SOLAR HEAT EFFECTS ON THE DIFFERENT STAGES OF COWPEA BEETLE CALLOSOBRUCHUS MACULATUS (F.)

Abstract

Cowpea seeds are one of the main sources of human dietary proteins, planted and harvested in summer and vulnerable to storage infestation by Callosobruchus maculatus (F.). Sunning was tried as possible and safe control method of stored cowpea seeds after harvest from C. maculatus infestation. The biological effects of direct solar heat on the different stages (eggs, first-instar larvae, two-week old larvae, newly formed pupae and adults) were studied when exposed these stages for 6 hours daily along 4-5 consecutive days in cowpea seeds which the day temperature ranged from 32-38 degree C with a mean of 35 degree C. Effectiveness was variable with insect stage and duration of sun exposure. Eggs were the most susceptible stage to solar heat followed by first instar larvae while last instar larval instar and the pupal stages were the most resistant stage. A significant reduction of both eggs hatch and its penetration ratio (14.4%) and adult emergence when eggs (1-2 days old) exposed six hours for four consecutive days. Exposing newly hatched larvae, also leads to a reduction in adult emergence as compared to control. Adult oviposition, mortality and progeny produced also decreased with increase of the exposure period. Percentage of reduction in adult emergence (Inhibition rate, IR %) increased with increasing of the exposure period. Sunning thus gave good effects by reducing infestation rates and could suppress insect attack by killing eggs and newly formed stages.