Density Effects of the Banana Weevil, Cosmopolites sordidus (Germar), on Its Oviposition Performance and Egg and Larval Survivorship

Abstract

The influence of banana weevil, Cosmopolites sordidus (Germar)(Coleoptera: Curculionidae), population density on oviposition rates and larval survivorship was studied in the laboratory at the Kawanda Agricultural Research Institute in Uganda. This study was undertaken to elucidate the relationship between density-dependent factors and rates of banana weevil increase in the field. Oviposition substrates (corm pieces) were offered to a range of densities of weevils maintained in buckets. Mean oviposition rates per female at densities of 10, 20 and 40 females per bucket were 29, 37 and 53%, respectively, lower than that at a density of 5 females. Nevertheless, total oviposition for the same groups was 1.4, 2.5 and 3.7 times higher than that of the 5-female group. Providing fresh corms daily instead of every five days did not increase oviposition. Larval survivorship was slightly higher at lower densities of immatures following insertion of different densities of eggs or first instars into banana corms. The results suggest that density-dependent factors can influence oviposition rates of individual weevils and survivorship of immatures, but appear to exert only modest influence in reducing banana weevil population growth. More likely, high mortality of weevil immatures under field conditions and /or higher rates of adult mortality and emigration than previously postulated contribute to the slow population build-up of this pest.