I thought you might be interested in an update on a series of observations that I have been making over the last couple of years: I have been observing an ichneumonid (parasitic wasp) ovipositing in Nematus pavidus (sawfly) larvae on Willow.
This is the start of the investigation in September 2006:
Here's a close-up of her injecting:
http://homepage.eircom.net/~hedgerow16/sept13.htm (bottom picture)
And here's my discovery that she lays up to 4 eggs in each larva:
Today I got (from Gavin Broad at the NHM, London) further fascinating information:
It turns out she's a Mesochorus sp. These are hyperparasites and only lay their eggs in larvae which have already been parasitised by other ichneumonids (or, indeed Tachinids - parasitic flies). Rather than being parasitic on the Sawfly larvae, Mesochorus larvae are parasitic on the primary parasite's larvae. So the photographs I have taken completely miss out an intermediate stage: the initial parasitisation. Given the time taken from the sawfly eggs hatching to my photographs being taken, the initial parasitisation must be very quick indeed. This is simply enthralling.
It might also explain the behaviour that I noticed being used when the hyperparasite was checking out the larvae. She banged her front feet down beside the head of the larva and appeared to be watching for the sawfly larva's normal defensive posture change. I previously thought she was checking to see if others like her had already paid a visit, in which case she would move on to another larva. It turns out she was checking to ensure that the larva had indeed been pre-parasitised, so that she could parasitise the primary parasite. Wonderful.
I'm very interested in species dependencies, and this one is four deep: Willow, Sawfly larva, primary parasite, hyperparasite.
As it happens, I saw my first ichneumonid of 2008 on Sunday, although I didn't realise it until I blew up the pictures on the PC. Here's the shot:
The photo contains 4 insects. The ichneumonid (top left), a wonderful crimson weevil (bottom right) and a copulating pair of Chrysomelid beetles (centre right). I can't go in any closer: each of the insects is less than 2mm long. The moving red dot of the weevil was all I could see with the naked eye. Now all I have to do is identify the weevil and the chrysomelids. It starts.
10 points for the plant. (Evil grin)