Papilio erskinei

[Chuck]

There is confusion on iNaturalist concerning the taxonomy of Papilio erskinei (Matthew, 1886), perhaps partly because no images exist in iNaturalist and few exist on the innerweb.

Tennent (1999) confirmed Papilio erskinei as a valid species based on range, morphology, and distinctive genitalia, all differing significantly from Papilio bridgei which is also in the Menelaides group. Sperling, Dupuis, Cotton & other Luminaries (2023) could not obtain a valid DNA sample, but continued with this taxonomy as a valid full species in the Menelaides group.

Papilio bridgei occurs with several subspecies throughout the geographic Solomon Islands, inclusive of Bougainville, with the exception of the eastern-most island of San Christobal and its satellite island Ugi. On these two islands, Papilio bridgei is replaced by Papilio erskinei (this is not unique to the Menelaides group, numerous other butterfly & beetle groups also have unique endemics on San Christobal.)

Morphologically, it's readily noted that submarginal spots on all bridgei ssp are yellow, whereas erskinei they are red.

MALE RECTO


MALE VERSO


FEMALE RECTO


FEMALE VERSO

[laurie2]

Nice post Chuck.

[Chuck]

Nice post Chuck.

Thanks. Miss seeing you around here.

[adamcotton]

Sperling, Dupuis, Cotton & other Luminaries (2023) could not obtain a valid DNA sample, but continued with this taxonomy as a valid full species in the Menelaides group.

Indeed, due to total lack of DNA evidence we maintained the morphological opinion of Tennent (1999).

Adam.

[jhyatt]

Very good post, Chuck! And I do like the use of "Luminaries"... although somehow I still like the older usage of "Virtuosi" for people like Tennent, Cotton, Sperling, et al.

Cheers,
jh

[Chuck]

I should add, I've been to San Christobal twice, and never saw one myself. This is odd, because Papilio bridgei, the equivilent throughout the remainder of Solomon Islands, is quite common. And not like I didn't find anything rare on San Christobal, or for lack of field time. I believe they are citrus feeders, and with San Christobal being much less populated, there are fewer citrus trees, ergo fewer erskinei.

[adamcotton]

and with San Christobal being much less populated, there are fewer citrus trees

Surely the species(?) cannot rely on cultivated Citrus for its existence? There must be a native forest species of Rutaceae (Citrus or another genus) that is the natural larval food plant.

I suspect that P. bridgei is able to exploit Citrus around human habitation and thus has increased its population size along with the increased number of cultivated Citrus trees/bushes (depending on species). I would expect that P. erskinei should also be able to take advantage of cultivated Citrus, but perhaps it only lives in the hilly interior rather than along the coast.

Adam.

[Chuck]

Yes, Adam is correct. If I wasn't clear, my apologies, and thanks for his more comprehensive discussion.

Note though that Papilio erskinei has been recorded from sea level to hundreds of meters elevation, and on both coasts. So it probably inhabits the entire island, minus the highest elevations, wherever the food plant(s) grow.

Papilio bridgei prefers heavy forest, but is not tied to it; they will nectar in yards and gardens. Contrast that with Papilio woodfordi which seldom if ever leaves the forest. Perhaps Papilio erskinei behaves more like woodfordi (just a guess).