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

of Victoria projected to become increasingly suitable over time, depending on the climate change scenario. Bactrocera neohumeralis presently occurs from the western Cape York Peninsula, Queens- land, south to Sydney, NSW [3, 7, 37]. Our model suggests that as climate changes, the range of this species may extend southward and, under some scenarios, into parts of Victoria. Previ- ous climatic analysis also suggested that this species is well adapted to conditions on the east coast of Queensland, with large populations occurring in areas north of Townsville [4]. Similar ecological characteristics are shared by B. neohumeralis and Qfly [68], yet while Qfly is preva- lent in sub-tropical and temperate areas of Queensland and NSW, B. neohumeralis is more prevalent in northern wet tropical areas [4, 5, 69]. The reason for this difference between the geographical ranges of these species is unclear, as both are polyphagous and use similar host fruits for their larval development [68, 69]. Our model for B. aquilonis indicates suitable conditions for this species in northern Queensland under baseline conditions, although it is presently only known from north-west- ern Australia [5]. The hosts of this species now include 40 commercial crops [6]. Expansion of the range of this species, or the growth of host plant industries in north-western Australia may necessitate the development of new monitoring, control and disinfestation procedures [65]. In addition, it has been argued that if B. aquilonis hybridises with Qfly, the resulting strain may

have greater potential for spread than B. aquilonis [4]. This, in turn, would require that disin- festation procedures be developed for the hybrids [65]. The distribution of B. bryoniae ranges from the Torres Strait Islands, across northern Aus- tralia, and along the east coast to north of Sydney, NSW. Our results indicate that suitable cli- mate may exist in Victoria, south of the species’ known range. However, previous studies have demonstrated that populations in northern NSW experience a marked decline in abundance through November–January [37]. This may be explained by a decline in the fruiting and flow- ering of native host trees, or seasonal climatic constraints that are not reflected in our model [37], which may also explain their absence in Victoria. Northern Queensland has the highest diversity of fruit flies in Australia, and some species with significant economic impacts are found only in this region [7]. The distribution of B. kraussi, B. musae and B. frauenfeldi is limited to north Queensland [3, 70], with recent trap data suggesting that these species do not occur south of Townsville [7]. Royer et al. [35] pre- dicted that B. frauenfeldi has suitable habitat in the Northern Territory and northern Western Australia, which is also suggested by our model. This species has expanded its range in north- ern Queensland due to continued planting of hosts, such as mango and guava [35]. Further increases within these horticulture industries in northern Queensland may increase the pest status of this fly [70]. Model errors and uncertainties

SDMs are useful for developing a broad understanding of how the distribution of suitable hab- itat may be influenced by climate change. However, the output of SDMs is known to be influ- enced by characteristics of the occurrence sample, including its size [71], sampling bias [72], and spatial autocorrelation [73], as well as the extent of the study area, selection of predictor variables [74], and selection of background points [75]. We addressed these issues by: (1) exploring alternate settings in Maxent to optimise models and reduce overfitting that may gen- erate unreliable estimates [48]; (2) reducing the number of predictor variables by assessing col- linearity; and (3) critically examining response curves. In addition, we acknowledge that the selection of a threshold for converting Maxent’s con- tinuous output into binary data (typically defined as distinguishing between “suitable” and 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 14 / 19