Agroecosystem Diversity and Pest Control: Data, Tentative Conclusions, and New Research Directions

Abstract

Recent criticism of the theory that increased diversity leads to increased stability has led to widespread skepticism about the value of using ecological theory to suggest strategies of agricultural diversification to better control insect pests. A total of 150 published studies which examine the effect of diversifying an agroecosystem on insect pest abundance are summarized; 198 total herbivore species were examined in these studies: 53% of these species were found to be less abundant in the more diversified system, 18% were more abundant in the diversified system, 9% showed no difference, and 20% showed a variable response. Two major problems with the studies were: (1) proper experiments were not conducted to show that differences in pest abundance between more and less diverse systems resulted in yield differences; (2) the ecological mechanisms accounting for the differences in pest abundance were carefully examined in only a few of the studies. A fundamental understanding of these ecological mechanisms is critical to the development of a predictive theory of how agricultural diversification affects insect pests. Empirical data and several theoretical arguments are presented which suggest that differences in pest abundance between diverse and simple systems can frequently be accounted for by the response of herbivore host-finding behavior to the patterns of resource availability, rather than the activities of natural enemies. The development of ecologically sound agroecosystems may well utilize within-field plant diversity, both in developing and in developed regions.