## 4 Discussion  
Volatile compounds emitted from plants are important cues in the host selection process of phytophagous insects. In a natural plant community, different plant species emit different qualitative and quantitative blends of VOCs, which guide insects to discriminate and locate their host plants [29; 30]. For flower thrips pests, a great number of studies have documented that _F. occidentalis_ exhibited significantly positive responses to the volatiles of host plants [13; 14; 15; 17; 18], and displayed a significant preference for specific host olfactory cues [16; 23]. Therefore, based on the bioactive compounds identified from the host plant volatiles, lures were developed and applied for the monitoring and control of _F. occidentalis_[19; 31; 32; 33; 34]. In the present study, _T. hawaiiensis_ were significantly attracted to the volatiles from _G. jasminoides_, _G. jamesonii_, _P. lactiflora_, and _R. chinensis_, and showed olfactory preferences with _G. jasminoides_ > _G. jamesonii_ > _P. lactiflora_ \(\geq\) _R. chinensis_. This is consistent with our previous field observations during which large numbers of _T. hawaiiensis_ were found in _G. jasminoides_ flowers [21]. Furthermore, the nutritional composition of _G. jasminoides_ flowers could adequately satisfy the nutritional needs of _T. hawaiiensis_ which could have a faster population development when fed on these flowers [35]. Figure 3: Behavioral responses of _T. hawaiiensis_ to the main _Ga. jasminoides_ volatiles. Asterisks indicate highly significant (**_p_ < 0.01) and significant (*_p_ < 0.05) differences in the selectivity of _T. hawaiiensis_ between two odors by \(\chi^{2}\) test. GC-MS analysis highlighted the presence of 29 compounds in the VOC profile of G. _jasminoides_ flowers, among which the most abundant compounds, linalool (27.45 %), (E3,E7)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (24.67 %), and (Z)-3-hexenyl tiglate (14.38 %), were considered to be related to the typical floral odor of this plant species [36]. Different concentrations of linalool (\(10^{-5}\)\(\sim 10^{-1}\)\(\mu\)L/\(\mu\)L), (Z)-3-hexenyl tiglate (\(10^{-5}\)\(\sim 10^{-1}\)\(\mu\)L/\(\mu\)L), and (E3,E7)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (0.1 \(\sim\) 200 \(\mu\)g/\(\mu\)L) were all attractive to _T. hawaiensis_, but the \(10^{-2}\)\(\mu\)L/\(\mu\)L, \(10^{-3}\)\(\mu\)L/\(\mu\)L, and 100 \(\mu\)g/\(\mu\)L concentrations, respectively, were the most attractive ones. Further, regarding these three compounds at their optimal attractive concentration, _T. hawaiensis_ had different olfactory preferences with (Z)-3-hexenyl tiglate \(>\) linalool \(>\) (E3,E7)-4,8,12-trimethyltrideca-1,3,7,11-tetraene. Therefore, (Z)-3-hexenyl tiglate seems to have greater potential for the development of a new attractant line for _T. hawaiensis_ monitoring and control. The behavioral responses of insects are influenced not only by individual compounds and concentrations but also by their ratios in mixtures [37; 38; 39]. So, the possible additive or synergistic effects among (Z)-3-hexenyl tiglate and the other attractive compounds identified in this study may require to be further evaluated through massive behavioral bioassays testing different doses and combinations of these VOCs. Moreover, field-trapping tests should be conducted to confirm their practically attractive effects [18; 19; 30; 37]. Pollens were considered to be an important factor involved in the preference of thrips for host plant flowers [40; 41; 42], as _F. occidentalis_ was attracted to the compound of (_S_)-verbeno identified from the volatiles of pine pollen [18; 33]. However, pollens of _G. jasminoides_ flowers were not involved in _T. hawaiensis_' olfactory responses in this study. Besides, the host preference of different thrips species were related to the color, shape, nutritional conditions or other physicochemical characteristics of host plants [13; 15; 17; 43; 44; 45]. Thus, more related physicochemical characteristics that may influence the behavioral responses of _T.