Experiments were carried out to determine the factors that influence the feeding behaviour of Culex tigripes, a mosquito whose larvae are predators of other mosquito larvae. The results indicated that the efficiency of predatory activities of Cx tigripes larvae increased as they developed from 1st to 4th instar with regard to the number of mosquito prey larvae they consumed in a given period of time. Fourth instars of Cx tigripes are the most voracious of all the stages and are better adapted for catching and consuming all stages of mosquito larvae. The mean number of mosquito larvae consumed in 24 hours increased with increasing prey density. When offered a mixture of different prey species and larval stages, Cx tigripes larvae consistently selected 4th instars of mosquitoes over pupae and preferred Aedes aegypti larvae to the larvae of Cx quinquefasciatus and Anopheles gambiae. Prey size, density and mobility were also found to influence prey selection by Cx tigripes.

Results of research on biology of Thinophilus guineensis Coul. et Neg. (Diptera, Dolichopodidae) confirm the importance of predaceous feeding behaviour of some other species of Dolichopodidae such as Medetera fisch, Hydrophorus fallen, Sciapus fatten, Diaphorus meigen, etc. Larval mortality of some pests (mosquitoes, blackflies, scolytes, etc.) reach 83 to 99%.

These species, because of their extraodinary ubiquity and their biocoenotical importance, could well be used in biological control programmes of vectors of pathogens affecting man and other animals or pests in agroforestry.

Coelomomyces indicus was reisolated from six larvae of Anopheles gambiae in Uganda. A crustacean copepod Cyclops sp. was found to be infected (63%). This indicated that the copepod could be an intermediate host for the fungus. All the four instars were highly susceptible to C. indicus but fourth instar Aedes aegypti was fairly susceptible (94.2%), while second instar An. gambiae (100%) and second instar C. fatigans (100%) were the most susceptible.

Laboratory tests were conducted to compare reproductive capacity and longevity of An. gambiae, C. fatigans and Ae. aegypti when infections of C. indicus were induced in each of the different larval instars. Infections of C. indicus sharply reduced the reproductive capacity and longevity of An. gambiae, C. fatigans and Ae. aegypti, regardless of the instar that were exposed and became infected. The reductions were highest when first and second instars were exposed. The tests indicated that introduction of C. indicus into laboratory populations of An. gambiae, C. fatigans and Ae. aegypti consisting of mixed larval instars, could significantly reduce the number and fertility of eggs and thus result in an average reduction of about 65.4% for An. gambiae, about 46.7% for C. fatigans and 58.7% for Ae. aegypti of the F1 progeny from those females that became infected. The importance of these results in biological control is discussed.

Studies were conducted with Ugandan isolate of Coelomomyces stegomyiae against mosquito larvae. Aedes aegypti first instar larvae was most susceptible (99.8%) within 6 days, and the fourth instar was least susceptible (44.4%). Culex quinquefasciatus suffered 70% mortality within 10 days. Mortality rates were 92.5% for Culex tigripes, 70% for Culex duttoni, 89.5% for Aedes africanus, 89.9% for Anopheles gambiase and 97.3% for Aedes simpsoni. There was no infection when two species of the predatory mosquito Toxorhynchites were exposed to infection. A few adults emerging from an infected larval population were found infected when dissected. Other mosquitoes that pupated died and the pupae were found infected. Infected females were produced by 19.2% of the fresh pupae exposed. The importance of the results in biological control is discussed.