Survivorship of the cassava whiteflies Aleurotrachelus socialis and Trialeurodes variabilis (Homoptera: Aleyrodidae) under different cropping systems in Colombia

Abstract

Survivorship of immature cassava whiteflies, Aleurotrachelus socialis Bondar and Trialeurodes variabilis (Quaintance), was studied in the Department of Tolima, Colombia during outbreak attacks. Survivorship indices, based on disappearance over time, were determined at 2-week intervals for age-synchronous whitefly cohorts. Survivorship in A. socialis from egg to adult was estimated at 5–8%. T. variabilis survivorship in the first two instars was estimated at 50%. Survivorship trends varied over time and were not necessarily followed by corresponding shifts in subsequent adult and egg density. Effects were undoubtedly confounded by whitefly movement patterns. Nevertheless, estimated survivorship helps explain continued increase in whitefly numbers from existing high levels. Predators and parasitoids probably accounted for, at most, 50% of larval and pupal mortality and usually much less. Natural enemy impact and total mortality were similar in intercropped and monoculture systems in spite of differences in host plant architecture, microclimates and/or host plant quality. Cropping system effects on whitefly density were related to host plant size (larger in monoculture) which probably affected immigration and emigration rates into the different systems.