Bt is a naturally-occurring soilborne bacterium that is found worldwide.
A unique feature is production of crystal-like proteins that selectively kill specific groups of insects.
These crystal proteins (Cry proteins) are insect stomach poisons
Insects stop feeding within two hours of a first bite and, if enough toxin is eaten, die within two or three days
Why does corn need protection from corn borers?
It is estimated that, each year, 40 million tons of corn never reach the market due to damage.
If corn borers are not controlled, the larvae will eventually turn into moths and the cycle continues.
Bt corn produces a protein that gives Bt corn built-in resistance to the corn borer – offering protection throughout the plant where the insect attacks.
Stalk tunnel after infection Tunneling of borer
How does Bt corn work?
Bt maize has built-in protection against corn borers, achieved through modern biotechnology, where the Cry1Ab gene has been added.
The Cry1Ab gene produces a Bt protein (Cry1Ab) which protects the plant from insect damage ( Bacillus thuringiensis )
Additionally, a marker gene as been added which gives the plant a tolerance to phosphinothrici. ( Streptomyces viridochromogenes )
Bt-11 insect-protected maize produces the Bt protein in its leaves, silks, stalks and ears throughout its life, enabling it to provide season-long protection against these devastating insect pests.
‘ Gene gun’ to transform corn to Bt
What are the benefits of Bt corn?
It represents an environmentally sustainable way to control devastating insect pests and, therefore, to ensure yield.
Also, grain from Bt corn is often of better quality than grain from conventional corn hybrids, since insect damage reduces grain quality.
Studies show that there is a significant economic return from growing Bt corn, with yields protected in years when there is a heavy outbreak of corn borer.
There is also evidence that Bt corn provides a form of protection to non-Bt corn by reducing the overall population of corn borers
Bt corn field
Performance of Bt hybrids over non Bt
Expected benefits are based on the following assumptions
Bt corn (MON810, BT11) provides 96% average control of European corn borer larvae,
Bt corn (event 176) provides 96% control of first generation corn borers and 75% control of second generation corn borers.
Insecticides provide 80% and 67% control of first and second generation borers, respectively.
Physiological losses average 5.5% and 2.8% for first and second generation tunnels, respectively.
Corn yields average 123 bushels per acre nationally.
Market price averaged $2.33 per bushel from 1991-1995.
Bt hybrids have no yield penalties.
Improved corn production will not affect corn price
How do you know Bt corn is safe?
The plant biology of Bt corn and its characteristics have been determined to be comparable, or substantially equivalent, to non-Bt corn.
These tests assess the composition, nutrition, and general wholesomeness of Bt corn compared to non-Bt corn.
Before Bt corn was approved for sale, it had to be demonstrated that any minor differences that were observed in scientific testing were within the range of normal variations in corn.
The safety of Bt corn for human and animal health has also been thoroughly addressed.
These assessments considered and tested the possibility of allergic reaction.
The assessments also evaluated the possibility that earlier techniques, which were used to select transformed plants, could be linked to antibiotic resistance.
This extensive research led to the conclusion that Bt corn is as safe as non-Bt corn for human and animal health.
Does growing Bt corn have any adverse effects on the environment?
Before Bt corn could be approved, regulatory authorities thoroughly considered a wide range of research examining the possible impacts of Bt corn on non-target organisms including bees, ladybirds, butterflies, beetles, birds and small mammals.
The mechanism whereby Bt protein controls the corn borer is highly specific, and most non-target organisms in the field are not affected by it. Rather, these animals digest the protein along with all the others in their diet.
Does Bt corn affect beneficial insects and natural enemies?
Many studies have shown that Bt Cry proteins are highly selective in killing larvae of moths.
Bt corn, however, does not affect beneficial insects including honey bees, lady beetles, green lacewing larvae, spiders, pirate bugs or parasitic wasps .
Indirect effects on natural enemies of European corn borer, however, could occur.
Predators, parasites and pathogens of the corn borer might decline as corn borer populations decline.
How exactly does Bt corn protect itself from the corn borer?
Specific strains of Bacillus thuringiensis produce a protein, often called “Bt protein”.
When eaten by a corn borer, Bt protein is broken down by digestive enzymes in the larva’s alkaline (basic pH) intestine, generating a shorter protein that binds to specific receptor proteins in the wall of the intestine of the target insect pest.
This damages the cell membrane, making it leaky, and stopping the larva in its tracks.
Can European corn borer develop resistance to Bt corn?
European corn borer may have the potential to develop resistance to Bt Cry proteins.
Insects are known for their ability to rapidly develop resistance to certain insecticides.
Resistance occurs particularly when insecticides are used repeatedly and at high concentrations
Some of these factors for the European corn borer include:
predictions for widespread use of Bt corn,
and two or more generations per year.
What is the best strategy for using Bt corn?
Insect control by Bt expression is only one trait that farmers need to consider in their selection of hybrids.
Bt genes only protect the yield potential inherent in the hybrid.
Corn borer populations fluctuate, looking at hybrid performance over several years is important
The best strategy for using Bt corn may be to protect fields likely to bear the heaviest brunt of European corn borer attack or fields with the highest yield potential
What future improvements to corn and other plants are planned?
As the example of Bt corn demonstrates, genetically enhanced crops can offer significant benefits.
It is an illustration of how a single modification – enabling Bt corn to protect itself against the corn borer – can make a tremendous difference.
But developments to date have only offered a glimpse of the contribution that genetically enhanced crops will make to world food production and human health in the future.
Key Steps to Implementing a Resistance Management Plan for European Corn Borers
Use Bt corn hybrids in fields where the risk of severe European corn borer infestations warrants the price premium for seed.
Carefully record and mark where Bt and non-Bt corn hybrids are planted, so Bt corn performance can be monitored and non-Bt corn can be scouted .
Plant non-Bt corn at a similar time and in close proximity to Bt corn.
Continue to use an IPM approach for all pests, as Bt corn is just one tool for European corn borer management.
Monitor Bt corn to verify European corn borer control for both first and later-season generations. Do not wait until harvest
Bt corn is not developed in India.
The first released Bt corn, (ie) Bt11 is not accepted in the market