Temporal and Spatial Distribution, Growth and Predatory Behaviour of Toxorhynchites brevipalpis (Diptera: Culicidae) on the Kenya Coast

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Abstract
The prevalence of the predatory treehole mosquito T. brevipalpis [a potential biological control agent] is seasonal on the Kenya coast. Dry season conditions enforce severe population reductions which increase the time lag between peaks in predator and prey abundance after rain. The predator occurred in bamboo traps set in or near a forest in preference to peridomestic or cultivated zones and showed no height preference between 1 and 10 m. Predator and larval distribution was clumped. The number of predators per trap fitted a negative binominal. Prey density in selected bamboo traps was reduced more than 2-3 .times. by the presence of predator larvae during periods of peak abundance. Decreases in median number of prey were associated with increases in the average instar class (age) of the predator and mean number of predators per trap. Predators selected prey of their approximate instar class and 4th instar predators preferred pupae of 4th instar prey in bamboo traps and/or laboratory simulations. Aedes and Eretmapodites prey were consumed in preference to Culex in laboratory environments, but predator diet in nature is determined by the frequency of concurrence with different prey species. Within a certain tested range both maximal prey consumption by 4th instars and killing by prepupae were linearly correlated with prey density, but prey densities associated with the predator in nature were less than the range tested in the laboratory. Fourth instar larvae weighed daily accurately described growth in the laboratory and predicted killing behavior and the competency to pupate. The frequency of prepupal killing increased from near 0 to over 80% from 30-40 mg. The approximate wt threshold needed for pupation was 26 mg. Most field-collected 4th instar larvae had not achieved a wt of 26 mg by collection time, suggesting that too few prey may limit growth of the predator under natural conditions.