The Biological Control of Callosobruchus maculatus (Fabricius) by Dinarmus basalis (Rendani) on Stored Cowpea (Vigna unguiculata Walp) Seeds

The control of Callosobruchus maculatus F. on cowpea seeds was studied in the laboratory using Dinarmus basalis Rendani as parasitoid. Five pairs of adult C. maculatus were allowed to oviposit onto ten sets of cowpea seeds. Five pairs of D. basalis were introduced at 3 days intervals (beginning from the 6th day after oviposition) into each of the nine sets of seeds. No D. basalis was introduced into the tenth set (control). No significant differences (p 0.05) were observed in the number of eggs laid per female C. maculatus in all the sets and this ranged from 37.80-41.20. No significant (p 0.05) differences were observed on adult C. maculatus that emerged when D. basalis was introduced at the 6, 9 and 12th Day After Oviposition (DAO). Percent emergence was 0.59, 0.53 and 1.85% at 6, 9 and 12st day, respectively. C. maculatus emergence increased from 67.81% in the treatment that was inoculated on the 21st DAO to 74.48 % on the 30th DAO. The total D. basalis per female in each culture was 12.81 and 17.56% on the 6 and 15th day and decreased significantly to 11.78% when inoculation was done on the 30th day. Percentage mortality of C. maculatus increased from 25.52 to 99.48% on the parasitised culture compared to 25.03 in the control. The time of introduction of the parasitoid critically affected the mortality of C. maculatus. Thus, introduction of D. basalis during the larval stage of C. maculatus caused higher mortality of the pest and had no effect on adult C. maculatus.