چكيده انگليسي :
Thrips from the Thysanoptera order are important plant pests that attack various ornamental and agricultural crops and cause considerable damage. Currently, insecticide application is the main method of combating thrips pests. The use of insecticides in agricultural systems is also one of the factors that can alter the thrips species composition. Differences in susceptibility to insecticides may account for the replacement of one species by another. In this study, in several field experiments, the effects of five commonly used insecticides, i.e. imidacloprid, profenofos, cypermethrin, matrine, flunicamid and control (water) were investigated on the thrips species composition and abundance, crop yield of onion and eggplant in Isfahan in 2021 and 2022. Thrips species composition of onion and eggplant fields was not influenced by the insecticides used. In this study, in the onion fields, only Thrips tabaci, and in the eggplant fields, only Frankliniella occidentalis were observed and recorded. The effects of the selected insecticides on the abundance of adult and immature thrips populations in the onion field showed that in the spring of 2021, matrine caused the highest decrease in the larval population by 75.70 percent reduction, while profenofos and matrine were the most effective insecticides on adult thrips by 78.09 and 77.93 percent reduction, respectively, compared to the control. In the fall of 2021, flunicamid, cypermethrin, and profenofos decreased adult population by 54.07, 51.32, and 47.55 percent reduction, respectively, and the profenofos was the most effective treatment on immature insects. In the spring of 2022, the highest effect in reducing onion thrips population was achieved with matrine and profenofos with a 48.19 and 41.06 percent reduction of adult insects and profenofos with a 53.28 percent reduction in T. tabaci larvae compared to the control. In the spring of 2021 matrine and profenofos increased onion yield by 38.10 and 27.45 percent, respectively, and in the fall of 2021 matrine increased the onion yield by 65.55 percent, however, in the spring of 2022 in flunicamid and marine treatments the highest yield increase was gained by 9.55 and 9.09 percent, respectively, compared to the control. By accounting the costs spent on chemical control, the economy of the product was also calculated. The highest economic performance was achieved by the use of marine in the spring and autumn of 2021 and flunicamid and matrine in the spring of 2022. The results obtained from the eggplant field showed that the flunicamid, matrine, and profenofos had the highest effect on adult thrips with a reduction of 70, 60.92 and 59.54 percent, respectively and all tested insecticides were significantly effective on immature F. occidentalis. Investigating the economic aspects of the chemical control of thrips in the eggplant product also showed that the use of flunicamid, profenofos, and matrine increased the yield by 86.22, 84.95, and 71.90 percent, respectively, compared to the control. It was also found that the severity of damage to the eggplant marketing value was reduced with the application of the insecticides, so that without insecticide treatment (control) the damage severity index was 3.07 percent, but in insecticide treatments this index ranged from 2.25 to 2.70 percent.
