Resistance of Bemisia tabaci Mediterranean (Q-biotype) to pymetrozine: resistance risk assessment, cross-resistance to six other insecticides and detoxification enzyme assay

BACKGROUND The whitefly Bemisia tabaci (Gennadius) is a severe pest that affects many field and glasshouse crops worldwide and has developed resistance to insecticides in most chemical classes. Pymetrozine, a neuroactive pyridine azomethine, is selective towards piercing-sucking pests in Hemiptera. The aim of this study was to assess the resistance of B. tabaci Mediterranean (MED) to pymetrozine in the laboratory. RESULTS After successive selection of 18 generations of MED in the presence of using pymetrozine, there was an 11.28-fold increase in the median lethal concentration (LC50). When the realized heritability (h(2)) of B. tabaci to pymetrozine in the field was assumed to be the value estimated in the laboratory (h(2) = 0.1360) and the mortality was 70-90%, only 7.2-15.9 generations were estimated to be needed to obtain a ten-fold increase in resistance to pymetrozine. Compared with the susceptible populations (G(0)), the Pyme-SEL strain (G(18)) showed a low level of cross-resistance to neonicotinoids (nitenpyram, imidacloprid, acetamiprid, and thiamethoxam) and no cross-resistance to chlorpyrifos or abamectin. With the G(0) and the Pyme-SEL strains (G(11) and G(18)) as test strains, the activity of multifunctional oxidase exhibited the greatest increase during selection, while the activities of carboxylesterase and glutathione-S-transferase did not change significantly. CONCLUSION This study show that a potential risk of development of resistance to pymetrozine exists in B. tabaci after continuous application. During the application of pymetrozine to control B. tabaci in the field, the frequency of its use in combination with neonicotinoids should be used with caution.