skip to main |
skip to sidebar
This is probably the best time of year for anyone interested in plant galls - those strange growths on plants caused by insects, mites and sometimes fungi. These are a few that I've seen locally over the last couple of weeks.
Leaf petiole of common lime Tilia x europaea with a gall chamber containing larvae of the gall midge Continaria tiliarum.
Ash flowers galled by the ash gall mite Eriophyes fraxinivorus.
An old oak apple gall caused by the gall wasp Biorhiza pallida, with exit holes where the adults have hatched.
Silk button galls on the underside of oak leaves, containing larvae of the gall wasp Neuroterus numismalis
Spangle galls on the underside of an oak leaf, containing larvae of the gall wasp Neuroterus quercus-baccarum.
Galls on leaf surface of sycamore caused by the eriophyid mite Eriophyes macrorhynchus aceribus. Click here for pictures of eriophyid mites.
Bean gall in the leaf blade of willow, containing the larva of the sawfly Pontania proxima
Robin's pin cushion or bedeguar gall on wild rose, caused by the gall wasp Diplolepis rosae.
For pictures of the gall wasp click here.
For pictures of the parasite that attacks the wasp, click here.
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
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......
The strange object in the upper image, looking like an alien visitor from outer space, is a young bedeguar gall caused by the gall wasp Diplolepis rosae, which lays its eggs in the dog rose host and triggers this proliferation of tissue. When fully grown, like the example in the bottom image, the core of the gall contains up to 60 chambers, each with a wasp grub inside and enclosed in a mass of mossy grown. These galls are just beginning to become conspicuous on rose bushes around here and by late September they’ll reach their full size. As winter progresses all that spectacular mossy red growth withers but the larvae inside continue to feed through the early part of the winter, pupate and hatch in May as adults that lay eggs in unopened leaf buds. A wide range of other organisms take up residence in the gall, alongside the gall causing organism. Some are inquilines – opportunist squatters that take up residence in the gall tissue - while others are parasites that lay their eggs in the Diplolepis rosae larvae. There are even parasites that attack the parasites – hyperparasites – in these complex communities. You can find more information on this gall, the insect that causes it and the ‘hangers-on’ at http://hedgerowmobile.com/Diplolepisrosa.html
Posts
