Smerinthus cerisyi Pupae

We have received four Smerinthus cerisyi (one-eyed sphinx) pupae originated from Colorado.

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 We currently have a single locally obtained and reared female Smerinthus ophthalmica pupa that is in diapause. Since we are uncertain if we are going to be able to obtain a pairing with just one female, especially when we don't know when the local population flies and when this pupa will eclose, we decided to get four Smerinthus cerisyi pupae just in case. Our thinking was that since S. cerisyi and ophthalmica are very close related, a female cerisyi should be able to call in a wild ophthalmica. 

We had expected the cerisyi pupae to look nearly identical to ophthalmica's, but when the pupae arrived we were in for quite a surprise. We cannot say for certain that the cerisyi and ophthalmica pupa that we have are each representative of the typical phenotype for their respective species, but we observed quite a few differences. First off, the cerisyi pupae are far smaller than we had imagined - the three males weigh 1.6, 1.4, and 1.1 g respectively while the female weighs 1.7 g, half the size of our female ophthalmica pupae which currently weighs 2.9 g (originally 3.1 g several months ago). This is such an incredible size difference that it is unlikely due to variation from rearing conditions but almost certainly genetic. In addition, three of the cerisyi pupae are distinctly glossy reddish brown in color rather than a slightly duller jet black like the ophthalmica, though the fourth cerisyi is on the darker side which we suspect is due it being close to eclosion. Further, the cerisyi seem to have pointier and larger cremasters in relation to body size and have narrower abdomens while the ophthalmica's is slightly blunter like Pachysphinx modesta's. 

We weren't expecting such differences between the two species and are now uncertain about the compatibility of the two in reproduction. Several authors still consider the two to be subspecies of each other rather than separate species, which by definition would mean they should readily produce offspring with near 100% fertility. However, looking at the huge size differences and slight pehnotypical differences between the two species, we are becoming somewhat doubtful about the viability of the eggs. However, if we do manage to hybridize these two species (or subspecies), then it will be extremely interesting to see whether or not the observed differences we have made are attributed to genetics or not. Ideally, it would be even better if we could produce a pure strain of both the Coloradan cerisyi and Californian Ophthalmica and treat them as control groups.

Another burning question of ours that an experiment like this would solve would be whether the four larval instars observed in Ophthalmica is truly genetic or simply a result of extremely ideal rearing conditions (doubtful, but that's what some have said). We assume that the Coloradan cerisyi had five larval instars as this seems to be the norm based on literature. Thus, if a S. cerisyi x ophthalmica cross produced offspring with significantly different proportions of larva that undergo four or five instars than the two pure strains, then we could conclude that the four instars in Ophthalmica truly is genetic and may be a defining trait of this species, or at least of the local population of this species.

And, one more thing - we are very curious to know the egg size of these Coloradan cerisyi because our local Ophthalmica females seem to lay disproportionately large ones for the size of the species, but each female lays very few (~100). This gives rise to larva with large birth sizes which becomes undermined by the fact that they only undergo fourth larval instars - in essence, a less extreme R-selected reproductive  strategy that favors fewer but larger (assumed fitter) offspring. This actually seems to be a pattern among Saturniids/Sphingids in California; the three Californian Saturnia females also all have enormous eggs but lay just 70-80, and larva of two/three of  the species undergo four rather than five larval instars. We also hear that California Antheraea polyphemus also have larger eggs than those from other parts of the country. Thus, if the Coloradan cerisyi eggs turn out to be much smaller than our local Californian ophthalmica's it will further suggest that this large egg size of Ophthalmica is likely characteristic of the species or at least the Californian population, and may have to do something with the pattern we have been seeing.

Below are photos of the four Smerinthus cerisyi pupae as well as side by side comparisons with S. ophthalmica and another relatively closely related Smerinthin, Pachysphinx modesta.

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Authors
Alan Liang