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

Final Report for OW10-327

Project Type: Professional + Producer
Funds awarded in 2010: $38,536.00
Projected End Date: 12/31/2013
Region: Western
State: Oregon
Principal Investigator:
Dr. Ramesh Sagili
Oregon State University
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Project Information

Abstract:

Honey bee colonies in the U.S have been recently 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. Some studies have implicated Nosema ceranae for the colony collapse disorder. Currently not much is known about the biology and epidemiology of this new Nosema species. Nosema ceranae has threatened the U.S beekeeping industry for the past two 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.

In this study we focus on undestanding the epidemiology and phenology of Nosema ceranae in the Pacific Northwest (PNW) region, evaluate efficacy of Fumagillin (antibiotic) delivery methods and develop a reliable sampling protocol to detect nosema infections. Our results suggest that Nosema ceranae is prevalent in honey bee colonies in the PNW region throughout the year, with a peak infection during May. Among the three Fumagillin delivery methods, spraying method (spraying bees with Fumagillin mixed in sugar syrup) was the most effective. A sample of 100 bees obtained from the brood area for counting spores was the most reliable method for detecting Nosema infection when compared to a sample size of 25 and 50 bees.

Introduction

Pollination requirement is huge for commercial agriculture in the PNW. A 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 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 the 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 are 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. That study was the first one to establish the fact that Nosema ceranae is wide spread in the PNW, but that study has not focused on establishing economic threshold levels for Nosema, its epidemiology and efficacy of existing treatments. Our study focused on these exclusive objectives. Here we proposed to develop an economic threshold for N. ceranae for the PNW and examine epidemiology of Nosema ceranea. We also proposed to 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.

Project Objectives:

1) Develop an economic threshold of Nosema ceranae for the PNW region 
2) Study the epidemiology of Nosema ceranae in the PNW region 
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

Cooperators

Click linked name(s) to expand
  • Karen Finley
  • George Hansen
  • Jan Lohman
  • Lynn Royce
  • Harry Vanderpool
  • Kenny Williams

Research

Materials and methods:

Epidemiology and phenology of Nosema ceranae:

A total of 140 honey bee colonies pertaining to both commercial and backyard beekeepers in the PNW region were used in this two-year longitudinal study to understand epidemiology and phenology of Nosema ceranae in the PNW region. Bee samples from these experimental hives were obtained every two months for Nosema analysis. Bee abdomens were macerated and Nosema spore intensity (mean spores per bee) was quantified using light microscopy techniques. Other colony parameters, such as adult bee population and brood area, were also recorded for these experimental colonies.

Efficacy of Fumagillin delivery methods:

We tested efficacy of the following three commonly used methods of Fumagillin application by beekeepers: 1) Fumagillin mixed in sugar syrup and fed to bees in a feeder, 2) Fumagillin mixed in protein supplement and fed to bees, and 3) Fumagillin mixed in sugar syrup and sprayed on bees (drenching).

Reliable sampling protocol to detect Nosema infection:

We compared the reliability of three different bee sample sizes (25, 50 and 100) in detecting Nosema ceranae infection in honey bee colonies.

Research results and discussion:

The two year longitudinal study revealed that Nosema ceranae is prevalent in honey bee colonies in the PNW region throughout the year, with a peak infection during May. Mean Nosema spores per bee during May 2011 and 2012 was 7.3 ± 1.1 million and 3.7 ± 0.7 million respectively. Among the three Fumagillin delivery methods, spraying method (spraying bees with Fumagillin mixed in sugar syrup) was the most effective. A sample of 100 bees obtained from the brood area for counting spores was the most reliable method for detecting Nosema infection when compared to a sample size of 25 and 50 bees.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

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

Number of beekeepers that attended the two  field days: 85 and 60 respectively
Number of beekeepers that attended the two workshops: 58 and 44 respectively
Number of beekeepers that attended the bee school: 70
Number of participants that attended the presentation at the 2012 Oregon State Beekeepers Association Annual Conference: 180 (approx.)
Number of participants that attended the presentation at the 2012 American Bee Federation Annual Conference: 120 (approx.)

Project Outcomes

Project outcomes:

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.

Economic Analysis

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.

Farmer Adoption

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.

Number of beekeepers that have started adopting the management recommendations based on our research findings: 90

Recommendations:

Areas needing additional study

Due to high variability in levels of Nosema infestation among experimental colonies, we were not successful in establishing an economic threshold level for Nosema cearane. Future studies can attempt to establish an economic threshold level for Nosema ceranae.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.