Ecotoxicological evidence of safe and effective low-dose mixture of spinosad–pyriproxyfen application under semi-field conditions

Chemical control of Aedes aegypti remains essential for reducing transmission of arboviruses in urban environments; however, intensive use of pesticides has increased the risk of metabolic and behavioral resistance. The aim of this study was to (1) examine the biological and biochemical responses of Aedes aegypti larvae exposed to a low-dose mixture of spinosad and pyriproxyfen, two larvicides with distinct modes of action and (2) determine whether reduced concentrations are able to maintain effective developmental inhibition. Semi-field trials and controlled lab assays were conducted using spinosad at 1.25 μg/L and pyriproxyfen at 0.63 μg/L, concentrations markedly lower than operational recommendations. Under semi-field conditions, this mixture suppressed more than 90% of adult emergence over 28 days and completely inhibited pupation. Lab observations noted rapid neurobehavioral disruption, including erratic swimming, tremors, lethargy, and immobility, followed by developmental arrest and mortality. Enzymatic analysis showed a transient metabolic response, characterized by early induction of mixed-function oxidases and intermediate activation of esterases, while glutathione S-transferases remained unchanged. These findings indicate short-lived detoxification activity rather than sustained resistance mechanisms. Overall, complementary neurotoxic and endocrine-disrupting actions of spinosad and pyriproxyfen were effective even at markedly reduced concentrations. Data support the use of low-dose larvicide mixtures as an environmentally responsible strategy consistent with Integrated Vector Management, potentially decreasing chemical inputs while maintaining larvicidal efficacy.