[Pollinator] Safety Assessment of Bt Crops for Adult and Larval Honeybees, FYI

[R. Thomas Van Arsdall]

The information below was forwarded to my attention by a colleague and may
be of interest to you.  Tom VA

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Safety Assessment of Bt Crops for Adult and Larval Honeybees

- by Eric Sachs, Yong Gao and Jian Duan, Presented March 29, 2007, Public
Hearing, Subcommittee on Horticulture and Organic Agriculture

Summary 

--Entomologists have not been able to determine the cause of CCD (colony
collapse disorder) in honey bees. 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
caterpillar 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. 

--Scientists perform extensive honeybee safety assessments on all
insect-protected crops, including Bt corn and Bt cotton. The Bt proteins in
these crops have been shown to have no adverse effect on the honeybee. 

--EPA risk assessments have demonstrated that Bt proteins expressed in Bt
crops do not exhibit detrimental effects to non-target organisms in
populations exposed to the levels of Bt proteins produced in plant tissues. 

--Specific studies involving Cry1Ab provide strong evidence of the safety of
MON 810 Bt corn to the honeybee (similar studies have been conducted with
other Bt proteins in genetically modified crops). 

--The EPA concluded that based on the weight of evidence there are no
unreasonable adverse effects of the Cry1Ab protein expressed in MON 810 Bt
corn to non-target wildlife or beneficial invertebrates. 

Colony Collapse Disorder in Honey Bees 

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. This
phenomenon has been described by honeybee experts 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. 

Safety of Commercialized Bt Proteins in Corn and Cotton 

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. The Bt proteins produced
in Bt corn and Bt cotton are present in microbial products used in
agricultural systems to control targeted pests. Bt proteins are extremely
selective and are toxic only to specific pests . A generalized mode of
action for Bt proteins includes ingestion of the protein crystals by
insects, solubilization of the crystals in the insect midgut and proteolytic
processing of the released Bt protein by enzymes, and binding of the
partially digested "activated" protein to specific high-affinity receptors
on the surface of the midgut epithelium of target insects . 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 caterpillar 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 honeybee (Apis mellifera) . 

Safety Assessment of Bt Crops 

Scientists perform extensive honeybee safety assessments on all
insect-protected crops, including Bt corn and Bt cotton. The Bt proteins in
these crops have been shown to have no adverse effect on the honeybee. EPA
evaluated studies of potential effects on a wide variety of non-target
organisms that might be exposed to the Bt protein, e.g., birds, fish,
honeybees, ladybugs, parasitic wasps, lacewings, springtails, aquatic
invertebrates and earthworms. Such non-target organisms are important to a
healthy ecosystem, especially the predatory, parasitic, and pollinating
insects . These risk assessments demonstrated that Bt proteins expressed in
Bt crops do not exhibit detrimental effects to non-target organisms in
populations exposed to the levels of Bt proteins produced in plant tissues. 

To illustrate how the different Bt proteins produced in Bt crops are
evaluated for safety to the honeybee, two representative studies are
described below for the Cry1Ab protein produced in MON 810 Bt corn. These
studies with Cry1Ab protein were conducted with the trypsin-resistant core
because this is the insecticidally-active portion of the Cry1Ab protein.
Specific studies designed to assess the potential for adverse effects to
developing larval and adult honeybees are described below. 

Honeybee Larva. 

The primary route of exposure for honey bee larvae to the Cry1Ab protein is
ingestion of pollen collected by foraging adults from genetically modified
plants. Therefore, honey bee larvae were exposed to Cry1Ab protein in their
natural diet by including a maximum hazard dose (20 parts per million in
distilled water mixed with honey) in developing brood cells. 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), and one set of larvae received no treatment (untreated
control). At least 50 bees (1 to 4 days old) were in each replicate, and
there were three replicates for each group. The treatments were administered
to each larval cell through an electronic micro-applicator, which delivered
5 microliters (?L) of the test diet. Once the first bee emerged on day 15,
daily counting of emerged bees was performed and emerged bees were removed
to an adult holding cage. The test diet was renewed daily and the study was
terminated 48 hours after the last bee had emerged on day 19. 

