Short communication. Control of American foulbrood disease in Argentine commercial apiaries through the use of queens selected for hygienic behaviour

American foulbrood (AFB), caused by the bacterium Paenibacillus larvae is a serious disease of honey bees worldwide that inflicts considerable economic losses on beekeepers. The aim of this investigation was to determine the spread of AFB in a commercial apiary headed by queens selected for hygienic behaviour (HB), and to estimate the agreement between microbiological methods for the isolation of P. larvae from honey samples (HS) or bee samples (BS). All work was undertaken in a commercial apiary that showed visual signs of AFB infection. Hives positive for AFB were isolated from the apiary and the queens of the remaining hives replaced by others selected for HB. The prevalence of AFB was then recorded by monitoring visual signs of the disease, and via the isolation of P. larvae spores from HS and BS. The hives showed no clinical signs of AFB although HS testing showed 50% to harbour P. larvae spores after one year. This percentage decreased to 26% by the end of the study. The spore loads of the HS and BS were low (between 0.33 and 5 CFU/plate for HS and 0.33 and 12 CFU/plate for BS). No agreement was seen between the two microbiological isolation methods as assessed by the Kappa coefficient (P > 0.05). Sixty percent false negatives were recorded for the HS method. The BS method was more sensitive and is the best option for the early diagnosis of AFB; this, plus the use of HB lines may be sufficient for the control of this disease. Additional key words: Apis mellifera, honey bees, microbiological methods, Paenibacillus larvae, prevalence.