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Battling the Two-Edged Sword in China:

Controlling Pests with Bt Cotton and Managing

Resistance Build-up with Refuge Policies

Fangbin Qiao

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 Bacillus thuringiensis Bt 

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On the one hand 

One the other hand 

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resistant

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 Refuge

resistant  susceptible

On plots with Bt cotton On plots with no Bt cotton

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 Is a US-style refuge policy really

 suitable for all the other countries?

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what are the optimal refuge polices for these countries?

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 It turns out that to properly model this issue, the context 

of the study (such as the dynamics of the pest  population, the nature of the cropping patterns; etc.)all matter. Therefore, a model on cotton is going to bedifferent than a model on corn

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0

20

40

60

  N o  r  t  h e  r

 C e  n  t  r a

  W e s  t e  r

   (   %

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0

1000

2000

3000

4000

5000

   1   9

   7   9

   1   9

   8   2

   1   9

   8   5

   1   9

   8   8

   1   9

   9   1

   1   9

   9  4

   1   9

   9   7

   2   0

   0   0

  (  1

 ,  0  0  0

   t o n s

  )

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 Helicoverpa

armigera

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9329

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On the one hand,

On the other hand,

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0

20

40

60

80

100

120

140160

180

1981 1985 1987 1995

Resistance factor of 

cotton bollworm to

pyrethroid

 In fact, this was not the first 

time that the bollworm

 population built up resistance.

 During the 1980s, it had built up resistance to

organophosphates.

So, farmers had to move to

using pyrethroid-based 

insecticides. The problem in theearly 1990s was that there was

nothing to move into.

This tendency of the bollworm to

evolve resistance is an

important characteristic that I 

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 Nice wine!

 Am I drunk?

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0

2000

4000

6000

1997 1998 1999 2000 2001 2002 2003 2004

  (  1 ,  0  0  0 

  h a

  )

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0

25

50

75

100

1997 1998 1999 2000 2001 2002 2003 2004

  (  %  )

 Henan, Shandong, and Hebei are the 2nd, 3rd and 4th largest cotton roduction rovinces in China

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 Bt is just another 

 pesticide. Will 

bollworms developresistance like they

did to OPs in the

1980s and 

 Pyrethroids in the1990s?0

40

80

120

1 10 18 33 38 44

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In the US: non-Bt cotton refuge

natural refuge crop

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In China: things are different There are“natural refuge crops” in the diverse croppingpattern

Definition of natural refuge crop: a crop otherthan cotton that can serve as a host for thecotton bollworm

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China’s cropping patterns are different than those in the US where cotton is often mono-cropped 

across huge areas. The typical view in China is like this. Cotton plots are planted among manydifferent crops. Farms are very diversified 

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 And, so the argument is that China does not need to spend the

time and effort developing, enforcing cotton refuges.

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In China: things are different There are“natural refuge crops” in the diverse croppingpattern

Definition of natural refuge crop: a crop otherthan cotton that can serve as a host for thecotton bollworm

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So, what are the cropping patterns like in Northern China? Are there

natural refuges? I use 3 tapes of data to show this. And information

 from these data sources are incorporated into my analysis

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my family farm (2006)

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hosted 

CORN

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∑

=

=+

−−=− geno

 geno

 geno

t t t t t 

MR D D g  D D

 No. 1

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∑

∑∑=

=

=

=

=

=

+

−−−+

−−−−+−−−=−

 geno

 geno

 geno

t t t t t 

 geno

 geno

 genot t t t t t 

 geno

 geno

 genot t t t t t t 

MR D D g ww

MR D D g wwwMR D D g wwww

∑

∑∑

=

==

+

−−−+

−−−−+−−−=−

 geno geno

t t t t t 

 geno geno

t t t t t t 

 geno geno

t t t t t t t 

MR D D g vv

MR D D g vvvMR D D g vvvv

 No. 2

 No. 3

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( )t t t t t t t 

T t 

t 

nbtcp

btcpq

nbtcpqbtcpqccpqcbt  D

t 

t 

t 

Min δ α  −+++∑=

=

≤≤

≤≤≤≤

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∑=

=

+ −−=− geno

 geno

 geno

t t t t t  MR D D g  D D

∑

∑∑

=

=

=

=

=

=

+

−−−+

−−−−+−−−=−

 geno

 geno

 geno

t t t t t 

 geno

 geno

 geno

t t t t t t 

 geno

 geno

 geno

t t t t t t t 

MR D D g ww

MR D D g wwwMR D D g wwww

∑

∑∑

=

==

+

−−−+

−−−−+−−−=−

 geno geno

t t t t t 

 geno geno

t t t t t t 

 geno geno

t t t t t t t 

MR D D g vv

MR D D g vvvMR D D g vvvv

)+

≤≤

≤≤

≤≤

=

=+−+++= t t t t t t t t 

nbtcpbtcpq

T t 

t DV nbtcpqbtcpqccpqcbt  D DV 

t 

t 

t 

Min δ α 

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        1

        0  .

        5

        0

  .        5

        1

0 5 10 15

(Year)

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       0

 .       2

 .       4

 .       6

 .       8

       1

0 5 10 15

 Even though 100% Bt cotton has been planted for 15 years, because

of these natural refuge crops, the share of the susceptible gene to Bt 

toxin is still hi h >80% at the 15th ear.

(Year)

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       0

 .       2

 .       4

 .       6

 .       8

       1

0 5 10 15

 However, if we assume natural refuge crops are not available, or cotton

is the only host plant for cotton bollworm, and if 100% Bt cotton has

been planted for 15 years, then the share of the susceptible gene to Bt 

toxin will be very low (near zero) at the 15th year. In other words, pest 

(Year)

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       0

 .       2

 .       4

 .       6

 .       8

       1

0 5 10 15(Year)

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       0

 .       2

 .       4

 .       6

 .       8

       1

0 5 10 15 20

(Year)

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       1

       0

 .       5

       0

 .       5

       1

0 5 10 15 20

(Year)

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Cost of zero refuge policy and optimal dynamic refuge

policy for 20-year plan

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        1

        0  .

        5

        0

  .        5

        1

0 20 40 60 80 100

(Year)

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Thank you!