Bt to Blame for Bee Colony Collapse?

Because honey bees play such a crucial role in agriculture, the recent news that large areas of the U.S. were experiencing a wide-spread sudden loss (or disappearance) of honey bee colonies caused alarm across the country.  While some honey bee experts question the severity of the disorder, this phenomenon has been described by others as Colony Collapse Disorder (CCD).  Groups critical of the widespread adoption of biotech crops in the U.S. and globally have recently begun a campaign alleging that CCD may be caused by crops expressing one or more Bt proteins.  Unfortunately, entomologists have not been able to determine the cause of CCD.  While the cause is not yet clear, there is strong evidence that the production of specific insecticidal proteins from the soil bacterium Bacillus thuringiensis (Bt) in crops to control targeted caterpillar pests and beetles does not pose a risk to honeybees.

There is extensive information on the lack of non-target effects to diverse groups of beneficial insects including honey bees and other pollinators from Bt microbial preparations that contain Bt proteins.  Bt proteins are ideal for use in organic production and in Bt crops because they bind specifically to receptors on the mid-gut of sensitive pests and have no deleterious effect on beneficial/non-target insects under the conditions of use, including predators and parasitoids of targeted caterpillar pests and honeybees.  The following is a synopsis of the Cry1Ab toxicity testing for larval and adult bees. 

Bees were exposed to the Cry1Ab protein via ingestion of diluted honey at a concentration of 20 parts per million.  This maximum nominal concentration of 20 ppm was approximately 100 times greater than the maximum expected Cry1Ab protein level in MON 810 pollen.  In addition to this treatment group, a negative control group was treated with distilled water.  Another control group was treated with heat-attenuated (inactivated) Cry1Ab protein (20 ppm).  There were no statistically significant (P>0.05) differences in honeybee larval survival to adult emergence among the treatment and control groups. 

The mean adult survival rates after emergence ranged from 92 to 96 percent across all groups, including the controls and Cry1Ab-treated groups.  At the end of the test for adults, mortality in the treatment and the negative control groups was 16 percent and 22 percent, respectively.  The heat-attenuated control group mortality was 33 percent.  There was no significant statistical difference (P>0.05) in mortality patterns between any of the groups.  (AgBioView, 4/12/07).