>Regarding a true brood effect on varroa reproduction, some of us have pointed out to those running tests for such an effect in naturally resistant populations in Europe that the effects of brood vs. adults need to be separated experimentally. Sealed brood has to be protected from actions of hygienic bees either by screening in the colonies, or removing to incubators.

Good post- thanks for the insights.

IMHO that is what makes the contemporary Scaramella et al research so intriguing- they isolated brood effect intraframe in three (3) distinct European populations- two (2) naturally selected and one (1) artificially selected and reported significantly elevated (but distinctly variable) brood effects in each population, all known to also exhibit hygiene behavior (also at variable levels):

https://www.sciencedirect.com/science/article/pii/S0020751923000929#s0055
 

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