الفهرس 
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Abstract
Laboratory experiments were conducted to evaluate the lethal toxicity of selected common and IGR insecticides, the synergistic effects of PBO on the selected IGR insecticides, and the biological effects of sublethal concentrations of the selected IGR insecticides on the 4th instar larvae of cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae). Results procured throughout this work can be summarized as follows: I- The lethal toxicity of selected common and IGR insecticides against 4th instar larvae of Spodoptera littoralis 1- The most toxic insecticide was chlorpyrifos with LC50 and LC90 values of 4.7 and 22.4 µg/ml after 24-h exposure. Methomyl showed moderate toxicity with LC50 and LC90 values of 121.3 and 283.7 µg/ml, respectively. Pyrethrins and spinosad showed the lowest toxicity insecticide among the tested compounds (the LC50 and LC90 values were 1381.8 and 2903.5 µg/ml for pyrethrins, and 1530.4 and 2513.5 µg/ml for spinosad). 2- Teflubenzuron was the most potent IGR insecticide tested (LC50= 6668.94, 5646.50, and 3950.11 µg/ml after 24, 48, and 72-h exposure, respectively). The least toxic IGR was kinoprene (LC50= 8273.84, 7155.22, and 6664.41 µg/ml after 24, 48, and 72-h exposure, respectively) suggested that the tested IGR insecticides may have another mechanism/s of action in addition to their basic ones that responsible for the acute toxicity seen to larvae. 3- According to the slope values, Spodoptera littoralis exhibited relative high homogeneity response to spinosad (5.9), pyrethrins (4.0), and methomyl (3.5) and relatively low homogeneity response to teflubenzuron (1.5), pyriproxyfen (1.8), and chlorpyrifos (1.9). Moderate homogeneity response was found with kinoprene (2.0) and azadirachtin (2.4) after 24-h exposure. 4- In general, Spodoptera littoralis displayed high homogeneity to the common insecticides and low homogeneity to IGR insecticides after 24, 48, and 72-h exposure. 5- The toxicity index according to LC50 values were 100, 3.87, 0.34, 0.31, 0.07, 0.07, 0.06, and 0.06 for chlorpyrifos, methomyl, pyrethrins, spinosad, teflubenzuron, pyriproxyfen, azadirachtin, and kinoprene, respectively. II- The synergistic effects of PBO on the selected IGR insecticides against 4th instar larvae of Spodoptera littoralis 1- Teflubenzuron was the most IGR insecticide that synergized by PBO, followed by pyriproxyfen and azadirachtin. In counterpoint, kinoprene was the least IGR insecticide that synergized by PBO. 2- The synergistic effect of PBO was significant especially after 72-h exposure. The LC50 value of teflubenzuron was 666.9 µg/ml and the synergistic ratio (SR) was 5.92-fold, while the LC50 value of kinoprene was 1208.7 µg/ml and the SR was 5.51-fold. 3- Spodoptera littoralis showed low homogeneity to all IGR insecticides in combination with PBO even after 24, 48, 72-h exposure. 4- The toxicity of teflubenzuron was increased from 1.18-fold after 48-h to 1.69-fold after 72-h compared to the toxicity after 24-h. The same trend was also found in combination with PBO. 5- Based on toxicity index values, teflubenzuron alone was more toxic than pyriproxyfen, azadirachtin, and kinoprene by 1.04, 1.11, and 1.24-fold, respectively, whereas in combination with PBO, teflubenzuron was more toxic by 1.50, 1.72, and 2.10-fold after 24-h exposure for the same corresponding compounds. 6- PBO may facilitate the IGR insecticides uptake or inoperative wide spectrum of detoxification enzymes in the central nervous system of the Spodoptera littoralis. III- The biological effects of sublethal concentrations of the selected IGR insecticides on 4th instar larvae of Spodoptera littoralis 1- The tested IGR insecticides delayed the duration of the larval stage and the larval duration was 11.32, 12.93, 10.98, and 11.31 days at the lowest tested concentrations, respectively and 14.36, 15.47, 11.99, and 14.07 days for the highest concentrations of teflubenzuron, pyriproxyfen, azadirachtin, and kinoprene, respectively. 2- The pupal duration was affected in all treatments and tested IGRs prolonged the pupal duration represented 15.39, 17.01, 10.31, and 15.74 days at the highest concentrations. Moreover, the pupal duration was 12.16, 13.61, 8.38, and 12.91 days for teflubenzuron, pyriproxyfen, azadirachtin, and kinoprene, respectively. These results may be due to the delaying of molting process. 3- At the lowest concentrations, the pupation percentage was increased (96.55%, 97.63%, 98.16%, and 97.89% for teflubenzuron, pyriproxyfen, azadirachtin, and kinoprene, respectively) while at the highest concentrations, there was decrease in pupation percentage (78.65%, 81.69%, 92.96, and 86.62% for the same corresponding compounds. 4- The percentages of adult emergence were highly decreased by 90.27%, 89.78 %, 86.89%, and 12.83% after larval feeding with the highest concentrations of teflubenzuron, kinoprene, pyriproxyfen, and azadirachtin, respectively. 5- At the lowest concentrations, the percentages of adult emergence were reduced by 70.98%, 70.89%, 68.09%, and 5.97% for teflubenzuron, kinoprene, pyriproxyfen, and azadirachtin, respectively. 6- The use of pyriproxyfen and kinoprene caused high increase in malformation especially in larval and pupal stages, followed by teflubenzuron then azadirachtin that could be related to their mode of action.