Traumatic parasitoid mating in mining bees
Stylops ovinae is a parasitoid of the mining bee Andrena vaga. Infested bees hatch earlier in spring than usual. S. ovinae develops in the host, feeding on it already during larval stage. In the adult bees, the anterior portion of the females is visible between the abdominal tergites of the host. The males are free-living and visit the females for mating.
In contrast to previous descriptions, researchers from Jena found that mating in S. ovinae is traumatic. Males are attracted by pheromones to the females for mating. They penetrate the cuticle of the invagination near the birth opening in the females cephalothorax. The sperm then fecundates thousands of eggs, which develop into thousands of small primary larvae. The mating in this parasitoid species takes also more time than usual: the researchers discuss this as a mechanism to avoid sperm competition. Males of this species hatch only during a few days in early spring. Several males compete for a single female, prolongued mating may reduce competition between their own sperm and that of other males.
Traumatic insemination can be costly for females because of the injury. S. ovinae females have a sort of “pouch” next to the birth channel, in which the sperm is injected. This may reduce the cost for the females, especially in case of multiple mating. At the end, the development of the larvae draws on the females, they do not survive the hatching of the larvae. Nor does the host: the completion of the parasitoid’s life-cycle ends with the death of the mining bees.