Insecticidal toxicity of two bruchid-resistant cowpea cultivar powders as cowpea seed protectants against Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae)

Abstract

Toxicity of bruchid-resistant cultivars MIT04K-399-1 and MIT07K-299-92 powders as cowpea protectants against Callosobruchus maculatus (Fab.) was investigated at an ambient temperature of 28 ± 2°C and a relative humidity of 75 ± 5%. Their efficacy was tested at dosage, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 g/20 g of cowpea seeds on adult mortality, oviposition, adult emergence, progeny development, seed damage, weight loss, and Beetle Perforation Index (BPI) by cowpea bruchid. The result showed that toxicity of the bruchid-resistant cowpea cultivar powders on adult bruchid is dosage- and time-dependent. At a dosage of 3.0 g/20 g, cultivars MIT04K-399-1 and MIT07K-299-92 powders achieved 70% and 72.5% lethal effect on adult C. maculatus after 4 days of treatment, respectively. Oviposition and percentage adult emergence of C. maculatus decrease with an increase in powder dosage. Conversely, reduction in progeny development of C. maculatus increases with an increase in powder dosage. The mean number of adult emergence decreased at 2 g/20 g, 2.5 g/20 g and 3 g/20 g.The MIT04K-399-1 and MIT07K-299-92 powders significantly affected egg development. The MIT07K-299-92 powder was more effective against oviposition and adult emergence at higher concentrations than MIT04K-399-1 powder, an effect that was not significantly different (P > 0.05) from each other. The BPI of 9.1 and 6.2 was recorded on cowpea seeds treated with MIT04K-399-1 and MIT07K-299-92 powders at a dosage of 3 g/20 g, respectively. The fear of residual toxicity on nontargeted organisms is not associated with the use of resistant cowpea cultivars as seed protectant. Subsistence farmers are familiar with the technology involved in the preparation and application of powders as protectants. Integration of bruchid-resistant cowpea cultivars MIT04K-399-1 and MIT07K-299-92 powders into the management of coleopteran pests will ensure availability of viable seeds for future farming in developing nations such as Nigeria.