Nymphs of the common bed bug (Cimex lectularius) produce anti-aphrodisiac defence against conspecific males.
BACKGROUND
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. 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.


RESULTS
Behavioural 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.


CONCLUSIONS
By 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.
Harraca
Vincent
V
Division of Chemical Ecology, Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Box 102, SE-230 53 Alnarp, Sweden.
Ryne
Camilla
C
Ignell
Rickard
R
D000447:Aldehydes / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001511:Bedbugs / Q000378:metabolism* / Q000502:physiology; D005260:Female; D008297:Male; D009758:Nymph / Q000378:metabolism / Q000502:physiology; D010675:Pheromones / Q000378:metabolism / Q000494:pharmacology*; D058618:Sensilla / Q000378:metabolism; D012726:Sexual Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D018709:Statistics, Nonparametric
C506590:4-oxo-2-octenal; D000447:Aldehydes; D010675:Pheromones; C057348:2-octenal; C010463:n-hexanal