A parasitoid fly invading Saturniidae pupae?

[lamprima2]

I recently received the cocoons of a US Saturniid Agapema anona. They were stored in a cage, covered with a standard window netting, and supposed to eclose soon. Instead of the moths, I found three flies in the cage, about 6-7 mm long, morphologically similar to houseflies (I do not know much about Diptera). There is no way they could get in the cage from outside. Are there any species of parasitoid flies, able to emerge from Saturniidae cocoons? Sorry, I do not have macro equipment to take a pic of these flies.

[adamcotton]

If they have distinctly bristled abdomens they will belong to family Tachinidae, which lay eggs on larvae or on the food plant and are subsequently ingested by the larva and the maggots develop inside the larvae.

Certainly no parasitoid will attack a healthy pupa inside a cocoon, but some flies lay eggs on dead pupae (mainly family Phoridae which are very small like fruit flies).

Adam.

[Chuck]

At least in NE USA, these flies are the most common parasite to emerge from Saturnid cocoons. Wild-caught cocoons may suffer up to 50% loss due to them. And yes, the great disappointment is when you find these flies with your cocoon. They pupate within the cocoon but outside of the pupa, so when collecting wild cocoons shake the cocoon and if it's already dead from these flies you'll generally hear the dry fly pupae rustling inside.

[kevinkk]

This is a problem with wild collected larva. I have had the larger share of Agapema cocoons be parasitized.
Anytime a person buys cocoons, or butterfly pupa from wild collected larva, you are flipping a coin.
That being said- sellers have a moral and ethical responsibilty to disclose if the larva have been wild collected.
I have more to say on this subject, but will stop short of complaining about particular sellers, who should know better.

[Trehopr1]

The Tachinid fly species most responsible for the widespread rampage on Saturniid populations of the East is Compsilura concinnata.

It is a parasitoid species native to Europe which WAS introduced into the US in 1906 to control populations of the Gypsy moth in the northeast states.

It apparently didn't just find gypsy moth larvae attractive as a food source. It is the reason why Saturniid specialists believe that the Cynthia moth of the Northeast is now confined to a few derelict ramparts and way sides in the state of New Jersey. It was once present in New York, Massachusetts, Connecticut (at the very least).

As such, there are those who believe that it has also had a significant impact on populations of the Cecropia moth. Cecropia moths have become increasingly hard to encounter even by seasoned collectors in these last 20 years (at least). Their familiar cocoons which one could occasionally find on trees like silver maple and boxelder have become almost non-existent in a great many places that one used to be able to find them !

[lamprima2]

Thanks to everyone who replied to my post.
The fly I caught does look like a Tachinid.
Decades ago I experienced problems with wild-caught larvae
of Deilephila elpenor: some were killed by Tachinidae
larvae just before the pupation, others - by parasitoid wasps,
emerging at Spring from overwintering pupae.
I've never had this type of problem with Saturniidae.
I guess I was lucky, besides the majority of the cocoons
I've dealt with results from captive breeding.

[kevinkk]

Tachinid introduced as a pest control. That's just nice. There is yet another of the examples of the intelligence of our people in charge.
And I can't get a legal Atlas moth. I enjoy the same sentiments when I see a flock of starlings land on my bushes, just before I get my air pistol-