South-western Western Australia is a global biodiversity hotspot renowned for exceptional diversity of plants and animals. The evolutionary processes that have generated this high biodiversity are not always clear, particularly for invertebrates, yet the area supports a very large number of endemic species that have diversified in situ. We use an integrative taxonomic approach based on adult and immature morphology, ecology, behaviour and molecular data to investigate the taxonomic status of a sympatric but seasonally isolated form (Neolucia agricola occidens Waterhouse & Lyell, 1914 form ‘Julimar’) of the polyommatine butterfly Neolucia agricola (Westwood, 1851) in south-western Western Australia. Our molecular dataset comprised 112 samples representing all Neolucia Waterhouse & Turner, 1905 species (100 COI 5′ sequences, 658 bp, plus 12 COI 3′, tRNA Leu, COII and EF1-α sequences, 3303 bp). Maximum likelihood phylogenetic analysis of the combined dataset recovered form ‘Julimar’ and N. agricola as reciprocally monophyletic, with a mean uncorrected ‘p’ pairwise divergence of 5.77% for the ‘barcode’ region of COI. Based on this and other evidence we recognise form ‘Julimar’ as a new species, Neolucia bollami Eastwood, Braby & Graham, sp. nov., sister to N. agricola and endemic to south-western Western Australia. As a result of these findings, we evaluated the evolutionary history of the two Neolucia species in WA and the processes that may have contributed to the diversification in sympatry or allopatry. We conclude that the multiple effect traits associated with a host shift, including host fidelity and temporal divergence, played an important role in the diversification process and in maintaining the reproductive integrity of the nascent allochronic species.

ZooBank: urn:lsid:zoobank.org:act:53D9AD14-9694-4B5E-889C-A8D533E7F57D