THE THERMAL DEATH TIMES OF THE AQUATIC STAGES OF SOME AMERICAN DARK-WINGED ANOPHELINES

Abstract

The mosquitoes studied show characteristic reactions to heat; the pattern of change in thermal death time during the development of the aquatic stages is similar for all, but the magnitude is different for each. In general, a progressive decrease in resistance was demonstrated in the following order: Anopheles quadrimaculatus, A. freeborni and A. aztecus. The differences found are larger and more consistent than would be expected on the basis of previous work, in races or possibly even subspecies (as in the Culex pipiens group.) The change in thermal death time from fourth stage larvae to pupae is much greater in A. freeborni and A. aztecus than in A. quadrimaculatus. This may indicate a closer relationship between the first two species than between either of these and A. quadrimaculatus. In the mosquitoes studied there is a regular change in the thermal death time in the aquatic stages. The earlier larval stages seem to be more resistant to heat and the later ones more susceptible. The pupal stage is then more resistant than the immediately preceding larva. The change in resistance seems to be gradual rather than stepwise from one instar to the next.