Thursday, 18 August 2011

Fungus time again

With all the rain we've had this year, I rather suspect we're going to have a good year for fungi: I'm seeing a few on the verges and in my garden, and yesterday I found this season's first specimen of Entomophthora muscae on a hoverfly. In my previous post, I mentioned that the Taphrina fungus alters the growth of the Alder for its own benefit by creating a large surface area for spore production and dispersal. This ability to alter a host for their own benefit is a recurring theme with fungi, and I never cease to be amazed at the lengths they go to in order to achieve this aim.

Entomophthora muscae is a fungus that uses flies as a tool for its spore dispersal. The fungal spores are ingested by the fly and the fungus rapidly grows inside the fly's abdomen. Eventually, the pink fungus breaks through the structure of the abdomen and becomes visible for a couple of days before it breaks down and the spores are released.

This is the shot of the hoverfly from a top-down perspective:

Hoverfly killed by the fungus Entomophthora muscae
The pink fungus can clearly be seen emerging from the abdomen of the hoverfly (which, unusually, is a Platycheirus species: Melanostoma scalare is the most frequent host in this area).

Two aspects of this photograph are of critical importance:

1) the hoverfly is at the very top of the plant (Ribwort Plantain)
2) the wings of the hoverfly are fully extended in an unusual forward-facing configuration

Both of these features will allow maximum airflow over the fungal mass and, more importantly, both are caused by the fungus. Before the fungus kills the fly, it causes it to move to the highest available point and then open its wings to the fullest extent. Then it kills it.

This ability of the fungus to control the fly's movement and configuration for its own benefit is astonishing enough, but it works with different flies from different families, so the fungus has found a way to control the movement of a whole range of different fly species.

Another feature of the configuration control is shown in this side view:

Side view of the fungal mass

The legs have also been fully straightened: yet another part of the configuration that maximises spore dispersal: truly amazing.

The fungal mass will break down and release spores over the next couple of days, leaving just a skeletal husk of the hoverfly on the plant.

It's not only nectaring insects that benefit from the Angelica. This is a shot of the miner Phytomyza angelicastri on the leaves:

Leaf-mining fly Phytomyza angelicastri on Angelica

The Rosy Rustic moth pupates underground until August, and this pristine specimen was resting on a low-level Dock leaf, so I rather suspect it had just emerged.

Rosy Rustic moth



Rob said...

The fungus-hoverfly story is amazing. Does anyone know how the fungus exerts control over the fly? Chemical effects on the fly's muscles?

The Weaver of Grass said...

I have never seen as many hoverflies as we have got this year Stuart - they are everywhere. And the same goes for field mushrooms - we are picking and eating them regularly and have been doing so since early August. Nobody remembers them this early before.
A friend saw a magnificent crop of Fly Agaric in a nature reserve last week - the best she has ever seen.

Stuart said...

Rob, I don't know of any conclusive studies, but I suspect the mechanism might actually be quite 'simple', but certainly chemical-based. Perhaps the fungus convinces the hoverfly that darkness is unattractive, making it move towards the light. However it is done, the results are most impressive.

Weaver: if your friend saw Fly Agaric last week, then it's time I went up to the deciduous woodland. That's certainly earlier than I would expect.

The hoverfly Episyrphus balteatus has had a very good year. It feeds on aphids and although we have a native population, the local numbers are dramatically boosted by migrants from across europe.

Caroline Gill said...

A fascinating story, Stuart ... most extraordinary. Excellent accompanying photos, too.