The endangered orangeblack Hawaiian damselfly (Megalagrion xanthomelas) is a lowland inhabitant of freshwater and brackish wetland environments. Formerly one of the most widely distributed native insects in Hawai‘i, it now appears restricted to small populations on the islands of O‘ahu, Moloka‘i, Maui, and Hawai‘i. On Hawai‘i island, anchialine pools provide important habitat for M. xanthomelas, and Kaloko-Honokōhau National Historical Park (Park) supports one of only a few documented populations on the western side of the island. This study aimed to estimate the population size of M. xanthomelas at this Park, characterize its habitat, and identify substrates on which females oviposit eggs. We conducted visual surveys for adult M. xanthomelas at anchialine pools during June 2016–August 2017. On average, the observed population was 10.7 individuals per month (range = 5–20; standard error = 1.3). Males were observed 6.1 times more frequently than females, likely reflecting the less cryptic nature of males compared to females. Females exhibited oviposition behavior on a variety of substrates, but small branches were used most frequently. Factors restricting this population are poorly known, but invasive fish may limit its distribution across the Park. Removal of invasive fishes from anchialine pools and ‘Aimakapā Fishpond may restore much habitat for this rare species in the Park.
