P. Rosenkranz notes in this excellent article http://www.moraybeedinosaurs.co.uk/V...rol-Varroa.pdf about the biology of varroa the following:
"The Korean type has worldwide spread on A. mellifera, while the Japanese / Thailand type has only been reported from A. mellifera colonies in Japan, Thailand and North and South America (Anderson and Trueman,
2000; De Guzman et al., 1998; Garrido et al., 2003; Muñoz et al., 2008). " p. 597
The first type is more virulent than the second.
What we know? In some places some queens are successful dealing with varroa mites, but when her daughters are taken to other places do not work so well.
If P. Rosenkranz is correct we can put this hypothesis: in some places some TF queens are successful at a colony level if the type of varroa that colonizes the hives is less virulent.
I have no idea if this hypothesis has already been properly tested.
Glycerin oxalic strips tested in Portugal and Spain were not as effective as the results reported in South America. One of the explanatory hypotheses is the difference in varroas' virulence in the two continents.