Pollinator Visitation Patterns, Floral Rewards and the Probability of Transmission of Microbotryum Violaceum, a Veneral Disease of Plants

1 We investigated patterns of pollinator visitation to plants of the white campion, Silene alba, and related these to floral nectar rewards in healthy female and male plants and in plants diseased with the anther smut disease Microbotryum violaceum (= Ustilago violacea). 2 Pollinators preferred plants with large floral displays, and also preferred males to females and healthy to diseased plants. Male plants consistently produced nectar with higher sugar concentration, thereby offering higher quality floral rewards than either females or diseased plants. 3 Variation in nectar production was also found among individual plants and different plant families, suggesting that more attractive plants may be predisposed to infection since pollinating insects also serve as vectors for this fungal disease. 4 Such patterns of pollinator preference could affect the dynamics of disease transmission within populations by influencing the probability that insect visitors make transitions between diseased and healthy plants. This vector transmitted disease may therefore modify the course of selection on floral traits by imparting a cost to pollinator attraction.