Defensive secretions of nymphs and adults of five species of Pyrrhocoridae (Insecta: Heteroptera)

Identification of the Alarm Pheromone of Hygia lativentris and Changes in Composition during Development

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.

The metathoracic scent gland of the leaf-footed bug, Leptoglossus zonatus

The metathoracic scent gland of 25-day-old adults of both sexes of the leaf-footed bug, Leptoglossus zonatus (Dallas) (Heteroptera: Coreidae), are described based on optical microscopy analysis. No sexual dimorphism was observed in the glandular composition of this species. The gland is located in the anteroventral corner of the metathoracic pleura between the middle and posterior coxal pits. The opening to the outside of the gland is very wide and permanently open as it lacks a protective membrane. In the internal part, there is a pair of metathoracic glands that consist of piles of intertwined and occasionally bifurcated cellular tubes or columns. These glands discharge their pheromonal contents into the reservoir through a narrow cuticular tube. The reservoir connects with the vestibule via two opposite and assembled cuticular folds that can separate muscularly in order to allow the flow of liquid away from the insect. The external part consists of an ostiole from which the pheromone is emitted. The ostiole is surrounded by a peritreme, a structure that aids optimum pheromone dispersion. The described gland is of the omphalien type.

Characterization of dog repellent factor from cuticular secretion of female yellow dog tick, Haemaphysalis leachi

During its natural life cycle, the yellow dog tick, Haemaphysalis leachi, has three hosts, and it has to spend enough time on each of them to complete a blood meal. When irritated, the females of this tick species produce a cuticular secretion that contains a dog-repelling allomone. This improves the tick's chances of survival by deterring the dog from biting the tick off its body. Employing response-guided isolation techniques in conjunction with gas chromatography-mass spectrometry, the defensive allomone of H. leachi was found to consist of the six homologous aliphatic aldehydes from hexanal to undecanal. A mixture of synthetic versions of these six aldehydes in quantities corresponding to those secreted by one tick elicited strong aversion reactions in the majority of dogs of various breeds.