Organic acids and thymol: unsuitable for alternative control of Aethina tumida (Coleoptera: Nitidulidae)?

To explore alternative strategies to synthetic insecticides for control of Aethina tumida, the small hive beetle (SHB), treatments already established against two other honeybee pests, Varroa destructor and Galleria mellonella, were investigated. In the laboratory, eggs, larvae, and adults of SHB were treated with thymol (10, 20, and 50 mg) or with organic acids: 85% formic acid (0.125, 0.25, 0.5, 0.75, 1.0, and 2.0 mL), 15% lactic acid (0.5, 1.0, 1.5, and 2.0 mL), oxalic acid (dihydrate crystals 35 g/L; 0.25, 0.5, 0.75, 1.0, and 2.0 mL), and 65% acetic acid (0.5, 1.0, 1.5, and 2.0 mL). Some of the chosen concentrations of formic and oxalic acid resulted in high mortalities of all SHB life stages. Therefore, they were further evaluated in the field utilising standard methods for control of V. destructor in Europe. After exposure to evaporating formic acid (85%, Nassenheider®) and oxalic acid (2 g dehydrate crystals, Varrox®), mortality in all SHB tested stages did not increase significantly. The same was true for trials with 85% (adults) or 60% (eggs and larvae) formic acid, evaporating from sponge tissues in diagnostic trays. In fact, some SHBs used the diagnostic trays to hide or oviposit. Despite treating extracted honey combs with 65% acetic acid, SHBs still reproduced on the combs’ pollen cells. In conclusion, none of the tested methods can be recommended to control SHBs.