Rhyssa persuasoria (I think)- Ovipositing

Aynia · Post by **Aynia** » Thu Jun 12, 2008 3:51 am

Two of these scarey beasties were outside the cabin the other day. Sun going in and out and hence the light is slightly different. Got some interesting pics. Here are three.

Doing the backflip - !!

rjlittlefield · Post by **rjlittlefield** » Thu Jun 12, 2008 7:09 am

Pictures 1 and 2 are beautiful behavioral shots of an ichneumon wasp probing to oviposit in a wood-boring larva of some other species. I also really like the composition, colors, and contrast of the subject against background in these shots.

Picture 3 shows behavior I haven't seen. I notice that the ovipositor assembly is split into at least 2 pieces in this shot. Does she move into this posture immediately after pulling out of the wood?

--Rik

Aynia · Post by **Aynia** » Thu Jun 12, 2008 7:22 am

rjlittlefield wrote: Picture 3 shows behavior I haven't seen. I notice that the ovipositor assembly is split into at least 2 pieces in this shot. Does she move into this posture immediately after pulling out of the wood?

--Rik

Yes she did. I wondered was it just a way of pulling out quickly or something. Though trying to figure it out in a tiny viewfinder is almost impossible. Blink and you miss it. I saw one of these in the garden a couple of years ago but hadn't seen them since and don't know much about them.

What's the difference between shots one and two in relation to the ovipositor? First one, the whole thing is in the hole and the second one the "tail" is out. Is there a difference in the victim species in the wood?

DaveW · Post by **DaveW** » Thu Jun 12, 2008 7:56 am

Found this on the Web Aynia:-

http://www.cirrusimage.com/hymenoptera_ ... sa_fem.htm

DaveW

rjlittlefield · Post by **rjlittlefield** » Thu Jun 12, 2008 8:10 am

What's the difference between shots one and two in relation to the ovipositor? First one, the whole thing is in the hole and the second one the "tail" is out. Is there a difference in the victim species in the wood?

As I understand the anatomy, the part you're calling the "tail" is a protective sheath for the real ovipositor, which is the smaller diameter shaft that emerges from the tip of that big triangular segment. (The link that DaveW just posted refers to the sheath as a "guide".)

In shot one, the ovipositor is inside the sheath, and both of them are penetrating some distance into what appears to be a pre-existing hole in the wood. In shot two, the ovipositor is removed from the sheath and is being inserted by itself.

Why the difference? Maybe she just ran into a tight place where the ovipositor would fit by itself, but not with the sheath in place. Or maybe this is a late stage of drilling, when there's no longer any need for the sheath. But this is sheer speculation. I know hardly anything about these beasts except what I've read, and I don't recall reading anything about this.

--Rik

lauriek · Post by **lauriek** » Thu Jun 12, 2008 11:43 am

Lovely shots! Particularly the second!

I know the ovipositors on some of these is so fine they can actually insert it in-beteen the fibers in the wood, where no pre-existing hole exists - to find a larvae deep in the wood!

The other thing I know about Ichneumons is they are buggers to get anywhere near to photograph or catch! So good work getting so close!!

Aynia · Post by **Aynia** » Sat Jun 14, 2008 1:51 am

Laurie, the two that I saw were easy to photograph and I could have caught them if I'd wanted. There are lots of existing holes in the tree and I bet there are lots of larvae in there. They were acting like the butterflies on my echinacea. I find they get so engrossed in the nectar that I can get very very close.

Perhaps you need some larvae to bribe them with.??!!

rjlittlefield · Post by **rjlittlefield** » Sat Jun 14, 2008 7:25 am

I'm guessing different behavior for different species. Almost all the ichneumons where I live are like Laurie's -- so flighty that it's hard to get close. But a few are almost tame. About this big one of yours, I've read on the web of people nudging them with fingers while they were ovipositing!

It's pretty much the same for all the groups of insects that I know. Some of the lycaenid butterflies are so flighty that I've never seen one at rest in the wild. But I've shot pictures of another one using my index finger for scale. The finger is touching the butterfly, but the butterfly continues to probe the ground with its proboscis.

It occurs to me that the photo record of insects must be heavily biased -- it's dominated by the kinds that will hold still!

--Rik