Chemical Recognition Mechanism of Telenomus remus Preference for Spodoptera frugiperda Eggs Based on Metabolomics with GC-MS

Although <i>Telenomus remus</i> is an important parasitoid of <i>Spodoptera frugiperda</i>, the chemical basis for its host selection behavior remains unclear. To elucidate the chemical basis of this behavior, this study combined behavioral ecology and chemical ecology methods to systematically investigate the host location and recognition behaviors of this wasp, as well as the semiochemicals that regulate these behaviors. In Y-tube olfactometer assays, <i>T. remus</i> exhibited a significantly stronger olfactory preference for eggs of <i>S. frugiperda</i> over those of <i>S. litura</i> (<i>p</i> < 0.05) or the non-host <i>Ostrinia furnacalis</i>. A total of 759 metabolites belonging to 11 categories were identified via metabolomics analysis, and principal component analysis (PCA) clearly distinguished between host eggs and non-host eggs. Analysis of differential metabolites revealed that the significantly upregulated metabolites in host eggs mainly included aldehydes, ketones and esters, followed by hydrocarbons, alcohols and amines. Subsequently, we screened and verified the effects of the significantly upregulated metabolites in host eggs compared with non-host eggs on the host-selection behavior of <i>T. remus</i>, including indole, 2-hexanol, and trans-1,2-dimethylcyclohexane, as well as 2-heptadecanone and n-nonadecane-two alkane compounds which are specifically upregulated on the surface of <i>S. frugiperda</i> eggs. Behavioral validation demonstrated that 2-hexanol exerted a significant repellent effect on <i>T. remus</i>, whereas trans-1,2-dimethylcyclohexane exhibited a significant attractive effect on the parasitoid wasp. Among the metabolites specifically upregulated in <i>S. frugiperda</i> eggs, 2-heptadecanone exhibited significant attractive activity at concentrations ranging from 0.1 to 1.0 mg/mL. This study is the first to report that the cycloalkane compound trans-1,2-dimethylcyclohexane acts as a potential broad-spectrum chemical marker for <i>T. remus</i> to recognize the eggs of host species belonging to the family Noctuidae, while 2-heptadecanone may further enhance its preference for the optimal host <i>S. frugiperda</i>. These findings provide novel candidate molecular targets for the development of behavioral regulators targeting egg parasitoids against <i>S. frugiperda</i>.