Survivors

Yesterday I posted some pictures of the ichneumon wasp called Orthopelma mediator that parasitises Diplolepis rosae, the gall wasp that causes bedeguar galls on wild roses. Today seven more parasites hatched out, but so did two surviving D. rosae gall wasps, pictured below. Large galls, like the one I collected, can contain up to 60 D. rosae larvae.

These dumpy little wasps, about 4mm. long, have a very distinctive profile with an enlarged red abdomen that's keeled underneath.

Almost all D.rosae individuals are female and reproduce parthenogenetically, producing fertile eggs without fertilisation by males, which are rare. The female inserts her eggs in rose leaf buds just before they begin to open and the plant cells that they are attached to proliferate to produce the spectacular mossy, crimson gall, which contains a nutritive tissue that the larvae feed on.

Below are a couple of pictures of the gall produced by this little wasp

Deadly Assassin

A few weeks ago I collected a bedeguar gall (aka Robin's pincushion gall) to see if I could hatch out the tiny gall wasps, called Diplolepis rosae, that cause these weird growths on wild roses (click here for pictures of the gall).

So far no gall wasps have appeared, but this little ichneumon wasps has.  It's called Orthopelma mediator and it's the only ichneumon that parasitises British gall wasp larvae. It's about 4mm. long and this is a male - the female has a needle-like ovipositor on the end of her tail, like an assassin's stiletto (see last photograph).

O.mediator lays its eggs in the larvae of Diplolepis rosae before the gall forms, then the parasite's larvae feed on the internal organs of the gall wasp larvae within the gall, until nothing is left but the host's skin and jaws. It may be that all the gall wasp larvae have been parasitised, but so far only two of the parasites have emerged from the gall.

I've constructed a little chamber for photographing tiny insects like this, made from two microscope slides with a spacer in between, which seems to work pretty well - although the lighting (flash) needs a bit or work. The trickiest stage is coaxing the insect into the narrow gap between the slides,

This is a female, with her lethal ovipositor extended


Sixteen insect species, including parasites, hyperparasites and inquilines live in bedeguar galls, together with the gall wasp larvae. One down, fifteen to go......