The Economics of Natural Refuge
Crops for Bt Cotton Production in
India
Rohit Singla and Anwar Naseem
McGill University
Montreal, Canada
Pros and Cons of Growing Bt Crops


Benefits of growing Bt crops (such as Bt cotton and Bt
corn) compared to non-Bt/refuge
•
Increased crop yields
•
Reduced production costs
•
Environment friendly
Resistance evolution problem
2
Refuge Requirements for Resistance
Management
• 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
Structured vs. Natural Refuge
• Structured refuge
– Mandatory refuge of the same crop
– More common in developed countries where farms
are big and cropping pattern is monocropped
– E.g. non-Bt cotton grown with Bt cotton
• Natural refuge (Unstructured refuge)
– Voluntary refuge of other crops hosting the same pest
– More common in developing countries where farms
are small and fragmented
– E.g. sunflower, pigeon pea, chilli, sorghum etc. grown
alongside Bt cotton
Effectiveness of Natural Refugia
• It has now been documented by a number of
studies (Huang et al. 2010; Singla, Johnson,
and Misra 2013; Ravi et al. 2005; Qiao et al.
2010; Gustafson, Head, and Caprio 2006) that
natural refuge can help in delaying pest
resistance in Bt crops by supporting target
pest populations.
Gaps in Knowledge
• Previous studies (examining refuge requirements
for Bt crops) considered all natural refuges
together in the model.
• Failed to examine the individual contributions of
various natural refuges.
Motivation
• To better understand the individual
contributions of different crops to act as
natural refuges
• To identify natural refuge crops and resistance
management strategies for optimal pest
control and profit maximization
Context
• Bt cotton in India
• We consider the implications for seven natural
refuge crops: sunflower, pigeon pea, corn,
chickpea, chillies, okra, tomato,
Modeling Framework
Biological Model:
•simulates the evolution of resistance in bollworms to Bt cotton/pesticides
•accounts for proportion of Bt cotton planted
•accounts for proportion of larvae in cotton and other host plants
•accounts for proportion of larvae in cotton sprayed with pesticides
Profit Model:
It is assumed that the representative producer chooses ‘qt’ that will maximize year t’s
profit without considering production possibilities in the future, subject to refuge type
0 ≤ qt ≤ rt ≤ 1; yield models; and other parameters
Regulatory Model:
objective is to choose a refuge requirement (rt) that maximizes discounted profits received during T
years, subject to: refuge type 0 ≤ rt ≤1; state transition equation
given by biological model; profit model; yield models; discount rate ρ; and other parameters
9
Data and Parameters
• Biological
– Relative densities of CBW on different crops from Ravi
et al (2005)
– Five generations of CBW in one year
• Assume environmental fitness factor of 0.6650
• Assume pesticide spray affects 3rd and 4th gen
• Bt and pyrethroid resistance parameters from Kranthi et al
(2005)
• Economic
– Cotton (lint) price of $1.49/kg; Yield 807.5 kg/ha;
Pesticide spray cost from Qaim (2003), Francis Kanoi
Approach
• What is the individual contribution of the
seven natural refuge crops?
• What are the cropping patterns under
different cropping patterns
• How sensitive are the refuge requirements to
different biological and economic parameter
values
Efficient structured refuge size
Planning
Horizons
Pigeon pea
Refuge
APVb
Chickpea
Refuge
APV
Sunflower
Refuge
APV
Okra
Refuge
APV
Tomatoes
Refuge
APV
Chilies
Refuge
APV
Corn
Refuge
APV
1
0
(0)a
824.99
0
(0)
823.65
100
(100)
803.96
0
(0)
826.19
0
(0)
816.41
0
(0)
811.28
0
(0)
824.03
2
0
(0)
824.96
0
(0)
822.54
100
(100)
803.96
0
(0)
825.83
0
(0)
815.78
0
(0)
810.75
0
(0)
823.99
3
0
(0)
824.96
7
(5)
820.51
100
(100)
803.96
0
(0)
825.55
2
(0)
814.50
7
(0)
810.17
0
(0)
823.93
4
0
(0)
824.78
15
(12)
818.77
100
(100)
803.96
0
(0)
824.88
13
(0)
813.48
13
(0)
809.38
0
(0)
823.71
5
0
(0)
824.67
22
(20)
817.53
100
(100)
803.96
3
(0)
823.65
20
(4)
23
(3)
808.78
0
(0)
823.37
6
0
(0)
824.58
26
(24)
816.51
100
(100)
803.96
10
(0)
822.46
27
(10)
811.86
30
(12)
808.42
0
(0)
822.80
7
0
(0)
824.49
33
(30)
815.76
100
(100)
803.96
12
(6)
821.50
34
(15)
811.34
32
(18)
808.07
2
(1)
821.93
8
0
(0)
824.34
35
(34)
815.12
100
(100)
803.96
19
(10)
820.61
35
(21)
810.92
38
(23)
807.82
6
(4)
820.94
9
0
(0)
824.19
40
(37)
814.56
100
(100)
803.96
21
(14)
819.88
41
(26)
810.54
40
(26)
807.62
11
(10)
820.11
10
0
(0)
823.94
41
(41)
814.10
100
(100)
803.96
26
(16)
819.28
41
(29)
44
(32)
807.43
17
(13)
819.35
812.53
810.25
a. Figures in parentheses are efficient refuge requirements when pyrethroid resistance is not considered in the base model.
