Heteropteran insects produce a series of volatile compounds from their scent glands that protect them from predators and parasites. These compounds also play roles in chemical communication that elicit aggregation, dispersal, and mating behaviors. Hygia lativentris (Coreidae) adults frequently aggregate on host plants. When disturbed, they quickly disperse with the release of a sour smell, suggesting that these bugs possess an alarm pheromone in their secretions. This adult secretion-induced dispersal has been examined with a laboratory assay. Hexanal, the predominant component of the adult secretion was identified as a component of the alarm pheromone by evaluation of the adult bug's response time and escape distance from the chemical source. Physicochemical analyses with gas chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy revealed that secretory components differed between nymphs and adults, and also during adult aging. Nymphs produced two unsaturated compounds, (E)-2-hexenal and (E)-4-oxo-2-hexenal, together with hexanal and 1-hexanol, which were found in all developmental stages. In adults, hexyl acetate was the major component of secretions within 3 days of emerging, while the amount of this ester decreased and those of hexanal, hexanoic acid, and hexanal trimer increased with aging. The decomposition of hexyl acetate into hexanal via 1-hexanol was attributed to the presence of esterases and alcohol dehydrogenases specifically found in adult secretory glands. In contrast, the formation of a hexanal trimer may be due to a non-enzymatic reaction under acidic conditions.
Keywords: Alarm pheromone; Alcohol dehydrogenase; Chemical polymorphism; Coreidae; Esterase; Heteroptera; Hexanal; Hygia lativentris.