Tick paralysis in spectacled flying-foxes (Pteropus conspicillatus) on the Atherton Tableland: impact of a terrestrial ectoparasite finding a non-terrestrial host.

Petra G Buettner1,7, David A Westcott2,3, Jennefer Maclean4, Lawrence Brown1, Adam McKeown2, Ashleigh Johnson4, Karen Wilson1, David Blair5, Jonathan Luly6, Lee Skerratt1, Reinhold Muller1,7, and Richard Speare1,7.

1School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Townsville, Australia; 2CSIRO Ecosystem Sciences, Atherton, Queensland, Australia; 3Centre for Tropical Environmental and Sustainability Science, School of Earth and Environmental Sciences and School of Marine and Tropical Biology, James Cook University, Cairns, Australia; 4Tolga Bat Hospital, Atherton, Australia; 5School of Marine and Tropical Biology, James Cook University, Townsville, Australia; 6School of Earth and Environmental Sciences, James Cook University, Townsville, Australia; 7Tropical Health Solutions Pty Ltd, Idalia, Townsville, Australia.

This paper used data collected by the Bat Hospital over 12 years. The study has demonstrated that the paralysis tick, usually considered a terrestrial ectoparasite, is affecting large numbers of SFF, a non-terrestrial host, in only a portion of the host’s range. The numbers of SFF in the study area, and the numbers and rates of SFF affected, were highly variable reflecting the difficulty of obtaining accurate population counts for a species that is highly mobile. More adult females were affected than adult males, and importantly higher juvenile mortality rates were observed during drier years. All of the tick-affected SFF camps lay within the core range of wild tobacco, S. mauritianum. Further studies are needed to better understand if this introduced plant is the major risk factor for acquisition of paralysis tick by this vulnerable host species, and whether feasible strategies to decrease the impact of tick paralysis can be developed. 


Wild Tobacco Tree (known as S. auriculatum for the period I've been researching) seems to have occurred widely in Qld but only been a major pest on the Atherton Tablelands. Apart from the fact that it comes from Mauritius or Madagascar, I don't know much about its introduction yet (research is in early stages). It was declared a noxious plant throughout the State in 1952 (Government Gazette notice 11 October 1952 p. 429) but had been declared earlier for the Shires of Barcaldine, Eacham and Tinaroo by at least 1931.

In 1950 it was described as the "most prevalent weed pest" on the Tablelands but was not common on the coast. It was said to develop thickly on newly cleared forest land and grew rapidly to 10-15 feet, and encroached on established paspalum pastures where these were neglected.
Jan Wagner (pers com)


Raising Public Awareness of Spectacled Flying Fox Issues

This project was a partnership between the Bat Hospital, CSIRO, Tablelands National Park Volunteers, and Queensland National Parks and Wildlife Service. With funding from Natural Heritage Trust and Environmental Protection Authority we were able to employ 2 volunteer coordinators Lisa Dwyer and Ceinwen Edwards to simulate about 2500 'mock bat' foraging events. The outcome: Spectacled flying foxes do defintely acquire ticks while feeding on wild tobacco bushes.

The next step is a project to look at when Solanum has ripe fruit over the course of the year, in its various microclimates across the Atherton Tablelands. This information will help us provide herbicide spraying recommendations to local government for this noxious pest plant. Unfortunately solanum fruit is an important food source for many animals, and so it is not a clear-cut solution to try to eradicate it from the Tablelands. Nor would it be easily done, as it occurs very widely and propagates itself very readily.

Our research was presented at the Australasian Bat Society conference in Cairns in 2005, the abstract is below. Unfortunately the research has not yet been published.


Spectacled flying fox with wild tobacco
photo: Andrew Dennis

Spectacled Flying-foxes, Paralysis Ticks and Introduced Solanum: a Novel and Lethal Ecological Interaction.

Andrew Dennis, Jenny Maclean, Ceinwen Edwards and Lisa Dwyer.

CSIRO Sustainable Ecosystems and the Rainforest Cooperative Research Centre.
Tropical Forest Research Centre, P.O. Box 780, Atherton 4883

Spectacled Flying-foxes, Pteropus conspicillatus, on the Atherton Tableland have suffered high levels of mortality from envenomation by paralysis ticks, Ixodes holocyclus, since at least the early 1990’s. Bats carrying a single tick always die unless treated, suggesting they are not a natural host. An hypothesis was developed early on that a change in foraging behaviour to include the fruit of an introduced weed (wild tobacco, Solanum mauritianum) may have brought the bats into contact with questing ticks. The hypothesis had never been adequately tested. This study used mortality and foraging data to design a sample regime to determine if paralysis ticks could infest flying foxes while they were foraging on tobacco bushes. A sample of 2360 mock bat foraging events on tobacco bushes resulted in the collection of 11 paralysis ticks up to 1.7m high. From our calculations based on infestation rates measured at a colony, we were expecting only one tick in each 2500 foraging events. The large number collected suggests two things: 1) spectacled flying-foxes do acquire ticks from tobacco bushes; and 2) mortality from paralysis ticks may be even greater than that measured at camps. Many bats may die and fall undetected away from camps. While wild tobacco may not be the only source of infestations, our results suggest that a campaign of tobacco bush eradication should significantly reduce mortality due to paralysis tick envenomation.