Developed jointly by Oliver Brooks and Albert Knight, this device was detailed in the Spring 1998 edition of Bee Improvement magazine. This page has taken the text more or less verbatim, but I have redrawn the diagrams.
Note - The diagram is a large file that may take some time to load... So please read the description first.
This thymol frame can be made up using parts from a spare deep brood frame (DN1). The only extra bits being some thin plywood and a piece of thin cloth material, such as linen.
A spare 22 mm top bar is cut to fit in, at the height to suit using shallow foundation. This should be unwired drone foundation so that drone larvae can be removed as a control measure against the mites when Thymol is not in use, i.e. during a honey flow.
shown in the cut - away sketch below is the trough in its working position. This is placed on the three pieces of side bar that are glued and nailed to the mid bar inserted for shallow foundation. A cover of wire mesh is provided on each side of the trough and these are held in place by wire rods threaded through staples set in the top bar and the bar above the frame of drone foundation. The wire mesh holds the trough in place. The vapour from the crystals flows downwards through the linen material and passes out through the wire mesh into the brood box.
Dose: 8 gms per week over 4 weeks. The frames should be 'warm' way, and the thymol frame should be at the rear of the brood nest (furthest away from the entrance). To be effective the evaporation rate should be such that most of the 8 gms is evaporated in a week. Obviously temperature plays an important role in the evaporation rate, so reasonable temperatures must prevail when applied.
The wire mesh will need the propolis cleaning off from time to time. (See comment at page bottom.)
The trough to hold Thymol crystals is made from two pieces of thin ply nailed and glued to two wooden end pieces (using part of the lugs cut from the top bar of the spare frame). Linen cloth (or very fine plastic mesh) is stretched across the bottom of the trough and glued to the sides..
The components required to make up this device are standard frame parts:-
a 22 mm wide top bar, two x 22 mm wide straight side bars, two x bottom bars (B1),
a mid bar that is effectively another top bar with the lugs cut off, two thin plywood strips 335 mm x 28 mm,
various pieces cut from 9 mm thick x 22 mm wide timber (a spare side bar), a piece of shallow drone foundation,
Thin linen cloth or very fine nylon mesh filter material.
Albert has commented...
"It is worth saying that when the frame is not in use the wire mesh panels are detached and placed in a freezer for 24 hours to make the propolis brittle, then the mesh can be cleared of propolis by a few sharp taps."