University researchers are investigating a caterpillar of a rare Queensland butterfly which appears to have the unusual ability to mimic its' host ants' odour so as to infiltrate ant nests and consume their young.
The caterpillar metamorphoses into the rare blue butterfly Acrodipsas illidgei , found in threatened mangrove habitats along the eastern seaboard. Entomology Department Associate Professor and Associate Director of the Co-operative Research Centre for Tropical Pest Management Myron Zalucki and his honours graduate student Jim Beale recently published a scientific paper on the habits and distribution of the butterfly.
Since graduating with his bachelor of science honours degree, Mr Beale has worked as a consultant advising the Hervey Bay City Council on the butterfly's status and the possible effects of measures to control biting midge at Mary River Heads. Subsequently, work was carried out for the Redland Shire Council to assess the butterfly's status at a site planned for urban development.
As with other members of this lycaenid genus, A. illidgei form a special relationship with ants. However, A. illidgei is not as generous to ants as other lycaenid butterfly larvae which trade protection by ants in exchange for excreting ant food such as sugars and amino acids.
'Instead, A. illidgei larvae appear to have mastered the ability to mimic the ants' odour so ants mistake them for their own eggs and larvae - you could describe them as ?chemical sneaks'. The ants carry the caterpillars into their nests found in the branches of mangrove, casuarina and eucalypt trees. Once inside the nest, the caterpillars devour ant eggs and larvae,' Dr Zalucki said.
'The butterfly larvae are very thin-skinned so if the ants realised they were alien, they could easily be killed and often are when the deception is unmasked.
'It is at the adult stage that the butterfly is at greatest risk of being detected as an intruder and must make a quick getaway from the nest. Covered in disposable scales (a kind of cuticle), the butterfly flees the nest with ant hordes in hot pursuit grappling with the scales left behind.'
Considered very rare, the butterfly was given permanently protected status by the Queensland Government in 1990. Colonies occur at each of three coastal mangrove areas of Australia - around Brunswick Heads in northern New South Wales, and Moreton Bay (Redland Bay and Point Halloran) and Mary River Heads near Maryborough in Queensland.
The research by Dr Zalucki and Mr Beale points to a sharp decline in the species range and population since increased mangrove clearance for development. Previously, it was collected at Bulimba (most recently in 1908), Southport (1941), Enoggera (1909), Hays Inlet (1973), Burleigh Heads (1984), Tallebudgera (1980) and Goat island (1904).
'The butterfly is no longer considered present at these localities as either the sites no longer exist due to urban development or the species has not been collected in recent years,' Dr Zalucki said.
'In recent times the main threat to populations primarily comes from pesticide use or other insect control measures in mangrove areas and urban encroachment to existing sites.'
He said the butterfly appeared to only infiltrate the nests of Crematogaster species ants and then only nests on particular trees. Dr Zalucki and Mr Beale found that out of 100 mangrove trees in a study area, only three contained A. illidgei caterpillars inside ant nests.
'We suspect the female butterfly tends to lay her eggs near the same ant nest she herself emerged from, limiting the butterfly's spread. Possible reasons for this are that she is a weak flier or that she responds more readily to the odour of her own home nest and the next generation of larvae has the right odour recipe for that particular ant colony,' Dr Zalucki said.
As researchers had never been able to rear the butterfly from egg to adult in the laboratory, Dr Zalucki and Mr Beale have developed special wooden boxes (artificial domatia) with removable covers to study the species in the field.
Wired to mangrove branches, the boxes have been colonised by ants. Dr Zalucki said it was hoped the butterfly's larvae would eventually be introduced to the ant colonies. Their development could then be monitored by intermittent removal of the covers.
For more information, contact Myron Zalucki (telephone 3365 2194 or email: M.Zalucki@mailbox.uq.edu.au).
