Oviposition in DDT-resistant and susceptible strains ofAëdes aegypti(L.) in relation to light preference.

Abstract

Seven strains ofAëdes aegypti(L.), three DDT-resistant (from Trinidad (2) and Haiti) and four susceptible (from West Africa (2), Arabia and U.S.A.) have been investigated with respect to their attraction to oviposition sites illuminated at different levels. The resistant strains have tended to choose the darker sites (at 0·02 lumen per sq. ft. and below) and susceptible strains those illuminated at between 3·5 and 6·5 lumens per sq. ft.Genetical crosses between a ‘dark-laying’ (resistant) strain and a ‘light-laying’ (susceptible) strain indicated that ‘light laying’ was fully dominant over ‘dark laying’ and it is suggested that the mechanism involved is probably simple. No linkage with the gene for physiological resistance to DDT could be demonstrated.The expressivity of this character varied in certain circumstances with a tendency among most strains to lay at darker sites after the second and subsequent blood-meals. In spite of these variations, behaviour at any one time remained reasonably predictable.The reflectance of the oviposition site did not appear to be important in determining the difference in behaviour between ‘dark-laying’ and ‘light-laying’ strains. On the contrary, it seemed probable that ‘dark-laying’ strains were attracted more to the dark situation in which the dimly-lit site was found rather than to the site itself. There was some evidence of exploratory activity in the initial stages of oviposition by a ‘dark-laying’ strain.Resting habits proved very similar in two strains differing markedly in oviposition habit. For both strains, 0·1 lumen per sq. ft. was apparently too low to be attractive and 12 lumens per sq. ft. too high. Besting behaviour did not appear to be under such critical control by light as was oviposition.Possible explanations for the differences in ‘oviposition light preference’ are discussed.