Abstract:
Callosobruchus maculatus is a major storage pest of cowpea (Vignaunquiculata) in Nigeria.This study was conducted under laboratory conditions of 28±20C and relative humidity of 75±5% to evaluate the entomocidal potency of oil extracts of Momordicacharantia against C. maculatus infesting stored cowpea seeds in Nigeria. The crude oil and different fractions of M. charantia oil were administered to 20g of cowpea seeds at the following rates of 10, 20, 30, 40 and 50μl dosages to assess insect mortality, oviposition, progeny production and weight loss of cowpea seed as well as the repellence activity of the adult beetle by the most effective fraction. Control experiments were also set up including two negative controls and one positive control. The crude oil and fractions applied at different dosages greatly reduced the number of eggs laid; eggs hatched and significantly inhibited adult emergence and seed damage by the weevils compared to the two negative controls. Results obtained indicated that fraction 3 was the most effective of all the fractions. Within 96h of exposure, fraction 3 achieved complete beetle mortality at 50 μl dose and its effect was significantly (P<0.05) different from other treatments. The amount of fraction 3 of M. charantiaoil required to achieved 50% and 95% mortality of C.maculatuswas very little when compared to other fractions and the crude oil. The GC-MS analysis of fraction 3 revealed the presence of Diethyl phthalate which was responsible for the entomocidal potency of the fraction and also accountable for the repellence activity of the adult beetle by the fraction. The result showed that fraction 3 of M. charantiaoil can be used as guard against store product insect pest infesting cowpea.
