According to the Insecticide Resistance Action Committee (RAC), Apivar is in Group 19 and Apistan is in Group 3, See http://extension.arizona.edu/sites/extension.arizona.edu/files/resourcefile/resource/marcop/IRAC%20MOA%20brochure_v4%202_Oct10.pdf ( or http://preview.tinyurl.com/azo4pzg ) So resistance to one should not translate to resistance to the other. Alternating between Apivar and Apistan could be a good idea since they have different modes of action and the odds against any one mite being resistant to both and also being fit seem small. I also wonder if any tests have been done using strips of each at the same time. *********************************************** The BEE-L mailing list is powered by L-Soft's renowned LISTSERV(R) list management software. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html Guidelines for posting to BEE-L can be found at: http://honeybeeworld.com/bee-l/guidelines.htm