Toxicidade de novas moléculas inseticidas a Leucoptera coffeella e seletividade a Chrysoperla externa.

Abstract

The search for new insecticidal molecules is crucial to maintaining the viability of agriculture in the face of pests with a history of low susceptibility, such as Leucoptera coffeella. However, in addition to efficacy against the biological target, it is essential that these new compounds exhibit selectivity to natural enemies, such as the predator Chrysoperla externa. In this context, the objective was to evaluate the toxicity and selectivity of tetronamide molecules on different life stages of L. coffeella and C. externa, respectively. The synthesis of menthol lactone (SABLAC) involves an acidic esterification process between mucochloric acid and menthol. Subsequently, different anilines were used in the nucleophilic substitution process of SABLAC, enabling the supply of fourteen tetronamide molecules. During the synthesis of the consolidated molecules, diastereomeric substances were formed, which were maintained as mixtures for conducting bioassays due to the high physicochemical similarity between the compounds. Independent bioassays were conducted to evaluate the effects of the synthesized molecules at concentrations of 2.0 and 4.0 mg mL⁻¹. Both experiments were conducted in a completely randomized design, with four replicates of ten pest insect specimens and five predator specimens. Mortality data were subjected to analysis of variance, followed by the Scott-Knott test at a 5% probability level when appropriate. Additionally, the six most promising molecules were subjected to concentration-response bioassays in five populations from five commercial coffee plantations located in Alfenas (MG), Araguari (MG), Guaraciaba (MG), Luís Eduardo Magalhães (BA), and Rio Paranaíba (MG), aiming to estimate the lethal concentrations 50% (LC₅₀) and toxicity ratios (RT₅₀). The results demonstrated that L. coffeella larvae were more susceptible to the effect of the molecules than adults. The molecules SAB3NO₂, SABTOL, ACM-P, and SAB3Cl promoted mortalities greater than 50.0% in the larval stages of the pest. RT₅₀ remained below 3.0 in all populations tested, indicating low variability. Regarding selectivity, SAB3NO₂ showed reduced impact on C. externa larvae at a concentration of 2.0 mg mL⁻¹, although it caused high mortality in first instar predator larvae at the highest concentration tested. The results indicate that SAB3NO₂ is the most promising molecule to advance in subsequent stages of new insecticide development programs, as it combines biological efficiency and response stability among L. coffeella populations, and a selective concentration window for C. externa larvae.