Determination of the resistance devoloping potential to different insecticides and the enzym activities of the biotypes B and Q of cotton white fly Bemisia tabaci (Genn.) (Hemiptera:Aleyrodidae)

Cotton whitefly Bemisia tabaci (Genn.) is an polyfagous pest that is widely distributed in tropical and subtropical regions. In this study, we determined resistance developing potential to insecticides and enzyme activities of the biotypes B and Q of B. tabaci. We identified the biotypes of B. tabaci populations by sequence analysis of Mitochondrial cytochrome oxidase I (mtCOI) region. After determination of biotypes, leaf dip bioassays were used to calculate initial lethal concentration (LC50) values of the biotypes. Cypermethrine and imidacloprid were applied to adult stage, spiromesifen to first nymph stage, and pyriproxyfen to eggs of whitefly in different concentrations to calculate LC50 values. Selection biyoassays were done as described above. After five times selection with cypermethrine, the resistance to cypermethrine was increased by 213 fold in Q biotype, 1.35 fold in B biotype. After selection with spiromesifen eight times, the resistance to spiromesifen resulted in 2 fold increase in Q biotype, 3.5 fold in B biotype. After selection with pyriproxyfen seven times, the resistance to pyriproxyfen was increased by 15.3 fold in Q biotype, 4 fold in B biotype. After selection with imidacloprid, the resistance development on biotype B and Q has not been noticed. At the end of the selection bioassays, change in the activities of Esterases, Glutathione S-Transferases (GST), Cytochrome P450 Monooxygenases (P450) and Acetylcholinesterases (AChE) of biotypes were determinated. Esterase activities with cypermethrin selection was increased by 128 fold in Q biotype, 1.35 fold in B biotype; spiromesifen selection by 2.15 fold in Q biotype, 1.61fold in B biotype; pyriproxyfen selection by 22 fold in Q biotype, 1.60 fold in B biotype. The changes in esterase activities were statistically significant in Q biotype but not in B biotype. After selection with imidacloprid, there were no significant difference in EST activities of both B and Q Biotypes. AChE activities with cypermethrin selection was increased by 1.69 fold in Q biotype, 1.71 fold in B biotype; spiromesifen selection by 2.26 fold in Q biotype, 2.50 fold in B biotype; pyriproxyfen selection by 1.92 fold in Q biotype, 1.83 fold in B biotype. The changes in AChE activities were statistically significant in both Q and B biotypes. After selection with imidacloprid, there were no significant difference in AChE activities of both B and Q Biotypes. P450 activities with cypermethrin selection was increased by 1.91 fold in Q biotype, 1.28 fold in B biotype; spiromesifen selection 1.77 fold in Q biotype, 1.08 fold in B biotype; pyriproxyfen 1.72 fold in Q biotype, 1.33 fold in B biotype. The changes in P450 activities were statistically different in Q biotype but no statistically difference in B biotype expect pyriproxyfen selection. After selection with imidacloprid, there were no significant difference in P450 activities of both B and Q Biotypes. The changes in GST activities resulted in decrase in all insecticides selections. In conclusion, the resistance developing potential of B biotype is limited. Biotype Q has ability to develop more resistance to cypermethrine and pyriproxyfen in a short period of time compared with biotype B. After selections of biotype Q with cypermethrine, pyriproxyfen and spiromesifen, the results showed that there was higher increase in EST activities. The EST activity value of biotype B was found to be high but increase in the activity was limited as a result of its resistance. According to our results Esterase activity is the main resistance mechanism of cypermethrin, spiromesifen and pyriproxyfen resistance, AChE and P450 activities has a limited role in the resistance mechanism, the resistance capability of biotype Q was as a result of its high Esterase activity.