Abstract: Spiromesifen is a systemic product belonging to the chemical group of spirocyclic tetronic acid derivatives, widely used against crop pests. This insecticide/miticide has become an important element in resistance management programs due to its mode of action and low toxicity against non-target organisms. It acts on lipid synthesis by inhibiting acetyl CoA carboxylase. An exploratory study was carried out to determine the biological effects of spiromesifen on Aedes aegypti. For this purpose, a field population (Guadalupe) with high frequency and intensity of resistance to temephos and the susceptible reference strain New Orleans were subjected to different concentrations of spiromesifen, a.i., to obtain the dose-response parameters: 0.01 to 15 mg/L (New Orleans) and 0.1 to 25 mg/L (Guadalupe) in early 4th instar larvae according to the protocol of WHO (1981). Mortality was monitored daily until the emergence of adults, and the inhibition of emergence (IE) was calculated. The results were subjected to probit analysis (PoloPlus 2.0) to determine LC50, whose values were 1.211 mg/L (95% CI: 0.4536-0.0699; slope: 0.5684; X2: 58.78) and 1.807 mg/L IC 95%: 0.6556-0.3089; slope: 0.9579; X2: 25.48) for New Orleans strain and Guadalupe population, respectively. Subsequently, early 4th instar larvae of the susceptible strain and the field population were exposed to their respective LC50 in separated groups for 24, 48, and 72h to analyze the effect on the biochemical components (proteins, carbohydrates, and lipids), biomarkers of oxidative stress (malonaldehyde and catalase) as well as evaluation of body weight and volume. The results show that the product reduced the larvae's growth in addition to inducing morphological aberrations and affecting the body volume and the content of carbohydrates, lipids, and proteins with a significant effect on exposure at 48h. Oxidative stress biomarkers and lipid content indicate that spiromesifen influenced metabolism, confirming its mode of action in lipid inhibition.
