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While advantageous to the reproductive success of the individual male, traumatic insemination imposes a cost on the females. When the female is ready to mate, as demonstrated by her large post-feeding body volume, she receives an average of five traumatic inseminations, not necessarily from the same male (Reinhardt et al. 2009a). The frequent wounding of female bed bugs during copulation has been shown to result in reduced lifespan and decreased reproductive output.
The evolution of the spermalege in female bed bugs is a possible counteradaptation to the harmful male traits (see [link] , [link] ). It has been suggested that the ectospermalege serves to alleviate the female’s costs associated with the physical piercing trauma of the male’s paramere, and that the mesospermalege restricts diffusion of the sperm within the female, thereby minimizing the female’s costs of receiving male ejaculates (Stutt&Siva-Jothy 2001).
Traumatic insemination between different species has also been documented. For example, researchers have observed male Cimex hemipterus traumatically inseminate Cimex lectularius , a different cimicid species. Traumatic insemination between these two different cimids prompts an immune response in the female; the female will swell up at the site of the wound in response to the ejaculates. This swelling further reduces the female’s lifespan, and there are even some cases where the swelling reaction causes immediate death. In addition to reduced longevity, fertile egg production in a female C. lectularius is also reduced when she mates with a male C. hemipterus. Among a population consisting of both C. lectularius and C. hemipterus , most of the female C. lectularius lay only sterile eggs when C. hemipterus make up more than 75% of the group. Scientists are unsure as to the exact reason why inter-species traumatic insemination occurs, but some have hypothesized they may occur out of carelessness or inter-species competition. (Newberry 2008).
Furthermore, there is support for the evolution of the spermalege resulting at least partly from selection to reduce the costs of mating-associated infection (Morrow&Arnqvist 2003; Reinhardt et al. 2003). Bed bugs spend the majority of their lifetime in dark and cramped crevices in the walls. These small spaces not only house many bed bugs, but they also contain their feces and dead bed bugs, making the bed bug’s living area very unsanitary. Therefore, when a male bed bug pierces the female with his paramere to deliver his sperm, he also introduces pathogens, which have potential to cause infections in females (Reinhardt et al. 2005).
Researchers have demonstrated that the spermalege has adaptive value in relation to traumatic insemination because female bed bugs that have been stabbed in the spermalege with a needle contaminated with bacteria have greater egg production and longevity than those stabbed elsewhere on the abdomen (see [link] ). Because egg production and longevity are indicators of an individual’s fitness, the greater the egg production and longevity in a female, the higher the fitness is for that same female.
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