## 4 Discussion
The classes of AIs most frequently encountered in our study are pyrethroids (such as tau-fluvalinate, permethrin, etofenprox, cypermethrin), carbamates (such as methomyl and methiocarb) of which piperonyl butoxide--one of the most frequently found active substances--is a synergism, and the class of organophosphates (such as coumaphos, chlorpyrifos and chlorpyrifos-methyl). They belong to cholinesterase-inhibiting insecticides (organophosphates and \(N\)-methylcarbamates) and pyrethroid insecticides that are overrepresented in the synergistic mixtures identified so far [69]. However, true synergistic interactions between chemicals are rare and often occur at high concentrations [70]. Addressing the cumulative rather than synergistic effect of co-occurring chemicals, using standard models, such as concentration addition, appears, therefore, to be the most important step in the risk assessment of chemical cocktails [70]. The evaluation and prediction of biological responses elicited by interaction of pesticides with each other (pesticide mixtures) requires an integrated, systematic toxicological approach and is a challenge to human and environmental risk assessment as demonstrated by the plethora of publications on the subject [69, 66, 67, 68, 69, 70, 71, 72, 73]. The identification of core features of pesticide mixtures at the molecular level, such as gene expression profiles, could be helpful to assess or predict the occurrence of interactive effects giving rise to unpredicted responses [69]. We also report that 38 of the 71 active substances identified during implementation of the Italian guidelines belonged to hazard classes I and II for active substances in pesticides, thus categorizing them as extremely (n = 2), highly (n = 8) and moderately dangerous (n = 28). Their simultaneous presence, in most cases, with other active substances confirms that honey bees could be very valuable sentinels of environmental health and consequently, of possible hazards to human health. In addition, all officially reported bee-killing incidents can be easily georeferenced with maps, showing their distribution across a given territory. As shown in Figure 1, most bee-killing incidents reported to the competent authorities occurred in northern Italy, with a lower number of reported cases scattered across central and southern Italy. The agricultural areas in the north were widely represented by non-irrigated arable land, fruit trees (predominantly apple orchards), berry plantations, olive groves, and vineyards; and by non-irrigated arable land, fruit trees (citrus), olive groves, and vineyards in the central and southern regions [74]). Mapping indirect honey-bee monitoring activities is a helpful means to more precisely locate affected areas and trends in events, permitting the implementation of further public health investigations to trace, back to their origin, identified pesticides or other dangerous substances, including unauthorized ones--such as permethrin, methiocarb, and methomyl--with the legal implications that this entails. To alleviate the negative effects of pesticide use, more measures need to be adopted to improve pesticide application and the related regulations. Effective monitoring and management of pesticides could not only reduce their use, but also protect the ecosystem and public health [75]. The One Health concept is based on the close interconnection between human, animal and environmental health, and emphasizes how human health depends on a healthy, functioning ecosystem [76]. Consequently, further biomonitoring actions should be deployed by competent authorities following a One Health approach, leveraging information provided by honey bees and their products. Honey bees and honey bee products can act as a natural, passive, inexpensive monitoring system capable of revealing potentially alarming or dangerous situations for human well-being and public health.