Hyalophora cecropia Cocoons Post-diapause Update - Cutting One Open

We decided to cut open one of the Hyalophora cecropia (cecropia moth) cocoons we took out of cold storage last month in order to examine the pupa.

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On February 10th, we took our cecropia cocoons out of cold storage for eclosion. At the time, we had anticipated they would only take about a month to eclose, but it has already been five weeks and temperatures have actually been quite nice lately (high 60s-mid 70s during the day). Thus, they should be eclosing anytime now assuming they aren't dead or have failed to break diapause. The former scenario is extremely unlikely since all cocoons weigh just as much as they did when they the caterpillars pupated. However, since we only overwintered the cocoons for two months at a constant 4 °C, it is possible that the chill period was to short to induce diapausing breakage, since in this strain's New York origin, they would have experienced several more months of chill and at a far low temperature. If they really have failed to break diapause, then there is little we can can do about it except for giving them another chill period and have them carry over diapause until next year. 

In order to confirm or refute our doubts, we decided to go ahead and cut open a cocoon. We picked a lighter one and it contained a black form male pupa. Like we thought, the pupa was clearly healthy and living as it was nice and plump. When squished gently, it feels very soft and is likely close to eclosion. We will see in a week or so if it ecloses. 

Interesting to note that the cocoon is in two layers, the outside papery and thin, and the inner one thicker and softer. Also, typical of Attacine silkmoths, the forewings are very large in relation to the body (compared to Saturniines), and the abdomen is uniform in width except for the last few segments which taper heavily. There are also bumps on the ventral side where the larval prolegs used to be.

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Authors
Alan Liang