Adaptations for fluid uptake among moths with hyper-elongated proboscises

The birth of coevolutionary studies can be traced to Charles Darwin's famous prediction of the existence of a moth species in Madagascar that would have a hyper-elongated proboscis (nearly 30 cm long) capable of pollinating the comet orchid, Angraecum sesquipedale. This moth, known as Morgan's sphinx moth, was discovered 40 years later and observed to feed from the orchid nearly 100 years after that. Previous studies have shown that other species of the sphinx moth lineage have an enlarged sucking pump in the head to facilitate fluid uptake through the food canal of the proboscis. Here, we focused our study on discovering other adaptations, particularly those of the proboscis, that might assist with fluid uptake. We performed a series of wetting experiments coupled with scanning electron microsopy on individuals of Neococytius cluentius, a sphinx moth from Ecuador that has a proboscis length nearly as long as Morgan's sphinx moth (28 cm). Similar to other lepidopteran species, we found a structurally-defined region as indicated by dorsal legulae shape and size; however, unlike other studied species, this structural demarcation does not correspond with a wetting dichotomy of the overall hydrophobic and hydrophilic regions. In particular, the proboscis of N. cluentius has a hydrophilic profile of approximately 90% of the proboscis length, compared to 10-20% found on butterfly species with shorter proboscises. We suggest that the enlarged hydrophilic region provides optimal fluid intake capabilities when feeding on nectar from enlarged floral tubes of some orchid species.