Homosexual interactions in bed bugs: alarm pheromones as male recognition signals

Homosexual mounting is a common behaviour in bed bugs as male sexual interest is directed towards any newly fed individual. The only mode of copulation in the common bed bug, Cimex lectularius, is by traumatic insemination, where the male pierces the female abdomen with his needle-like penis. Homosexual mating would result in abdominal injuries in mounted males, as males lack the female counteradaptive spermalege structure. I here show that bed bug alarm pheromones, previously hypothesized to be a predator chemical defence, can be used by newly fed males to signal their sex and reduce the risk of homosexual mating. Mechanical blocking of the male pheromone glands significantly increased homosexual mounting duration compared to control males, while applying male extracts containing mainly alarm pheromone onto male-female mating pairs completely interrupted or shortened mating duration and reduced sperm transfer. Males confined with other males received piercing scars, demonstrating that homosexual mating occurs. The focal males in the all-male confinement experiment had reduced longevity compared to singly held males, but why this reduction in longevity occurred is not clear. Mounted males thus benefit from being able to discharge alarm pheromones, while mounting males consider the alarm signal a major sex identification cue, suggesting that male bed bugs use alarm pheromone communication to avoid homosexual harassment and mounting. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.