Terry Griswold

Patterns of widespread decline in North American bumble bees

Bumble bees (Bombus) are vitally important pollinators of wild plants and agricultural crops worldwide. Fragmentary observations, however, have suggested population declines in several North American species. Despite rising concern over these observations in the United States, highlighted in a recent National Academy of Sciences report, a national assessment of the geographic scope and possible causal factors of bumble bee decline is lacking. Here, we report results of a 3-y interdisciplinary study of changing distributions, population genetic structure, and levels of pathogen infection in bumble bee populations across the United States. We compare current and historical distributions of eight species, compiling a database of >73,000 museum records for comparison with data from intensive nationwide surveys of >16,000 specimens. We show that the relative abundances of four species have declined by up to 96% and that their surveyed geographic ranges have contracted by 23–87%, some within the last 20 y. We also show that declining populations have significantly higher infection levels of the microsporidian pathogen Nosema bombi and lower genetic diversity compared with co-occurring populations of the stable (nondeclining) species. Higher pathogen prevalence and reduced genetic diversity are, thus, realistic predictors of these alarming patterns of decline in North America, although cause and effect remain uncertain.

Sampling bee communities (Hymenoptera: Apiformes) in a desert landscape: Are pan traps sufficient?

Abstract Pan traps (colored plastic bowls) are frequently used as an efficient standardized method of sampling bee faunas. We explored the utility of pan traps in three colors compared to net collecting using simultaneous sampling at biweekly intervals throughout the flowering season (May–Sep) at 11 sites in the eastern Great Basin Desert. Pan traps deployed for one day (9:00–16:00) on average captured significantly larger samples than net collections (2 hr.) at all intervals except the latter half of May. Average species richness for net collections exceeded pan traps only during late May and late September, periods with abundant floral resources. Capture rates were similar between colors. The composition of bees was also similar; Sørensens similarity values exceeded 0.7. Color preferences for pollen specialists did not match flower color of their hosts. There were significant differences in species composition between net collections and pan trap collections. Almost one-third of the species showed a strong bias toward one method and in some cases between pan trap colors. The methods appear complementary: Halictinae and Perdita were predominantly collected in pan traps (85%); three genera, Anthidium, Colletes, Epeolus were largely or entirely detected by netting. Net collecting should be used in addition to pan traps if comprehensive inventories are desired. Though pan trapping constitutes a standardized method that avoids collector bias, it may not be unbiased; capture rates were lowest when flowering plant richness was greatest.

Substrates and materials used for nesting by North American Osmia bees (Hymenoptera: Apiformes: Megachilidae)

Abstract Nesting substrates and construction materials are compared for 65 of North America’s 139 described native species of Osmia bees. Most accounts report Osmia bees nesting in preexisting cavities in dead wood or pithy stems such as elderberry (Sambucus spp.), with cell partitions and plugs made from a pulp of finely masticated leaf tissue. Mud is widely used by species constructing free-form clumps of nest cells against stone surfaces. Some Osmia bees adopt abandoned nests of other Hymenoptera, particularly those of mud dauber wasps (Sceliphron spp.) and larger ground-nesting bees (e.g., Anthophora spp.). Reports of subterranean nesting by Osmia species are uncommon but possibly under-represent the habit, because subterranean nests are obscure and likely to be scattered. Ground- or surface-nesting habits are suspected for species that are absent from intensive trap-nesting programs in their native ranges but that otherwise have been commonly taken at flowers. The range of nesting habits and materials of European species are largely comparable, although records indicate that far more European species may nest in empty snail shells.

Detecting Insect Pollinator Declines on Regional and Global Scales

Recently there has been considerable concern about declines in bee communities in agricultural and natural habitats. The value of pollination to agriculture, provided primarily by bees, is >

Might Flowers of Invasive Plants Increase Native Bee Carrying Capacity? Intimations From Capitol Reef National Park, Utah

200 billion/year worldwide, and in natural ecosystems it is thought to be even greater. However, no monitoring program exists to accurately detect declines in abundance of insect pollinators; thus, it is difficult to quantify the status of bee communities or estimate the extent of declines. We used data from 11 multiyear studies of bee communities to devise a program to monitor pollinators at regional, national, or international scales. In these studies, 7 different methods for sampling bees were used and bees were sampled on 3 different continents. We estimated that a monitoring program with 200-250 sampling locations each sampled twice over 5 years would provide sufficient power to detect small (2-5%) annual declines in the number of species and in total abundance and would cost U.S.

Interspecific geographic distribution and variation of the pathogens Nosema bombi and Crithidia species in United States bumble bee populations

2,000,000. To detect declines as small as 1% annually over the same period would require >300 sampling locations. Given the role of pollinators in food security and ecosystem function, we recommend establishment of integrated regional and international monitoring programs to detect changes in pollinator communities.

