The History of Chemical Varroacide Practices in Germany (1996–2024) in Relation to Winter Colony Losses of the Western Honey Bee

Using surveys, we document the history of chemical control measures against the parasitic mite Varroa destructor in Germany between 1996 and 2024 and relate the application history to winter loss rates of the western honey bee during this period. More than 153,000 data sets with geographic delimitation, varroacide use and valid loss data were gathered of which more than 134,000 can be geo-referenced by postal code. A gradual shift from synthetic to natural chemical substances, including peaks of specific varroacide usage, is documented. By 2009 more than 50% of all respondents reported using only natural organics acids (formic, oxalic and/or lactic acids) (2024: 72%). Neither magnitudes nor oscillations of annual colony loss rates were affected by the shift. Instead, clustered geographic variation in loss rates within and among years was identified that was independent of varroacide application history. However, apiaries using a combination of varroacides throughout the year, here, formic acid in combination with coumaphos before the shift or oxalic acid thereafter, had significantly lower average losses compared to those using only formic acid. Our database allows future studies to address how environmental heterogeneity should be considered in treatment recommendations.