda pupae was estimated with relation to insecticide treatment and ant foraging activity. Carbofuran reduced ant foraging activity and increased population levels of the fall armyworm. Ant predation was apparently responsible for a higher pupal removal rate in the plots with no insecticides. Chlorpyrifos significantly reduced ant foraging activity as well as densities of the fall armyworm, but it resulted in higher levels of the corn leafhopper. The results of this study are discussed in light of the possibility of developing integrated pest management programs in which ants may play an important role as agents of biological control. In such a case, ant susceptibility to chemical insecticides should be taken into consideration.