The nocturnal mating rituals of hairy scarab beetles are helping pollinate one of Perth's most common native trees, in a discovery that shows the adaptiveness of Australian plants and the unexpected pollination strategies still to be discovered.
A four-year study led by La Trobe University discovered that the Candlestick Banksia is a rendezvous site for beetles to mate and feed on the flowers en masse at night.
It was long thought birds and mammals such as Honeyeaters and Honey Possums were primarily responsible for the pollination of the Candlestick Banksia, one of the most common and distinctive trees in suburban Perth.
However, observations of the trees along a 150-kilometre stretch of coast north of Perth revealed the most visited animal to the flowers were scarab beetles, which picked up the unusually gooey pollen on their hairy underside during feeding and mating, helping to transfer it between plants.
Senior author Dr Ryan Phillips, from La Trobe's Department of Ecological, Animal and Plant Sciences said further investigations found the beetles were lured to the flowers by specific compounds that smell like rockmelon.
"This discovery of pollination by beetles using the flower as a 'rendezvous site' has revealed unexpected parallels with beetle pollination in tropical plants in South America and Asia," Dr Phillips said.
The research was led by Stanislaw Wawrzyczek as part of his PhD at La Trobe. Now working in conservation, Dr Wawrzyczek said the finding was significant as many of the remaining populations of Candlestick Banksia occurred in small habitat remnants within suburban or agricultural environments.
"Our work raises the question of whether these beetle pollinators are persisting in remnant habitat and if their potential loss adversely affects reproduction of the Banksia, which is a dominant tree species in Banksia woodland," Dr Wawrzyczek said.
"This research highlights that unexpected new pollination strategies remain to be discovered in Australian plants, particularly those with nocturnal pollinators. It also demonstrates the diversity of adaptations that plants can have to lure their pollinators."
The study, Attraction of nocturnal scarab beetles by unusual floral volatiles in a Banksia (Proteaceae) with functionally diverse pollinators, has now been published in the journal Plant Biology.
Experiments are now underway to understand whether this 'rendezvous site' pollination strategy operates through pollinator learning or innate attraction to the flowers.
"From a conservation point of view, the next step is to understand if the pollinating beetles can live in fragmented or urbanised landscapes and how to best facilitate their persistence," Dr Phillips said.
The study was conducted in collaboration with researchers from the University of Western Australia, Kings Park Perth, Swedish University of Agricultural Sciences, Queensland University of Technology, Edith Cowan University and Royal Botanic Gardens Victoria.
The research was completed using floral visitor surveys aided by camera traps and video recordings, and quantified insect pollen loads.
DOI: 10.1111/plb.70226
