The effects of temperature and humidity on the eggs of Aedes aegypti (L.) and Aedes albopictus (Skuse) in Texas

Abstract

Causative influences that impact the separation of Ae. aegypti and Ae. albopictus populations in different geographic areas were determined, as well as how they are affected by the abiotic conditions as seen in the habitats they frequent in Texas. The eggs of Ae. albopictus and Ae. aegypti collected from McAllen and Brownsville, Texas, and laboratory populations of these two species were subjected to 25 different temperature and relative humidity conditions for up to three months. In most treatments, Ae. aegypti eggs had a greater percent hatch than Ae. albopictus, regardless of temperature or relative humidity. With an increase in relative humidity, the percent hatch for both species increased, but at the higher temperatures of 32° and 35°C the amount of time the eggs were exposed to those temperatures had a greater negative effect on the percent hatch than did the positive effect of increase in relative humidity. The surface area, volume and surface-area-to-volume ratio of Ae. aegypti and Ae. albopictus eggs with and without the chorionic egg pad, and the size of the chorionic egg pad were calculated for fifty eggs of each species of mosquito from populations collected in McAllen and Brownsville and from the laboratory populations. Ae. aegypti had a larger egg volume, and a larger surface area; but, it is likely their larger egg pad compensates for this high surface-area-to-volume ratio by holding moisture along the egg’s surface and that the egg pad is associated with the high desiccation resistance seen in Ae. aegypti eggs. Development rates for both species of mosquitoes from populations collected in Galveston and Brownsville, Texas, and laboratory populations were produced by measuring the development time from a hatched egg to the adult at seven temperatures. The temperature optima (28°-33°C) were similar for all populations; however, the rate of development for Ae. aegypti was significantly faster at the temperature optima. It is likely that this faster development rate in the Ae. aegypti population helps to maintain a population in climates that have this range of temperatures given that Ae. albopictus is a superior competitor in the larval and adult stages.