Tuesday, 30 June 2009

If at first you don't succeed...

The Lissonota sp. ichneumonids have started to lay their eggs in unsuspecting moth larvae hidden inside grass seedheads. I've been following these for a week, now, and yesterday I was rewarded with a couple of shots of the egg-laying taking place:

Notice the antennae being used to pinpoint (ouch!) the location of the larva.

This shot shows the ovipositor at the moment it was being retracted. It's finer than a human hair.

This shot appears to be of a male (of a completely different species):

Staying with parasitic insects, these two Tachinids were on adjacent Bramble leaves. It looks as if they were pointedly ignoring each other. I see a great many Tachinids, and this shows just how many larvae of moths and butterflies are parasitised each year.

Some leaf-miners are very easily identified as such. This is Agromyza filipendulae, on Meadowsweet.

But the mines of Phyllonorycter species can easily be overlooked. This is Phyllonorycter rajella, on Alder. The pupa is only 2mm long, so the adult moth will never be recognised as such in flight.

That's the year half over, and it was only just new year.


Gill said...

Fantastic shots of the egg-laying. How do you suppose the antennae detect the larva - movement, chemical signals, or something else?

As you say, extraordinary to think how much of this is going on all the time.

Stuart said...

In terms of sheer numbers, I see many more Ichneumonids and Tachinids than I see larvae each year. Of course, not all larvae are on the surface: many are hidden at low levels, deep in vegetation, but each Ichneumon kills one larva to succeed. Tachinids are more productive: they can get up to 10 or more larvae from a single caterpillar.

In terms of antennae, I tend towards the chemical end of the touch/scent spectrum. Other antennae appear to be designed to trap airborne material...think of moths with feathered antennae and beetles with their split clubs and combs. I've certainly seen micromoths swirling their (thin) antennae through the air like whips, in the same manner as Caddis Flies. Tachinids certainly use smell/sight: their antennae are tiny, and can't even reach a host larva. Then again, they are exoparasites and their targets are much more visible.

I guess heat could be another property to sense.

Anonymous said...

Hi Stuart,
I have watched a longhorn micro moth Nematopogon metaxella swirling its antennae in the manner you described, on rushes in marshes near Sandown, IoW. The performance was quite balletic.
It was also impressive to see how well it could navigate between plants with such very long appendages.
Best wishes, Rob

Stuart said...

Rob, yes...I've seen Caddis Flies use a motion very reminiscent of the movement of the rod in fly-fishing, but some micromoths swirl their antennae like a cartoon front-crawl armstroke. Ichneumonids do appear to like to touch things with their antennae, however. I suppose it's the pinpointing aspect, rather than a long-distance detection.