Papilio polyxenes, zelicaon, & ♀ ​polyxenes asterius × ♂ zelicaon Fourth and Fifth Instar Comparisons

Here we compare the fourth and fifth instar larvae of the black swallowtail (Papilio polyxenes asterius), anise swallowtail (Papilio zelicaon) and a ♀ Papilio ​polyxenes asterius × ♂ Papilio zelicaon hybrid cross.

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The hybrid larvae are still behind, so there quite aren't any fifth instars yet. However, we still took some more photographs of the fourth instar compared to the two pure crosses.

​The hybrids are truly perfect intermediates, no matter if they are dark or light forms. They share the same bulgy, shiny appearance as Papilio zelicaon, but aren't quite as spiky. The light forms seem to be patterned similar P. polyxenes asterius in the amount of white they have but still have thicker black bands than the pure breed and have broken saddles. Both the dark and light forms have smaller spots than Papilio zelicaon like P. polyxenes asterius. A good way to look at it overall is that the P. zelicaon are messy, the P. polyxenes asterius are smooth and clean, and the hybrid are just in between.

There are lots of fifth instar P. polyxenes asterius now, and they look distinctly different than P. zelicaon fifth instars. The P. polyxenes asterius still have much smaller and more circular spots such that they don't break the black bands and the spots on the thick thoracic band of P. zelicaon are still mostly absent. Because of this, they actually look blacker than P. zelicaon despite all being much lighter in the fourth instar. The greenish white bands seems to be to be much more even, at least for now, without any blue bands mixed in between that are common in P. zelicaon. The shape of the P. polyxenes asterius resembles tigers much more than P. zelicaon​ because they are so long and skinny with very large thoraxes; P. zelicaon tend to be slightly more bulgy between segments. Overall, the P. zelicaon are much more cryptic on flowers than the P. polyxenes asterius may seriously reflect on the different climates that they come from and what they feed on. In fact, we have put in some flower for the P. polyxenes asterius to see if they will feed on it and so far they have not. 

As for size, it now seems that the P. polyxenes asterius might actually have a chance to get bigger. They certainly look larger in the photos, but it is unknown just how much they have fed already. In the fourth instar, the P. polyxenes asterius seemed just slightly smaller with most at o.3 whereas 0.4 dominates P. zelicaon based on previous rearings. Very surprisingly, we now have a single 0.5 g P. polyxenes asterius which is the rare maximum for P. zelicaon, so there is clearly a lot of variation. But no matter what they are in the fourth instar, the fifth instar is the bulk of the growing so anything could happen. . .

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Authors
Brian Liang

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