Mite eruption late fall - change in brood rearing?

[JWChesnut]

After a pleasant summer with virtually no varroa, mites erupted in my hives in October.  Drones had been ejected before the outbreak.  I live in coastal California and temps encourage forage activity through the fall, though the nectar in the brown hills doesn't really support any surplus.  Dwarf Wing Virus really devastated some hives-- in fact the DWV seems more severe than the relatively mild mite counts.

Have others observed a sudden peak in mites and especially DWV in the period when hives have ejected their drones and converted to a winter brood pattern?

I know varroa follows an epidemic doubling pattern, but the summer counts didn't seem to build-- and were lower to non-existent in August-September than May.   I'm supposing that winter brood may take a day or two longer to hatch and the extra time might push the mite and DWV infection, or the absence of drones might concentrate mites on the winter brood.

I drizzled 3.2% Oxalic in 50:50 syrup today.  I was waiting for the "winter cluster" but on the coast that occurs only sporadically in December.  Couldn't put off treatment and still expect to have survival.

[buzzbee]

When the brood break comes,the varroa move out of the capped cells and onto the host.It makes the mite more susceptible to treatment.If your bees have little brood at this time,it is a good time to treat with oxalic.The treatments now actually are helping the health of the hive for next winter.

[Michael Bush]

It always seemed that the explosion of the Varroa population in the fall was more than I could account for by just all of the mites having no brood to hide in anymore.  But there is also robbing and bringing back those mites.  I had never thought of a longer brood cycle because of colder weather, but that  might be something to consider.

[rdy-b]

  when was your last treatment -before this one-the time between treatments
 has more impact on threshold limits than the season in my location-your bees should
 have plenty brood at this time-that means mites under the cap-RDY-B