Susceptibility Of Five Cowpea (Vigna unguiculata) Varieties To Attack By Callosobruchus maculatus (Fab.) [Coleoptera: Bruchidae]

Abstract

Cowpea is a rich source of protein and carbohydrates in the diets of many people in developing countries. The seed, however, suffers considerable damage during storage through infestation by the cowpea weevil, Callosobruchus maculatus (Fab.). Five improved varieties of cowpea (Vigna unguiculata) namely Asontem (IT82D-32), Bengpla (IT83S-818), Soronko (TVX2724-01F), Asetenapa (IT81D-1951) and Adom (CR-06-07) released by the Crops Research Institute of the CSIR for cultivation in Ghana were screened for susceptibility to the cowpea beetle, C. maculatus, in storage for a period of 30 days in the laboratory at an ambient temperature of 27.5 ± 0.9oC and relative humidity of 64.6 ± 2%. Each variety was placed in a plastic bag and kept in a freezer at -5oC for 24 hours to eliminate C. maculatus infestations coming from the field. Two hundred grammes of each cowpea variety was placed in a glass container and each infested with a male and female C. maculatus that were reared in the laboratory. The set up was left in the laboratory until 30 days after infestation. The total number of weevils that emerged and the developmental period were recorded. The susceptibility index was determined for each variety based on the total number of F1 adults that emerged and their developmental periods. Susceptibility indices were 17.58 ± 1.16, 16.75 ± 1.81, 15.81 ± 2.08, 14.02 ± 0.62, 12.84 ± 0.53 for Bengpla, Asontem, Soronko, Asetenapa and Adom respectively. Mean developmental period was highest in Adom (26.70 ± 0.49), followed by Asontem (26.30 ± 1.20), Asetenapa, (25.5 ± 0.89), Bengpla (23.90 ± 0.40) and Soronko (23.50 ± 0.00). To reduce post-harvest losses of cowpea, it is recommended that the cultivation of Adom which was the least susceptible amongst the five varieties be encouraged.

Journal of the Ghana Science Association Vol. 10 (2) 2008: pp. 85-92