Effects of different microplastic types and co-exposure on the survival of Apis mellifera ligustica (Spinola, 1806) and its associated microbial communities

Microplastics (MPs) are one of the most significant environmental threats of this century. Honey bees, and their associated microorganisms, can be used as sentinel models for monitoring environmental quality due to their continuous and active interaction with plants, soil, and water. This study aimed to assess the effects of three types of MPs by setting up laboratory assays in which bees were fed with polystyrene, polyethylene and polymethyl methacrylate, either individually or in combination. Bee survival was evaluated, together with the quantification of bacterial taxa known to be involved in beneficial functions related to bee health, by quantitative PCR. The MP treatments significantly reduced bee survival compared to the Control, the treatment with all three MP types together having a major effect. The bee microbial community was affected by time- and treatment-specific effects. More than half of the bacterial taxa analysed showed an increasing trend over time, with a stronger acute increase in bees fed with MPs, possibly due to an initial compensatory response aiming to maintain microbial functional stability. Understanding shifts in gut bacteria following bee exposure to MP may be key to comprehending their impact on the environment.