Diversity and community structure of macro-moths (Lepidoptera) in lowland forest habitats on Viti Levu, Fiji.

The Fiji Islands are a biodiversity hotspot with a large proportion of their flora and fauna being endemic. Over the last 200 years since the colonial era taxonomic studies have been conducted and a relatively large proportion of the country’s biodiversity has been documented. However, more detailed information on distribution and population structure of some taxa remains virtually unknown. The total number of insect species inhabiting the Fiji group is estimated to be in excess of 3,500. Out of all the island groups in the Pacific, Fiji has one of the highest numbers of endemic insect genera, second only to Hawaii. In terms of the study of Lepidoptera in Fiji, the research of its ecology has had a greater focus on butterflies rather than on moths, highlighting an important gap which this study aims to address. In general, this study aims to investigate the abundance, species richness and assemblages of macro-moth fauna in lowland rainforests of Viti Levu and their responses to light, forest type and climate.

The first part of the study was an evaluation of sampling methods, comparing three light trap types: a manually operated mercury-vapour light trap, a ultra-violet bucket trap, and a fluorescent bucket trap. The final selection of the high-power mercury-vapour trap was based on its ability to attract a higher species richness and abundance of macro-moths within a short time period. As a result of this study, a minimal collection time of four nights was determined in order to collect a representative sample and describe the species richness, community structure and relative abundances of the macro-moth species using a high power mercury-vapour light trap.

Using the above method, a comparative study was then conducted investigating the macro-moth composition in three different types of lowland forest: native, exotic and mixed. A high diversity of macro-moths was captured in each of the forest type, with the native forest identified as the most different because of the abundance and diversity of the endemic species it contained. Noctuidae, Geometridae and the Arctiidae families were identified as potential indicator taxa for forest quality after successful application of a standard forest quality index.

A seasonality study followed investigating the macro-moth fauna in a mixed forest over a 12 month period. Significant trends were not observed when looking at changes in abundance and species richness at a family level but became more apparent at species level. A significant quantity of occurrence data was obtained during this study which has high value as a baseline study for assessing future trends.

In addition, a complete taxonomic treatment of the sampling catch from each preceding study is presented and placed in the context of an overview of the known macro-moth fauna of Fiji. As a result of this study, a new moth record for Fiji (Dactyloplusia impulsa) belonging to the Noctuidae family was made.

Overall, this study is an original contribution to the body of knowledge on Lepidopteran ecology and taxonomy in Fiji and is important baseline for future studies. The study has also yielded valuable information that can inform and feed into conservation and forest management policies through the National Biodiversity Strategic Action Plan process and help ensure sustainable development in Fiji.