LAUSR

Simple Summary The 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 to F. 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, repelling F. occidentalis while attracting its natural enemy, Orius similis Zheng (Hemiptera: Anthocoridae), and reducing the oviposition preference choice of F. occidentalis. This study provides a theoretical basis for the control of F. occidentalis. Abstract Frankliniella occidentalis is a destructive pest of horticultural plants, while Orius similis is a natural enemy of thrips. It has been demonstrated that exogenous calcium could induce plant defenses against herbivore attack. We examined whether CaCl2 supplementation altered the volatile emissions of kidney bean plants, which influence the oviposition preference of F. occidentalis. We also assessed the influence of volatile cues on O. similis. Using Y-tube olfactometer tests, we found that exogenous CaCl2 treatment inhibited the selectivity of F. occidentalis but attracted O. similis. In addition, CaCl2 treatment reduced the oviposition preference of F. occidentalis. Gas chromatography–mass spectrometry analyses revealed that CaCl2 treatment 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 (10−2 μL/μL), β-lonone (10−2 μL/μL), and (E,E)-2,4-hexadienal (10−3 μL/μL) repelled F. occidentalis but attracted O. similis. Overall, our results suggested that exogenous CaCl2 treatment induced defense responses in kidney bean plants, suggesting that CaCl2 supplementation may be a promising strategy to enhance the biological control of F. occidentalis.