Parasitism of Plutella xylostella (L.) (Lepidoptera: Plutellidae) Populations on Cabbage Brassica oleracea var. capitata (L.) by Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) in Ghana

The study was carried out at the Weija Irrigation Company site at Weija, in the Greater Accra Region of Ghana, to determine the seasonal abundance of the major parasitoid of Plutella xylostella (L.) populations on cabbage, Brassica oleracea var. capitata (L.) during the rainy and the dry seasons. The results indicated that Cotesia plutellae (Kurdjumov) was the most abundant and important parasitoid of P. xylostella on cabbage. It accounted for about 92% of the parasitoids, and occurred in all the three seasons of planting. The rest consisted of four facultative hyperparasitoids: Oomyzus sokolowskii, Aphanogmus reticulatus, Elasmus sp. and a Trichomalopsis sp., and two primary parasitoids, Pediobius sp. and Hockeria sp. A significantly higher rate of parasitism (68.6 ± 12.9%, P < 0.05) of P. xylostella by C. plutellae occurred during the major rainy season and the least (9.9 ± 7.1) in the minor rainy season. Cotesia plutellae acted in a density dependent manner, and its numbers increased as that of the host in all three seasons. The coefficient of correlation was highest in the major rainy season (r = 0.97) with a coefficient of determination of 0.97. In the minor rainy season r = 0.55, and in the dry season r = 0.66. The annual coefficient of correlation was r = 0.51 and the coefficient of determination = 0.262. Hence, in an annual production of cabbage, 26.2% of the variation in parasitism was due to the variation in the number of P. xylostella. The results, therefore, indicate that C. plutellae can be used in the development of an integrated pest management programme (IPMP), against P. xylostella in Ghana.