Nicotine does not reduce Nosema ceranae infection in honey bees

Bee-collected pollen and nectar contain multiple phytochemicals that can have anti-pathogenic effects when ingested. For example, the plant alkaloid, nicotine, can reduce infections by the trypanosome gut parasite ( Crithidia bombi ) in bumblebees. Parasitized bumblebees may be drawn to nicotine and thereby self-medicate their infection. We tested the hypothesis that nicotine can reduce infections of a common microsporidian pathogen, Nosema ceranae , in the honey bee gut. We found, however, that that a field realistic exposure dose of 1 ppm nicotine was not preferentially consumed by Apis mellifera foragers fed live Nosema spores (5 × 10 4 spores per bee; N = 160). One-day-old bees infected with Nosema (1 × 10 4 spores per bee; N = 160) showed no repression of nosemosis over a chronically applied exposure gradient of 0, 10 −2 , 10 −1 , 10 0 , 10 1 , 10 2 , 10 3 or 10 4 ppm nicotine. Since imbibed nicotine may not effectively reach the spores in the bee gut, we conducted an in vitro experiment, in which Nosema spores were exposed up to 10 4 ppm nicotine in vials, rinsed of nicotine, and then fed to 1 day old bees (2 × 10 4 spores per bee; N = 216). However, the in vitro nicotine-treated spores remained infectious. Nicotine did impair bee mortality at high concentrations. Dietary nicotine is evidently not a treatment for nosemosis, but future studies should continue to examine the role of phytochemicals and bee health.