Traumatic Insemination - Bed Bug Adaptation

Bed Bug Adaptation

The effects of traumatic insemination are deleterious to the female. Female bed bugs have evolved a pair of specialized reproductive organs ("paragenitalia") at the site of penetration. Known as the ectospermalege and mesospermalege (referred to collectively as spermalege), these organs serve as sperm-receptacles from which sperm can migrate to the ovaries. All bed bug reproduction occurs via traumatic insemination and the spermalege. The genital tract, though functional, is used only for laying fertilized eggs.

The ectospermalege is a swelling in the abdomen, often folded, filled with hemocytes. The ectospermalege is visible externally in most bed bug species, giving the male a target through which to impale the female with the paramere. 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 mesospermalege is a sac attached to the inner abdomen, under the ectospermalege. Sperm is injected through the male's penis into the mesospermalege. In some species, the ectospermalege directly connects to the ovaries – thus, sperm and ejaculate never enters the hemolymph and thus never trigger an immune reaction. (The exact characteristics of the spermalege vary widely across different species of bed bugs.) The spermalege are generally found only in females. However, males in the Afrocimex genus possess an ectospermalege. Sperm remains in the spermalege for approximately four hours; after two days, none remains.

Male bed bugs have evolved chemoreceptors on their penises. After impaling a female, the male can "taste" if a female has been recently mated. If he does, he will not copulate as long and will ejaculate less fluid into the female.

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