> > >if I observe mite infestation rate to exceed 5%, I consistently see virus >> infection in the broodnest. If I keep the mite infestation down to less >> than 2% at highest (lower for most of the season), then the brood remains >> healthy. >> > Is this your own experience? Are there other references/experiences about > treatment thresholds? > Umberto, there is a large body of thresholds. Look at ScientificBeekeeping varroa IPM Reconnaisance for dated ones. Most of us commercial beekeepers now use much lower thresholds. The 2% figure came from limited studies that found that naturally resistant bees appear to attempt to hold mite levels to about that level. I'm sure that this is a ballpark figure, but is perhaps the point of diminishing returns. It works for my operation, and it is my personal experience that I start to see virus problems at about 5% infestation (again ballpark, as neither the bees, the mites, nor the viruses keep track). At 15% you can kiss the colony goodbye. The above figures apply to my bees, in my operation, in the foothills of the Sierra Nevada around Grass Valley, CA, which may be similar to your Italian climate. Have you got any data or observations to share for Italy? -- Randy Oliver Grass Valley, CA www.ScientificBeekeeping.com *********************************************** 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