Biological, Toxicological Potency and Field Persistence of New Insecticides against Spodoptera littoralis (Boisduval)

Conventional insecticides exhibited negative effects on environment components and natural enemies. The tested noval insecticides, viz pyridalyl, emamectin-benzoate and indoxacarb compared to chlorfluazuron were evaluated against 2nd and 4th larval instar of Spodoptera littoralis (Boisd.) laboratory strain and their latent effects on some biological aspects were studied. Also, field persistence residues of these tested compounds against field strain of this pest were estimated via determination of Lt50 values. On basis of LC50 values, emamectin benzoate was the most effective compound, followed by indoxacarb and chlorfluazuron, while pyridelyl was the least toxic one, where the LC50 values were 0.539, 5.218, 29.83 and 39.32 mg a.i./L after 48 h, while the LC50 values were 0.278, 2.732, 7.198 and 27.3 mg a.i./L after 72 h from exposure, respectively against 4th larval instar of S. littoralis. From these results, the toxicity of the tested compounds increased with the increasing in the exposure time and decreased by increasing the larval instars. The latent effects of the tested compounds according to sublethal concentrations against 4th instar larvae of laboratory strain were significantly decreased in pupal duration, pupal weight, percentage of normal pupae, adult emergence, fecundity, fertility and adult longevity compared to the control, while these compounds increased significantly larval duration and malformed pupae. Based on the semi-field application, pyridalyl and emamectinbenzoate proved to be the most effective in initial and residual activity causing 100 and 54% mortality for pyridalyl and 100 and 42.13% for emamectin-benzoate, respectively, while indoxacarb was the least effective. Also, pyridalyl show significant, superior persistence residual activity against 4th larval instar of the field strain with Lt50 valued 7.74 days, emamectin-benzoate and chlorfluazuron come in second order, with Lt50 5.59 and 5.56 days, respectively, indoxacarb showed the shortest (1.4 days). From the results, pyridalyl and emamectin-benzoate could be used into Integrated Pest Management against Spodoptera littoralis under field conditions.