AAEA July 2007

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Information about AAEA July 2007
Education

Published on January 28, 2008

Author: Valentina

Source: authorstream.com

Battling the Two-Edged Sword in China: Controlling Pests with Bt Cotton and Managing Resistance Build-up with Refuge Policies:  Battling the Two-Edged Sword in China: Controlling Pests with Bt Cotton and Managing Resistance Build-up with Refuge Policies Fangbin Qiao California State University, Fresno Introduction:  Introduction The development of Bacillus thuringiensis (Bt) crops globally is the most successful application of agricultural biotechnology 2004: 23 million hectares (globally) (Million hectares) Bt corn: 12 countries Bt cotton: 8 countries:  Bt corn: 12 countries Bt cotton: 8 countries It is believed that both the number of the countries where Bt crops are planted and the total planting area of Bt crops will keep increasing in the future. The main function of Bt crops:  The main function of Bt crops Bt crops are produced by inserting the gene from bacterium Bacillus thuringiensis – frequently abbreviated as “Bt” – into the DNA of a crop. What does the Bt toxin do? Kills many types of caterpillars: In the US, bollworm, budworm and others In China, bollworm and others Bt crop is a “two-edged sword”:  Bt crop is a “two-edged sword” On the one hand, Bt crops help farmers by providing pest control services One the other hand, there are worries about its success: One of the major worries is the buildup of pest resistance Pest control and pest population dynamics (the theory in the US) :  Pest control and pest population dynamics (the theory in the US) If 100% of farmers plant 100% Bt crop Bt crop kills most of pests BUT, those that survive are likely have a resistant gene. Buildup of resistance: If the share of the total population with a resistant gene grows large enough, Bt crop is not effective in controlling the pest One strategy to combat the build-up of resistance: Refuge:  One strategy to combat the build-up of resistance: Refuge Bt crop kills most of pests Non-Bt field as refuge Those surviving are likely have a resistant gene Pest with susceptible gene will survive. Slow down the buildup of the resistance Re-production On plots with Bt cotton On plots with no Bt cotton The US is the first country where refuge is required:  The US is the first country where refuge is required US EPA: Fixed refuge policy 5% if the farmer does not spray any conventional pesticide 20% if the farmer sprays Other countries (both developed and developing) basically follow the same strategy. For example: Mexico; India; Canada. Refuge Slide9:  BUT, refuge is also a two-edged sword In addition to BENEFITS Slows down the buildup of the resistance, so that Bt crop can be used for a longer time There are also COSTS Most pests will survive and they can cause MORE damage Goal of Refuge Policy: Find the “optimal refuge size” that balances the benefits and costs Main question for my presentation:  Main question for my presentation Even though all these countries follow the US-styled refuge policies, surprisingly, there is almost no research basis for these choices, In other words, there is no empirical study to answer: Is a US-style refuge policy really suitable for all the other countries? The first objective of my study:  The first objective of my study Is US-styled refuge policy appropriate for all countries where Bt crops are grown? My focus is on developing countries. Should developing countries require farmers to plant refuge? But, in fact, this is going to be relevant even for the US. Studies (Livingston et al., 2004 ) show that the size of the US refuge is too big. In other words, farmers can get more benefit if a smaller refuge size was required. The second objective of my study:  The second objective of my study If the US-styled refuge regulations are not appropriate, what are the optimal refuge polices for these countries? Again: I will focus on the case of developing countries. I will try to develop a method to guide policy makers in their decisions on two dimensions: 1. Size of the refuge 2. Whether it should be fixed or “dynamic”. In other words, should we fix the refuge size as required by the current policies? Or, should we allow the size to change over time: maybe small or zero in the first years after adoption and larger over time, maybe the opposite. Narrowing the scope:  Narrowing the scope Because these objectives are very broad, I must narrow the focus of the study. Focus on Bt Cotton (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 be different than a