Evaluation of deltamethrin persistence and efficacy on cotton discs exposed to simulated sunlight and rain: role of UV absorbers and olive oil
摘要
Nine deltamethrin formulations were evaluated for their residual toxicity against Ceratitis capitata on cotton discs, and the persistence of deltamethrin after three cycles of exposure to sunlight and rainwater. Every cycle included six hours of solar simulation followed by a six-minute submersion in 400 ml of water. Six deltamethrin formulations were prepared using xylene solvent; deltamethrin K-Othrin WP®, Delta-Kill EC®, and Delta-Kill EC®, which contained 7-hydroxyl-6-methoxy coumarin as a UV absorber, were dissolved in water. Deltamethrin formulations applied to cotton fabric discs after each cycle were tested for residual toxicity against C. capitata. The results show that the mortality rate obtained from a cumulative aggregate of three cycles for deltamethrin plus olive oil was 86.67%, and it was 90% for deltamethrin plus olive oil and UV absorbers, while deltamethrin alone had 0% mortality. After the third cycle, the EC formulation containing the selected UV absorber also demonstrated enhanced efficacy and mortality (36.67%), whereas the EC formulation without UV absorbers was 23.33%. Cotton disc deltamethrin residues were further evaluated using ELISA after three cycles to determine the quantity of free deltamethrin residues remaining. The recovery of unmodified deltamethrin from discs treated with deltamethrin, olive oil, and UV absorber was 88.8 ± 1.62%, followed by deltamethrin plus olive oil at 87.85 ± 6.52%, whereas deltamethrin alone was undetected. An indirect ELISA method was also used to determine the bound residue on cotton discs that was not recovered by the extraction method.