First record of Doleschallia tongana (Lepidoptera: Nymphalidae) for Guam Island

Introduction

On October 23, 2017, a butterfly was taken from the underside of a leaf of soursop, Annona muricata, by a student (JM) assembling an insect collection as a requirement for the General Entomology course at the University of Guam. The collection site was the University of Guam campus in Mangilao, Guam (13.430478° N, 144.800419° E).

The specimen was pinned, images were made (Figure 1), documented in iNaturalist¹ and deposited in the University of Guam insect collection (Accession code: iNat8515898).

Figure 1. First specimen of Doleschallia tongana collected on Guam.

This specimen does not match any of the descriptions in Butterflies of Micronesia², the standard reference for Guam’s butterflies.

Identification

Digital images of the specimen were sent to DB and JT for identification. On 7 November 2017, DB tentatively identified the specimen as a species in the genus Doleschallia, and indicated it possibly belonging to the bisaltide complex. On 24 February, 2018 JT determined the butterfly as Doleschallia tongana Hopkins, 1927, based on images and comparison with the extensive collections of the Natural History Museum, London.

In common with other species in the “bisaltide species-group, D. tongana is individually variable.

The convex outer margin of the forewing; the general appearance of the specimen; and geography all suggest D. tongana (tongana Hopkins, 1927, is a name to replace drusias Fabricius, 1781, the type locality for which is Tonga). Some minor ‘unusual’ features include the fact that tongana usually has a sub-apical ‘half-moon’ series of 4–5 spots on the forewing, lacking in this specimen, which only has two, but this lies within the wide individual variation of the species. Considering a distribution of Papua New Guinea (including the Bismarcks), the Solomon Islands, Fiji, Samoa, Tonga and New Caledonia, we are confident of associating this specimen with D. tongana. No doubt further material will confirm this association in due course. The species-group is in need of some revision³. The GBIF Backbone Taxonomy lists the accepted name for this taxon as Doleschallia bisaltide subsp. tongana Hopkins, 1927⁴. However, the taxon record is tagged as a "name parent mismatch" issue.

D. tongana is listed in the iNaturalist database⁵ and has been assigned the vernacular name ’Pacific orange leafwing’.

Geographical distribution

D. tongana, as it is currently understood, occurs throughout much of New Guinea, including the island groups in the east (see above).

Occurrence of D. tongana in Samoa is a relatively recently recorded range expansion. It was first detected on Tutuila Island in American Samoa in 1997⁶. Cook and Vargo 2000⁶ state that "The inclusion of Samoa in this species’ range by Parsons, 1998⁷ appears to be based on a misreading of Hopkins (1927)."

Description of caterpillar

Cook and Vargo 2000⁶ provide a description of a last instar D. tongana caterpillar:

“Just prior to pupation, the caterpillar measured ca. 50 mm in length. It possessed a black ground color with light speckling dorsally and prominent cream colored stripes running longitudinally, located dorso-laterally and ventro-laterally. Each body segment had seven prominent black spines, with numerous smaller secondary spines. The base of each primary spine was pale metallic blue. From a distance, the most prominent features of the caterpillar are the black ground color with metallic blue spots, and the pair of light parallel stripes running longitudinally on each side.“

Only a few larval host plants have been recorded for D.tongana (Table 1).

Discussion

An informal survey has been initiated on Guam to search for more specimens of D. tongana and to record host plants.

This insect has the potential to do economic damage because it has been reported to feed on breadfruit, Artocarpus altilis⁸.

Data availability

All data underlying the results are available as part of the article and no additional source data are required.