model on corn) Does not explicitly consider enforcement costs in the modeling, though I discuss how this might affect the final answer on refuge policy at the end Focus on China Why China?:  Why China? One of the leaders in the creation and use of Bt crops: 3.7 million ha in 2004, two thirds of all the cotton in China More than 6 million farmers planted Bt cotton Also this is an important policy issue inside China: whether China needs to re-think its zero refuge policy Empirical data: key to determining the optimal refuge size Refuge in China? - A “hot” debate:  Refuge in China? - A “hot” debate Others are a proponent of a ZERO refuge policy (e.g., Wu et al., 2002) Some advocate a US-styled refuge policy (e.g., Xue, 2002) NO! YES! Who is winning the debate? The first group: China is the only country in the world with a refuge requirement = 0 Rest of my presentation:  Rest of my presentation The “Story” of Bt Cotton in China (this will provide the “facts” for the rest of my analysis) Modeling Approach Results Conclusions Bt cotton in China:  Bt cotton in China In this section, I will introduce some of the key points about the cropping system, technology and pest population in my study area China’s cotton production in general Buildup of resistance in the pest population Bt cotton’s rise Debate on whether China needs to have refuges These topics have been chosen because they are going to play an important role in my analysis Main cotton production regions:  Main cotton production regions Western or Northwest Northern or Yellow River Valley (My study will focus on Northern China) Central or Yangtze River Valley Northern: largest cotton production region :  Northern: largest cotton production region Average Shares of Main Cotton Producing Areas, 1979 - 2000 But, Northern region is beginning to lose its “No.1” position in the early 1990s:  But, Northern region is beginning to lose its “No.1” position in the early 1990s Northern Central Western Annual production of main cotton production regions, 1979-2000 Why falling: emergence of serious cotton bollworm problems:  Why falling: emergence of serious cotton bollworm problems The Cotton Bollworm: Latin name: Helicoverpa armigera According to Estimates by China’s Pest Control Extension Agents: Cotton producers suffered great yield losses due to pests in Northern China:  According to Estimates by China’s Pest Control Extension Agents: Cotton producers suffered great yield losses due to pests in Northern China Virtually, during the field survey, every farmer that I talked to told me that if they did not spray conventional pesticides, they would harvest nothing. In response: China’s cotton farmers use more pesticides than farmers in almost any other country in the world:  In response: China’s cotton farmers use more pesticides than farmers in almost any other country in the world Sources: a CCAP data; b Tomas W. Fuchs Summary: cotton production in Northern China in early 1990s:  Summary: cotton production in Northern China in early 1990s Largest producing area in China Began to lose its No 1 position in early 1990s (actually declined in absolute area) Main cause of decline: rising cotton bollworm population On the one hand, cotton producers in Northern China use more pesticides than farmers in almost any other country in the world On the other hand, they suffered great yield losses Why? Main problem: buildup of resistance to the conventional pesticides:  Main problem: buildup of resistance to the conventional pesticides 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 the early 1990s was that there was nothing to move into. This tendency of the bollworm to evolve resistance is an important characteristic that I will consider in my modeling. As buildup of resistance, pesticide is not effective in controlling cotton bollworm:  Conventional pesticide Nice wine! Am I drunk? As buildup of resistance, pesticide is not effective in controlling cotton bollworm During the field surveys, I have seen farmers put conventional pesticide directly on the cotton bollworm. And what we saw is that the cotton bollworm could move as fast as before, if not faster. So, indeed, in the early 1990s: China’s cotton industry was in crisis:  So, indeed, in the early 1990s: China’s cotton industry was in crisis Response? China’s government commercialized Bt cotton in 1997 The adoption of Bt cotton has been nothing short of Remarkable:  The adoption of Bt cotton has been nothing short of Remarkable From a very small number in 1997 to 3.7 million hectares in 2004 Non-Bt cotton Bt cotton (Year) The adoption rates of Bt cotton in Northern