Monitoring the susceptibility of different populations of tomato leaf miner, Tuta absoluta to indoxacarb and its combination with azadirachtin

Tomato leaf miner, Tuta absoluta, is one of the most detrimental biological agents in tomato cultivation, and there have been many reports of its worldwide resistance to various insecticides. This study aimed to evaluate the resistance of six T. absoluta populations collected from four provinces of Iran, including Ardabil, Tehran, Alborz, and Khuzestan to the widely-used insecticide indoxacarb. Leaf-dipping method bioassay was performed against the second-instar larvae. Estimated 72 h-LC50 values had not any overlapping between their 95% confidence intervals in all populations, indicating the presence of significant resistance in six populations compared to the susceptible one. The highest to lowest resistance ratios were obtained for the populations of Ziba Shahr (25.83), Mohammad Shahr (13.08), Parsabad Moghan (8.68), Safiabad (8.52), Ardabil (4.23), and Benoot-e Bala (2.19), respectively. The indoxacarb mixed with azadirachtin at the LC10: LC10 ratio showed an additive effect, while the LC25: LC25 ratio showed a synergistic effect. Also, the larval mortality caused by a mixture of LC25 values of indoxacarb and azadirachtin was significantly higher than mortality due to their separately used LC50 values in the susceptible population. In conclusion, some indoxacarb-resistant levels were documented in field second-instar larvae of T. absoluta. However, adding azadirachtin enhanced insecticidal efficiency of indoxacarb, which may be applicable in the suitable and safe management of this detrimental insect pest.