Abstract
Parasites alter the physiology and behaviour of their hosts. In domestic honey bees, the microsporidia Nosema ceranae induces energetic stress that impairs the behaviour of foragers, potentially leading to colony collapse. Whether this parasite similarly affects wild pollinators is little understood because of the low success rates of experimental infection protocols. Here, we present a new approach for infecting bumblebees (Bombus terrestris) with controlled amounts of N. ceranae by briefly exposing individual bumblebees to parasite spores before feeding them with artificial diets. We validated our protocol by testing the effect of two spore dosages and two diets varying in their protein to carbohydrate ratio on the prevalence of the parasite (proportion of PCR-positive bumblebees), the intensity of parasites (spore count in the gut and the faeces), and the survival of bumblebees. Overall, insects fed a low-protein, high-carbohydrate diet showed the highest parasite prevalence (up to 70%) but lived the longest, suggesting that immunity and survival are maximised at different protein to carbohydrate ratios. Spore dosage did not affect parasite infection rate and host survival. The identification of experimental conditions for successfully infecting bumblebees with N. ceranae in the lab will facilitate future investigations of the sub-lethal effects of this parasite on the behaviour and cognition of wild pollinators.
Highlights
Bees face a large diversity of parasites and pathogens that negatively affect their physiology [1,2,3], behaviour, and cognition [4], altogether compromising the fitness of individuals and colonies [5]
N. ceranae invades the epithelial cells of the honey bee midgut where it replicates [6,7]
Apis mellifera workers from unknown age came from a colony in our experimental apiary
Summary
Bees face a large diversity of parasites and pathogens that negatively affect their physiology [1,2,3], behaviour, and cognition [4], altogether compromising the fitness of individuals and colonies [5]. The microsporidia Nosema ceranae is one of the most prevalent parasites of honey bees worldwide and a major cause of colony declines [2]. The parasite disrupts the carbohydrate [8,9] and lipid [10] metabolisms of the host. This causes energetic stress leading to increased consumption of sucrose solution [11,12,13], and alteration of gene expression in the brain [14], inhibition of the apoptosis of epithelial cells [15], and deregulation of immune responses [2]. At the behavioural level, infected honey bees start foraging earlier in life [16,17,18], exhibit more frequent but shorter foraging flights [19,20,21], show reduced homing abilities [22], and display lower olfactory learning performances [23,24]
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