region are nearly 100%:  The adoption rates of Bt cotton in Northern region are nearly 100% Should this concern policy makers in China? Recall: In the US, farmers must maintain a refuge? Henan Shandong Hebei Henan, Shandong, and Hebei are the 2nd, 3rd and 4th largest cotton production provinces in China In addition, entomologists told us that cotton bollworm CAN build up resistance in the laboratory - So, there is a reason for concern:  In addition, entomologists told us that cotton bollworm CAN build up resistance in the laboratory - So, there is a reason for concern Bt is just another pesticide. Will bollworms develop resistance like they did to OPs in the 1980s and Pyrethroids in the 1990s? (Generation) Resistance factor However, no evidence of buildup of resistance in the field – Good news:  However, no evidence of buildup of resistance in the field – Good news Why no buildup of resistance in the field?:  Why no buildup of resistance in the field? In the US: non-Bt cotton refuge In China: things are different  There are “natural refuge crops” in the diverse cropping pattern Definition of natural refuge crop: a crop other than cotton that can serve as a host for the cotton bollworm Why no buildup of resistance in the field?:  Why no buildup of resistance in the field? In the US: non-Bt cotton refuge (look at Texas and see why cotton refuges might be needed) In China: things are different  There are “natural refuge crops” in the diverse cropping pattern Definition of natural refuge crop: a crop other than cotton that can serve as a host for the cotton bollworm Cropping Pattern with U.S. Characteristics:  Cropping Pattern with U.S. Characteristics Cropping patterns with Chinese characteristics:  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 many different crops. Farms are very diversified cotton peanuts corn Cropping patterns with Chinese characteristics apple trees Extremely fragmented plots act as a “natural refuge” :  Extremely fragmented plots act as a “natural refuge” And, so the argument is that China does not need to spend the time and effort developing, enforcing cotton refuges. cotton corn When I was in china doing my field work, I took 100s of pictures like this, you could not find an area like Texas Why no buildup of resistance in the field?:  Why no buildup of resistance in the field? In the US: non-Bt cotton refuge (look at Texas and see why cotton refuges might be needed) In China: things are different  There are “natural refuge crops” in the diverse cropping pattern Definition of natural refuge crop: a crop other than cotton that can serve as a host for the cotton bollworm Natural refuge crops in China:  Natural refuge crops in China Which crops are the host plants of cotton bollworm in China? Wheat Maize Peanuts Soybeans Weeds Fruit trees And many other crops Focus of this study: Northern region of China’s cotton-producing areas:  Focus of this study: Northern region of China’s cotton-producing areas Western Northern Central Main areas in which farmers in China use Bt cotton Also it is the area of greatest bollworm infestations. 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 Looking at the “Macro View (county level data)”, it appears as if China’s diversified cropping patterns are pervasive :  Looking at the “Macro View (county level data)”, it appears as if China’s diversified cropping patterns are pervasive The green: areas where the share of cotton area is less than 5%; The red: even in the most intensive cotton growing areas, the share is more than 60% Hebei Henan Shandong Diversified cropping patterns at the micro-level (village level data):  Diversified cropping patterns at the micro-level (village level data) Villages in the heart of the Northern cotton production region Source: CCAP Slide42:  My hometown Shandong Hebei Henan Diversity of cropping pattern on my family farm (2006):  Diversity of cropping pattern on my family farm (2006) Total: 0.7 acres Cotton (0.2 acres), Corn (0.2 acres), Peanut (0.1 acres), Soybean and Vegetables (0.2 acres) My parents are still farmers. I was also a farmer before I went to college. In fact, even after I went to college, during summer holidays, I spent most of time on conventional pesticide spray in the cotton field. I know every step of cotton production, from breeding to harvest. I and my sister lost some of the land after we went to college, which make our family farm even smaller. Summary: Why China may not require a refuge policy for Bt cotton:  Summary: Why China may not require a refuge policy for Bt cotton Bollworm can be hosted by “natural refuge crops” In one