D3031: Mutation screening and expression profiling of ryanodine receptor in the soybean Looper, Chrysodeixis includens

The soybean looper (Chrysodeixis includens) (Lepidoptera: Noctuidae) is a migratory pest of soybean and responsible for 16% of total insect damage in soybean in Mississippi due to its defoliation damage. The pest annually migrates between the Central America and the United States. Diamide insecticides such as flubendiamide and chlorantraniliprole have been successfully manage the pest population for more than a decade. However, stated failures in the management of the pest upon application of an insecticide belonging to diamide insecticide class (IRAC MOA Group 28 Family) in Puerto Rico by the field studies have increased the suspicion of resistance against the insecticides in the pest. This suspicion has encouraged us to study the molecular mechanism of the diamide resistance in soybean looper, focusing on ryanodine receptors (RyR) which is an intracellular Ca²⁺ channel maintaining Ca²⁺ homeostasis. We cloned the full-length sequence of RyR gene from the soybean looper using partial-cloning strategy resulting in an extraordinarily long coding sequence (15,360 kb). Later, we performed genotype screening on a field population from Puerto Rico to find out potential mutation sites in the resistant strains. Our results showed that no mutation was detected at both I4790M and G4946E loci, which are known for the RyR resistant sites in other lepidopteran insects. Finally, we conducted spatial, temporal, and chlorantraniliprole induction experiments to profile RyR gene expression levels in the soybean looper. Lastly, to understand resistance mechanisms against diamides in the pest, further studies on the effect of diamides in the soybean looper will be performed.