Insect Resistance

Question 1

What happened in with insecticide in Spain?

Answer 1

Farmers sprayed less insecticide, profit per hectare was increased.

Question 2

What is Bacillus thuringiensis (Bt)?

Answer 2

Aerboic gram-positive spore forming bacteria
Produces delta-endotoxins during sporulation.
Delta-ednotoxin crystals dissolve in the insects gut and get broken down by the digestive system, forming the active toxin.
Toxin disrupts cell membranes and kills gut.

Question 3

How is Bt applied to fields?

Answer 3

Toxins are extracted from the bacteria and sprayed on the fields.

Question 4

What are the benefits of using the Bt toxin over chemical pesticides?

Answer 4

• Specificity (for pests, activities)
• Bt is readily degraded in the environment
• Some pesticides are highly toxic

Question 5

What are targets of Bt?

Answer 5

• Diamond black moth
• Tobacco mudworm
• Colorado beetle

Question 6

What are the advantages of the Bt toxin?

Answer 6

• Not toxic to mammals
• (Maybe) impossible for resistance as bacteria and host had coexisted for a long time

Question 7

What are the disadvantages of the Bt toxin?

Answer 7

• Quickly broken down so has to be resprayed often
• Must come into contact with the target

Question 8

What are the advantages of GM crops that express Bt?

Answer 8

• Don’t need to repeatedly spray crops
• All parts of the plant contains Bt
• Highly effective

Question 9

What are the disadvantages of GM crops that express Bt?

Answer 9

• Selection pressure for insects resistance is higher
• Bt gene may be transferred to other plants
• Impacts on non target organisms

Question 10

What is Bt cotton otherwise known as and what does it do?

Answer 10

Bollgard
- Protects against Tobacco budworm and pink bullworm
- Bollgard I: contains 1 toxin (cry1A)
- Bollgard II: contains 2 toxins (cry1A cry2B)

Question 11

What are the problems with Bt?

Answer 11

• Effectiveness: Bollgard protection is not complete
• Impacts on non target organisms
• Impacts of Bt pollen on monarch butterflies
• Toxin persists in environment plant material

Question 12

Why don’t GM studies compare like for like?

Answer 12

Access to GM plants is restricted by contracts
GM licensing takes a long time

Question 13

What are the solutions to problems with resistance?

Answer 13

• Use as part of an integrated pest management scheme
• Use multiple toxins
• Rotate crops
• Plant mosaics
• Use refuges to maintain sensitive population

Question 14

What are refuges?

Answer 14

Non Bt variety grown in same field as Bt variety, tries to lower resistance

Question 15

What are problems with refuges?

Answer 15

• Unpopular with farmers
• Poor compliance