Morphological and Molecular Species Identification of Termites Attacking Ironwood Trees, Casuarina equisetifolia (Fagales: Casuarinaceae), in Guam

Abstract

Ironwood trees (Casuarina equisetifolia subsp. equisetifolia L.) are ecologically and economically important trees in tropical and subtropical regions of the Indo-Pacific. Ironwood is one of the dominant tree species in Guam, but since 2002, this tree has been declining dramatically. A previous study showed that numerous sick or dead trees were under termite attack. However, the species of termites were not identified. As a first step to investigate causal relationships between termites and ironwood tree death, we assigned termites collected from ironwood trees to species using a combination of morphological characters and DNA barcoding of the 12S, 16S, COI, COII, and ITS2 regions. Based on morphology and comparisons to reference sequences in NCBI GenBank, the most likely species assignments were Nasutitermes takasagoensis (Nawa) (Blattodea: Termitidae) found to infest 45 trees, followed by Coptotermes gestroi (Wasmann) (Blattodea: Rhinotermitidae) (2 trees), Microcerotermes crassus Snyder (Blattodea: Termitidae) (2 trees), and an additional unidentified Microcerotermes species (1 tree) with no close sequence match to identified species in NCBI GenBank. However, taxonomic revisions and broader representation of DNA markers of well-curated specimen in public databases are clearly needed, especially for the N. takasagoensis species complex.

Keywords: DNA barcoding; Rhinotermitidae; Termitidae; ironwood tree decline; wood-feeding pest.