year, bollworms reproduce 4 times. Or, there are four generations per year. 1st generation: wheat 2nd and 3rd generations: soybean, peanuts, weeds, fruit trees, etc. 4th generation: soybean, peanuts, weeds, fruit trees, etc. + CORN Whether China need to re-think its zero refuge policy?:  Whether China need to re-think its zero refuge policy? On the one hand, bollworms tend to quickly develop resistance (so, maybe “yes”) On the other hand, there are many natural refuge crops (so maybe “no”) Therefore, we need a quantitative–based analysis to try to answer this question more precisely Modeling Approach:  Modeling Approach Explain the structure of the model Biological part Economic part Describe where the parameters come from My own survey and interviews in China Data from entomologists and breeders Data from economists and other previous studies Model simulation Biological part & economic part:  Biological part & economic part Biological part is used to simulate the dynamic of the nature of the pest population Economic part is used to estimate the impact of different refuge policies The economic part is easy to understand after we understand the biological part, so in the following, I will start with the biological part The model: biological part:  The model: biological part Three state variables: total pest population fraction of the susceptible gene to the Bt toxin fraction of the susceptible gene to conventional pesticides Two control variables: Bt cotton Conventional pesticides Renewable resource model (non-zero fitness cost) The model: biological part:  The model: biological part Two-locus four-allele model Susceptible gene to Bt toxin Susceptible gene to conventional pesticide The susceptible (X) and resistant (x) alleles to Bt toxin at locus one; and the susceptible (Y) and resistant (y) alleles to conventional pesticide at locus two Divide the total pest population into nine types of pests with different genes: XXYY, XXYy, XXyy XxYY, XxYy, Xxyy xxYY, xxYy, xxyy For example: one type of pests:  For example: one type of pests XXYY is one type of pests with: double susceptible (X) alleles to Bt toxin, and double susceptible (Y) alleles to conventional pesticide. In other words, it is a susceptible homozygote. And accordingly, it have a high mortality rate if it is controlled either with Bt toxin or conventional pesticide. To figure out the fraction of pest population with different genes, follow 3 steps::  To figure out the fraction of pest population with different genes, follow 3 steps: Step 1: Assume “w” is the fraction of susceptible gene to Bt toxin Step 2: Assume “v” is the fraction of the susceptible gene to conventional pesticides (… How do you get estimates of “w” and “v”? Its like taking all of the pest in China, grinding them up into one big pot and then sampling how many X’s , how many x’, how many Y’s, and how many y’s ). Where did I get it in reality? I got this from a colleague of mine from CAAS (Wu Kongming who is one of the world’s leading authorities on bollworms …) Step 3: after I know “w” and “v”, I can use formulas from genetics to determine the fractions of the 9 types of pest. (This can actually be taken from any basic genetics text book. In fact, I studied genetics in college. And found these formulas in the text books that I used. 9 types of pests & their fractions:  9 types of pests & their fractions A simple sketch of the biological part:  A simple sketch of the biological part New Born bollworms Spray No spray Bt cotton field Non-Bt cotton field Death Spray No spray Natural refuge crops Now we understand what the population looks like in a static manner. Next, we need to know how it evolves through time, which means we need to know something about the birth-mortality dynamics Slide54:  There are basically 4 ways that bollworms die: they can be treated with conventional insecticide or not, or they can die on Bt area or non-Bt area. This means that there are four types of land on which the population changes over time Bt cotton with CP spray Bt cotton without CP spray Non-Bt cotton with CP spray Non-Bt cotton without spray and natural refuge crops 2 treatments & 4 types of lands Nine genotype pests, their fractions, and mortality rates in different fields:  Nine genotype pests, their fractions, and mortality rates in different fields 9 types of pests with different genes Fractions of these 9 types of pests Mortality rates of these 9 types of pests in 4 different types of land 4 types of land So how do I use these mortality rates? – calculate the dynamics of the 3 state variables:  So how do I use these mortality rates? – calculate