Comparative prevalence of Nosema ceranae infection between wild and managed honey bee(Apis mellifera) colonies in South Texas

Abstract

Over the last few decades, honey bee (Apis mellifera) populations have been challenged by multiple factors including pathogens and parasites, which often act concurrently to cause severe health problems. One honey bee pathogen linked to colony losses worldwide is the microsporidian Nosema spp., which affects adult bees. Workers infected with Nosema often exhibit shorter lifespans, forage prematurely, and are susceptible to other pathogens. Our main goals were to quantify the levels of Nosema spp. infection in a wild honey bee population at the Welder Wildlife Refuge (WWR) in south Texas, and to compare them to infection levels in colonies from a nearby managed apiary. We hypothesized that wild colonies would have lower infection levels than managed colonies due to their unique life history traits, including lower colony density per unit area, which decreases the likelihood of cross-colony disease transmission. We collected foragers from the entrance of 18 wild colonies at the WWR and 19 managed colonies at the nearby apiary. We then performed individual Nosema spp. spore counts on ten workers per colony to calculate an average spore count per bee. On average, wild colonies had 25,556 spores/bee, while managed colonies had 130,526 spores/bee, both considered to be low. There were no differences in infection levels between colony types. All samples tested positive for N. ceranae; no N. apis was detected. Our results suggest that wild colonies at the WWR have historically been infected with Nosema spp. at low levels and can thrive in the absence of human intervention.