Regionality in vector control: effect of fluctuating temperature in the susceptibility of Aedes aegypti (Diptera: Culicidae) larvae to Pyriproxyfen

Using Pyriproxyfen to control Aedes aegypti populations shows great potential considering its high competence in low dosages and environmental safety. As an endocrine disruptor, temperature can interfere in its efficiency, related to a decrease in larval emergence inhibition in hotter environments. However, previous studies have been performed at constant temperatures in the laboratory, which may not precisely reflect the environmental conditions in the field. This study aimed to assess the effect of the fluctuating temperatures in pyriproxyfen efficiency on controlling Aedes aegypti larvae. We selected maximum and minimum temperatures from the Brazilian Meteorological Institute database from September to April for cities grouped by five regions. Five fluctuating temperatures (17–26; 20–28.5; 23–32.5; 23–30.5; 19.5–31 ºC) were applied to bioassays assessing Pyriproxyfen efficiency in preventing adult emergence in Aedes aegypti larvae in five concentrations. The proportion of emergence inhibition was compared among treatments and within treatment. In thermal conditions with the lowest temperatures, Pyriproxyfen was efficient to prevent the emergence of twice the larvae than in the hottest temperatures with the lowest concentration applied (average ± SD: 0.61 ± 0.09 in coldest treatment; average ± SD: 0.65 ± 0.12 in the hottest treatment, p value = 0.00015). The concentration that inhibits the emergence of 50% of the population was lower than that preconized by the World Health Organization (0.01 mg/L) in all treatments, except for the hottest temperatures, for which we estimated 0.010 mg/L (SD ± 0.017). Applying fluctuating temperatures in laboratory bioassays provides a more realistic result for vector surveillance strategies. For a country with continental proportions such as Brazil, considering regionalities is crucial for a rational use of insecticides.