Potter_Craven_whole_thesis.pdf (2.56 MB)
Conservation management to protect the threatened ptunarra brown butterfly (Oreixenica ptunarra) from the threat of predation by introduced vespid wasps in Tasmania, Australia
thesisposted on 2023-05-28, 09:35 authored by Potter-Craven, JL
Butterfly numbers are declining worldwide primarily due to habitat loss and habitat degradation, resulting in many species now being classified as threatened. Many butterfly species are further endangered by the additional threats of fragmentation, agricultural chemicals, climate change and introduced predators. In Tasmania, Australia, the threatened ptunarra brown butterfly (Oreixenica ptunarra) has recently come under threat from predation by introduced vespid wasps, which have the potential to further reduce their numbers, possibly causing local extinctions. The nature of this new threat and possible conservation actions to mitigate it are the subject of this thesis. The present study investigated whether vespid wasps were having a significant impact on O. ptunarra numbers, ways of controlling the wasps or excluding them from O. ptunarra's habitat, and methods of creating new populations of O. ptunarra by translocating individuals within its historical range. Vespid wasp control was performed by using toxic baits containing fipronil, as well as directly poisoning wasp nests. Transect surveys to count vespid wasp and O. ptunarra numbers performed at wasp control sites and monitoring sites, were compared to determine whether the wasp control was effective and whether the wasps were having a negative effect on O. ptunarra numbers. Vegetation transect surveys were also performed at sites with and without O. ptunarra to determine the relationship between flora species and O. ptunarra numbers and which species O. ptunarra prefers. Translocations of O. ptunarra were attempted by moving female imagoes and eggs to suitable sites within the species' historical range to create new, self-sustaining populations. The buffer size necessary to exclude wasps from O. ptunarra habitat was also investigated by analysing the vegetation around the Poa grasslands that comprise O. ptunarra's habitat at various buffer distances, using GIS. The vegetation analysis was compared to vespid wasp and O. ptunarra numbers to determine which vegetation types affected their numbers and the buffer size required to exclude wasps from O. ptunarra habitat. It was determined that vespid wasps were having a negative impact on O. ptunarra numbers and that, when wasp numbers were controlled, O. ptunarra numbers rose marginally. Unfortunately, wasp numbers were not decreased enough to protect O. ptunarra sufficiently, suggesting that wasp control efforts need to be increased. O. ptunarra was successfully translocated to one of four release sites, with a persistent population of butterflies being detected in the following four years. Analysis of the vegetation composition at the sites determined that O. ptunarra preferred sites containing the species Poa labillardierei and P. hiemata and a high abundance of flowering nectar plant species. These attributes should be taken into consideration during the selection of potential sites for future translocations of O. ptunarra. The buffer analysis determined that plantation forests were having a significant negative effect on O. ptunarra numbers and a positive effect on vespid wasp numbers. A buffer around the Poa grasslands of 300-500 m, containing native vegetation and excluding plantation forest, was suggested as a means to exclude vespid wasps and further protect O. ptunarra.
Rights statementCopyright 2019 the author Chapter 3 appears to be the equivalent of a post-print version of an article published as: Potter-Craven, J., Kirkpatrick, J. B., McQuillan, P. B., Bell, P., 2018. The effects of introduced vespid wasps (Vespula germanica and V. vulgaris) on threatened native butterfly (Oreixenica ptunarra) populations in Tasmania, Journal of insect conservation, 22(3-4), 521-532. Post-prints are subject to Springer Nature re-use terms