Abamectin resistance and synergism in Brazilian populations of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Failures in the control of the tomato leafminer Tuta absoluta (Meyrick) by means of abamectin in Brazil, and a recent report of abamectin resistance in Brazilian populations of this pest species, led to the investigation of the possible involvement of detoxification enzymes using insecticide synergists. Resistance to abamectin was observed in all populations when compared with the standard susceptible population, with resistance ratios ranging from 5.2- to 9.4-fold. Piperonyl butoxide was the most efficient synergist with abamectin synergism ratios ranging from 3.0- to 5.3-fold and providing significant resistance suppression, but complete suppression of abamectin resistance was only obtained in one population of T. absoluta. Triphenylphosphate was an abamectin synergist which was not as efficient as piperonyl butoxide, but it provided complete suppression of abamectin resistance in four of the six resistant populations studied, suggesting a major involvement of esterases as an abamectin resistance mechanism in these populations. The importance of cytochrome P450, inhibited by piperonyl butoxide, seems secondary to esterases. Diethyl maleate also synergized abamectin in nearly all populations, but provided only partial suppression of abamectin resistance in the leafminer populations studied. Therefore, glutathione-S-transferases seem to be of minor importance as an abamectin resistance mechanism in Brazilian populations of T. absoluta.