Exogenous Calcium Suppresses the Oviposition Choices of Frankliniella occidentalis (Thysanoptera: Thripidae) and Promotes the Attraction of Orius similis (Hemiptera: Anthocoridae) by Altering Volatile Blend Emissions in Kidney Bean Plants

Simple SummaryThe western flower thrips,Frankliniella occidentalis(Pergande) (Thysanoptera: Thripidae) is an economically damaging invasive pest that is difficult to control due to their resistance to insecticides. Utilizing plant-induced defense responses is a new strategy to increase plant resistance toF. occidentalis. A growing number of studies have shown that calcium plays an important role in enhancing plant resistance to pest-induced stresses. In this study, we found that exogenous calcium treatment could alter the composition of volatile compounds in kidney bean plants, repellingF. occidentaliswhile attracting its natural enemy,Orius similisZheng (Hemiptera: Anthocoridae), and reducing the oviposition preference choice ofF. occidentalis. This study provides a theoretical basis for the control ofF. occidentalis.AbstractFrankliniella occidentalisis a destructive pest of horticultural plants, whileOrius similisis a natural enemy of thrips. It has been demonstrated that exogenous calcium could induce plant defenses against herbivore attack. We examined whether CaCl2supplementation altered the volatile emissions of kidney bean plants, which influence the oviposition preference ofF. occidentalis. We also assessed the influence of volatile cues onO. similis. Using Y-tube olfactometer tests, we found that exogenous CaCl2treatment inhibited the selectivity ofF. occidentalisbut attractedO. similis. In addition, CaCl2treatment reduced the oviposition preference ofF. occidentalis. Gas chromatography–mass spectrometry analyses revealed that CaCl2treatment altered the number and relative abundance of the volatile compounds in kidney bean plants and that (E)-2-hexen-1-ol, 1-octen-3-ol, β-lonone, and (E,E)-2,4-hexadienal might be potential olfactory cues. Furthermore, the results of the six-arm olfactometer test indicated that 1-octen-3-ol (10−2μL/μL), β-lonone (10−2μL/μL), and (E,E)-2,4-hexadienal (10−3μL/μL) repelledF. occidentalisbut attractedO. similis. Overall, our results suggested that exogenous CaCl2treatment induced defense responses in kidney bean plants, suggesting that CaCl2supplementation may be a promising strategy to enhance the biological control ofF. occidentalis.Keywords:Frankliniella occidentalis;Orius similis;exogenous calcium;induced defense;herbivore-induced plant volatiles;olfactory response;gas chromatography–mass spectrometry