## 3 Discussion  
It was reported that cucumber and rose flowers are the preferred host plants of _F. occidentalis_[25; 26; 27; 28]. Here, when compared with cucumber and rose, _H. cordata_ was not a preferred host plant, and it even repelled _F. occidentalis_ in behavioral assays using the volatiles of _H. cordata_ leaves. Usually, phytophagous insects rely on semiochemicals to search for suitable food, oviposition, and mating sites [29; 30; 31]. Therefore, the identification of behaviorally active compounds, either attractants or repellents, can provide a means for the monitoring and direct control of insect pests and can be used to improve integrated pest management systems. Gas chromatography-mass spectrometry revealed 38 volatile compounds in _H. cordata_, among which decanal, 1-decanol, dodecanal, and \(\beta\)-myrcene were the most abundant. Figure 4: Behavioral responses of _Orius similis_ to decanal, dodecanal, and decanoyl acetaldehyde in a six-arm olfactometer. The control was mineral oil. Each box plot represents the median and its range of dispersion (lower and upper quartiles and outliers). Above each box plot, the same letter indicates no significant differences (Friedman test, \(p\) > 0.05). Further, EAG showed that these four main compounds were perceived by the peripheral olfactory systems of _F. occidentalis_ females in a wide range of concentrations, with responses scaled in a dose-dependent manner. Although decanoyl acetaldehyde showed a relatively lower content among the volatile components of _H. cordata_, it is a characteristic component of the _H. cordata_ odor [22; 23]. Similarly to the above four main components, decanoyl acetaldehyde also elicited significant EAG responses in _F. occidentalis_. In the six-arm olfactometer bioassays investigating the biological activity of these VOCs, _F. occidentalis_ showed varying behavioral responses. \(\beta\)-Myrcene was attractive to _F. occidentalis_ at various concentrations (0.1-50 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{\SIUnitSymbolMicro L}\)), and its most attractive concentration was 5 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{\SIUnitSymbolMicro L}\). This compound has been reported as attractive at low concentrations to another thrip pollinator, _Cycadottrips chudwicki_ (Thysanoptera: Aeolothripdae), and is also a repellant at high concentrations [32]. For 1-decanol, _F. occidentalis_ showed no attraction except at the concentration of 5 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{\SIUnitSymbolMicro L}\). Olfactory repellence was seen in _F. occidentalis_ to the other three compounds (decanal, dodecanal, and decanoyl acetaldehyde) over the range of concentrations (0.1-50 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{\SIUnitSymbolMicro L}\)) used in this study. To a certain extent, this may explain why _F. occidentalis_ exhibits negative responses to the odor of _H. cordata_ leaves. For thrips, the repellence of some plant odors can be attributed to single constituents. For example, _Megalurothrips sjostedti_ (Thysanoptera: Thripidae) is repelled by volatiles from freshly cut lemongrass (_Cymbopogon citratus_) leaves, with one of the major compounds being the volatile monoterpenoid citral [33]. However, the influences of the ratios of plant volatiles on behavioral responses have also been highlighted for many phytophagous insects, including _F. occidentalis_[34; 35; 36; 37]. Further, olfactory repellence in thrips has been demonstrated to be concentration-dependent, with some volatiles being effective only at specific concentrations and others over a range of concentrations [38]. Therefore, the present study used different concentrations of decanal, dodecanal, and decanoyl acetaldehyde individually, and it is possible that more compounds identified from the _H. cordata_ volatiles are involved. The role of combinations of the VOCs and the ratio of their concentrations on the repellence or control of _F. occidentalis_ should be further investigated in the field in future.