Unexpected Callosamia promethea Eclosion

A female promethea silkmoth (Callosamia promethea) eclosed from one the cocoons spun earlier this summer. Stock originated as eggs from New York, June 2018.

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Completely unexpectedly, a female eclosed from one of the five cocoons spun from the larvae we reared earlier this summer. We had assumed the pupae were all in diapause since this species appears to be univoltine based on reported sightings in this area. The larvae were reared outdoors in the last instar, so they would have experienced normal photoperiod and temperature changes. But alas, we have learned by now based on other species we've reared in Ithaca that more often than not things tend to eclose as long as it's warm enough and most species really aren't completely univoltine (i.e. not obligate diapausers) even if the reported sightings suggest so. 

What is noteworthy and reassuring is that this individual came out of the last cocoon that was spun out of the five, so perhaps this one was an exception and the remaining four are in fact diapausing (since you would expect the moths to eclose in order of when their cocoons were spun). In that case, then this would indicate a small partial second brood and a population with both obligate and facultative diapausers? Or maybe this all just a mistake and this individual really wasn't supposed to eclose but was confused from the indoor conditions during the first three larval instars. 

The moth had already worn itself down quite a bit by the time these photos were taken since it was trapped in the small plastic box that we were keeping the cocoons (since we didn't expect any eclosions). We doubt we would be able to call in male with this individual since there probably aren't many wild males in flight this late in the season. 

Update: to date, none of the other four cocoons eclosed – they are likely all in diapause as we had originally assumed (or [hopefully not], dead!). As for the female that eclosed, no pairing was obtained. 

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Alan Liang​
​Alan Liang is a student at Cornell University in Ithaca, New York pursuing an undergraduate degree in entomology. He is co-owner and a main contributor of the Liang Insects blog and photographs.

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