Tachinid: when do "your" maggots emerge?

[skates4marty]

Wyvern wrote (in the failure to progress thread) that he had 3 C's with maggots. To the best of my recollection, all "my" maggots have come out when my cats are in J. In the past few days, I've lost 4 J's (perhaps they were the fourth and fifth instars I found on a newly-discovered patch of milkweed). I put them in a covered container -- 17 maggots! What is everyone else's experience about when the maggots come out?

[Mona Miller]

I've also gotten them coming out of pupae and from the larvae hanging in the J. The larvae goes to form the J early, they are usually small. I had a horrible problem a few years ago. I was using netting that allowed the fly to lay right thru it. When the caterpillar is molting on the netting, the fly can lay right thru some types of netting. Or, they get laid on in the wild. The bigger the caterpillar, the more likely they've been laid on.

http://www.mymonarchguide.com/2008/01/d ... d-fly.html

[Wyvern]

I've always believed that when you get the maggots coming out of the chrysalis it most likely meant that the caterpillar was infected at a later instar stage than those that have maggots emerge while the cat is still a cat.

[Mona Miller]

Interesting. I've never had them emerge from anything other than a J or a pupa.

[Mona Miller]

I just remembered that there's some good research on this very topic:

http://www.monarchlab.umn.edu/Lab/Resea ... fault.aspx
Parasites & Natural Enemies Research Projects

[skates4marty]

I asked one of the experts a couple of years ago -- probably Monarch Lab -- if there were any instars safe from T fly. I figure that if the fly lays the eggs on an instar that is too small, surely the maggots will outgrow the caterpillar before the maggots are old enough to pupate, so the fly will choose caterpillars of a certain size...? She would not say that any instar is safe, just that the longer they are in the wild, the greater the risk.

[Wyvern]

Interesting. I've never had them emerge from anything other than a J or a pupa.

Yup. I would say this year about half of my flies came out of 3rd/4th instar cats that died for no apparent reason (as opposed to deaths that could likely be ruled as from black/green/bacterial deaths). The cats would be fine one day and then the next start acting lethargic. By the evening or next morning they'd be dead. I set the carcasses in lidded cups and wait a day or two.. usually I would find anywhere from 1-3 fly pupa after the wait. The other half of my fly infections this year were from 5th instars that failed in the "j" or came from the chrysalis. With the chrysalis they would be fine at first, but after a day or so would get this light dirty brown soft spot and then they would become a very pale green instead of the bright green. Sometimes it was easy enough to see the chrsyalis would survive long enough for you to see the beginnings of a butterfly almost ready to emerge, but then never emerge..later it would turn a dark solid black and not long after that fly pupas would be seen on the bottom of the containers. I then freeze the nasty little flies.

Oh, this morning while collecting milkweed from my yard, I found the carcass of a Tachinid fly on a milkweed leaf. Apparently it had been hunting for pillars to infect and a spider nailed it's little butt. sucked it dry. Go spiders! LOL.

[Mona Miller]

I read somewhere that the parasite will keep its host alive as long as it is needed for the parasite to mature. YUCK!!

[skates4marty]

Re: the 2006-07 study: Interesting, thanks for posting the link.

Even firsts are not completely safe! "I was not successful in determining which monarch instar stages were preferred by tachinid flies. There were only two successful parasitisms on first- and fourth-instar monarch larvae..." However, I assume that if a first is parasitized, it must die pretty soon after?

It also says, "Monarch larvae collected during later instars did not have a significantly higher chance of being parasitized than earlier instars (0.1>p>0.05). It was unexpected that fourth-instars were not parasitized since third- and fifth-instars were. This occurred even with a large sample size (n=25)."

[Mona Miller]

This is one reason, I use my screen tent. Net or raise a female. Gravid or let them breed. Let her lay inside the tent, the larvae are safe that is if you don't let the flies in. That has happened to me, too. It is a battle. I actually have flies and other predators following me around because I must smell like butterflies.