Shared phytochemicals predict efficacy of essential oils against western flower thrips (Frankliniella occidentalis) in the greenhouse

Abstract

Abstract Western flower thrips (Frankliniella occidentalis; Thysanoptera: Thripidae), or WFT, are a global pest of commercial crops, particularly those grown in greenhouses. Current management recommendations often involve judicious use of pesticides to which WFT have evolved multiple resistance phenotypes. Essential oils (EOs) have shown promise as a less toxic alternative for WFT greenhouse management. However, challenges remain in predicting which EOs are most likely to be insecticidal to WFT and ensuring that the efficacy of EOs under bioassay conditions reflect performance in whole-plant application scenarios. To address these challenges, 9 EOs were tested for contact toxicity against WFT in small container assays, then gas chromatography–mass spectroscopy (GC–MS) profiles of each EO were used to quantify concentrations of 22 chemicals shared by at least 5 or more of the plant species. Of these, 13 compounds were positively correlated with thrips mortality. Effective compounds were a mixture of sesquiterpenes, cyclic monoterpenes, and noncyclic monoterpenes. Interestingly, no bicyclic monoterpenes shared among the essential oils tested correlated with thrips mortality. Whole-plant assays of the four best EOs from the container assay showed significant reduction in the number of thrips per plant, although mortality in EO treatments in the whole plant assay was lower than in the container assay. In addition, all four EOs were as efficacious as the conventional insecticide flonicamid. Identifying other EOs with high concentrations of the efficacious compounds that were identified in this study and using container assays to screen these oils for WFT thrip mortality and phytotoxicity could help integrated pest management (IPM) practitioners and greenhouse staff to more rapidly accumulate a suite of EOs as low toxicity alternatives for management of WFT in greenhouse settings. Graphical Abstract