Received Iowa Papilio glaucus & Papilio polyxenes asterius Eggs

We received eastern tiger swallowtail (Papilio glaucus) and black swallowtail (Papilio polyxenes asterius) eggs from Iowa. The state of the eggs and potential differences between Iowa and local populations of the two species is speculated upon and discussed. 

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We received approximately 80 F0 ("wild") eggs each of Papilio glaucus and P. polyxenes asterius from a supplier in Iowa. The glaucus eggs are shown below:

Most of these glaucus eggs have already reached the late stages of the yellow mottling phase. A few are partially black and may hatch tomorrow while a few also are green and therefore likely infertile. In addition, we noticed that some of the partially developed eggs had collapsed; this was not the case with the P. polyxenes asterius eggs, which were received in the same package. This is interesting because we have struggled with hatching glaucus-group eggs in particular in the past, namely, with P. rutulus but rarely with those of machaon-group species. It may be that glaucus-group eggs are inherently more susceptible to damage than machaon-group eggs, perhaps owing to their differing ecology (glaucus-group eggs are laid on trees whereas machaon-group eggs are laid on forbs), though this is purely speculation. ​​​

​The polyxenes eggs, shown below, are in excellent shape, for the most part. They seem to be much more varied in age than the glaucus though. Some of the eggs have already almost completed development and will likely hatch tomorrow.

It will be interesting to see how these differ from the local, Ithaca populations of these species seeing as Iowa has a strong population of the mimicry model, Battus philenor, which is absent in Upstate New York. In Iowa, female glaucus are reportedly 95% the black form, whereas the local glaucus are predominantly yellow (personally, we have yet to see a black female at all). We shall see whether this is the case for ourselves when we rear the glaucus eggs. As for polyxenes, we have recently noted how the wild female that we captured yesterday had a substantial amount of yellow scales, which should be undesirable in mimetic selection, so we are interested to know how the Iowa adults turn out. There will likely be other differences in life history traits between the populations of both species depending on what host plants are preferred in the respective localities and the climate. While the glaucus here are probably almost always obligately univoltine, the Iowa glaucus are said to be bivoltine, which is another way of saying they can be reared indefinitely without diapause under the right conditions. This will be advantageous for rearing a larger second generation of these eggs since pupae tend to die or have unreliable eclosion after a period of overwintering. While we have yet to take note of the voltinism of the local polyxenes, it is almost certain that these Iowa types are strongly multivoltine.

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​Brian Liang
Brian 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, insects articles, and site design.

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