Effectiveness of synthetic acaricide treatments and development of resistance in Varroa destructor in Italy: historical overview and current considerations

The invasive ectoparasitic mite Varroa destructor represents the most significant health challenge for Western honey bees, Apis mellifera , and for apiculture worldwide. Its effective control is crucial to counteract the high colony mortalities it causes and ensure the sustainability of the beekeeping sector. To achieve such control, beekeepers rely heavily on the application of acaricide products to limit parasite loads. However, the effectiveness of these treatments is increasingly hindered by the growing issue of acaricide resistance. This problem is further intensified by the climate crisis: rising temperatures and the associated phenological shifts in honey bee colonies may limit the conditions under which non-synthetic acaricides can be applied, effectively narrowing viable control options to synthetic compounds. Here the authors review the current state of knowledge on V. destructor pharmacoresistance to synthetic acaricides in Italy, the country with the longest and most extensive history of investigations on the topic. To better capture resistance dynamics, relevant grey literature has also been included. We show how research findings on resistance have progressively influenced the development and adoption of miticides against V. destructor in Italy, and how rapidly these changes have occurred. The limitations of peer-reviewed scientific literature in capturing the full breadth of the phenomenon are also discussed. Like for many other countries, urgent additional research is needed in this field; despite the extensive historical body of work on V. destructor resistance, the current paucity of contemporary studies represents a serious concern for the future, limiting the ability to assess the scale of the problem and design effective strategies to counteract it.