Mortality factors affecting Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) under field conditions in Niger

Abstract

An experiment was conducted to study the impact of various factors affecting the development of Callosobruchus maculatus (F.) by infesting cowpea pods with eggs and exposing them to field conditions in Niamey, Niger. It was designed to determine the extent of field mortality of the pest from oviposition to adult emergence. The duration of the life cycle ranged from 18 to 28 days with a mean of 22.9 days. A higher mortality was recorded in the egg stage than in any other developmental stage. Egg parasitism by Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) was the most important mortality factor identified, followed by the disappearance of eggs from the surface of pods. These two factors together accounted for the loss of three quarters of the total number of eggs. Natural death in the larval stage in the seeds was the third most important mortality factor, whereas parasitism by Eupelmus vuilleti (Cwf.) (Hymenoptera: Eupelmidae) and natural death in the pupal stage were the least important factors. These results indicate a great degree of regulation of bruchid populations by natural mortality factors acting at field level.