There were no statistically significant (P>0.05) differences in honeybee
larval survival to adult emergence among the four treatment groups. The mean
adult survival rates after emergence ranged from 91.7% to 96.0% across all
groups, including the controls and Cry1Ab-treated groups. This study
demonstrates that honeybee larvae were not adversely affected after being
exposed to Cry1Ab protein at a concentration of 20 ppm in their diet. 

Adult Honeybee. 

Adult bees reared in bee hives were immobilized using CO2. The test diet was
prepared by mixing the appropriate amount of the insecticidally-active
Cry1Ab protein with a honey-water (50-50) syrup to a concentration of 20
parts per million (?g protein/g diet; ppm). The negative control group was
fed the same diet with the exception that no Cry1Ab protein was added to the
honey-water mixture. A second control group was fed heat-attenuated
(inactivated) Cry1Ab protein at the same concentration (20 ppm) as the
treatment group. A fourth test system was an empty cage to measure the
amount of diet loss due to evaporation. All diets were presented to the bees
in a 6 ml shell vial inserted through a cork in the holding cage lid. Three
replicates of four test groups of at least 40 adult honeybees were selected
and placed in each holding cage. Two observations were made the first day
and were made daily for the duration of the 9-day study. At the time of the
daily observation, the test diets were replaced with fresh vials containing
the appropriate concentration of test material. The test was terminated on
day 9 when the mortality rate in the negative control group exceeded 20%. 

Adult honeybees exposed to the Cry1Ab protein in a honey-water solution for
9 days at a concentration of 20 ppm showed no signs of treatment-related
mortality or toxicity. At the end of the testing period, the mortality
percentage was calculated for each group. Mortality in the treatment and the
negative control groups was 16.20% and 22.28%, respectively. The
heat-attenuated control group mortality was 32.59%. Mortality showed a sharp
increase in all three groups from days 6 through 9. At the termination of
the test, the highest mortality was observed in the group that was fed the
heat-attenuated Cry1Ab protein diet, while the lowest mortality was observed
in the group that was fed the Cry1Ab protein diet. The mortalities in the
treatment group are not considered to be treatment-related because the two
control groups showed a higher percentage of mortality over the same time
interval. There was no significant statistical difference (P>0.05) in
mortality patterns between any of the groups. 

The EPA concluded that based on the weight of evidence there are no
unreasonable adverse effects of the Cry1Ab protein expressed in MON 810 Bt
corn to non-target wildlife or beneficial invertebrates . They reported no
measurable deleterious effects were observed in submitted studies of the
Cry1Ab protein administered to honey bee larvae, honey bee adults, parasitic
wasps, Ladybird beetles, green lacewings, Collembola (springtails), and
Daphnia. 

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1. Wolfersberger et al., 1986; Hofmann et al., 1988a; Hofmann et al., 1988b;
Van Rie et al., 1989; Van Rie et al., 1990 

2. Dulmage, 1981; Klausner, 1984; Aronson et al., 1986; Whiteley and
Schnepf, 1986; MacIntosh et al., 1990 

3. Hoffman et al., 1988a, Hoffman et al., 1988b; Van Rie et al., 1989; Van
Rie et al., 1990; Wolfersberger et al., 1986 ; English and Slatin, 1992 

4. Wolfersberger et al., 1986; Hofmann et al., 1988a; Hofmann et al., 1988b;
Van Rie et al., 1989; Van Rie et al., 1990 

5. Cantwell et al., 1972; Krieg and Langenbruch, 1981; Flexner et al., 1986;
EPA, 1988; Vinson, 1989; and Melin and Cozzi, 1990 

6. US EPA. Bt Plant-Pesticides Biopesticides Registration Action Document.
http://www.agbios.com/docroot/articles/2000264-A.pdf 

7. US EPA. Bt Plant-Incorporated Protectants October 15, 2001 Biopesticides
Registration Action Document.
http://www.epa.gov/pesticides/biopesticides/pips/bt_brad2/1-overview.pdf

Bee Ready for National Pollinator Week, June 24-30, 2007! For more info: 
www.pollinator.org 
 
R. Thomas (Tom) Van Arsdall, Public Affairs Representative for Coevolution
Institute/NAPPC
   Van Arsdall & Associates
   13605 McLane Place
   Fredericksburg, VA  22407-2344
   (540) 785-0949
   tom at vanarsdall.com