Susceptibility levels of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) to minor classes of insecticides in Brazil

The tomato leafminer, Tuta absoluta (Meyrick), is one of the most important pests of tomato worldwide. The use of chemicals is still the major tactic of control against this pest in Brazil, where spray overuse leads to resistance, frequently associated with control failures in the field. In this study, a survey of the susceptibility to indoxacarb, metaflumizone, chlorfenapyr, cartap, and abamectin aimed to determine the resistance status of T. absoluta populations. Also, the major enzyme systems associated with metabolic resistance were assessed to infer variability. The LC₅₀ values varied among the populations for abamectin (0.54–3.38 mg a.i./L), cartap (93.1–589.8 mg a.i./L), chlorfenapyr (0.62–2.83 mg a.i./L), indoxacarb (0.86–2.89 mg a.i./L), and metaflumizone (0.35–7.44 mg a.i./L). Resistance ratios varied among populations being 6.2-, 6.4-, 4.6-, 3.3-, and 21.2-times for abamectin, cartap, chlorfenapyr, indoxacarb, and metaflumizone, respectively. Only the cartap confidence limits of the LC₈₀ bracketed the recommended label concentration for three populations (Anápolis, Guaraciaba do Norte, and Tianguá), suggesting control failures. No cross-resistance was observed between indoxacarb and metaflumizone, and natural variation may explain the variability of response to this latter insecticide. The activity of enzymes frequently associated with metabolism of insecticides significantly differed among populations, and glutathione S-transferases and cytochrome P450-dependent monooxygenases were variable among the populations of T. absoluta, while alpha and beta-esterases were very homogeneous. T. absoluta resistance to abamectin and cartap has not been critical in Brazil despite their long use and together with chlorfenapyr appear to be an interesting option of rotation with indoxacarb, for which there is no cross-resistance to metaflumizone.