Genotypic Diversity in the Suitability of Cowpea (Rosales: Leguminosae) Pods and Seeds for Cowpea Weevil (Coleoptera: Bruchidae) Oviposition and Development

Abstract

The suitability of cowpea pods for Callosobruchus maculatus (F.) oviposition varied significantly among 36 diverse genotypes, among 3 pod maturity stages, and between the first 6 h or remaining 18 h periods of the test. The differences in mean number of eggs laid per pod between the most and least suitable genotypes for dry, yellowing, and mature green pods were 14-, 7-, and 3-fold, respectively, and were clearly sufficient to demonstrate nonpreference resistance of cowpea pods to cowpea weevil oviposition. The oviposition on pods of one stage was not correlated with suitability of a genotype in the other two stages. Cowpea weevils oviposited on all stages of all genotypes and the differences in the suitability were in part a result of oviposition being delayed on some stages or genotypes more than others. The suitability of dry pods for oviposition was not correlated with suitability of that genotype for offspring development. The differences in oviposition between the most and least suitable seeds of these same 36 genotypes was only 2-fold. This may indicate that pods have a more diverse array of oviposition stimuli than seeds and may thus be a richer source of nonpreference resistance.