Binding affinities and expression of CAPA GPCR in western flower thrips, Frankliniella occidentalis

Insect neuropeptides (NPs) and G protein-coupled receptors (GPCRs) are relatively recently proposed biological targets for next-generation pesticides. NPs are synthesized in neurosecretory cells and released to the target tissues for various biological processes. GPCRs—seven-transmembrane proteins composed of an extracellular complex—are activated by specific NPs and subsequently couple with G proteins to induce intracellular signal transduction. These receptors are involved in essential biological processes during insect life stages. CAPA (capability) peptides are common NPs belonging to the PRX-NH₂ (X= variable) family of peptides, characterized by PRV or PRI₂ in C-terminal ends, and function in a variety of biological processes, such as water regulation, anti-diuresis, and desiccation.

Western flower thrips (Frankliniella occidentalis) have persistently plagued the nursery industry due to their cryptic nature, fast generation time, high rate of transport, and ability to transmit devastating plant viruses. Targeting these thrips with high-volume, broad-spectrum pesticides often culminates in insecticide resistance. In this study, our biological target is CAPA peptides and their GPCRs of western flower thrips. By transfecting the CAPA receptor into the continuous insect cell culture, Sf9, and testing for binding strength in vitro with variations of its natural and modified peptides using FLIPR Calcium 6 assays, we can better understand the GPCR activity and relationships associated with peptide structure. Our preliminary data, including binding affinity, gene expression, and feeding trials, further facilitate the discovery and development of bioactive peptides for a thrips-specific control option.