Identifying key threats to a refugial population of an endangered Hawaiian moth

Abstract

Abstract The dramatic worldwide decline in insect biodiversity has highlighted the need for insect conservation. However, management is hindered by incomplete knowledge of what drives species mortality. Even when drivers are identified, it can be difficult to quantify their effects. Using data from six naturally occurring cohorts observed over 2 years, we created partial ecological life tables for Blackburn's sphinx moth, Manduca blackburni, a federally listed endangered moth endemic to the Hawaiian Islands. We identified mortality factors impacting eggs and quantified mortality for both eggs and larvae of M. blackburni. Life table analysis demonstrated that total mortality was above 99%, highlighting the severe threats faced by this critically endangered species. Disappearance, likely driven by invasive ants, and predation were the two primary causes of egg mortality. While egg mortality contributed the most to total mortality, apparent mortality was high for all developmental stages observed, indicating substantial risk throughout the moth's pre‐adult life cycle. Our results show that M. blackburni likely experiences unsustainably high mortality across its pre‐pupal life stages and highlight the dangers invasive predators pose for the focal species and naïve species in general. The threats facing M. blackburni may bear directly on other declining insect species and their management. Future conservation efforts should focus on mitigating the impacts of invasive ants and other arthropod predators to promote species recovery for this charismatic Hawaiian endemic.