the dynamics of the 3 state variables No. 1 Change of the bollworm population from generation (t) to generation (t+1) New born bollworms in generation (t) Total number that die, which incorporates the mortality rate from the previous slide Dynamics of the other 2 state variables:  Dynamics of the other 2 state variables These two equations show the dynamics of the two other state variables – changing fraction of genes that are susceptible to Bt or conventional pesticides from generation to generation, although these are more complicated. These state variables evolve over time, depending on the mortality rates and crosses of the different types of cotton bollworms No. 2 No. 3 The model: economic part:  The model: economic part The economic part is used to estimate the impact of different refuge policies A social planner minimizes the total cost: Damage cost caused by the pests Control costs of planting Bt cotton Control costs of spraying conventional pesticide Objective function:  Objective function Damage cost Control cost of planting Bt cotton Control cost of spraying conventional pesticide Note: all of the costs are linear. This is going to be important when we solve the problem. The full model (both parts):  The full model (both parts) Subject to: Parameters: default value:  Parameters: default value How do I use the model?:  How do I use the model? Short run plans 15 year time horizon 20 year time horizon Long run plan 100 year time horizon 15-year plan: planting refuge is NOT economic:  15-year plan: planting refuge is NOT economic 100% Bt cotton 0% conventional pesticide 0% 100% 100% Conventional Pesticide Land planted Bt cotton Note: in my problem, it is possible that farmers BOTH spray and plant Bt cotton. Recall this is one type of my land use. Assume: farmers can plant natural refuge crops, so the proportions in this graph is the share of total cotton area (Year) The key: the role of natural refuge crops :  The key: the role of natural refuge crops Share of susceptible gene to Bt toxin (with Natural Refuge) 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 high (>80%) at the 15th year. (Year) The key: the role of natural refuge crops:  The key: the role of natural refuge crops With Natural Refuge Without Natural Refuge 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 developed resistance. (Year) Recovers of the susceptibility to Conventional Pesticide (CP):  Recovers of the susceptibility to Conventional Pesticide (CP) Remember that in China, CP are not very effective. Why? Because there is such a low % of the bollworm population that is susceptible, and the rest are resistant to CP Share of the susceptible gene to CP Share of the susceptible gene to Bt (Year) 20-year plan: conventional pesticide (CP) is used when susceptibility to CP recovers:  20-year plan: conventional pesticide (CP) is used when susceptibility to CP recovers Share of the susceptible gene to CP Share of the susceptible gene to Bt (Year) 20-year plan: conventional pesticides are used:  20-year plan: conventional pesticides are used Share of land planted with Bt cotton Share of land sprayed with CP (Year) 20-year plan: optimal dynamic policy provides lower cost:  20-year plan: optimal dynamic policy provides lower cost Cost of zero refuge policy and optimal dynamic refuge policy for 20-year plan Because of transaction costs, zero refuge is better in the 15-year and 20-year models:  Because of transaction costs, zero refuge is better in the 15-year and 20-year models Transaction costs are ignored in the model Cost associated with enforcement Monitoring costs How high are monitoring costs? In the summer of 2004, I conducted 96 village-level survey in Hebei, Shandong and Henan provinces My goal: to generate an estimate of the cost of monitoring refuges Results of my survey: US$ 6.97 per hectare/year > US$ 2.46 Now lets turn to the “Long-run plan”:  Now lets turn to the “Long-run plan” Expectation: in a long run, farmers use these two weapons alternatively to control pests Conventional pesticide Bt cotton and, 100-year plan: alternative use of Bt and conventional pesticide (CP):  100-year plan: alternative use of Bt and conventional pesticide (CP) Share of land sprayed with CP Share of land planted with Bt cotton (Year) Conclusions:  Conclusions The US-styled refuge policy is not appropriate for China The optimal refuge policy for China is zero refuge policy for short run The reason for zero refuge policy: diverse cropping pattern  natural refuge crops  slow down the buildup of resistance Slide74:  Thank you!

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