Friday, 21 March 2008

Fly-killing fungus

For a couple of years, I've been tracking the fly-killing fungus Entomophthora muscae. This fascinating fungus invades the reproductive tracts of female flies - especially hoverflies - and eventually kills them. I can find dozens of dead hoverflies within a few square metres of verge or pathway, so it is clearly an important factor in population regulation.

This is a sample I investigated last year:

From that particular sample I put a few freshly-dead specimens on a slide to see if I could get any spores. Today I remembered to check:

The magnification is x 100, and the spores appear to be rather 3-d and surrounded by a membrane of some kind. I wonder if they're sticky.

Anyway, this fungus is quite fascinating in a number of ways:

It gets ingested by the female fly and migrates to her abdomen. It then begins to expand quite rapidly, emerging from between the tergites as a pink mass. The fungus then compels the fly to climb to the highest part of a stem of grass, or a flowerhead. It then forces the fly to open her wings and extend her legs so that the maximum area of her abdomen is exposed to the wind. It then kills her in situ. The fungus rapidly breaks down and spores are released to be carried by the wind. This compulsion to climb is known as 'Summit Disease', and is an amazing ability for a fungus to have developed.

Current theory (due mostly to genetic sequencing) says that each species of fly is killed by a different form of the fungus. So in future, instead of the generic Entomophthora muscae, we might have e.g. Entomophthora scutellae, and so on.


Gill said...

Fascinating. Entomophthora seems to be much less common here in Yorkshire - I looked quite hard last year and only saw two specimens, both small hoverflies. Maybe climate related?

Stuart said...

It's interesting that you should suggest that. One of the recommended locations for finding Entomophthora specimens is 'near water'.

That describes all of Donegal.