Development of a gel formulation of formic acid for control of parasitic mites of honey bees

Formic acid has been used in various countries for the control of parasitic mites of honey bees (Apis mellifera), particularly the Varroa mite (Varroa jacobsoni) and the tracheal mite (Acarapis woodi). Its corrosivity and con sequent fear of liability have precluded commercial interest in the United States, and its rapid vaporization requires frequent reapplication. We have developed a gel formulation of formic acid which provides controlled relea se over 2-3 weeks and improves the convenience and safety of handling of fo rmic acid. The strong acidity of formic acid restricts the choice of gellin g agents; vegetable gellants such as agar are destroyed, and bentonite clay derivatives do not gel, even with high-shear mixing. Polyacrylamides lead to viscous liquids lacking thixotropic properties. High-molecular-weight po ly(acrylic acids) and fumed silicas provided gels with suitable physical ch aracteristics. The poly(acrylic acid) gels were difficult to mix and gave s lower and nonlinear release behavior, while the fumed silica gels were easy to prepare and linear in formic acid vaporization.