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

Extracts of the exuviae (cast skins) of nymphal bed bugs (Cimex lectularius) were analyzed for volatile compounds that might contribute to arrestment of adult bed bugs. Four volatile aldehydes, (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, and 4-oxo-(E)-2-octenal were consistently detected in the headspace of freshly shed exuviae regardless of the developmental stages from which the exuviae were obtained. Quantification of the aldehydes in the solvent extracts of homogenized fresh, 45- or 99-d aged 5th instar exuviae indicated that the aldehydes are present in the exuviae and dissipate over time, through evaporation or degradation. Microscopic observation of the fifth instar exuviae indicated that the dorsal abdominal glands on the exuviae maintained their pocket-like structures with gland reservoirs, within which the aldehydes might be retained. Two-choice olfactometer studies with the volatiles from exuviae or a synthetic blend mimicking the volatiles indicated that adult bed bugs tend to settle close to sources of the aldehydes. Our results imply that the presence and accumulation of bed bug exuviae and the aldehydes volatilizing from the exuviae might mediate bed bugs' interaction with their microhabitats.

Topics: Aldehydes; Animals; Bedbugs; Behavior, Animal; Blood Cells; Nymph; Olfactometry; Olfactory Perception; Pheromones; Rabbits; Scent Glands; Smell; Solid Phase Microextraction; Volatilization

We examined whether shared volatiles found in various heteropteran species and developmental stages function to repel predators. The nymphal dorsal abdominal gland secretions of Riptortus pedestris (Heteroptera: Alydidae) and Thasus acutangulus (Heteroptera: Coreidae), and the metathoracic scent gland secretion of Euschistus biformis (Heteroptera: Pentatomidae) adults were identified by gas chromatography/mass spectrometry (GC/MS). (E)-2-Hexenal, 4-oxo-(E)-2-hexenal (4-OHE), and (E)-2-octenal were found in all three species and deemed likely candidates for repelling predators. In addition to (E)-2-alkenals, the adult E. biformis secreted (E)-2-hexenyl acetate, (E)-2-octenyl acetate, and four hydrocarbons. We evaluated the potential predator repellent properties of these compounds and compound blends against a generalist, cosmopolitan insect predator, the Chinese praying mantid (Mantodea: Mantidae: Tenodera aridifolia sinensis). Mantids that experienced (E)-2-hexenal, (E)-2-octenal, and (E)-2-octenyl acetate moved away from the site of interaction, while 4-OHE and (E)-2-hexenyl acetate did not affect mantid behavior. The compound blends did not have additive or synergistic repellency effects on predator behavior. Compound repellency was not related to compound volatility. Instead, the repellent effect is likely related to predator olfaction, and the affinity of each compound to receptors on the antennae. Our results also suggest the repellents might intensify the visual defensive signals of aposematism (T. acutangulus nymphs) and mimicry (R. pedestris nymphs) in heteropteran bugs.

Topics: Aldehydes; Animals; Gas Chromatography-Mass Spectrometry; Heteroptera; Pheromones; Predatory Behavior; Scent Glands