Assessment of Summer 2018 Hyalophora cecropia Cocoons

Almost all of this summer's Hyalophora cecropia larvae have spun cocoons, so we decided to sort them out share some thoughts on this year's rearing.

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​Though there are still two larvae left that have yet to spin cocoons, we went ahead and sorted out all the finished cocoons. We have a total of 26 cocoons (not including a couple that we disposed of because they seemed dead). There are 21 from the first pairing, 4 from the second, and 1 from the third. From first instar to cocoon, mortality was obviously quite high, especially for the second and third strains. It seemed most larvae from these strains got diseased before making it to the fifth instar, while a decent amount of the first pairing larvae were already in fifth before disease started spreading which explains why many more survived. The cocoons are all quite variable in size, shape and color. Some are pale and greyish while others are a rich brown color. There doesn't seem to be any difference between the maple and serotina cocoons.

We removed the dead plant material woven into the cocoons as best as possible and weighed each one. The weights for the first pairing cocoons were 4.02, 4.52, 3.62, 5.30, 5.15, 5.19, 4.38, 4.04, 4.06, 3.05, 7.27, 4.04, 4.86, 5.95, 3.28, 4.77, 3.62, 4.72, 6.66, 4.50, and 5.93 grams; for the second pairing cocoons were 3.70, 3.92, 4.89, and 4.95 grams; and for the third pairing cocoon was 3.37 grams. Sample size is definitely too small to try comparing weights between the lineages, and there were probably a number of confounding factors due to disease and the way they were reared. anyway.

Overall, this year's cocoons are surprisingly small compared to those from previous years. We've never had cocoon weights as low as the 3-4 gram range in the past, which is extremely small in general, especially if any are female. We had originally expected that this year's cocoons would be larger than the previous rearings back in California, since we have access to more typical host plants and are in their native environment here in Ithaca. Although it is true that better host quality (?) and the warmer and wetter Ithaca summers would have definitely helped their growth, we suspect any positive effects of these factors could have been superceded by the negative effects from the severe overcrowding compared to previous rearings.  We attempted to rear far more larvae than the previous rearings and had many more larvae make it to the final instar which really overwhelmed us. Thus, it seems this year was a year of quantity over quality for cecropia. 

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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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