Numerical response of predatory ladybirds (Coccinellidae) to aphid outbreaks and their diversity in major rice ecosystems of Cameroon.

摘要

A field study conducted in upland rice fields in North Cameroon during 1995, 1996 and 1999-2002 showed that Rhopalosiphum rufiabdominalis and Hysteroneura setariae were more important pests of rice than Rhopalosiphum maidis and Schizaphis minuta in terms of density. The 13 species of predatory coccinellids were dominated by Xanthadalia effusa subsp. rufescens and Scymnus species. The dynamics of the individual species varied with the growing season. H. setariae and Scymnus spp. were the most numerous during the early rice growing season, whereas during the mid- to late growing period, high occurrence of R. rufiabdominalis and X. effusa rufescens was recorded. In both growing seasons, synchronization between the development of aphids and coccinellids was observed. A significant positive correlation was observed between aphids and ladybirds during the second half of the growing season. Species richness and the Shannon indexes fluctuated from year to year in irrigated rice plots..