It was attracted towards light
Achaea robinsoni. Robinson (1974) listed this as Achaea serva. However, Holloway (1982) reported that A. serva was a species complex of which only A. robinsoni occurred in Fiji. Moths in Fiji websit records this species as A. robinsoni.
Ths is a big moth - hence its identification as A. robinsoni rather than A. janata - the other representative in this genus here in Fiji. Don't have any images to show whether the inner white bar on the hindwing is continuous or broken.
Holloway, J.D. 1982. Taxonomic appendix in Barlow, H.S. An Introduction to the Moths of South East Asia. Malayan Nature Society.
Robinson, G 1974. Macrolepidoptera of Fiji and Rotuma.
The Ophiusina are a subtribe of noctuoid moths. As such, they are placed in the tribe Catocalini of subfamily Catocalinae in the owlet moth family (Noctuidae). They do not seem to be very closely related to the Noctuinae – the core group of owlet moths – and in an alternate classification scheme, the Noctuidae are reduced in extent, and the present group is placed in a separate noctuoid family Erebidae and upranked to full tribe Ophiusini...