Herbarium Specimens Reveal Putative Insect Extinction on the Deforested Island of Mangareva (Gambier Archipelago, French Polynesia)

Human activities are expected to result in extinction of many organisms in taxonomically neglected lineages; however, actually documenting these extinctions is very difficult for soft-bodied organisms that do not leave a subfossil record. Subfossil and historic records reveal that human-induced extinction has been particularly marked for gastropods and terrestrial vertebrates on Pacific islands, but whether human activities resulted in similar biodiversity loss in soft-bodied, taxonomically neglected animals (such as insects) remains unclear. However, in cases in which specialized plant-feeding insects leave diagnostic feeding damage on plants, herbarium specimens coupled with resurvey efforts may indicate potential extinctions or extirpations during historic times. Here, I report the discovery of leaf mines in herbarium specimens of the plant Phyllanthus wilderi (Phyllanthaceae: Glochidion sensu lato) from the island of Mangareva (Gambier Islands, French Polynesia). These mines were not rediscovered in recent surveys on Mangareva but are similar to those made today by leaf-mining moths (Lepidoptera: Gracillariidae) on many other islands in southeastern Polynesia. This is, to the best of my knowledge, the first report of a potential insect extinction from Mangareva, an island already well known for its history of anthropogenic habitat destruction and biodiversity loss. This result indicates that herbarium specimens may be used to identify potentially extinct and extirpated insect taxa. Future biodiversity surveys on Pacific islands and elsewhere should use herbarium specimens as a guide both to documenting potential extinctions and to search for rediscovery of rare taxa.