Mortalities of the Immature Stages of Species B of the Anopheles Gambiae Complex in Kenya: Comparison Between Rice Fields and Temporary Pools, Identification of Predators, and Effects of Insecticidal Spraying
Larval and pupal populations of species B of the Anopheles gambiae complex were sampled in Kenya from rice fields and small ponds and pools. Time-specific life tables were constructed from the frequencies of the age distribution of age classes. In both types of habitats mortality from egg hatching to adult emergence was estimated as 93%, but whereas in the rice fields mortality was more or less constant, in the more temporary habitats percentage mortality was higher in the older than in the younger instars. Many larvae were infected with pathogens, including microsporidians, Coelomomyces and nematodes. To detect natural predators of An. gambiae, antiserum to An. gambiae, prepared by immunizing rabbits, was used in precipitin tests performed on the gut contents of 2295 possible predators collected from rice fields and 454 collected from pools and ponds. This serological technique identified over 42 predator species, the most important of which were Coleoptera larvae, Hemiptera and predaceous adult Diptera. The predator fauna and intensity of predation differed between the rice fields and the pools and ponds, and this was considered a possible cause for the differently shaped survivorship curves shown by An. gambiae in these 2 habitats. Insecticidal spraying of the rice fields killed both An. gambiae and predators. The former reestablished themselves very quickly, but recolonization by the predators was slower. This possibly accounted for the apparent reduction in preadult mortality (84%) found in An. gambiae after spraying.