Secretions from the ventral eversible gland (VEG) of Spodoptera exigua elicit activity of defense related enzymes and emission of volatile organic compounds in tomato, Solanum lycopersicum

Secretions from the ventral eversible glands (VEG) of lepidopteran larvae have been associated with defense against predators and the production of anti-aggregation pheromones. However, the role of the VEG in arthropod–plant interactions remains unclear. Here, we tested the hypothesis that secretions from the VEG gland of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae) will elicit activity of plant defense related enzymes and emission of volatile organic compounds (VOCs) in response to insect herbivory. To test this hypothesis, we compared the expression levels of four defense related enzymes (Peroxidase (POD), Polyphenol oxidase (PPO), Phenylalanine-ammonia-lyase (PAL) and Lipoxygenase (LOX)) and VOC profiles in tomato damaged by caterpillars with intact VEG gland (VEG intact) versus plants damaged by caterpillars with the VEG gland ablated (VEG ablated). The selected defense enzymes were expressed in significantly higher amounts in tomato plants damaged by VEG intact caterpillars than in plants damaged by VEG-ablated caterpillars.  Furthermore, quantitative and qualitative differences in headspace VOC emissions were recorded between plants damaged by VEG intact versus VEG ablated caterpillars. Specifically, more volatile components were emitted and in higher amounts in tomato plants damaged by VEG intact caterpillars than in plants damaged by VEG ablated caterpillars. These results suggest that the VEG of caterpillars contain elicitors of plant defense related enzymes and VOCs in tomato.

Key Words: Ventral Eversible Gland (VEG), Plant defense, Enzymatic activity, Volatile Organic Compounds (VOCs)