## Materials and Methods
### Y-Tube Olfactometer Experiments  
According to the results of greenhouse cage experiments and wind tunnel bioassays, the _B. tabaci_-infested plants--i.e., eggplant, cucumber and cotton--showed similar tendencies in terms of attracting _S. japonicum_ adults. However, it was still unclear whether the attraction was caused by the volatiles of plants, the visual stimulation of the ladybird or a combination of the two. Accordingly, a Y-tube olfactometer was executed to evaluate whether the volatile compounds of these plant species had different effects on the performance of _S. japonicum_. Different odor source groups were tested: (1) uninfested eggplant _versus B. tabaci_-infested eggplant, (2) uninfested cucumber _versus B. tabaci_-infested cucumber, (3) uninfested cotton _versus B. tabaci_-infested cotton _versus B. tabaci_-infested cotton _versus B. tabaci_-infested cucumber and (6) _B. tabaci_-infested eggplant _versus B. tabaci_-infested cucumber.  
The Y-tube olfactometer device was installed according to [PERSON] et al. [20]. Briefly, purified air generated from an air pump (Beijing BCHP Analytical Technology Institute, Beijing, China) was filtered by an activated charcoal jar and a distilled water jar, then passed through a rotor flowmeter set at a constant airflow of 200 mL/min, entered 3 L volatile source bottles and finally flowed through each branch of the Y-tube olfactometer. Each arm of the Y-tube olfactometer had a 2.5 cm internal diameter and 10 cm length, and the two side-arms were approximately 60\({}^{\circ}\). A piece of gauze was used in the junction between the Y-tube olfactometer and a Teflon rubber tube to prevent the insect from entering the Teflon rubber tube. Potted plants were covered with oven bags (EasyOven polythene bags, Reynolds Kitchens, USA) and tied with Teflon tape to fence out volatiles from a pot with soil,and then they were placed into volatile source bottles. Plants were kept behind a black cloth to prevent insects from visually recognizing them during the experiment. Potted plants were put in 3 L volatile source bottles for 30 min to allow odors to stabilize before testing. All glass devices and Teflon rubber tubes were cleaned by 70% alcohol solution and deionized water. Glass devices were baked at 120 \({}^{\circ}\)C and tubes for at 70 \({}^{\circ}\)C each for 2 h.  
The discrimination criterion of _S. japonicum_ behavior was calculated to according to the definition of _Harmonia axyridis_[21]. The naive ladybeetle (newborn within a week) was placed at the downwind end of the main tube. An effective choice was recorded when the individual chose and entered one arm tube, passed one-third of the length of the arm tube and remained for 30 s. If an individual did not make a decision within 5 min, it was considered a non-responsive insect. After every five ladybeetles were tested, the Y-tube was reoriented by 180\({}^{\circ}\) to reduce the error that could be introduced by the device position. After every 10 ladybeetles were assayed, the Y-tube was replaced with a new one to avoid odor bias from its kind. After every 20 ladybeetles were examined, the glass chambers, potted plants and Teflon tubes were replaced with new ones to avoid plant odor effects. Data were collected for 40 individual ladybeetles. The experiments were conducted between 14:00 and 18:00 on several consecutive days.