Larvae twisting & turning like dogs

[Tia]

Mona, don't cry -- but among the larvae that hatched at Girl Scout camp, a few are doing that horrid twisting, turning, and rolling thing. They are in quarantine, and will probably go in the freezer after my daughters go to bed; then it's bleach and dishwasher time. One of Chip Taylor's old posts (snip below) describes the MOTION perfectly -- but these are 1 & 2nd instars. Could it possibly be tachinid fly infestation? They're so small! And I found two just dried up; they were barely 2nd instars. No discoloration. Thoughts?

Some anonymous scout did leave their cage unzipped for perhaps up 30-60 minutes before I noticed the opening and zipped it shut. Flies could have found them, I guess. And these larvae were a bit more crowded than I usually have them -- but air flow was good.

Ideas, anyone? I fed them a variety of milkweed, all from the middle of my yard, so insecticide, if my neighbors used any, should be impossible. They were outdoors most of the time, but in the shade and this week's been a lot cooler than last -- so I don't think temperatures did it.

Snipped from an old Chip post:
>>Monarch larvae that have been oviposited on by a fly drop from the plant and curl into a C shaped position and begin to turn the C inside out rolling over and over. This writhing can continue for several minutes and may be an attempt to "rub off" the egg or perhaps the fly larva. At some point the monarch larva stops rolling and climbs the plant and continues feeding. The flies evidently do not oviposit in first, second and early third instar larvae but direct their attention to larger larvae.

Tia in Alexandria, VA

[Mona Miller]

Sorry Tia,

Some of the larvae were from the wild and also some of the eggs. Some I found in a gas pipe line area. The others were from my tent, but if the heat, flies, got to them. Who knows. Also, possible pesticide/herbicide problems.

I'm not seeing any problems, yet.

But, I am hearing that people are having problems this year. Larvae dying, pupae not pupating. I'll let you know if I see problems here. Glad you made it through the week.

[Becky C-M]

My first year raising Monarchs (yay!) & I'm wondering if a new wild caterpillar I found last night has a parasite.

Got some milkweed for my current caterpillars from the forest preserve & there was a 4th or 5th instar cat already on the milkweed, so I took him home to keep him safe.

When cleaning the milkweed of other insects, etc., I purposely touched the new cat on the back to see what he'd do.

He immediately reared his front half up & over to the side, and did just like you mentioned here - twisted & turned like a dog... but ONLY HIS FRONT HALF. He did NOT curl up into a "C" shape & do this with his whole body.

Does this sound like a possible parasitization by the tachinid fly, or could the cat just have been reacting to my touch?

I touched him again later after settling him in his new cage, and he did not have the twisting/turning reaction.

I've got him separated from the rest of my caterpillars just in case, but I just need to know if the fly parasites might be an issue for the poor little guy!!!

Thanks for any help you can give!!!

[Mona Miller]

This is a good 15 minutes of searching:

http://www.monarchlab.umn.edu/lab/resea ... easey.aspx
6th paragraph down:
"A study by Etchegaray et al. (1975) showed tachinid flies prefer to lay eggs on late second-, third-, or early fourth-instar monarch larvae and are usually unable to lay eggs on fifth-instars because these instars are able to shake off fly eggs. Although unusual, Etchegaray found that tachinid flies were able to lay eggs on first-instar monarch larvae. Etchegaray also observed superparasitism when 20 or more tachinid eggs were laid on a single monarch larva; the monarch larva and tachinid larvae died as a result (1)."

http://www.monarchwatch.org/update/2003/tachinid.html
Large pictures of the fly pupae and fly

http://www.monarchwatch.org/update/2003/0717.html#8
This update tells about the symptoms of a larvae that has been parasitized.

http://www.mymonarchguide.com/2008/01/d ... d-fly.html
The Dreaded Tachinid Fly

http://www.mlmp.org/Results/Findings/Default.aspx
There's a lot of good research here.
http://www.mlmp.org/Results/Findings/Ob ... m_2007.pdf
Parasitism of Monarch Butterflies (Danaus plexippus) by
Lespesia archippivora (Diptera: Tachinidae)
Page 316
"Three flies emerged from monarchs collected as eggs in her MI Sites; these were
identified as Lespesia archippivora."
"The odds ratios indicate that the likelihood of being parasitized roughly doubles for successive stadia."

Mona's Note: 3rd and 4th instar are more susceptible. Apparently, 5th may be able to withstand an attach and keep the fly from laying.