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United States Department of Agriculture

Agricultural Research Service


Location: Pollinating Insect-biology, Management, Systematics Research

Title: Interspecific geographic distribution and variation of two bumble bee pathogens, Nosema bombi and Crithidia bombi, in United States populations

item Cordes, Nils
item Huang, Wei-fone
item Strange, James - Jamie
item Cameron, Sydney
item Griswold, Terry
item Lozier, Jeffrey
item Solter, Leellen

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2011
Publication Date: 11/18/2011
Citation: Cordes, N., Huang, W., Strange, J.P., Cameron, S.A., Griswold, T.L., Lozier, J.D., Solter, L.F. 2011. Interspecific geographic distribution and variation of two bumble bee pathogens, Nosema bombi and Crithidia bombi, in United States populations. Journal of Invertebrate Pathology. Journal of Invertebrate Pathology 109:209-216.

Interpretive Summary: Recently, declines in several North American bumble bees have been documented. A fungal pathogen has been implicated in the disappearance of these bees. Despite these implications, little is known about the prevalence of this pathogen and other bumble bee pathogens in natural communities. The present study sought to document the prevalence of two important bumble bee pathogen across 36 bumble bee species throughout the contiguous united states. Nearly 10,000- bumble bees were examined in the study which sampled bees from 284 sites. Through microscopic examination of bumble bee gut tissues, the levels of two pathogens, Nosema bombi and Crithidia bombi were determined in bumble bee communities. Levels of the pathogens varied significantly among species and among sampled sites, with declining species showing elevated levels of pathogens relative to most of the stable species. Globally, Nosema bombi was found in 2.9% of the bees surveyed while Crithida bombi was found in 2.7% of all the surveyed bees. To test for the possibility that a novel pathogen may have invaded from Old World bumble bees, a molecular marker was evaluated in several bumble bee specimens for variation in the DNA sequence. In general sequences matched those already know from Europe with the exception of one molecular variant. This variant was uncommon and may represent a novel north American isolate. No patterns of disease strain were found with declining and stable species. Must be written so a lay person can understand the document.

Technical Abstract: 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 rigorously test this hypothesis. In a nationwide survey of the U.S., 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 the trypanosome Crithidia bombi. Prevalence of C. bombi was =10% for all host species examined but was recorded from 21% of surveyed sites. This pathogen was isolated from 15 of the 36 Bombus species screened, and was most commonly recovered from B. bifarius, B. bimaculatus, B. impatiens and B. mixtus. Nosema bombi was isolated from 22 of the 36 collected U.S. species; prevalence reached 37.2% in Bombus occidentalis and 15.2% in B. pensylvanicus, two species that are reportedly undergoing population declines in North America. Nosema bombi was isolated from these two hosts in more than 40% of surveyed sites, significantly more than for other hosts, and spore intensity in midgut tissues was higher than in non-declining species. Variants of a tetranucleotide repeat in the internal transcribed spacer (ITS) of the N. bombi rRNA gene, thus far not reported from European isolates, were isolated from most U.S. Bombus hosts, appearing in varying ratios in different host species with the possible exception of B. occidentalis. Given the overall genetic similarity, the presence of a unique N. bombi isolate in U.S. bumble bees does not preclude introduction of an exotic strain into North America, but it could reveal one or more native North American strains and indicate that N. bombi is enzootic across the Holarctic Region, exhibiting some genetic isolation.

Last Modified: 08/17/2017
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