Hi. Just my 5 cents of observation. I have used Apistan before 1999. No appreciable drop off onto the bottom boards. Anywhere between below 10 to plus 50 in 14 colonies.( Spring 1999, Fall 1998) Modified bottom boards to screened ones in july 1999. Applied Coumaphose in Fall ( End August ,Beginning Sept.) 1999 and counted 2000 to 5000 mites on bottomboard. Daily for 2 weeks.Then deminishing to zero drop off. No evidence of varroa spring 2000. Theory : The space between combs is too narow to allow bees to get maximum contact to miticide. Therefore, either ( In 10 frame Hive bodies) the strip was placed in the spot where the frames were spread apart to allow bees to walk AROUND the strip and just not being in contact with the edges. Or as with 9 frame bodies there is enough space for bees to get sufficient contact.July is usually known as conducive to varroa increase, so I was informed. This summer I treat with FGMO fogging method. In Fall I will check with Apistan and Coumaphose as well as formic acid to compare the drop off. Interesting side line info from Dr Tom Sanford Apis letter this month's relative to pesticide contamination of honey research results. JDF