Establishing Economic Threshold and Epidemiology for Nosema Ceranae, A Relatively New Species of Microsporidian Parasite in the Honey Bee for PNW

Establishing Economic Threshold and Epidemiology for Nosema Ceranae, A Relatively New Species of Microsporidian Parasite in the Honey Bee for PNW

Summary

Honey bee pollination is estimated to be worth more than $20 billion in the U.S and worth $2 billion in the Pacific Northwest (PNW). Pollination requirement is huge for commercial agriculture in the PNW. Strong and healthy beekeeping industry is of immense value to the PNW agricultural economy that is vast and diverse. Recent honey bee colony losses attributed to colony collapse disorder and a steady decline of colonies for past two decades have caused serious concern and alarm. According to recent PNW honey bee colony winter mortality survey, the colony loss was 30%, which is alarming and unsustainable (Burgett 2009). Currently not much is known about the health of honey bee colonies in the PNW. Hence for a sustainable pollination and apiculture there is an urgent need to understand current honey bee health problems and develop appropriate management tools to overcome these problems.

Honey bee colonies are constantly under threat from existing pests and disease complex and also from other new species invasions. Recently honey bee colonies in the U.S have been reported to be infested with Nosema ceranae, a gut parasite which is prevalent in the Asian honey bee. Apparently this new species has jumped hosts and is now dominant in honey bees in the U.S and Europe. Nosema ceranae results in increased winter mortality (Higes et. al 2006). Some studies have implicated Nosema ceranae for the colony collapse disorder. Currently not much is known about biology and epidemiology of this new Nosema species. Nosema ceranae has threatened the U.S beekeeping industry for the past two years. It appears to be a silent killer without much overt symptoms compared to Nosema apis, which was more common in the U.S. Studies have confirmed that N. apis has been displaced by N. ceranae in the past couple of years. Beekeepers have been forced to treat their colonies prophylactically with the antibiotic Fumagillin to protect their colonies from N. ceranae without information on the presence or absence of Nosema or its threshold. This prophylactic treatment has significantly increased hive management costs for beekeepers, as fumagillin is expensive. Prophylactic use of fumagillin is not only a financial burden for beekeepers, but its excessive use may lead to the development of resistance and the beekeepers might loose this Nosema control tool from their limited arsenal. Also, excessive and unwarranted use of fumagillin can contaminate honey that is consumed by humans.

Economic thresholds for Nosema ceranae is not established yet for PNW nor for the U.S. An economic threshold allows the beekeeper or producer to take appropriate and timely control measures and also allows them to pursue non-chemical control tactics to the extent possible. Development of a threshold will primarily help the beekeepers to assess Nosema levels and intervene with chemical treatment accordingly. Thus, it will not only significantly reduce the operating costs but will also aid in judicious use of antibiotic Fumagillin that will help delay the development of Fumagillin resistant strains of Nosema.

One of the research and education proposals (SW07-055) funded by Western SARE reports that N. ceranae has almost replaced N. apis within PNW honey bee populations, and colony health ramifications of this novel pathogen are currently unknown. This study was the first one to establish the fact that Nosema ceranae is wide spread in the PNW, but this study has not focused on establishing economic threshold levels for Nosema, its epidemiology and efficacy of existing treatments. Hence this study will focus on these exclusive objectives. This professional + producer project will develop economic threshold for N. ceranae for the PNW and will examine epidemiology of Nosema ceranea. We will also develop a reliable sampling protocol to estimate Nosema spore counts from infested bee colonies. The long term goals are to reduce beekeepers excessive reliance on chemical treatments, decrease the probability of resistance development for the existing chemical treatments, and promote cleaner hive products. We will set up the experiments in different cooperating apiaries for two years to develop economic thresholds for Nosema ceranae and to examine the epidemiology of N. ceranae.

Objectives/Performance Targets

1) Develop the economic threshold of Nosema ceranae for the PNW

2) Study the epidemiology of Nosema ceranae in the PNW

3) Evaluate efficacy of delivery methods of Fumagillin for Nosema control

4) Develop a reliable and simple sampling protocol to estimate Nosema spore counts in the infested colonies

Accomplishments/Milestones

We have established the epidemelogy/phenology of Nosema ceranae for the Pacific Northwest region (Fig. 1 and 2).

We have also developed a relable sampling protocol for estimation of Nosema spores in infested colonies.

Two field days, two workshops, and one bee school were organized to train beekeepers.

Results of this study were presented at Oregon State Beekeeeprs Association annual meeeting and American Bee Reserach Conference in 2012.

• Nosema epidemiology and phenology

Impacts and Contributions/Outcomes

Our study has established the epidemiology/phenology of Nosema ceranae in the PNW, and this information is currently being used by beekeepers in the PNW to tackle Nosema disease in an effective and economical way. Further, our analysis of Fumagilin delivery methods and reporting of the most efficient method (spraying bees with fumagilin containing sugar syrup) of delivery have enhanced the efficacy of Nosema treatment.

Collaborators: