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Title:The role of pathogens in the decline of North American bumble bees with a focus on the microsporidium nosema bombi
Author(s):Cordes, Nils
Advisor(s):Solter, Leellen F.
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Bumble bee decline
Bombus sp.
Nosema bombi
Crithidia bombi
Abstract:Several bumble bee species in North America appear to have undergone rapid declines in abundance and distribution. Bombus franklini is probably extinct; B. occidentalis and B. affinis currently are experiencing extensive range reductions; and a shift in the range of B. pensylvanicus indicates a similar trend. In an unprecedented survey, 9,909 specimens of 36 bumble bee species in 38 states were collected and evaluated for presence of pathogens, but I focused on the microsporidium Nosema bombi and its prevalence in two putatively declining species, B. occidentalis and B. pensylvanicus, and four stable species, B. impatiens, B. bimaculatus, B. bifarius and B. vosnesenskii. Crithidia bombi, a protozoan bumble bee pathogen was common in some species, particularly B. mixtus, B. impatiens and B. bimaculatus. It was present in 2.6% of all examined specimens and occurred across most of the United States. Nosema bombi was recovered from 2.9% of all collected specimens. It was present in bumble bee populations in 26 of the surveyed states, predominantly in B. occidentalis (37%) and B. pensylvanicus (15.2%), the species considered to be declining. N. bombi infections occurred in these two hosts in more than 40% of surveyed sites, significantly more than for other hosts. Recovered N. bombi isolates were genetically identical to European strains. The only variation in the pathogen among host species was found in the internal transcribed spacer (ITS) region of the rRNA gene, indicating the presence of multiple alleles and a single nucleotide polymorphism (SNP) that may be unique to North American bumble bee species. Slight variation in infectivity was documented, with only B. occidentalis bees developing infections after oral inoculations. It is still unclear whether N. bombi is contributing to population declines, but correlation of declining species and pathogen prevalence suggest higher susceptibility of these host species. The findings of this thesis support the hypothesis that N. bombi is Holarctic in distribution.
Issue Date:2010-05-18
Rights Information:Copyright 2010 Nils Cordes
Date Available in IDEALS:2010-05-18
Date Deposited:May 2010

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