Insecticide Resistance, Resistance Mechanisms, and Phylogeny of Three <em>Myzus persicae</em> Populations in Cabbage from Three Agroclimatic Zones of Sri Lanka

The aphid, Myzus persicae is an important sucking pest and a virus vector in many crops. The management of M. persicae is mainly through synthetic pesticides. The development of resistance against common pesticides has resulted in control failures of M. persicae. The objective of this study was to examine the status of pesticide resistance and the genetic structure of M. persicae populations. Samples were collected from cabbage cultivations in the dry (Anuradhapura), wet (Kandy), and intermediate (Badulla) zones of Sri Lanka during 2017-2019. Bioassays were conducted against five insecticides using the leaf dip method. Biochemical assays examined the activity of insecticide detoxifying enzymes and the insensitivity of the organophosphate/carbamate target site, acetylcholinesterases (AChEs) in the Badulla and Kandy populations. A 636 bp mtCOI gene sequence was used to infer the phylogeny. The resistance spectrum of the populations was low to moderate; 17-25% resistance to thiamethoxam, 11-15% to acetamiprid, 20-28 % to carbosulfan, 20-41 % to etofenprox, and 4-9 % to profenofos. Elevated activity of esterases (specific activities 0.91-1.11 μmol/min/mg protein) and glutathione S-transferases (1.27-1.82 μmol/min/mg protein) were observed for increased metabolism of pesticides. Monooxygenase-based detoxification was noticeable in neonicotinoid resistance. Insensitive AChEs contribute to organophosphate and carbamate resistance. Phylogenetic analysis revealed that 2 haplotypes of the studied mtCOI gene sequence are present in the three populations tested, indicating that environmental and biological pressure, including pesticide selection pressure, may be contributing to the emergence of novel genotypes of M. persicae.