The ectospermalege is visible externally in most bed bug species, giving the male a target through which to impale the female. In species without an externally visible ectospermalege, traumatic insemination takes place over a wide range of the body surface.
Exactly why males 'comply' with this aspect of female control over the site of mating is unclear, especially as male P. cavernis appear to be able to penetrate the abdomen at a number of points independent of the presence of an ectospermalege. One possibility is that mating outside the ectospermalege reduces female fecundity to such an extent that the mating male's paternity is significantly reduced ... The ectospermalege appears to act as a mating guide, directing the male's copulatory interest, and therefore damage, to a restricted area of the female's abdomen.
The spermalege structure serves to reduce the wounding and immunological costs of traumatic insemination. The piercing wound typically occurs in the exocuticle of the mesospermalege, and is repaired by "scarring substance" developed in the epidermis. At least nine species of bacteria and fungi have been identified from the male intromittent organ, and the mesospermalege reduces the likelihood of infection from such pathogenic organisms.
Read more about this topic: Spermalege
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