Collection of conidia of Podosphaera xanthii by honey bee workers

Honey bees, Apis mellifera, actively collect a range of materials including pollen and fungal spores. However, the interaction between honey bees and fungal spores is largely unexplored. Therefore, this study aimed to assess the corbicular contents of workers foraging on zucchini leaves severely affected by powdery mildew. The dimensions (length and width) of conidia removed from the corbiculae of honey bee workers and from the zucchini leaves were similar and conidia matched the description of Podosphaera xanthii, the causal agent of powdery mildew of cucurbits. Our findings that corbicular loads comprised only conidia of P. xanthii confirm that honey bees exhibited constancy, just as they almost always forage on a single species of flower per foraging trip, and highlight the importance of understanding the behaviour of honey bee workers in regards to the collection of fungal spores.