Investigation on the resistance of different growth stages of cotton whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to spirotetramat

The cotton whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the important pests of agricultural products that causes great economic losses. In this research, the effect of spirotetramat on three different developmental stages of the pest was studied in several populations that were collected from different provinces of Iran. Bioassay was done by leaf disk method. The results showed a higher sensitivity of the 2nd nymph stage compared to the adult stage and the egg stage; while the adult stage showed the least sensitivity to spirotetramat. The highest rate of resistance in different developmental stages was observed in the Jiroft population The LC50 ratios of adults in Karaj, Yazd, Pishwa, and Jiroft populations to sensitive one (Marand) were 7.6, 6.2, 4.2, and 9.6, respectively. For second instar nymphs, the ratios were 2.0, 2.2, 2.1, and 5.5 respectively. The investigation on detoxification enzymes indicated the higher activity of monooxygenase enzyme in the resistant population of Jiroft (3.34-fold) compared to the Marand population, which indicates the effective role of these enzymes in creating resistance. According to the results, to prevent resistance development, it is necessary to use other chemical compounds with different modes of action to prevent the occurrence of cross-resistance while affecting different developmental stages of pests.