## 4 Discussion  
Most previous studies in this area have focused on the fact that plant species significantly affect the development, survival, population establishment and control efficiency of natural enemies [25; 26; 27], and a few works in the literature have focused on the behavior of natural enemies [28; 29]. The labybeetle _S. japonicum_ has a great potential to suppress whitefly populations in an agricultural ecosystem. However, the locational behavior of _S. japonicum_ toward _B. tabaci_-infested plants has seldom been reported. In the present study, we found support for our hypotheses that (1) _B. tabaci_ adults are able to identify odors from different plants, and that _S. japonicum_ adults can perceive volatile odors from different host plants of _B. tabaci_; and (2) uninfested and _B. tabaci_-infested eggplant are significantly preferred by _B. tabaci_ and _S. japonicum_. In the greenhouse experiments, _B. tabaci_ and _S. japonicum_ adults have clear preferences for different host plant species. _Bemisia tabaci_ adults significantly preferred eggplant, cucumber and tobacco to cotton and tomato, and _S. japonicum_ adults--a natural enemy of _B. tabaci_--preferred eggplant, cucumber, cotton, tobacco and tomato. Similar to our results, previous findings showed that eggplant was the most suitable host plant for _B. tabaci_ and that tomato was the least suitable [30]. In addition, the survivorship from egg to adult of _B. tabaci_ was highest on eggplant [31]. Eggplant was a suitable trapping plant to manage _Trialeurodes vaporarium_ ([PERSON]) (Hemiptera: Aleyrodidae) and _Bemisia argentifolii_ Bellows & [PERSON] (Hemiptera: Aleyrodidae) in poinsettia [32]. There are no earlier reports on the influence of the prey's host plant species on the performance of _S. japonicum_, but cucumber was reported to be the most preferred plant by its sibling species _Searangium parcesetosum_ Sicard (Coleopterara: Coccinellidae) compared with tomato [33]. Similarly, the predatory labybeetle _Delphastus catalinae_ ([PERSON]) (Coleopterara: Coccinellidae) exhibited lower performance on _B. tabaci_-infested tomato [34]. _Searangium japonicum_ laid more eggs on _B. tabaci_-infested eggplant and cucumber plants [35]. Interestingly, we found that uninfested tobacco plants could attract _B. tabaci_ adults, but _B. tabaci_-infested tobacco plants were largely rejected by _S. japonicum_ adults. The preference of _B. tabaci_ for tobacco might be related to the high contents of 2-Hexenal and 3-Hexen-1-ol in tobacco [36]. Our previous data revealed that _B. tabaci_-infested tobacco was not an appropriate host for the development and oviposition of _S. japonicum_[35], but the reason that tobacco was rejected by _S. japonicum_ was still unclear. These findings suggest that the host species of prey strongly affect the performance and fitness of predators. In the wind tunnel experiments, eggplant plants were highly preferred by _B. tabaci_ adults compared with tomato plants, and _S. japonicum_ adults preferred eggplant to tobacco. The results are consistent with the findings of our greenhouse experiments. In the Y-tube olfactometer experiment, _S. japonicum_ could recognize uninfested cotton and _B. tabaci_-infested cotton, but it did not successfully distinguish the odors from eggplant or cucumber plants. Furthermore, egg deposition by _B. tabaci_ did not make eggplant and cucumber more attractive to _S. japonicum_ adults than uninfested eggplant and cucumber. Therefore, it is suspected that _S. japonicum_ may need other factors (vision or taste sense) to locate its prey's host plants. _Harmonia axyridis_ depended on its smell sense and vision when looking for prey [37]. _Propylaea japonica_ was reported to utilize olfactory and visual cues to locate aphid-infested cotton but mainly relied on olfactory odors [7]. At the same time, an earlier article reported that the attraction behavior of _H. axyridis_ toward _Myzus persicae_ ([PERSON]) (Hemiptera: Aphididae) infested cabbage was affected by aphid density [21].