Wednesday, 26 August 2009

Nematus pavidus

Those of you who have been following my exploits will know that I have been following the larval stages of the Sawfly Nematus pavidus for a few years.

To summarise very briefly, the larvae appear around this time of year in large batches, and consume vast swathes of Willow leaves, defoliating entire branches. During that time they are visited by parasites and predators of all kinds, with secondary parasitisation taking place. I tend to follow the life-cycle very closely, and keep a photographic record of what I see, so today is day 1 of that process for 2009.

The eggs are laid in batches on the underside of the leaf:

You can clearly see the single ocellus (eye cell) of the larva inside the egg, which is about 1mm long.

The larvae hatch out and spread over the surface of a single leaf:

Notice the characteristic s-shape of the larvae, which are about 2mm. long at the end of day 1.

When I took the shots, I had no idea that surprise number one was already waiting for me. When I got the pictures onto the computer, I spotted this truly minute (1 mm!) parasitoid exploring the larvae:

Based on size and shape, I'd venture that this is one of the Chalcids (parasitic wasps, related to Ichneumonids). So already we have something new for this increasingly interesting project.

The orange spots are a fungal rust.

While I was taking the shots of the larvae, I spotted this Chironomid (non-biting midge) wandering over the leaves:

1 comment:

Gill said...

Fascinating, as ever. I find it quite mind-boggling that something only 1mm long can have enough space for a complete insect with all its organs and senses and wings and legs....

"The orange spots are a fungal rust." Interesting that the larvae seem to be ignoring it - like us they must not like their food mouldy :-)