Nicotine does not reduce Nosema ceranae infection in honey bees
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Insectes Sociaux
RESEARCH ARTICLE
Nicotine does not reduce Nosema ceranae infection in honey bees H. P. Hendriksma1,2 · J. A. Bain1 · N. Nguyen1 · J. C. Nieh1 Received: 26 January 2020 / Revised: 26 January 2020 / Accepted: 18 February 2020 © International Union for the Study of Social Insects (IUSSI) 2020
Abstract 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 × 104 spores per bee; N = 160). One-day-old bees infected with Nosema (1 × 104 spores per bee; N = 160) showed no repression of nosemosis over a chronically applied exposure gradient of 0, 10−2, 10−1, 100, 101, 102, 103 or 104 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 1 04 ppm nicotine in vials, rinsed of nicotine, and then fed to 1 day old bees (2 × 104 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. Keywords Apis mellifera · Host–parasite interaction · Intracellular parasite · Nectar · Preference · Self-medication
Introduction The Western honey bee, Apis mellifera, is one of the most abundant pollinator species in both natural and agricultural habitats, but, in many regions, honey bees have poor health (Garibaldi et al. 2013; Hung et al. 2018). In regions of Europe and the USA, honey bee colonies have shown declines due to a variety of stressors, including the spread of diseases (Goulson et al. 2015; Moritz and Erler 2016). A honey bee disease survey found that approximately 70% of managed colonies in the USA are annually infected with the microsporidian pathogen Nosema, at an average Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00040-020-00758-5) contains supplementary material, which is available to authorized users. * H. P. Hendriksma [email protected] 1
Division of Biological Sciences, Section of Ecology, Behavior, and Evolution, University of California San Diego, 9500 Gilman Drive, MC0116, La Jolla, CA 92093, USA
Present Address: Institute for Bee Protection, Julius Kühn-Institut, Messeweg 11/12, 38104 Brunswick, Germany
2
of approximately 500,000 spores per infected bee (Rennich et al. 2012). Infection with
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