Researchers in the US have investigated how female bed bugs protect themselves against infection during the somewhat traumatic mating process.
Bed bug mating occurs through a process called traumatic insemination. The male bed bug has a needle-like penis that he uses to pierce the abdomen of the female. His sperm is injected through the wound into the abdominal cavity and the sperm then diffuse through the hemolymph to the ovaries and fertilise the eggs.
Females full of blood are highly attractive to males and may be the recipient of more than one mating. Indeed a traumatic process! With females available for mating after every blood meal, females who are regular feeders will experience regular traumatic insemination events from multiple males. With such behaviour, the chance of picking up a sexually transmitted infection is high.
Recent research has found that females are able to boost their immune system in anticipation of a traumatic insemination, thus protecting themselves from infection. Further research is required to determine how the immune system is controlled.
Further reading: Michael T. Siva-Jothy, Weihao Zhong, Richard Naylor, Louise Heaton, William Hentley, Ewan Harney. Female bed bugs (Cimex lectularius L) anticipate the immunological consequences of traumatic insemination via feeding cues. Proceedings of the National Academy of Sciences Jul 2019, 116 (29) 14682-14687; DOI: 10.1073/pnas.1904539116