Inferred structure of the A. apis mating type locus. MAT-1 and MAT-2 mating types are represented by isolates “A10” and “0.5–1A”, respectively. A) MAT-1 allele containing an α-box domain transcription factor. B) MAT-2 locus containing a HMG domain transcription factor. Arrows indicate the location and direction of PCR primers used in this study. GenBank or the Bee Pests and Pathogens (AAPI) accession numbers are provided in Additional file 1:Table S1.