TREATMENT OF SEALED HONEY-BEE BROOD WITH FORMIC-ACID FOR CONTROL OF VARROA-JACOBSONI

Combs with sealed brood, 8 to 16 days old, infested with Varroa jacobsoni. were treated outside the colonies with formic acid (85%) in closed plastic foam boxes and the mite mortality and brood damage were evaluated. The treatments applied were 50 ml for 1 h (A), 50 ml for 2 h (B), 100 ml for 1 h (C) and no formic acid for 2 h (D). The treatments were applied to 6 combs evenly spaced in 10-frame boxes. The results show that formic acid as applied, effectively kills Varroa mites in sealed brood cells. In treatment A. 99% of the mother mites were dead 2 days after treatment (N = 86). In treatment B (N = 164), C (N = 70) and D (N = 78), the mortality of mother mites was 100%, 100% and 4%, respectively. The older Varroa progeny was more resistent to treatment than the mother mites in A, but in B and C all progeny died from treatment except 1 adult daughter in C. More than 90% of the brood survived treatments A and B, while losses might have been higher in C. The most vulnerable stage of the treated brood was during transition from stretch larva to pupa.