Effects of cocoa tree phenology and canopy microclimate on the performance of the mirid bug Sahlbergella singularis

Abstract

Populations of the cocoa mirid, Sahlbergella singularis Haglund (Hemiptera: Miridae), on cocoa, Theobroma cacao L. (Malvaceae), display sharp seasonal fluctuations in population size. To better understand factors and mechanisms involved in seasonal variation, we studied the life history traits of 10 successive generations of a caged population under field conditions. Nymphal survival and development were assessed on pods stored under cocoa canopy, whereas female survival and fecundity were evaluated on sleeved pods in cocoa trees. At the same time, cocoa phenology and cocoa canopy microclimate were characterized. A life table analysis was conducted with survival and fecundity temporal data. Reproductive parameters showed far more variation than nymphal development parameters, both within and among generations. We obtained low intrinsic rates of natural increase (about 0.04), the variation of which was mainly linked to the decrease in fecundity. Fecundity as well as life table parameters varied in accordance with natural population fluctuations, suggesting that S. singularis seasonal variation might be mainly linked to variation in female fecundity. A multiple regression analysis showed that variation in female fecundity was first correlated with the presence of young fruits on cocoa trees. Fecundity was also weakly affected by daily minimum r.h. and daily mean temperature. The usefulness of our results for modeling of S. singularis population dynamics and for the improvement of IPM strategies is discussed.