The above hive has a thermometer with 12" stem placed in the center of the brood nest
to determine the exact brood temperature during the treatment period.
The average brood area temperature in four out of our five initial test hives was 94° Fahrenheit in early September. These hives had at least six to eight full depth frames of brood and kept a constant 94° F temperature with outside daytime temperatures ranging from 70° - 80° F and nightime temperatures from 50° - 60° F. The only hive that showed a lower temperature was one that superceded their queen and had large areas in the brood nest full of pollen instead of brood. During August when preliminary tests were conducted with temperatures averaging in the mid- to upper 90's, we found numerous bees fanning at the entrance to cool the inside temperatures of the hive. The high outside temperature and fanning bees caused an evaporation increase of 150% of the acid treatment as compared with the lower temperature ranges and few bees fanning. We used three wicks in our August experiments and cut back to two in our September experiments, in order to get the right amount of evaporation. The September experiment with two wicks and lower temperatures, showed evaporation of 90 - 100 ml of acid/water treatment per day, as compared with the three wick treatment, with fanning bees and higher temperatures, where evaporation was 200 - 250 ml per day of the treatment. The higher evaporation rate killed most of the uncapped brood.
Using the 18% formic, 4% acetic and 78% water mixture, we found that evaporation of 90-100ml a day did not seem to kill any brood in our tests (one hive body). Greater evaporation would have killed much of the brood up to 5 days old and kill some newly emerging and recently emerged young bees. We filled the PVC Deal™ with 500 ml of the acid mixture, using wicks made with two 5/8" x 11" strips of specialty paper. We found a five to seven day treatment would kill about 90% of the mites in the cells. It is difficult to get an exact count of mites killed until three weeks after an uninterrupted brood cycle. Right after the acid treatments, some areas of brood show 0% live mites and others showed a high of 20% live mite infestation. Right after the treatment, many of the mites in the cells that were still alive died a few days later. The steady five-day dose really effected the mites with no noticeable harm to the brood or bees. The acid acted like the essential oils: mites in the cells become sick (lethargic) and unable to reproduce and/or attach to their hosts and eventually died.
The two control hives that were not treated showed a dramatic increase in mite infestation early in October and had to be treated with 60% formic acid pads because of patchy brood patterns, mite-PMS and heavy infestation. This late treatment may not do any good because the bees will not have enough time to hatch at least two healthy brood cycles needed to get them through the winter. A few days after this treatment, I noticed about 60% of the open brood in the cells was dead. It was hard to control evaporation from the pads. As soon as we put the pads in, there was a high rate of evaporation followed by a rapid decrease in the rate of evaporation. Evaporation from pads cannot be controlled as it can be with the low acid dose wick system in the PVC Deal™, where the constant brood temperature and wick action finely controls the rate of evaporation.
Timing of treatment is most critical. Treatment must take place in our area of the country by early September when there is a lot of bees and brood with a constant 94° Fahrenheit brood temperature, and outside temperatures are below 90° Fahrenheit¹.
We conclude that acid treatments during high temperatures of 90° Fahrenheit or more makes it difficult to control the evaporation of the acid in the PVC Deal™ with bees fanning at the entrance; but with temperatures below 90° F and almost no fanning, the temperature and evaporation stay constant in hives with full brood patterns. The positioning of the wicks relative to the central brood pattern is also critical to the efficacy of the treatment.
¹ This temperature range has not yet been determined.
The hive above is a formic acid test hive with PVC Deal™ reservoir, inner cover with 1" hole open in the center for a bee way and queen excluder in place. The queen excluder is used to keep the queen and all brood in the lower brood chamber for ease of treatment. The one inch bee way allows for bees to enter the treatment super below: the acid mixture knocks off any mites that are on the bees when they enter the lower brood box during the five day treatment period. This hive maintained a 94° F temperature during the five day trial test treatment period with excellent results. This hive had at least a 90% kill of Varroa in the cells with no noticeable loss to any brood or young bees. There is a fine line on the dosages. The dose used in this hive was 4% acetic acid, 18% formic acid and 78% water, using one full-depth brood chamber maintained at 94° F temperature, with outside temperatures ranging from 70° - 80° F. We used this same formula in August, in preliminary test hives with two 5/8 inch x 11 inch (1.7cm x 28.1cm) specialty paper wicks, temperatures in the mid 90's and with many bees fanning at the entrance to cool the brood. the result was evaporation of 200 - 250 ml of treatment or a 150% increase over the 90 - 100 ml required to kill the mites with no harm to the bees or brood. About 60% of the open brood and several young bees were found dead due to this higher evaporation rate.
Click Here: For Fahrenheit and Centigrade Conversions
Some Fahrenheit to Centigrade Conversions:
94° F = 34.4° C
90° F = 32.2° C
80° F = 26.6° C
70° F = 21.1° C
60° F = 15.5° C
50° F = 10° C