Hi John

> My bees have a way higher percentage of drone infestation
> (varroa) in spring than in later summer

Is it the case that your bees have relatively few drone brood in spring and many in summer?  A colony holding Varroa numbers stable would have a high proportion of drone brood infested when there are few, and a low proportion when there are many simply because there is an overabundance of brood for them then.

all the best

Gavin

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