> I also  frequently observe this during cool weather in springtime.  This despite zero pesticide exposure.

So, examination revealed worn wings and other signs of "old age", or is the "zero pesticide exposure" an assumption?

Years ago, I also assumed that my bees were enjoying "zero pesticide exposure" when they were working Sourwood up at elevation deep into the George Washington and Jefferson National Forests in VA, only to find that the Dept of the Interior was *daytime* aerial spraying imidacloprid to control the Hemlock Woolly Adelgid, a pest that kills Hemlock trees in a matter of weeks.  Why daytime?  Because the low-bidder crop-dusting pilot they hired had neither the instruments in his aircraft nor the night rating to fly and spray at night.

So I learned all about the Hemlock Woolly Adelgid is, while the Forest Service learned all about ex-pate preliminary injunctions.
They hired a more qualified sprayer who had night flight and IFR ratings.

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