Be quick or be dead: high temperatures reduce Aedes aegypti (Diptera: Culicidae) larval development time and pyriproxyfen larvicide efficiency in laboratory conditions

Abstract

Several studies have assessed the efficiency of insect growth regulators to control Aedes aegypti under laboratory conditions. However, empirical evidence evaluating how insect growth regulators respond to different temperatures is scarce. In this paper, we evaluate whether temperature may influence the efficiency of pyriproxyfen. To do so, we analyzed the effect of three temperatures (20, 25 and 30 °C) combined with five pyriproxyfen concentrations (0.0001, 0.001, 0.01, 0.1 and 1 mg L−1) on Ae. aegypti larval control. Each experiment had five replicates containing 250 mL of the test solution and 20 larvae according to WHO protocol. Tests were conducted until all mosquitoes had either fully emerged from the control beakers or died. The outcomes showed that, as we increased the temperature, not only did the larval developmental time decrease (from 23.5 to 10.7 days) but also the concentration of larvicide required for 50% (EC50 of 0.0002 and 0.0050 mg L−1 for 20 and 30 °C, respectively) and 95% efficiency increased (EC50 of 0.009 and 0.013 mg L−1 for 20 and 30 °C, respectively). We highlight how temperature changes produce different results from larvicide applications (p < 0.05) and provide data that allow scientists and the government to evaluate field populations’ responses and integrate the use of larvicides more appropriately. We suggest that the effects of environmental factors on larvicide applications should be tested for field mosquito populations so that different temperature conditions can be integrated with the surveillance programs of Aedes aegypti.