Anatomical, phenological and genetic aspects of the host-parasite relationship between (Hymenoptera) and (Strepsiptera).

is an endoparasite of the mining bee with extreme sexual dimorphism and hypermetamorphosis. Its population structure, parasitization mode, genetic diversity and impact on host morphology were examined in nesting sites in Germany to better understand this highly specialized host–parasite interaction. The shift in host emergence due to stylopization was proven to be especially strong in . Around 10% of bees hosted more than 1 , with at maximum 4. A trend in ' preference for hosts of their own sex and a sex-specific position of extrusion from the host abdomen was found. Invasion of eggs by primary larvae was depicted for the first time. Cephalothoraces of female were smaller in male and pluristylopized hosts, likely due to lower nutrient supply. The genes , and were highly conserved, revealing near-absence of local variation within . Ovaries of hosts with male contained poorly developed eggs while those of hosts with female were devoid of visible eggs, which might be due to a higher protein demand of female . Male , which might have a more energy-consuming development, led to a reduction in head width of their hosts. Host masculinization was present in the leaner shape of the metabasitarsus of stylopized females and is interpreted as a by-product of manipulation of the host's endocrine system to shift its emergence. Stylopization intensified tergal hairiness, most strongly in hosts with female , near the point of parasite extrusion, hinting towards substance-induced host manipulation.