Identifying genetic contributors to diamondback moth insecticide resistance in Georgia and Florida

The diamondback moth (DBM), Plutella xylostella, a major pest of cruciferous crops, has developed resistance to multiple insecticides. Genetic contributors to insecticide resistance in DBM have been of recent interest in Georgia and Florida populations. Four target site mutations (E1338D, Q4594L, I4790M, and G4946E ) of the DBM ryanodine receptor (RyR) have been discovered in recent studies of diamide (IRAC class 28) resistance in Chinese populations. DBM from resistant field populations in Colquitt, Crisp, and Tift counties in Georgia and Manatee County in Florida were collected and screened to determine the presence/absence of these mutations via polymerase chain reaction (PCR) and sequencing. The G4946E mutation, the most prevalent of the four mutations in Asian populations, was present in each of our sampled populations. The other three mutations were not detected in these samples. Dose response assays were also performed to determine the LC₅₀ values for populations from Colquitt County, Georgia and Manatee County, Florida, using the leaf dip bioassay technique to expose 3^rd instar larva to the insecticides Coragen, Exirel, and Radiant. These LC₅₀ values will be correlated with prevalence of relevant target site mutations in the different populations, as well as enzymatic upregulation (such as cytochrome p450s) in response to insecticidal exposure of DBM.