Vol. 9 No. (2): 41 - 50 (2018): Effects of Dichlorvos Insecticide and Environmental Conditions on Reproductive Attributes of Cowpea Weevil (Callosobruchus maculatus), Infesting Stored Cowpea (Vigna unguiculata)

The Influence of insecticide treatment and environmental conditions on reproductive attributes
(egg fertility, adult survivorship rate and daily adult emergence) of beans weevil (Callosobruchus
maculatus) infesting stored grains was investigated. Insecticide-free grains of white cowpea
(Vigna unguiculata) and test insecticide (Dichlorvos) were obtained from cowpea and
agrochemical vendors respectively, in Minna, Nigeria. Nulliparous female individuals of C.
maculatus, for the experimentation, were obtained from Stored Produce Research Institute, Ilorin.
The weevils were exposed to five graded concentrations of the insecticide prior to experimentation,
with negative and positive Controls. All experimental set-ups were in 5 replicates. The results
revealed significant effects of the insecticide on all reproductive traits investigated. Increase in
insecticide concentration significantly (P < 0.05) affected egg fertility (76.63±6.98, 35.75±7.67),
adult survivorship rate (44.29±5.48, 19.21±5.49 (%)) for Negative Control (NC) and Treated beans
(T5) respectively, as well as, daily adult emergence. Correlation between adult emergence and
Temperature (r = -0.2706, -0.8222); relative humidity (r = 0.47657, -0.2747) for NC and T5
respectively. The tested insecticide had significant effects on reproductive attributes of the insect
species. This information can assist cowpea farmers and stakeholders in pre and post storage
planning activities, as well as, monitoring insecticide contamination in stored grains.