Some of the highest levels of HMF that I encountered were during the first wave of problems in 2006-2007. Although our surveys and later work indicated that HMF was not associated with massive colony depopulation, we did find one beekeeper who did have an HMF kill - he stored his syrup in a steel tank on a truck, had a stirring unit, and because his morning were cold, was heating the syrup in the tank to make it flow better. Metal + heat is a bad combination when it comes to HMF formation.
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