Competition in Mosquitoes.1 Density and Species Ratio Effects on Growth, Mortality, Fecundity, and Production of Growth Retardant2

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Abstract
A laboratory study of selected factors important to competitive displacement showed that the yellow-fever mosquito, Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae), was uniformly more vigorous than a competitor species, A. (S.) albopictus (Skuse). After a single flooding period, egg hatch of A. aegypti was 95% vs. 60–85% in A. albopictus. If eggs were continuously Hooded for 5 days, 50% of A. aegypti eggs hatched in 2 hours, while nearly 2 days were needed for 50% hatch of A. albopictus eggs. Egg mortality was greater in A. albopictus in all cases. Species population ratios of 10:90, 50:50, and 90:10, plus control groups of each species were reared at densities of 0.1 larva per milliliter and 0.8 larva per milliliter. A. aegypti development time was consistently more rapid than that of A. albopictus, particularly at low density. At high density, larval development time was longer in both species, the relative increase being greater in A. aegypti than in A. albopictus. Density and species ratio effects were essentially the same for males as for females. Competition between A. aegypti and A. albopictus larvae in various stages was clearly shown. Larval mortality was consistently higher when the species were reared together than in single species controls. If A. albopictus and A. aegypti were reared together at high density, larval development time of both was proportional to percent A. aegypti. The increased larval development period was shown to be caused by a heat-stable distillable metabolite of A. aegypti larvae.

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