The taxonomy and ecology of D elias aestiva Butler, 1897 stat. rev. ( L epidoptera: P ieridae), a unique mangrove specialist of E uphorbiaceae from northern A ustralia

Taxonomic investigations of the D elias mysis ( F abricius, 1775) complex from northern A ustralia indicate two additional species in the A ustralian fauna: D elias aestiva   B utler, 1897 stat. rev. and D elias lara ( B oisduval, 1836). The latter species, which is illustrated from A ustralia for the first time, was until recently known under the name D elias mysis onca   F ruhstorfer, 1910. Evidence from adult morphology (male genitalia), colour pattern of the adult and immature stages, behaviour, and ecology indicates substantial phenotypic divergence between D . aestiva and D . mysis . Within A ustralian limits, all three taxa are allopatric: D aestiva is endemic to the T op E nd, N orthen T erritory, D . mysis mysis is restricted to northern and north‐eastern Q ueensland, whereas D elias lara lara is known only from three specimens from the T orres S trait islands, Q ueensland. D elias aestiva is perhaps the most remarkable member of the complex and indeed the genus, breeding in tropical mangrove habitats in coastal estuarine areas where the larvae specialize on mature foliage of the tree E xcoecaria ovalis   E ndl. ( E uphorbiaceae). This host preference is novel given the general tendency of D elias to feed on hemiparasitic plants in the order S antalales ( L oranthaceae, S antalaceae and V iscaceae). Under laboratory conditions, however, larvae successfully completed development on the mistletoe genera A myema , D endrophthoe and D ecaisnina (all L oranthaceae) with no significant reduction in larval survival. These findings, together with phylogenetic hypotheses of the A poriina and D elias , indicate a recent evolutionary host shift from L oranthaceae to E uphorbiaceae. The foliage of E xcoecaria produces toxic latex, which is composed of a variety of secondary plant compounds, including diterpenoids, triterpenoids, alkaloids and phorbol esters. The mechanism of detoxification has not been established, although the larvae of D . aestiva are gregarious, regurgitate fluid as part of their chemical defence, and the adults are highly aposematic. Adults are seasonal, being chiefly on the wing during the cooler dry season; during the wet season, the larval food plant is seasonally deciduous and it is suspected that the butterfly undergoes pupal diapause. The cryptically coloured green pupa and tendency to pupate singly in concealed situations of D . aestiva are highly unusual traits among D elias and are hypothesized to be adaptive responses associated with pupal diapause during the wet season. The unique habitat association, novel food plant specialization, and restricted distribution of D . aestiva emphasizess the biogeographical peculiarities of northern A ustralia, especially patterns of historical (vicariant) differentiation between the T op E nd and C ape Y ork P eninsula within the A ustralian M onsoon T ropics. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society , 2012, 107 , 697–720.