Hi Chris: I am interested in finding out why everyone believes that leaving the strips in over winter would produce resistant mites. Perhaps the manufacturer could point us to any studies that were done to establish the recommended 42 day application period. It would appear that it is more to ensure that two rounds of brood are treated than to discourage resistance build up. Since drones take 24 days to emerge, and are the favoured brood for mites, one would think that 48 days would be a better choice. Best regards --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.419 / Virus Database: 235 - Release Date: 13/11/2002