Biology And Ecology Of The Predatory Mosquito, Culex (Lutzia) Tigripes Grandpre And Charmoy (Diptera:Culicidae) In South-Eastern Ghana.

Abstract

Culex (lutzia) tigripes Grandpré and charmoy is a larvivorous mosquito with all instars of the larvae feeding primarily on the immature stages of other mosquito species found in their habitats. They breed in a wide range of water bodies but seem to prefer those already containing larvae of other mosquito species. The fluctuations in the population of the larval instars and pupae were studied by weekly sampling throughout the year. It breeds throughout the year and the population peaks either coincide with or follow that of the preys; with both fluctuating with the rainfall. The larval densities of c. (L) tigripes were very small compared with those of other mosquito species; thus only 392-952 larvae of the predator were collected in the peak periods of May to July compared to 2786-8676 larvae of the prey mosquitoes.

No significant correlation was noted between variations in the numbers of C. (L) tigripes and the following physical and chemical properties of the breeding water: pH, Temperature, Chloride, Dissolved Oxygen and Total Alkalinity. Life-table studies showed the existence of high mortalities in the later stages of the predator. Starting from egg rafts collected from the field and providing C. quinguefasciatus larvae as the larval food and chicken as a source of blood, a colony of C. (L) tigripes was started but poor insemination appeared to be the major obstacle to successful and permanent colonization.

vi Artificial insemination and copulation were also not successful.The optimum larval developmental temperature was 30°C, and 32°C for the pupae. Even though more prey larvae were consumed between 30-32°C than between 20-26°C, there was a reduction in weight of the final instar larvae and pupae at the higher temperatures. Depending on temperature each predator consumed between 160-229 larvae of C.quinguefasciatus during its entire larval development. With this rate of prey destruction, the predator can have big impact on the prey population despite the low proportion (1:7-9) of predator to prey.When larvae of C. (L) tigripes were reared on three non living diets namely; Cerelac infant cereal, dog biscuit and milk casein, the developmental period of all instars was greatly prolonged and only one larva, reared on milk casein developed into adult mosquito. The weights of the final instar larvae reared on non-living diets were significantly lower than those reared on larvae of C. quinquefasciatus. Culex (L) tigripes has well developed mandibles and serrated mouthbrushes for effective predation. The effect of the following factors on prey capture were studied: mobility, size, posture, the density and the extent to which prey and predator occur simultaneously in the same habitat. Ae. aegypti which moves more frequently was more preyed upon than An. gambiae and C. quinquefasciatus, and similarly, C.quinquefasciatus was selected more than chironomid. The strong integument of the pupae together with their large

vii sizes, spherical shape, posture in the water and ability to move quickly afforded them a better chance of escaping predation by C. (L) tigripes. The effect of prey stage, predator stage and prey density on the predation rate was investigated using (C. quinquefasciatus) as prey.It was shown that the rate of predation increased with increase in the size of the predator and the density of the prey but decreased with increase in prey size. The functional response of the predator to changing prey densities followed Hollings type II model. The handling time of the predatory larvae on preys decreased as the length of time in which they were deprived of food was increased but the daily prey consumption was not affected. Cannibalism occurred in all larval stages of the predator. The rate was higher among the early instars; was lower in the presence of mosquito prey and increased with crowding.