## 1 Introduction
In Italy, since 2003, significant honey bee mortality has been recorded in springtime, mainly related to the side effects of maize seed dressed with neonicotinoid insecticides [34]. Due to the significant increase in these events in 2008, a nationwide surveillance network, named ApeNet (2009-2010), was implemented to monitor the health status of beehives and determine the consistency and possible causes of mortality. From about 100 apiaries distributed throughout most of Italy, they increased to 300 with approximately 3000 beehives in 2011 in the framework of the BeeNet project (2011-2014). The Italian Ministry of Agriculture, Food and Forestry Policies [35] funded both initiatives. In this context, a Bee Emergency Service Team (BEST) was established, managing beekeepers' reports, contributing to the assessment of events' severity, organizing and participating in field interventions, and coordinating the technicians recruited for their deployment, in agreement with and in support of the competent authorities [36]. During these monitoring studies, 126 honey bee samples related to honey bee-killing incidents, confirmed by BEST, were analyzed. Approximately 50% were positive for at least one active substance, the most frequently detected being imidaloprid, chlorpyrifros, thiachloripid, chlothianidin and thiametoxam. The number of detected pesticides was positively related to the size of the agricultural area surrounding the apiaries [37]. Commission Directive 2010/21/EU requires that member states ensure that monitoring programs are carried out where and as appropriate to verify the real exposure of honey bees to pesticides in areas used by bees for foraging [38]. Furthermore, since beekeepers still frequently report bee deaths at certain times of the year, and considering the strong public attention to this problem, various Italian regions deemed it appropriate to adopt a more systematic approach to the management of bee mortality where pesticide poisoning is suspected. Accordingly, the General Directorate of Animal Health and Veterinary Medicines of the Italian Ministry of Health issued the \"Linee guida per la gestione delle segnalazioni di moria o spopolamento degli alveari connesse all'utilizzo di agrofarmaci\" (Guidelines for the management of reports of death or depopulation of bee colonies related to the use of plant protection products) [39]. They provide operational indications for the management of death and depopulation events of the hives in order to make the intervention activity more homogeneous both for the procedures adopted in the field and in the laboratory. The aim of the guidelines is to collect information on the causes of death and depopulation of hives with particular regard to the use of PPPs [39]. In addition, the implementation of a biomonitoring program on the environmental exposure of honey bees to pesticides could have an interesting return for human epidemiological studies. Considering the well-known risks related to direct and indirect human exposure to pesticides [1; 2; 3; 4; 5], verification of their presence in honey bees and their products could serve as an early warning system for public health interventions. Our study reports on the presence of pesticide residues in dead honey bees and associated matrices received at our laboratory from 2015 to 2020, following implementation of the above guidelines. Besides providing relevant, possibly obvious, considerations about honey bee health, our findings are presented within the framework of the valuable role that honey bees could play in a nationwide monitoring system, with implications for public health.