Chromosome-scale genome assembly of the rusty patched bumble bee, Bombus affinis (Cresson) (Hymenoptera: Apidae), an endangered North American pollinator.

The rusty patched bumble bee, Bombus affinis, is an important pollinator in North America and a federally listed endangered species. Due to habitat loss and large declines in population size, B. affinis is facing imminent extinction unless human intervention and recovery efforts are implemented. To better understand B. affinis biology and population genetic and genomic landscapes, we sequenced and assembled the B. affinis genome from a single haploid male. Whole genome HiFi sequencing on PacBio coupled with HiC sequencing resulted in a complete and highly contiguous contig assembly that was scaffolded into a chromosomal context, resolving 18 chromosomes distributed across the 365.1 Mb assembly. All material for both HiFi and HiC sequencing was derived from a single abdominal tissue segment from the single male. These assembly results, coupled with the minimal amount of tissue destructively sampled, demonstrate methods for generating contiguous and complete genomic resources for a rare and endangered species with limited material available and highlight the importance of sample preservation. Precise methods and applications of these methods are presented for potential applications in other species with similar limitations in specimen availability and curation considerations.

Novel Microsatellite Markers for Osmia lignaria (Hymenoptera: Megachilidae): A North American Pollinator of Agricultural Crops and Wildland Plants.

Comprehensive decisions on the management of commercially produced bees, depend largely on associated knowledge of genetic diversity. In this study, we present novel microsatellite markers to support the breeding, management, and conservation of the blue orchard bee, Osmia lignaria Say (Hymenoptera: Megachilidae). Native to North America, O. lignaria has been trapped from wildlands and propagated on-crop and used to pollinate certain fruit, nut, and berry crops. Harnessing the O. lignaria genome assembly, we identified 59,632 candidate microsatellite loci in silico, of which 22 were tested using molecular techniques. Of the 22 loci, 12 loci were in Hardy-Weinberg equilibrium (HWE), demonstrated no linkage disequilibrium (LD), and achieved low genotyping error in two Intermountain North American wild populations in Idaho and Utah, USA. We found no difference in population genetic diversity between the two populations, but there was evidence for low but significant population differentiation. Also, to determine if these markers amplify in other Osmia, we assessed 23 species across the clades apicata, bicornis, emarginata, and ribifloris. Nine loci amplified in three species/subspecies of apicata, 22 loci amplified in 11 species/subspecies of bicornis, 11 loci amplified in seven species/subspecies of emarginata, and 22 loci amplified in two species/subspecies of ribifloris. Further testing is necessary to determine the capacity of these microsatellite loci to characterize genetic diversity and structure under the assumption of HWE and LD for species beyond O. lignaria. These markers will inform the conservation and commercial use of trapped and managed O. lignaria and other Osmia species for both agricultural and nonagricultural systems.

Genetic and Usurpation Data Support High Incidence of Bumble Bee Nest Invasion by Socially Parasitic Bumble Bee, Bombus insularis.

Cuckoo bumble bees (Psithyrus) (Lepeletier, 1832) (Hymenoptera: Apidae) are a unique lineage of bees that depend exclusively on a host bumble bee species to provide nesting material, nutritional resources, and labor to rear offspring. In this study, we document usurpation incidence and population genetic data of Bombus insularis (Smith, 1861) (Hymenoptera: Apidae), a bumble bee species in the Psithyrus subgenus, on field-deployed B. huntii colonies in northern Utah, United States. Within 12 d of deploying B. huntii Greene, 1860 (Hymenoptera: Apidae) colonies at two field sites, 13 of the 16 colonies contained at least one established B. insularis female. Although our results demonstrate that field-deployed bumble bee colonies are highly susceptible to B. insularis usurpation, applying a fabricated excluder to prevent the inquiline from invading a colony was 100% effective. Sibship analysis using microsatellite genotype data of 59 B. insularis females estimates that they originated from at least 49 unique colonies. Furthermore, sibship analysis found siblings distributed between the field sites that were 7.04 km apart. Our result suggests that B. insularis females have the capacity to disperse across the landscape in search of host colonies at distances of at least 3.52 km and up to 7.04 km. Our study underscores the detrimental impact B. insularis usurpation has on the host bumble bee colony. As B. insularis significantly impacts the success of bumble bee colonies, we briefly discuss how the utilization of excluders may be useful for commercial bumble bee colonies that are used to pollinate open field crops.

The Invasion of Megachile policaris (Hymenoptera: Megachilidae) to Hawai'i.

Islands are insular environments that are negatively impacted by invasive species. In Hawai'i, at least 21 non-native bees have been documented to date, joining the diversity of >9,000 non-native and invasive species to the archipelago. The goal of this study is to describe the persistence, genetic diversity, and natural history of the most recently established bee to Hawai'i, Megachile policaris Say, 1831 (Hymenoptera: Megachilidae). Contemporary surveys identify that M. policaris is present on at least O'ahu, Maui, and Hawai'i Island, with the earliest detection of the species in 2017. Furthermore, repeated surveys and observations by community members support the hypothesis that M. policaris has been established on Hawai'i Island from 2017 to 2020. DNA sequenced fragments of the cytochrome oxidase I locus identify two distinct haplotypes on Hawai'i Island, suggesting that at least two founders have colonized the island. In their native range, M. policaris is documented to forage on at least 21 different plant families, which are represented in Hawai'i. Finally, ensemble species distribution models (SDMs) constructed with four bioclimatic variables and occurrence data from the native range of M. policaris predicts high habitat suitability on the leeward side of islands throughout the archipelago and at high elevation habitats. While many of the observations presented in our study fall within the predicted habitat suitability on Hawai'i, we also detected the M. policaris on the windward side of Hawai'i Island suggesting that the SDMs we constructed likely do not capture the bioclimatic niche flexibility of the species.