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

## TL;DR

This study identifies specific chemicals that attract Telenomus remus wasps to Spodoptera frugiperda eggs, helping control this agricultural pest.

## Contribution

The study is the first to identify key chemical compounds involved in T. remus host selection behavior.

## Key findings

- T. remus wasps show a stronger preference for S. frugiperda eggs due to specific aldehydes, ketones, and esters.
- Trans-1,2-dimethylcyclohexane acts as a universal attractant for Noctuidae host eggs.
- 2-Heptadecanone enhances preference for S. frugiperda eggs, while 2-hexanol repels the wasps.

## Abstract

Telenomus remus is a natural enemy of Spodoptera frugiperda, a major agricultural pest, during its egg stage. To elucidate how it locates and selects host eggs, we investigated its behavioral responses to eggs of different insect species and analyzed the chemical profiles of these eggs. The study found that this wasp shows a stronger preference for the eggs of its natural host, S. frugiperda. Through comparative chemical analysis, we found that the level of specific aldehydes, ketones, esters and other substances was significantly upregulated in the host eggs. Further experiments identified several key compounds: trans-1,2-dimethylcyclohexane, a cycloalkane, exhibited an attractant effect on the wasps and may serve as a universal signal for its recognition of noctuid host eggs; 2-heptadecanone could specifically enhance its preference for the optimal host, the eggs of S. frugiperda. In contrast, 2-hexanol exhibited a repellent effect on the wasps. This study is the first to identify the key chemical compounds underlying the host selection behavior of T. remus, thereby providing potential molecular targets for the future development of novel products that attract this wasp to achieve greater control of S. frugiperda.

Although Telenomus remus is an important parasitoid of Spodoptera frugiperda, 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, T. remus exhibited a significantly stronger olfactory preference for eggs of S. frugiperda over those of S. litura (p < 0.05) or the non-host Ostrinia furnacalis. 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 T. remus, 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 S. frugiperda eggs. Behavioral validation demonstrated that 2-hexanol exerted a significant repellent effect on T. remus, whereas trans-1,2-dimethylcyclohexane exhibited a significant attractive effect on the parasitoid wasp. Among the metabolites specifically upregulated in S. frugiperda 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 T. remus to recognize the eggs of host species belonging to the family Noctuidae, while 2-heptadecanone may further enhance its preference for the optimal host S. frugiperda. These findings provide novel candidate molecular targets for the development of behavioral regulators targeting egg parasitoids against S. frugiperda.