4-oxo-(e)-2-hexenal and tridecane

The brown marmorated stink bug, Halyomorpha halys, is an agricultural and urban pest that has become widely established as an invasive species of major concern in the USA and across Europe. This species forms large aggregations when entering diapause, and it is often these aggregations that are found by officials conducting inspections of internationally shipped freight. Identifying the presence of diapausing aggregations of H. halys using their emissions of volatile organic compounds (VOCs) may be a potential means for detecting and intercepting them during international freight inspections. Headspace samples were collected from aggregations of diapausing H. halys using volatile collection traps (VCTs) and solid phase microextraction. The only compound detected in all samples was tridecane, with small amounts of (E)-2-decenal found in most samples. We also monitored the release of defensive odors, following mechanical agitation of diapausing and diapause-disrupted adult H. halys. Diapausing groups were significantly more likely to release defensive odors than diapause-disrupted groups. The predominant compounds consistently found from both groups were tridecane, (E)-2-decenal, and 4-oxo-(E)-2-hexenal, with a small abundance of dodecane. Our findings show that diapausing H. halys do release defensive compounds, and suggest that volatile sampling may be feasible to detect H. halys in freight.

Topics: Aldehydes; Alkanes; Alkenes; Animals; Diapause; Gas Chromatography-Mass Spectrometry; Heteroptera; Odorants; Volatile Organic Compounds

One characteristic of true bugs (Heteroptera) is the presence of dorsal abdominal glands in the immature nymphal stages. These glands usually produce defensive chemicals (allomones) that vary among taxa but are still similar in closely related groups. Knowledge of the chemistry and prevalence of allomones in different taxa may clarify the evolution of these chemical defensive strategies. Within the infraorder Pentatomomorpha, the known secretions of nymphs of Pentatomidae tend to contain the hydrocarbon, n-tridecane, a keto-aldehyde, and an (E)-2-alkenal as the most abundant components. In the Coreidae, the dorsal abdominal gland secretions of nymphs often contain little or no hydrocarbon, and the most abundant keto-aldehyde and (E)-2-alkenal are often of shorter chain-length than those of pentatomids. We hypothesized that the long chain compounds would be less potent than their shorter homologs, and that bugs that carry the former would benefit from a synergistic effect of n-tridecane. To test this hypothesis we used three different behavioral assays with ants. A predator-prey assay tested the deterrence of allomones toward predators; a vapor experiment tested the effectiveness of allomones in the gaseous phase toward predators; and application of allomones onto predators tested the effect of direct contact. The results substantiate the hypothesis of a synergistic effect between n-tridecane and longer chain keto-aldehyde and (E)-2-alkenal in deterring predators. The short chain keto-aldehyde 4-oxo-(E)-2-hexenal was highly effective on its own. Thus, it seems that different groups of the infraorder diverged in their strategies involving defensive chemicals. Implications of this divergence are discussed.

Topics: Aldehydes; Alkanes; Animals; Ants; Gas Chromatography-Mass Spectrometry; Hemiptera; Nymph; Pentastomida; Pheromones; Predatory Behavior

We tested the hypotheses that host-searching behavior of the egg parasitoids Telenomus podisi and Trissolcus basalis may be differentially influenced by the different blends of volatiles released from the metathoracic glands of adult stink bug host species. We further studied whether such a differential response is due to different individual components of these glands and whether these responses reflect host preferences. Y-tube olfactometer bioassays were carried out with crude extracts of metathoracic glands of five different host species of neotropical stink bugs. Additionally, we tested the parasitoids' responses to synthetic standards of individual compounds identified in these stink bug glands. Results showed that females of T. basalis and T. podisi responded differentially to crude gland extracts of the different species of host stink bugs and to the compounds tested. The parasitoid T. basalis showed a positive taxic behavior to Nezara viridula methathoracxic gland extracts of a host species preferred in the field, i.e., N. viridula. Furthermore, T. basalis responded positively to 4-oxo-(E)-2-hexenal and (E)-2-decenal, two components of N. viridula glandular secretion. Higher residence time, reduced linear velocity, and higher tortuosity in the arm of the olfactometer supplied with 4-oxo-(E)-2-hexenal showed that this compound modifies the kinetics of some traits of T. basalis walking pattern and suggests that it might stimulate the searching behavior of this parasitoid. The parasitoid T. podisi was attracted to crude gland extracts of the preferred host (Euschistus heros) and also to 4-oxo-(E)-2-hexenal. Additionally, this parasitoid responded positively to (E)-2-hexenal and to the hydrocarbon tridecane, both of which are defensive compounds released from the metathoracic glands by several stink bugs. The results indicate some degree of specialization in the response of two generalist parasitoid species toward defensive secretions of stink bugs.

Topics: Aldehydes; Alkanes; Alkenes; Animals; Eggs; Feeding Behavior; Female; Hemiptera; Host-Parasite Interactions; Hymenoptera; Male; Odorants; Time Factors