The Effect of Host-plant Density on the Numbers of Mexican Bean Beetles, Epilachna varivestis

Abstract

The purpose of this study was to determine whether an increase in bean (Phaseolus vulgaris) density results in increased incidence of attack by Mexican bean beetles Epilachna varivestis Mulsant (Coleoptera:Coccinellidae), a specialist herbivore of legumes. Bean density in experimental patches was manipulated by replacing beans with nonhost plants (squash) while keeping patch area, shape and total number of plants constant. The average number of Epilachna beetles per plant significantly increased with host density. This experimental result supports the resource concentration hypothesis, which postulates that plants growing under high density conditions should be more heavily attacked by herbivorous insects than plants growing in localities of low plant density.