Insecticidal effect of abamectin against lesser grain borer (Rhyzopertha dominica (Fabrius) (Coleoptera: Bostrichidae) on cowpea seed (Vigna unguiculata (Linnaeus))

Abstract

Laboratory tests were carried out to evaluate the efficacy of Abamectin against Rhyzopertha dominica on cowpea under ambient laboratory conditions (28-350C and 65-70% r.h.). Thirty unsexed adult insects were bioassayed on 50g cowpea grain sample treated with the Abamectin insecticide at five concentrations: 0.0 (control), 1.0, 1.5, 2.0, 2.5 and 3.0 ml/kg. Mortality of exposed adults were assessed after 7, 14 and 21days exposure to treated grain. Number of progenies were assessed after 56 and 112 days after removal of parent insects. Significance differences in adult mortality were noted between different concentrations and exposure periods. Increase in concentrations and exposure period resulted in higher adult mortality and progeny suppression. 14 days exposure to the 3rd highest dose rates of 2.0ml/kg resulted in 100% adult mortality. Progeny production was considerably suppressed even with lowest concentrations of 1.0ml/kg, where 1.2±0.6 and 1.0±0.5 F1 and F2 adult progeny were recorded compared with untreated control with 98.2±5.4 and 127.4±5.6 after 56 and 112days of storage, respectively. Percentage of insect damaged kernel and weight loss decreased with increase in concentrations. At 3.0ml/kg no grain damage and weight loss were recorded as compared to 100% and 92.4%, in the untreated control, respectively. Furthermore, the result indicate that germination loss decreased with increase in concentrations of Abamectin. The present results show high insecticidal efficacy of Abamectin towards R. dominica and represent a suitable alternative to the traditional grain protectants.