2.1 STUDY SPECIES: BUMBLEBEES AND PARASITES
As previously stated, two different co-occurring species of bumblebees have been selected for this study, Bombus terrestris (Linnaeus 1758) and B. pascuorum (Scopoli 1763). These are common pollinators in Europe and widely adopted model species with well-known ecology and biology (Rasmont et al. 2008; Theodorou et al. 2021 ). These two important wild pollinators are usually found in several contexts that range from natural to urbanized sites (Tommasi et al., 2022; Meeus et al. 2021; Polce et al. 2018; Intoppa et al. 1995). Therefore, they are suitable for understanding how wild pollinators are affected by land-use change and which strategies they adopt to cope with urban stressors (Eggenberger et al. 2019; Theodorou et al. 2021). In addition, these two species have different demands in terms of foraging and nesting habits.
Three different taxa of pathogens known to affect both honeybees and wild bees have been selected, namely microsporidians (Phylum: Rozellomycota), trypanosomatids (Phylum: Euglenozoa) and neogregarines (Phylum: Apicomplexa) parasites. Relatively little is known on these three group epidemiology dynamics in wild pollinators, therefore all bumblebee specimens have been tested for all taxa to help shed light on endoparasite transmission in wild pollinator communities. Among the microsporidians, Nosema spp. is known to affect managed and wild bees and is transmitted through oral-fecal routes (Solter, 2014). Specifically, Nosema bombi and N. ceranae are the most common species detected both in bumblebees and Apis mellifera(Graystock et al., 2013; Higes et al., 2010). Among trypanosomatids,Crithidia spp. have been previously detected in several wild bee species (Strobl et al., 2019; Yourth et al., 2008). It is a common parasite target of several research on bumblebees and is transmitted via oral-fecal routes like Nosema spp (Brown et al., 2000.). Effects of Crithidia spp. vary from the chronic reduction of foraging efficiency to acute increasing mortality (Gegear et al., 2006; Brown et al., 2000). Similarly, the neogregarines are understudied parasites of bees and the only known species detected in honey bees, bumblebees and solitary bees is Apicystis bombi (Tian et al., 2018; Plischuk et al., 2011; Lipa & Triggiani, 1996). Bumblebees infected by this species are known to have reduced fat bodies and increased mortality (Graystock et al., 2016b.).