Abstract
BackgroundAbdominal wounding by traumatic insemination and the lack of a long distance attraction pheromone set the scene for unusual sexual signalling systems. Male bed bugs (Cimex lectularius) mount any large, newly fed individual in an attempt to mate. Last instar nymphs overlap in size with mature females, which make them a potential target for interested males. However, nymphs lack the female's specific mating adaptations and may be severely injured by the abdominal wounding. We, therefore, hypothesized that nymphs emit chemical deterrents that act as an honest status signal, which prevents nymph sexual harassment and indirectly reduces energy costs for males.ResultsBehavioural mating assays showed that males mount nymphs significantly shorter time compared to females, although initial mounting preference was the same. In support of our hypothesis, nymphs experienced the same percentage of mating with sperm transfer as females if they were unable to emit (E)-2-hexenal, (E)-2-octenal 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal, from their dorsal abdominal glands. We report that the aldehydes and 4-oxo-(E)-2-hexenal are detected by olfactory receptor neurons housed in smooth and grooved peg sensilla, respectively, on the adult antennae, at biologically relevant concentrations. Behavioural experiments showed that application of 4-oxo-(E)-2-hexenal or the two aldehydes at a nymph-emitted ratio, to a male/female pair during mounting initiation, decreased mating frequency to a rate comparable to that of a male/nymph pair.ConclusionsBy combining behavioural and sensory studies, we show that the nymph-specific alarm pheromone plays an important role in intra-specific communication in the common bed bug. Alarm pheromones are commonly looked upon as a system in predator/prey communication, but here we show that alarm pheromones may be used as multipurpose signals such as decreasing the risk of nymphal mating by males.See commentary: http://www.biomedcentral.com/1741-7007/8/117
Highlights
Abdominal wounding by traumatic insemination and the lack of a long distance attraction pheromone set the scene for unusual sexual signalling systems
Mounting of females resulted in 79.2% mating with sperm transfer, whereas no mating with sperm transfer was observed in mounted nymphs (Mann Whitney: Z = -4.574, P < 0.001)
This study demonstrates that the alarm pheromone produced by the dorsal abdominal glands of C. lectularius nymphs is detected by males and acts as a protection against traumatic extragenital insemination
Summary
Abdominal wounding by traumatic insemination and the lack of a long distance attraction pheromone set the scene for unusual sexual signalling systems. Male bed bugs (Cimex lectularius) mount any large, newly fed individual in an attempt to mate. We hypothesized that nymphs emit chemical deterrents that act as an honest status signal, which prevents nymph sexual harassment and indirectly reduces energy costs for males. The occurrence of alarm pheromones has been known since the 1970 s [1] but, in the light of traumatic insemination (the only mode of copulation in the Cimicidae), new discoveries concerning the usage of alarm pheromones by bed bugs. With the male piercing a secondary genital opening in the female with its lanceolate paramere and ejaculating directly into the abdominal cavity [3,4]. Multiple mating injuries have been shown to be costly for females, probably due to increased immunological threat [6], and lead to a reduced life span [7]
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