Intercropping as cultural pest control: Prospects and limitations

Agriculturalists have been intercropping (simultaneously growing several crops in the same field) for centuries, and the use of polycultures continues as an important form of agriculture among indigenous peoples in the New and Old World tropics and subtropics One demonstrated advantage of intercropping is a reduction in insect pest populations, explained by higher numbers of natural insect enemies in the intercrop and/or reduced herbivore colonization and tenure time in the intercrop A review of 150 published field studies in which 198 herbivore species were studied shows that 53% of the pest species were less abundant in the intercrop, 18% were more abundant in the intercrop, 9% showed no difference, and 20% showed a variable response Two major problems of the published studies are 1) lack of experimental evidence demonstrating that reduced pest numbers in the intercrop resulted in higher yield, and 2) lack of experimental evidence demonstrating the ecological mechanisms responsible for the intercrop effect There is some theoretical and empirical work suggesting that herbivore movement patterns, rather than natural insect enemies, are often more important in accounting for reduced pest abundance in an intercrop Several examples from the author's work are presented that demonstrate ways of studying the ecological mechanisms underlying pest suppression in intercrops. The successful design of new intercropping systems to reduce pests will require a better theoretical understanding of such ecological mechanisms It is emphasized that intercropping has potential in both developed and developing countries and that many of the impediments to incorporating appropriate strategies of diversification are social rather than technological