More clockwork

Last Thursday I predicted that parasitisation of the Nematus pavidus sawfly larvae would take place either on Monday or Tuesday. Monday was a complete washout, but sure enough yesterday saw the initial egg-laying taking place.

I need to set this next image in context. The leaf is now a bare skeleton and most larvae have moved to another leaf. A few are still left on the original leaf and the female Campodorus is busy making sure each one is parasitised.

She moves to the underside of the leaf and curls her abdomen round close to where the larvae are:

Then she moves her abdomen around in the direction of the larvae (you can just make out the stubby little ovipositor in this shot):

Her abdomen approaches the larva (I have no idea how she senses their position so accurately), and the larva attempts to make an avoiding manoeuvre:

But the stabbing move is made unerringly, and the parasitisation takes place:
The egg will now remain unhatched inside the sawfly larva until it pupates, at which time the Campodorus egg will hatch and the Campodorus larva will consume the contents of the pupa.

Unfortunately for the Campodorus, a certain Mesochorus hyperparasite has different ideas. Perhaps Thursday or Friday will enable me to show another twist in this saga.

Post-script: Whilst I was musing about the amazing similarity between the abdomen and an elephant's trunk, I thought I would look a bit more closely, and I wonder if the abdomen is fitted with sensors of some kind. A trawl through yesterday's images delivered this shot showing the ovipositor and what seems to be two holes. 'Nostrils', anyone?

Late Campodorus shots

Since the sawfly larvae are now nearly full size, and the leaves are turning brown, I don't think I'll get too many more shots of the Campodorus.

The first shot shows the Campodorus ovipositing into a pavidus larva that is just on the other side of the leaf, through the hole. I have no idea how she knows where it is. Note the wings held high, presumably to protect them from damage should the sawfly flail around, which they often do.


In this next instance I watched the whole approach. The Campodorus walked from a higher leaf and arrived on the leaf shown. Within a second she had spun round and tried to lay in the tail of the larva, but its reflex triggered and she was thrown about a centimetre away. Undaunted, she tried a very slow, sneaky, second approach, this time aiming for the front of the larva, which doesn't move during the reflex. The reflex was triggered a second time, but she was untouched and continued to lay.

Campodorus/Mesochorus timings confirmed

The secondary parasite - Mesochorus sp. was seen ovipositing late on September 9th. First as an atmospheric sillhouette:

And then in full glorious colour:

Notice that the larvae are not exhibiting their normal defensive reflex. I think this is how the Mesochorus females detect the presence of the egg of the Campodorus.

So we have a timing of 2 days from primary parasitisation to secondary parasitisation. It is clear that the secondary parasite is targetting the egg of the primary parasite. This actually makes more sense. (See the full discussion on http://homepage.eircom.net/~hedgerow26/nematus-pavidus-parasitoids.htm)

As an aside, the primary parasite was still lurking: there are other batches waiting for her attention: