Bioactivity of Essential oils of selected plants against Callosobruchus maculatus (f.) (Coleoptera: Chrysomelidae) on stored cowpea seeds (Vigna unguiculata L. Walp)

Abstract

The use of synthetic insecticides in the control of stored product insect pests including Callosobruchus maculatus has led to the development of resistance and other undesirables side effects. Therefore, present study was conducted to evaluate the bioactivity of essential oils of coriander, fennel and sweet almond against C. maculatus (F.) on stored cowpea seeds. The bioassays used three dosages of each essential oil (2.0, 4.0 and 6.0 ml /100 g seed and the untreated control 0.0 g/100 g seed) at 27 ± 2°C and 45 ± 5% relative humidity (r.h.) to assess adult mortality, number of adult emergence, percentage seed damage, weight loss and germination. At 1 day after treatment (DAT), 100% adult mortality was observed at the highest dosage of coriander essential oils (6 ml/100 g) which was significantly (p < 0.05) different from the untreated control. Similar trends followed at 3 and 5 DAT. All the treatments significantly (p < 0.05) reduced F1, F2 adult emergence, seeds damage as well as weight loss compared to the untreated control. They also negatively affected germination of cowpea seeds. It is therefore concluded that essential oils of coriander, fennel and sweet almond could be used against Callosobruchus maculatus and can serve as alternative to synthetic insecticides.