They then gently swirl the bees for about a minute before turning the jar upside down and shaking for two minutes over a tray to capture the mites as they fall. Those mites are then counted, and the count is divided by three to find the number of mites per 100 bees. The sugar roll is typically done with the intent to prevent killing the sampled bees, but whether the vigorous shaking causes damage is not known . For an alcohol wash, which is the most effective method, the sampler collects about 300 bees using the same cup. The bees are submerged in alcohol with a concentration of 70% or higher. A lid is placed over the jar to seal it, and the mixture is shaken vigorously for two minutes before it is poured over a 1/8" wire mesh screen into a tray. The mites are then counted, and the resulting number is also divided by three. This method kills all sampled bees. The sticky board method does not kill any bees. For this method, a sticky board with a thick coating of petroleum jelly is placed under the brood chamber under a screened bottom board (or similar 1/8" wire mesh screen). The board is retrieved after three days, and the beekeeper takes a count of the mites on the board. This number is divided by three to find the average 24-hour mite drop. This method does not kill any bees, but takes longer for results. "Varroa" mites can be treated with commercially available acaricides. Acaricides must be applied carefully to minimize the contamination of honey that might be consumed by humans. Proper use of miticides also slows the development of resistance by the mites. However, the most effective long-term way of protecting bees against "V. destructor" is by breeding bees that are resistant to these mites. "Varroa" mites can also be controlled through nonchemical means. Most of these controls are intended to reduce the mite population to a manageable level, not to eliminate the mites completely. Researchers have been able to use RNA interference to knock out genes in the "Varroa" mite. Efforts also have been made to breed for changes in the honey bees. Two strains have been developed in the United States that can detect damaged pupae under cappings and remove them before the infestation spreads further. The “IN”/Indiana strain is under development at Purdue University to develop lines that groom off and bite phoretic "Varroa" to kill the mites.