Detection of target-site mutations in insecticide-resistant field populations of Tuta absoluta (Lepidoptera: Gelechiidae)

The invasive pest Tuta absoluta (Meyrick) poses a significant threat to tomato production worldwide. The use of different classes of insecticides to control T. absoluta led to the development of resistance. Presently, insecticides such as chlorantraniliprole, flubendiamide, emamectin benzoate, indoxacarb, and spinosad are widely used worldwide. Insecticide resistance in South Indian field populations of T. absoluta from Tamil Nadu (Coimbatore, Krishnagiri, and Dharmapuri), Andhra Pradesh (Kalikiri and Tirupati), and Karnataka (Bengaluru and Kolar) has been reported. Resistance-associated mutations were identified by analyzing insecticide target sites, thereby elucidating the molecular mechanisms underlying target-site alterations. In all seven populations, two mutations in the ryanodine receptor gene, positioned at I4746M and G4903E, both linked to diamide (chlorantraniliprole and flubendiamide) resistance, were observed. Homology modeling and molecular docking revealed reduced binding affinity of flubendiamide to ryanodine receptor in resistant populations compared to susceptible ones, supporting diamide resistance. Though the T. absoluta populations had shown moderate resistance to insecticides other than diamides, we found no target-site mutations in the glutamate-gated chloride channel, voltage-gated sodium channel, and nicotinic acetylcholine receptor genes, respectively, associated with emamectin benzoate, indoxacarb, and spinosad resistance, suggesting a focus on other mechanisms such as metabolic detoxification. This study presents the first report of target-site mutations in Indian populations of T. absoluta and highlights the need for insecticide resistance management strategies to mitigate further resistance development.