Recovery of insecticide susceptibility and transcriptome analysesin thiamethoxam-resistant field populations of Asian citrus psyllid, Diaphorina citri Kuwayama

The stability of thiamethoxam resistance among populations of Asian citrus psyllid, Diaphorina citri, was investigated in the field by initiating two different rotation schedules in plots that were previously treated with consecutive thiamethoxam applications. The resistance ratio (RR) for thiamethoxam reached between 1266.2 and 1395 after three and four consecutive applications of thiamethoxam, respectively. However, the RR for thiamethoxam remained low (RR= 1.71-5.28) under both rotations. The field investigations indicated susceptibility to thiamethoxam fully recovered after five D. citri generations under mode of action rotation. In addition, we performed transcriptome analyses on D. citri populations from two locations (Wauchula and Lake Alfred, FL) that exhibited 1,300-fold resistance to thiamethoxam. RNA-seq analysis showed 388 and 368 differentially expressed genes (DEGs) in Lake Alfred and Wauchula D. citri populations, respectively. Gene ontology (GO) annotation associated with cellular process, cell and catalytic activity were assigned to DEGs. The DEGs from Lake Alfred and Wauchula populations were mapped to Kyoto Encyclopedia of Gene and Genomes (KEGG) pathways and implicated enrichment of metabolic pathways, oxidative phosphorylation, extracellular matrix (ECM)-receptor interaction, terpenoid backbone biosynthesis, and insect hormone biosynthesis in the resistant populations. The investigation demonstrated that resistance to thiamethoxam can be readily managed in populations of D. citri by rotating modes of action. Our results suggest that insecticide resistance to thiamethoxam in D. citri is more complex than previously thought and implicate a broad array of novel resistance genes and possible resistance mechanisms.