Fig 1.
Prevalence of M. plutonius varies widely by yard and operation for migratory (A, C, D, E, F, K) and stationary (B, H, J, M, N, marked with*) beekeepers in Michigan (2021-2022).
Each dot represents a yard grouped by operation (x-axis) with the percentage of colonies in the yard positive for M. plutonius by duplex PCR (y-axis). Boxplots show distribution and median values for the plotted yards. Operations with fewer than 3 yards (G, I, X) and yards with fewer than 5 colonies (L) were removed from this figure. Operation N had no information on clinical disease; size is not representative of disease prevalence for this operation.
Fig 2.
Percentage of asymptomatic colonies sampled in each yard that were infected as determined by PCR detection of Melissococcus plutonius, grouped by disease status of the yard.
Each dot represents a yard where 5 or more colonies were sampled. Yards with at least one symptomatic colony (more than 10 larvae affected) are on the left (blue), while yards where no clinical EFB was found are on the right (brown).
Fig 3.
Rates of both Melissococcus plutonius and clinical EFB among sampled colonies peaks in June.
Bars represent the percent of colonies inspected in each month that screened positive by duplex PCR for M. plutonius (light blue – right) and the percentage that had clinical EFB at the time of sampling (purple – left). Error bars represent the standard error for each month.
Fig 4.
Proportion of colonies with clinical disease by duplex PCR results.
‘Both’ represents colonies that screened positive for both typical and atypical strains. Error bars represent standard error.
Fig 5.
Core gene phylogenetic tree of Melissococcous plutonius strains (sequenced for this study and publicly available).
* Sequence type was determined by MLST and labeled along the tips of the tree. Heatmap shows if the strain is typical or atypical; presence, absence and subtype of pMP1 and pMP19 plasmids.
Fig 6.
Melissococcus plutonius genotypes are distributed broadly across the US. Minimum spanning networks for (A) typical isolates and (B) atypical isolates.
Nodes represents genotypes and are scaled according to the number of genotypes. Nodes are colored proportionally to the source of the genotypes (see keys). Nodes outlined in solid lines represent isolates from migratory operations. Nodes outlined in dashed lines represent isolates from stationary operations. The numbers in black and along nodes indicate the years of isolation 20xx. *: two different genotypes isolated from a single larval sample. The numbers in blue and along edges are the numbers of SNPs separating two genotypes.
Fig 7.
K-mer clustering reveals genetic variation within pMP1 and pMP19 plasmids.
Networks were constructed using the k-mers shared between the strains. The solid colored circles (nodes) represent plasmids from a single isolate of M. plutonius and related nodes are connected by lines (edges). Networks with different colored nodes represent genetic subtypes of that plasmid.