An Assessment of Nysius wekiuicola Populations and Thermal Microhabitat Conditions on Cinder Cones of the Maunakea Volcano, Hawai'

The endemic Hawaiian wekiu bug (Nysius wekiuicola) is a carnivorous scavenger that only inhabits volcanic cinder cones above ~3,500 m elevation on the mountain, Maunakea, Hawai'i. As a species of conservation concern threatened by invasive species, climate change, and habitat alteration, a greater understanding of wekiu bug populations and habitat use through time is needed to inform habitat restoration efforts and conservation management decisions. In this study, locations on a high elevation and a lower elevation cinder cone were sampled using attractant traps in a buffered random design six times from June 2016- 2017 to examine wekiu bug distribution patterns within cinder cone habitats and across seasons. A generalized linear mixed model (GLMM) was used to explore the relative importance of cinder cone characteristics (topographic aspect, surficial minerals, and elevation) hypothesized to influence wekiu bug distributions. Additionally, thermal conditions were described and compared within the insects' habitat (within 2-30 cm depth of cinder substrate). Results indicate that wekiu bugs had a highly aggregated distribution, with up to 40 times higher bug densities at the higher elevation cinder cone, and the density of bugs changed within and between cinder cones throughout the year. Our GLMM indicated that sample month, topographic aspect, and elevation on a cinder cone influences wekiu bug distributions with abundance increasing with elevation within a cinder cone, and the highest captures are predicted to be on the northeast aspects of the higher elevation cinder cone year-round. Temperature data shows multiple microclimates exist throughout cinder cone habitats at any given time, and the ash substrate layer could provide an important habitat refuge for the wekiu bug, as this layer rarely freezes. We recommend preserving contiguous cinder cone habitats for the persistence of the wekiu bug, and monitoring populations in a random sample design in known or restored habitats to effectively monitor wekiu bug densities.