Mosquito larvae of Culex pipiens were subjected repeatedly to selection pressure with the bacterial agent Bacillus thuringiensis var. israelensis (B.t.i.) in the laboratory. Only 2.78-fold increase in tolerance to B.t.i. was induced in C. pipiens as a result of 20 generations of selection. The tolerance of C. pipiens to B.t.i. decreased by about 58% after stopping the selection for three generations. Larval selection with B.t.i. caused a reduction in the reproductive potential of mosquito adult survivors but did not affect the adult longevity and the time of blood meal digestion ingested by female mosquitoes.

The biological effects of the IGR cyromazine on the reproductive potential of Culexpipiens and Aedes epacticus when fed to adult mosquitoes via the sugar solution have been evaluated. The results indicated that cyromazine treatments led to a reduction in the egg-laying capacity, but did not affect the hatch of eggs or the biting behavior. A marked prolongation in the time needed for blood meal digestion ingested by mosquito females was also occurred. Moreover, the results indicated that feeding cyromazine to adult mosquitoes was sufficient to inhibit the larval development in larvae that hatched from their eggs. Cyromazine treatments, however, affect neither sex ratio nor adult longevity.

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