Number of mites collected per month on the bottom board (mean ± S.E.) from April 2002 to June 2004. Mites were not counted between October 2003 and December 2003. ◊ represent mean number of mites in VSB (n = 12 colonies), ▫ represent control colonies (n = 16). (* Significant statistical differences, Mann-Whitney test, P < 0.05).