Stylops melittae

Females of Stylops melittae in the abdomen of a willow Sandbiene

Stylops melittae is a species of Strepsiptera, the parasite in different species of sand bee ( Andrena ). The males are winged, mature females remain in their puparium between the abdominal segments of the sand bees.

Way of life

The females of Stylops melittae bear a large number of live primary larvae, which are distributed to flowers. From there, they can together with the pollen reach the nest systems of sand bees, to which the species is dedicated. In the nest plant, the primary larva penetrates the host larva and molts to the exclusively endoparasitic secondary living larva. This migrates eating in the pub around, settles after a few more molts in the abdomen and breaks with her front body through the webbing between two abdominal segments, where they pupate. The exit point is usually between the 4th and 5th, rare between the 3rd and 4th abdominal segment.

There are many more females ( 77-92 %) than males ( 8-23 %). The females remain in this life and puparium are visited here for copulation by the male. The winged males already left the puparium after a short period, survive only a few hours and can therefore be due to their small size and only rarely observed. The females emit a pheromone ( 3,5,9 - Trimethyldodekanal ), which very effectively attracts the males. Stylops melittae requires 30-40 days between copulation and birth of the first primary larvae.

Stylops melittae can occur in two generations, but usually occurs in only one generation, so that infected sand bees are usually found only in the spring months of March to May.

Influence on the host species

Stylops melittae parasitized mainly sand bee species that use the flowers range in a variety of ways, so are polylektisch. Sand bee species that are specialized on the flowers one or a few plant species are rarely affected. This distribution would not be expected in host specificity. Stylops melittae has a very variable appearance. The proportions of the cephalothorax of the females have a wide variation and were therefore time, a series of seemingly host-specific species described, but which have now compiled into a species. Sand bees parasitized females are far more common than males.

Stylopisierte female sand bees are sterile and correspond in appearance and behavior rather their male counterparts. The pollen collecting apparatus is reduced, the abdomen flat and also the coloration often reminiscent of male individuals. Also, leave the stylopisierte female bees do the maternal nest a few days earlier than non stylopisierte females, similar to the healthy males. The earlier fledging of stylopisierte females are the parasite more time for the development of primary larvae. Stylopisierte females are no longer active after they have dug her nest, while healthy females then fly out to feed their offspring. The rare stylopisierte sand bee males are less affected in their appearance, but rather to remind reversed females.

Since the development cycle of Stylops melittae accompanied by the death of the host, it is at Stylops taken melittae strictly a parasitoid and not a parasite.