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ABSTRACT.-The fungal pathogen Nosema bombi impacts bumblebee fitness and is a factor in population declines throughout North America. Pesticides are also thought to contribute to declines, because they harm the innate immune system of insects, making them more susceptible to disease. A total of 232 bumblebees were collected at nine different farms across Michigan (U.S.A.), including farms that used pesticides and those that did not, in summer 2017. The bees were identified and tested for Nosema bombi. All bees were found to be free from N. bombi infection, suggesting this microsporidian may not yet have a biologically important impact on bumblebee populations in Michigan.
INTRODUCTION
Pollinator species, such as honeybees (Apis spp.) and bumblebees (Bombus spp.), provide pollination for over one-third of the food we eat and the plants that grow around us (Klein el ai., 2007). Annual pollination services account for 206 billion dollars worldwide and 1.2 billion dollars in the United States alone (Otti and Schmid-Hempel, 2007; Partap and Ya, 2012). The worldwide population decline of bumblebees has made apparent both their ecological and economic importance. It was found there was a 23% to 87% reduction of the Bombus species throughout North America within the last 20 у (Cameron etai, 2011).
There are many suggested causes for the population decline of bumblebees, including habitat loss and reduced floral abundance and diversity (Goulson et ai, 2008). Emerging pathogens, such as microsporidia in bumblebees, bave also been shown to contribute. Bumblebees that are commercially-reared have higher pathogen prevalence than wild bees. Pathogens, such as microorganisms (Apicystis bombi, Crithidia bombi, Nosema bombi), and miles (Locustacarus buchneri), are thought to be carried by commercial bumblebees and transmitted to wild bees (Colla et ai, 2006). These pathogens were found in bumblebees that were commercially reared by three main producers in Europe, which claimed to be parasite-free (Graystock et ai, 2013). Crithidia bombi was also found to infect 27% of bumblebees near greenhouses with commercially reared bees in Ontario, Canada as compared to an absence of infected bees found at sites lacking a greenhouse and commercially reared bees (Colla et ai, 2006). Pathogen spillover of commercially reared bumblebees within North American may cause an epidemic in the wild species (Meeus et ai, 2011). These population declines are believed...