Spruce Budworm Caterpillars and Parasites

[rjlittlefield]

These are from July 15-16, when I went hiking again up the South Tieton / Conrad Basin area. Around 5000-6000 ft elevation, I encountered numerous small caterpillars (1" length) hanging on silk strands under fir trees. When I looked closer, it seemed that many of these caterpillars had been attacked by some kind of parasite whose larva had just emerged and was hanging on around the thorax of the caterpillar. One of the caterpillars seemed to have had a particularly bad life, having both one of these larvae and also the egg of a tachinid fly attached to its thorax. On closer investigation, I discovered that the caterpillars seemed to be associated with quite a lot of damage to the young needles on fir trees, and I also found a few of what I presume are pupae of the same critters.



I am posting pictures of these beasts here for your viewing pleasure(?). Perhaps some of my Lepidopterists' Society friends can tell me what these critters really are, and how badly I have misinterpreted the relationships.

By the way, yes, the caterpillars really did come in two colors -- brown and green. I have no idea what the difference is.

--Rik

Edit Aug 08, 2006: changed title to use correct name of caterpillars

[salden]

Interesting images. I never seen anything riding on a cat before, or maybe I never looked close enough. It is a hard world out there, even for the smallest of critters.

[Ken Ramos]

Interesting composites there Rik. Our big concern out here is the Woolly Adelgid, which is destroying our hemlocks. I can't be sure but it seems like I have seen these cats around here too.

[paul]

Very interesting story, Rik, beautifully documented.

[rjlittlefield]

I can't be sure but it seems like I have seen these cats around here too.

That seems likely. Based on appearance and host plant, one of my Lep Soc friends thinks that these caterpillars are probably Spruce Budworm, Choristoneura fumiferana. That species extends east to the Atlantic, not as far south as your place, but probably there are related species that cover your area also. There are also "pine tip moths" that look quite similar.

I was particularly intrigued by my friend's comments about the parasites. He thinks that the larvae are probably wasps with an ectoparasitoid lifestyle, living on the outside of the host all the time until the host dies. I had never run into such beasts, but it makes a lot of sense given the appearance and behavior of these parasites. I kept a couple of the caterpillars with parasites in the refrigerator for a few days, and the parasites never did anything interesting or even move away from their host, like they would if they were just emerged and ready to pupate. He mentioned Eulophidae as one family of wasps like this. What little I've found suggests that Eulophid larvae are found in groups and are smaller than the individuals that I found, but this is pretty uncertain data. It's interesting stuff anyway -- yet another example of it being a lot easier to find questions than answers!

--Rik

[beetleman]

Very interesting photos and info. Thank you. The closeups are great, nice and sharp....a picture IS worth a thousand words!!

[rjlittlefield]

Based on appearance and host plant, one of my Lep Soc friends thinks that these caterpillars are probably Spruce Budworm, Choristoneura fumiferana.

A minor update... Another Lep Soc person with good local knowledge suggests that the caterpillars are more likely Choristoneura occidentalis (same genus, different species). More info about the biology can be found here, with distribution maps here.

The moths of these two species are very similar -- see the (really quite remarkable!) series of photos at
http://mothphotographersgroup.msstate.e ... odges=3640 .

And by the way -- thanks, everybody, for the compliments on these pictures!

--Rik

Edited 25 July 2021, to fix broken link.

[rjlittlefield]

A follow-up posting, showing dense congregation of adult moths at a car dealership in Salmon, Idaho, can be found here.

I'm still trying to find out what the ecto-parasitoids are. I'll let you know if I find out.

--Rik

[Jackie]

A Braconid Wasp Meterous trachynotus and two Tachinid Flies Ceromasia auricaudata and Madremyia saundersii are known to attack the Spruce Budworm larvae. Fly larva usually have a breathing tube at the rear end. Wasp larva doesn't.

This is my first post. I'm not an expert, just interested in insects and biodiversity - where everybody is somebody else's lunch.

Cheers,
Jackie

[rjlittlefield]

A Braconid Wasp Meterous trachynotus and two Tachinid Flies Ceromasia auricaudata and Madremyia saundersii are known to attack the Spruce Budworm larvae. Fly larva usually have a breathing tube at the rear end. Wasp larva doesn't.

This is my first post. I'm not an expert, just interested in insects and biodiversity - where everybody is somebody else's lunch.

Cheers,
Jackie

Jackie, welcome aboard! Be aware that you've arrived in the middle of switching the forums to a different URL. You might be interested in surfing through the old site also, http://www.photomacrography1.net/forum/. (You don't need to register, to just read.)

Thanks for the info about the parasites. You're the first to mention these to me. Google suggested the spelling Meteorus trachynotus, and that got me to an excellent page at https://web.archive.org/web/20060906103 ... udworm.htm as well as other helpful pages. For example https://web.archive.org/web/20100609084 ... udworm.htm says that "Wasps, such as Meteorus trachynotus and Phaeogenes hariolus, are the most prevalent parasites, however, flies such as Lypha setifacies, will also prey upon the spruce budworm (Johnson and Lyon 1984). "

I'm still hoping for somebody to recognize the specific ectoparasitoid that I happened to take these pictures of. On the other hand, the longer the search goes on, the more I learn about the complex bug-eat-bug world that these guys live in.

--Rik

Edit 25 July 2021, to point broken links into the Internet Archive.