Anatomical, phenological and genetic aspects of the host–parasite relationship betweenAndrena vaga(Hymenoptera) andStylops ater(Strepsiptera)

Abstract

AbstractStylops ateris an endoparasite of the mining beeAndrena vagawith 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 inA. vaga. Around 10% of bees hosted more than 1Stylops, with at maximum 4. A trend inStylops' preference for hosts of their own sex and a sex-specific position of extrusion from the host abdomen was found. Invasion ofAndrenaeggs byStylopsprimary larvae was depicted for the first time. Cephalothoraces of femaleStylopswere smaller in male and pluristylopized hosts, likely due to lower nutrient supply. The genesH3,18Sandcytochrome c oxidase subunit 1were highly conserved, revealing near-absence of local variation withinStylops. Ovaries of hosts with maleStylopscontained poorly developed eggs while those of hosts with femaleStylopswere devoid of visible eggs, which might be due to a higher protein demand of femaleStylops. MaleStylops, 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 femaleStylops, near the point of parasite extrusion, hinting towards substance-induced host manipulation.