http://rspb.royalsocietypublishing.org/content/285/1875/20172849

Nursing protects honeybee larvae from secondary metabolites of pollen
Matteo A. Lucchetti, Verena Kilchenmann, Gaetan Glauser, Christophe
Praz, Christina
Kast
Published 21 March 2018.DOI: 10.1098/rspb.2017.2849

Abstract

The pollen of many plants contains toxic secondary compounds, sometimes in
concentrations higher than those found in the flowers or leaves. The
ecological significance of these compounds remains unclear, and their
impact on bees is largely unexplored. Here, we studied the impact of
pyrrolizidine alkaloids (PAs) found in the pollen of *Echium vulgare* on
honeybee adults and larvae. Echimidine, a PA present in *E. vulgare*
pollen, was isolated and added to the honeybee diets in order to perform
toxicity bioassays. While adult bees showed relatively high tolerance to
PAs, larvae were much more sensitive. In contrast to other bees, the
honeybee larval diet typically contains only traces of pollen and consists
predominantly of hypopharyngeal and mandibular secretions produced by nurse
bees, which feed on large quantities of pollen-containing bee bread. We
quantified the transfer of PAs to nursing secretions produced by bees that
had previously consumed bee bread supplemented with PAs. The PA
concentration in these secretions was reduced by three orders of magnitude
as compared to the PA content in the nurse diet and was well below the
toxicity threshold for larvae. Our results suggest that larval nursing
protects honeybee larvae from the toxic effect of secondary metabolites of
pollen.

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