Phylogeny and biogeography of bees of the tribe Osmiini (Hymenoptera: Megachilidae)

Abstract We compared the native bees visiting the flowers of three species of invasive plants, saltcedar (Tamarix spp.) and white and yellow sweet clover (Melilotus albus, M. officinalis), with those visiting seven concurrently blooming native plant species in mid-summer at three sites in Capitol Reef National Park, Utah. Overall, as many total species of bees visited the flowers of the three invasive plant species as visited the seven natives. On average, invasive species were visited by twice as many bee species as were natives. With a single exception, visitors of invasives were generalist bees, rather than specialists. Colletes petalostemonis, the only native legume specialist recorded, was an abundant forager on the flowers of both species of Melilotus, demonstrating that at least some specialist bees will move to invasive plants that are closely related to their usual hosts. Species abundant on the flowers of invasives tended to collect both pollen and nectar, suggesting that bees are using pollen of Tamarix and Melilotus to provision their offspring. We argue that invasives with entomophilous flowers are unlikely to either facilitate the reproduction of uncommon native plants or consistently compete with them for pollinators. Rather, they are likely, over time, to selectively increase the carrying capacity and population size of native bees, specifically generalists, and specialists of closely related plant species.

The reproductive biology and effective pollinators of the endangered beardtongue Penstemon penlandii (Scrophulariaceae)

Several bumble bee (Bombus) species in North America have undergone range reductions and rapid declines in relative abundance. Pathogens have been suggested as causal factors, however, baseline data on pathogen distributions in a large number of bumble bee species have not been available to test this hypothesis. In a nationwide survey of the US, nearly 10,000 specimens of 36 bumble bee species collected at 284 sites were evaluated for the presence and prevalence of two known Bombus pathogens, the microsporidium Nosema bombi and trypanosomes in the genus Crithidia. Prevalence of Crithidia was ≤10% for all host species examined but was recorded from 21% of surveyed sites. Crithidia was isolated from 15 of the 36 Bombus species screened, and were most commonly recovered from Bombus bifarius, Bombus bimaculatus, Bombus impatiens and Bombus mixtus. Nosema bombi was isolated from 22 of the 36 US Bombus species collected. Only one species with more than 50 sampled bees, Bombus appositus, was free of the pathogen; whereas, prevalence was highest in Bombus occidentalis and Bombus pensylvanicus, two species that are reportedly undergoing population declines in North America. A variant of a tetranucleotide repeat in the internal transcribed spacer (ITS) of the N. bombi rRNA gene, thus far not reported from European isolates, was isolated from ten US Bombus hosts, appearing in varying ratios in different host species. Given the genetic similarity of the rRNA gene of N. bombi sampled in Europe and North America to date, the presence of a unique isolate in US bumble could reveal one or more native North American strains and indicate that N. bombi is enzootic across the Holarctic Region, exhibiting some genetic isolation.

Phylogeny of the bee family Megachilidae (Hymenoptera: Apoidea) based on adult morphology

The Osmiini (Megachilidae) constitute a taxonomically and biologically diverse tribe of bees. To resolve their generic and suprageneric relationships, we inferred a phylogeny based on three nuclear genes (Elongation factor 1-alpha, LW-rhodopsin and CAD) applying both parsimony and Bayesian methods. Our phylogeny, which includes 95 osmiine species representing 18 of the 19 currently recognized genera, is well resolved with high support for most basal nodes. The core osmiine genera were found to form a well-supported monophyletic group, but four small genera, Noteriades, Afroheriades,Pseudoheriades and possibly Ochreriades, formerly included in the Osmiini, do not appear to belong within this tribe. Our phylogeny results in the following taxonomic changes: Stenosmia and Hoplosmia are reduced to subgeneric rank in Hoplitis and Osmia, respectively, Micreriades is recognized as a subgenus in Hoplitis and the subgenus Nasutosmia is transferred from Hoplitis to Osmia. We inferred a biogeographic scenario for the Osmiini applying maximum likelihood inference and models of character evolution. We provide evidence that the Osmiini originated in the Palearctic, and that extensive exchanges occurred between the Palearctic and the Nearctic. The latter finding may relate to the fact that many osmiine species nest in wood or in stems, facilitating dispersal by overseas transport of the nests.

Obtaining a better taxonomic understanding of native bees: where do we start?

Penlands beardtongue, a rare endemic plant of the Colorado Plateau, displays a mixed breeding system. Plants are partially self-compatible but set more fruits when cross-pollinated than when self-pollinated. Fruit production is significantly increased by pollinators. However, in two years of study there was no indication that fruit set was being limited by inadequate pollinator visitation. Pollinator effectiveness was judged by correlating bee behavior at the flowers with analysis of the pollen carried on bee bodies. The most important pollinators were native megachilid bees, particularly in the genusOsmia. The bees that pollinate Penlands beardtongue are essential to its reproduction and must be preserved along with this rare plant.