Impacts of climate change on high priority fruit fly species in Australia

species is projected to expand and shift south regardless of whether novel environments are included or excluded (Figs 1 and 2 and Table 2). When regions containing novel climate are included, 31.6% of Australia (i.e. ~2,400,800 km2) is projected to have been suitable in the baseline period for at least one of the 11 species, increasing to more than half of the continent by 2070 (Table 2). However, only Queensland’s Wet Tropics is likely to be suitable for all 11 species into the future. When novel environments are excluded from maps, less than 30% of Australia is projected to be suitable for at least one of the species by 2070 (Table 2). Hence, exclusion of novel envi- ronments substantially impacts the size of suitable habitat (i.e., projections of suitable habitat frequently occur in areas with novel climatic conditions). However, extrapolation primarily occurs in northern regions of Western Australia, Northern Territory and the Cape York Pen- insula, decreasing confidence in projections across these regions. From the Wet Tropics and southward, little extrapolation occurs. As such, the Wet Tropics bioregion is projected to remain suitable for 10–11 species, indicating that the major commercial host plants within this bioregion may continue to be at risk of invasion by most or all of these high priority species. Major commercial host plant regions along the coastal strip of south-east Queensland and north-east NSW are likely to have areas that are suitable under all future scenarios for B. bryo-

niae, B. jarvisi, C. capitata and Z. cucumis (S1 File). Under some scenarios, these regions may also be suitable for B. halfordiae, B. neohumeralis and B. tryoni (S1 File). Some major commer- cial host plant regions in southern NSW and Victoria are also projected to be suitable for B. jarvisi, B. tryoni and C. capitata under all scenarios (S1 File) and for B. halfordiae, B. neohu- meralis and Z. cucumis under a limited number of scenarios (S1 File). Horticultural regions in Tasmania are projected as suitable for B. jarvisi, B. tryoni and C. capitata (S1 File). In south-west Western Australia, major horticulture regions are likely to remain suitable for B. jarvisi, B. tryoni and C. capitata, although the latter species is currently not found in this region (S1 File). Commercial horticulture regions in northern region of the Northern Terri- tory are also likely to be suitable for B. jarvisi, B. kraussi, B. musae, B. tryoni and Z. cucumis under all scenarios, and B. frauenfeldi under some climate scenarios. Discussion Our study suggests that the Wet Tropics bioregion has climatically suitable habitat for the larg- est number of high priorities tephritid pest species under both baseline conditions (1960– 1990) and as a result of climate changes projected to occur through to 2070. Cape York Penin- sula and the Northern Territory are also likely to be vulnerable, although novel climates are projected to occur in these regions, and the extrapolation of SDMs to these conditions may be

unreliable. The east coast of Australia is also likely to remain suitable for multiple species until at least 2070. As such, major horticulture regions in north-western Australia, the Northern Territory, southern-central regions of NSW, southern Victoria and north Tasmania may become increasingly suitable to high priority fruit flies. Two species, B. tryoni (Qfly) and C. capitata (Medfly), are projected to have suitable conditions in all states and territories of Aus- tralia, under all considered climate change scenarios, until at least 2070. Over the past 30 years, numerous studies have modelled suitable habitat for Qfly using CLI- MEX and Maxent, at various spatial resolutions [8, 40, 58, 59] and extents. While generally giv- ing similar projections, a key difference is that our model projects Tasmania to have been suitable in the baseline period (1960–1990), whereas fine scale modelling using CLIMEX indi- cates that it is unlikely to become suitable prior the mid-21st century [59]. Our models for both Qfly and Medfly were driven primarily by temperature parameters, rather than precipitation. Previous studies have identified climatic constraints on the Impacts of climate change on high priority fruit fly species in Australia PLOS ONE | https://doi.org/10.1371/journal.pone.0213820 February 13, 2020 10 / 19