The assertion was made that screened bottoms were *never* meant to be used alone but with other treatments. If you look at this history of it, however, it was claimed that the bottom board could *eliminate* chemical treatments. The history of bottom screens: Original idea, posted by Jean-Pierre Le Pabic at http://www.apiculture.com/plateau-anti-varroas/index_us.htm quote: The principle of the anti-varroa bottom board has come from the fact that: wild colonies of honey bees can be found, free of varroa, in highly infested areas. The assumption is that many varroa mites fall from the colony and are eliminated in this way, having no means to climb back. On the contrary, in a hive, they do not have any difficulty joining up with their initial environment from the classic bottom boards. The Legris anti-varroa bottom board is designed so that they fall through the tubes under the hive. According to my experience on my colonies, *this bottom board eliminates any need for chemical treatment*. The varroa mites are not fully eliminated, but they remain in such a small number that they are no longer harmful. In the worst case, only one treatment per year might have to be done, which is enough to economically justify it. -- end quote quote from Apis: Drs. J. Pettis and H. Shimanuki of the USDA-ARS Bee Research Lab published their results using especially designed bottom boards to reduce Varroa populations (American Bee Journal, Vol. 139, No. 6, pp.471-473, June 1999). The good news is that in the 30 colonies fitted with modified bottom boards, there was an approximately 14 and 28 percent lower mite fall when compared with normal bottom boards in June and July. The bad news is that the results were not statistically significant, and by September mite levels in all colonies (experimental and controls) reached damaging levels. Thus, it appears that the modified bottom boards slowed Varroa population development, but cannot be relied on as a single, effective treatment for these mites. The authors remain optimistic that physically separating the bee nest from the hive floor by use of a wire mesh (#8 hardware cloth) used in conjunction with resistant stock, smoke, dusts or other control agents should provide a more integrated approach to Varroa control, reducing use of conventional pesticides in the bargain. The above conclusions coincide with those of Troy Hart and Dr. R. Nabors at the University of Missouri, who studied pollen traps to control Varroa (American Bee Journal, Vol. 139, No. 5, pp. 366-367, May 1999). The principal is the same. The bee's nest is separated from the trapped pollen by a screen mesh. A byproduct of Drs. Pettis and Shimanuki's investigation was that colonies on modified bottom boards produced significantly more brood seven weeks after being established with packages than those with conventional bottom boards. The authors state that this result appears to correlate with those obtained using a slatted rack. In the same issue of American Bee Journal, pp. 747-476, Dr. Keith Delaplane at the University of Georgia reports on a three-year study using the slatted rack. In this investigation, the modification did produce more brood near the hive entrance, but did not result in a general brood production increase when compared to controls. -- end quote Note the following: * by September mite levels in all colonies (experimental and controls) reached damaging levels * more brood near the hive entrance ... not ... a general brood production increase when compared to controls * The authors remain optimistic (Optimism is a good thing but not when it obscures the facts.) From Hoosier Buzz quote: [Rinderer] tested an IPM program of Screened bottoms, formic acid, both, and no treatment. Results were as follow for Russian stock - 1% to 8% using all four. Using both formic acid and screen did have lowest mite population, no treatment had highest mites but still low. Domestic stock results were, 9% for both, 21% with formic acid, 69% with screen, and 70% with no treatment. It was also found that the Russians are more hygienic then domestic stock. -- end quote This study seems to point to an increase in effectiveness of formic acid, but this small increase pales before the effectiveness of requeening with Russian stock. Russians with formic and traps: 1% infection rate Russian controls: 8% Domestic with formic and traps: 9% Domestic controls: 70% infection rate -- Peter Borst Ithaca, NY [log in to unmask] http://www.people.cornell.edu/pages/plb6