Status of pyrethroid resistance and mechanisms in Brazilian populations of Tuta absoluta.

The tomato leafminer, Tuta absoluta, is a major pest of tomato crops worldwide. This study surveyed the resistance of T. absoluta populations from four regions in Brazil to pyrethroid insecticides, the frequencies of L1014F, T929I and M918T Na channel mutations, and the role of detoxification metabolism in the resistance. Resistance ratios varied from 1- to 11-times among populations and insecticides, but control failure likelihood assays showed that all pyrethroids assessed exhibited no efficacy at all (and thus, 98-100% control failure likelihood) against all T. absoluta populations. The activity of glutathione S-transferase and cytochrome P450-mediated N-demethylation in biochemical assays was significantly correlated with the level of resistance to deltamethrin and permethrin suggesting that these enzymes may play a role in resistance. TaqMan assays were used to screen for the presence of knockdown resistance (kdr) mutations and revealed that the L1014F kdr mutation was fixed in all populations and associated with two super-kdr mutations, M918T and particularly T929I, at high frequency. Altogether, results suggest that control failures are because of mutations in the domain II of the sodium channel, as a prevailing mechanism of resistance to pyrethroids in populations of T. absoluta in Brazil. But, enhanced cytochrome P450-dependent monooxygenases and GST activities also play an important role in the resistance of some populations, which reinforce that pyrethroids must not be used overall to control T. absoluta.