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.).