Thermotolerance and Acclimation in the Immature Stages of Aedes Aegypti (L) (diptera: Culicidae) to Simulated Thermal Stress

Temperature tolerance is an important factor limiting the distribution of arthropod vectors, with limited information on the ability of mosquitoes to evolve different temperature levels. Under laboratorial conditions effect of thermal stress in late third instar larvae of Aedes aegypti determined by subjecting them to temperature regimes such as 37 °C, 39 °C, 41 °C, 43 °C and 45 °C, and the lethal time required to inflict mortality of 50% (LT50) and 90% (LT90) were also computed. To understand the adaptive thermotolerance in immature stages of Ae.aegypti, late third instar larvae were exposed to 37 °C and 39 °C, and these larvae were further re-exposed to temperatures 43 °C and 45 °C respectively. The median mortality of the larvae exposed to sub-lethal temperatures at 43 °C and 45 °C was 140 and 30 min respectively. While the median mortality for the larvae adapted at 39 °C and exposed to 43 °C and 45 °C was 230 and 50 min. All the larvae exposed at 39 °C were survived up to 420 min whereas at 45 °C within 60 min of exposure time 100% mortality was observed. Larvae pre-adapted at 37 °C and 39 °C were re-exposed to 43 °C and 45 °C and it was observed that larvae pre-adapted at 39 °C were more thermotolerant than larvae pre-adapted at 37 °C. LT50 values were 82.9 and 213.7 min as compared to the non-adapted larvae. Similarly, the LT50 values were 30.5 min and in larvae pre-adapted at 39 °C when re-exposed to 45 °C showed 2 fold increases in thermotolerancein comparison to the same stage larvae kept at room temperature. Larvae pre-adapted from higher temperature showed more thermotolerance than the larvae pre-adapted at lower temperature.