Section on reproduction of the bed bug article on wikipedia:
All bed bugs mate by traumatic insemination. Female bed bugs possess a reproductive tract that functions during oviposition, but the male does not use this tract for sperm insemination. Instead, the male pierces the female's abdomen with his hypodermic genitalia and ejaculates into the body cavity. In all bed bug species except Primicimex cavernis, sperm are injected into the mesospermalege, a component of the spermalege, a secondary genital structure that reduces the wounding and immunological costs of traumatic insemination. Injected sperm travel via the haemolymph (blood) to sperm storage structures called seminal conceptacles, with fertilisation eventually taking place at the ovaries.
Male bed bugs sometimes attempt to mate with other males and pierce the latter in the abdomen. This behaviour occurs because sexual attraction in bed bugs is based primarily on size, and males will mount any freshly fed partner regardless of sex. The "bed bug alarm pheromone" consists of (E)-2-octenal and (E)-2-hexenal. It is released when a bed bug is disturbed, as during an attack by a predator. A 2009 study demonstrated the alarm pheromone is also released by male bed bugs to repel other males who attempt to mate with them.
C. lectularius and C. hemipterus will mate with each other given the opportunity, but the eggs then produced are usually sterile. In a 1988 study, one of 479 eggs was fertile and resulted in a hybrid, C. hemipterus × lectularius.