New insights into the unusual nesting biology of the bee Trichocolletes orientalis (Hymenoptera: Colletidae, Neopasiphaeinae), particularly its larval 'oil bath'

Trichocolletes orientalis is an Australian solitary, ground-nesting bee, reported to have some unusual aspects to its nesting biology. Prime among these, and a focus for the present study, is the production of copious amounts of oil by post-feeding pre-defaecating larvae. To better understand the mechanism of oil production, we examined the bee's floral resources and larval provisions and compared the fatty acid profiles of the provision and larval oil exudate using gas chromatography. The study population was monolectic on the legume Hardenbergia comptoniana. Unusually for Neopasiphaeinae, larval provisions were liquid but contained no obvious free oil. Differences in the fatty acid composition of the provision and larval oil lead us to conclude that larvae must secrete the oil. Fully fed larvae prevented from curling produced a yellowish, non-oily liquid from the anus. The Malpighian tubules are implicated in the production of this liquid and perhaps the oil (which has not been reported for any other bee species). While likely preventing water loss from resting larvae, the oil contains some fatty acids with known antimicrobial and antifungal properties and might protect the larvae from pathogens. Additionally, we provide a complete life cycle calendar for the bee.