The effects of food and space on the occurrence of cannibalism and predation among larvae ofAnopheles gambiaes.l.

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Abstract
Competitive interactions among the aquatic stages of the malaria mosquitoAnopheles gambiaes.l. (Diptera: Culicidae) may affect the resulting adult densities and, hence, the risk of malaria. We investigated the impact of the presence of a fourth‐instar larva (An. gambiaeGiles s.s. orAn. arabiensisPatton), the quantity of food, and the available space on the survival and development of freshly hatched larvae ofAn. gambiaes.s. andAn. arabiensis. To analyse the results, two proportional hazard models were constructed. The first estimated the effects of all covariates on mortality rate and the second estimated the effects of the covariates on development rate into the third larval instar (L3). A time‐dependent covariate for density, which changed during the experiment as a result of death or development to L3, was included in both models. In the presence of a fourth‐instar larva (L4), survival of the experimental larvae was significantly reduced, but no difference was detected between the presence of L4An. gambiaeand L4An. arabiensis. The observation that the majority of dead larvae were not recovered in trays with an L4 present suggested that cannibalism and predation occurred readily. Limitation in space significantly increased mortality of larvae, whereas a limitation of food reduced larval development rate, but did not cause mortality per se. From this, we concluded that both cannibalism and predation were enhanced as a result of more frequent interactions within smaller environments, but did not occur for reasons of food shortage. This study shows that inter‐ and intraspecific interactions among larvae of theAn. gambiaecomplex strongly affect survival and development, and that the quantity of food and the available space are important determinants of the outcome of these interactions. Implications of the results are discussed with respect to the population dynamics of both malaria vectors in the field.