DEFORMED WING VIRUS (DWV) TRANSMISSION ACROSS POLLINATORS OF HAWAI‘I

Abstract

These studies explore the impact Deformed wing virus (DWV) on the pollinators of Hawai‘i. DWV is a well-studied virus, now commonly associated with the European honey bee, Apis mellifera (Hymenoptera: Apidae), populations. The documented decline of honey bee populations worldwide led past researchers to determine this virus played a vital role in their dwindling numbers. Research attention had now shifted to look at the DWV presence in non-Apis communities in the mainland, but only recently has research explored the unique ecology Hawai‘i offers. The first chapter investigates the indirect role of the Varroa destructor mite, a honey bee pest, and how its introduction to the state of Hawai‘i in 2007, influences the continued spread of DWV, not only within honey bee communities, but to surrounding insect populations. In this study, we utilized the limited distribution of the Varroa mite in the Hawaiian archipelago to compare DWV prevalence on non-Apis flower visitors, and test whether Varroa presence is linked to a viral spillover to these populations. We select the two islands: O‘ahu, where V. destructor has been present since 2007, and Maui, where the mite remains absent. Individuals of A. mellifera, Ceratina smaragdula, and Polistes spp. were assessed and used to compare the DWV prevalence in the Hymenoptera community of the two islands. DWV was detected in the non-Apis Hymenoptera collected from O‘ahu but was absent from samples collected on Maui. These results suggest an indirect, but significant, increase on the DWV prevalence in the Hymenoptera community in mite-infected islands. The second study focused on the DWV prevalence in the bee genus, Hylaeus (Hymenoptera: Colletidae). The Hawaiian Islands are home to more than 60 endemic species of Hylaeus, commonly referred to as yellow-faced bees. Their ecological history and distribution are unique to the archipelago and their numbers have unfortunately dwindled in the past years. The decrease in populations have to do with many factors which include destruction of natural habitats, the introduction of predatory wasps, and the introduction of ants to the islands. The introduction of pathogens and diseases has also been suspected but not documented. We sampled populations of two non-native species of Hylaeus, on Oahu, to determine their DWV status. Additionally, DWV strains for these species are reported. For the first time, DWV presence was found for this genus in Hawai‘i. DWV viral levels of combined Hylaeus species were comparable to those of Hymenoptera in previous Hawai‘i studies. However, when divided across the two species, H. albonitens had almost twice the DWV prevalence when compared to H. strenuus. These results may indicate that despite being ecologically and evolutionarily closely related, DWV prevalence can still have great variability within a genus, and DWV strain types vary across non-Apis groups. The third chapter sets a foundation for future DWV research in Hawai‘i, by making a preliminary list of the groups of flower-visiting insects that carry DWV at sites where they overlap with honey bee populations. Pollinators, which rely on flowers as their food source, also encounter a myriad of pathogens when visiting these sites. Yet, determining when and which pathogen a pollinator will encounter during a flower visit is a difficult task. The disease interactions between flower visiting insects is a diverse and complex web, made up of many variables and factors. By mapping these interactions, we can start to better understand the spread of diseases between pollinator communities at these sites, especially when we consider the potential impact DWV may have on these communities. This survey, conducted over a period of 4 years, across various sites on the island of O‘ahu, explores the prevalence of DWV in different flower-visiting insects, and how these viral rates differ over time and across species.