## 4 Discussion
Thus, another explanation for our results is that different host plant species process different leaf areas, and the same density of _B. tabaci_ adults possibly results in different damage intensities. Finally, _S. japonicum_ adults failed to identify the odors from host plants in Y-tube bioassays. In addition, the orientational behavior of _S. japonicum_ may not only need a combination of vision and olfactory organs but also a certain learning behavior. [PERSON] and [PERSON] (1995) reported that experienced _Chilocorus nigritus_ (F.) (Coleoptera: Coccinellidae) adults were attracted by prey and the prey's host plants [38]. Naive predatory mirid bug _Dicyphus hesperus_ Knight (Hemiptera: Miridae) had no preference between uninfested and _Bactericera cockerell_ Sulcer (Hemiptera: Triozidae) egg-infested tomato; however, _D. hesperus_ females with foraging experience preferred infested tomato [39]. In addition, the morphological characteristics of plants, such as trichome, leaf color, leaf shape and so on, also affect the seeking behavior of pests and natural enemies [40; 41]. Our results showed that the different host plants emitted different kinds of volatile chemicals. The constituents of volatiles were different among three plant species, and they qualitatively varied between uninfested and _B. tabaci_-infested plants of the same species. Cotton released the most volatile species, while eggplant emitted the least volatile species. A total of nine substances were detected in three plant species simultaneously, and it is speculated that these substances might play an important role in the host-seeking behavior of _S. japonicum_. Nonanal and (Z)-3-hexenyl acetate were detected in _Spodoptera litura_ Fabricius (Lepidoptera: Nocutiidae)-infested eggplant [42]. The volatile Nonanal from _Sophora japonica_ flowers markedly attracted _H. axyridis_[43], and a high content of Nonanal was also found in plant odors that attracted _Franklinella occidentalis_ (Pergande) (Thysanoptera: Thripidae) [40]. Many alkane species were detected and even reported in other plants [43; 44]. Furthermore, the present results found that four volatiles, D-limonene, \(\beta\)-ocimene, Caryophyllene and Benzaldehyde, were identified in plant species preferred by _S. japonicum_. We speculate that these four substances might play an important role in the host-seeking behavior of _S. japonicum_. D-Limonene and \(\beta\)-ocimene contents were significantly correlated with the olfactory response of _P. japonica_[8]; Caryophyllene and Benzaldehyde attracted predatory linewings [45; 46]. Further studies are needed to explain the function of these substances in the orientational behavior of _S. japonicum_. In addition, PCA results showed that different plant species could be distinguished by the content of volatiles, but the content of volatiles failed to separate the same plant species in uninfested and _B. tabaci_-infested conditions. However, according to the Y-tube olfactometer assays, between _B. tabaci_-infested and uninfested plants, _S. japonicum_ distinguished the odor from cotton only and did not recognize the odors from eggplant or cucumber. When a pairwise combination of three different _B. tabaci_-infested hosts acted as odors, the orientational choice of _S. japonicum_ showed no significance. Thus, it is suspected that other factors (such as vision sense)--not only the smell sense--play a role in the localization behavior of _S. japonicum_. An \"attract and reward\" model can use non-target plants grown within or around the target crop to alleviate pest populations, and it also can attract more natural enemies to the crop [41; 47]. Our results showed that eggplant was the favorite host plant of _B. tabaci_ and the predatory ladybeetle S. japonicum_. Thus, we propose an innovative method--i.e., an eggplant + _B. tabaci_ + _S. japonicum_ system--to control _B. tabaci_ in greenhouses and fields. In this system, eggplant can act as a trap plant to attract _B. tabaci_ and reduce its damage to target plants before the rapid increase in the _S.