Field infestation of pigeonpea (Cajanus cajan (L.) Millsp.) by Callosobruchus chinensis (L.) in Uganda

Studies were conducted in Uganda to determine the importance of field infestation of pigeonpea by bruchids, and whether or not the susceptibility of the pigeonpea pod to infestation changes during pod and seed development. A survey of farmers’ fields in the major pigeonpea growing areas in northern Uganda showed that bruchids did infest pigeonpea in the field. In all three districts surveyed (Apac, Gulu and Lira), infestation levels were similar and by one species only, Callosobruchus chinensis. Once harvested, infestation of stored seeds was four times greater than stored pods. In a separate study, caged pigeonpea pods were infested at seven different developmental stages by C. chinensis. The number of eggs laid increased with development, from pod formation to the mature yellow stage, but declined thereafter. When pods were incubated, there was no adult emergence from pods infested after they had matured and started to dry. The frequency of C. chinensis adult emergence varied significantly over time; a bimodal frequency pattern of emergence was observed from pods infested at mature green stage and, to a lesser extent at the preceding late pod filling state, suggesting the occurrence of polymorphism.