Control of Callosobruchus maculatus (Coleoptera: Chrysomelidae) Using Fractionated Extracts from Cameroonian Hemizygia welwitschii (Lamiaceae) Leaf on Stored Vigna unguiculata (Fabales: Fabaceae)

Bioassays were conducted to assess the individually insecticidal activities of hexane, acetone, and methanol extracts from Hemizygia welwitschii Rolfe-Ashby leaves powder against Callosobruchus maculatus (F.). The extracts were applied at 2, 4, 6, and 10 g/kg of cowpea and the untreated seeds served as negative control. Treatments were arranged in a complete randomized design with four replications. Adult mortality, F(1) progeny emergence, as well as insect population increase, seeds damage, and seeds germination were carried out. The results obtained showed that the three extracts of H. welwitschii were very effective in protecting stored cowpea against C. maculatus at the highest dosage (10 g/kg) 7 d after treatment. There was no F(1) progeny emergence of C. maculatus in cowpea treated with hexane extract at the dosage of 10 g/kg, while, at the same dosage, acetone and methanol extracts almost completely inhibited the F(1) progeny emergence. Also, the different concentration levels significantly protected the seeds with regard to seed damage caused by C. maculatus compared with the untreated control after 3 mo storage. The viability of seeds was not affected by the extracts. Because of their effectiveness, the three extracts of H. welwitschii leaves powder could be a good candidate in pest management programs, especially against C. maculatus in stored cowpea grains, in Cameroon and other developing countries.