b. APV values are reported in the US dollars/hectare.
Efficient refuge under different pest
density/acreage under a natural refuge
Cotton: Natural
Pest density
Min
refuges relative
proportion
Pest Density
1: ½
24
(1)a
1:1
11
(0)
1:1½
11
(0)
1:2
0
(0)
Pest density
Average
Pest density
Max
48
(23)
26
(3)
15
(0)
10
(0)
85
(72)
47
(29)
36
(14)
27
(4)
Note: The model was run for cotton-okra planted on adjacent plots of equal size.
a. Figures in parentheses are efficient refuge requirements for 5 years
Efficient refuge under various cropping
patterns
Natural refuge crops
Cropping
patterns
1
Cotton
Pigeon pea
Sunflower
2
Cotton
Pigeon pea
Chili
3
Cotton
Pigeon pea
Chickpea
4
Cotton
Pigeon pea
Chickpea
5
Cotton
Okra
Tomato
6
Cotton
Chili
Corn
7
Cotton
Okra
Corn
8
Cotton
Sunflower
Corn
Sunflower
Tomato
Refuge
requirements
65
(49)a
20
(0)
18
(0)
43
(18)
33
(11)
28
(2)
11
(0)
47
(27)
Note: It was assumed that cotton and natural refuge crops are grown on adjacent plots of equal size.
a. Figures in parentheses are efficient refuge requirements for 5 years starting from 2011-12 cropping
season
Sensitivity Analysis: 5-year planning horizon
PARAMETERS/VALUES
Value
Biological Parameters
RR Bt Fitness
0.85
RS Bt Fitness
0.46*
SS Bt Fitness
0.02
RR Bt Fitness Untreated/
0*
Fitness costs
RR Pyrethroid Fitness
0.29
RS Pyrethroid Fitness
0.0418*
SS Pyrethroid Fitness
0.0002*
RR Pyrethroid no selection
0.66
pressure
Environmental Fitness
0.27
Economic Parameters
Insecticide use equation
α = 22.39
parameters
β = -113.61
Yield loss function parameters δ = -3.11
γ=0
Pyrethroid application cost
5.0
Fixed Production costs Bt
270.44
Fixed Production costs non-Bt
260.68
Output price
0.92
Interest rate
4
Refuge Value
(%)
Refuge Value
(%)
Refuge Value
(%)
Refuge
(%)
0
0
51
16
0.90
0.60
0.06
0.05
0
23
42
12
0.95
0.70
0.25*
0.1
0
46
0
6
1*
0.80
0.35
0.15
0
70
0
4
0
0
0
0
0.4845*
0.1324
0.042
0.77
0
0
0
0
0.66
0.24
0.07
0.89
0
0
0
0
0.85
0.4
0.1
1*
0
0
0
0
0
0.4732
0
0.665*
0
0.8
0
0
α = 35.03*
β = -63.06
δ = -2.39*
γ = 0.14*
9.27*
323.0*
301.06*
1.49*
7.75*
0
α = 39.24
β = -46.22
δ = -2.15
γ = 0.21
12.02
390.28
320.08
1.75
8.2
0
α = 47.67
β = -12.52
δ = -1.67
γ = 0.31
15.06
420.42
380.28
2
9
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
100
0
0
0
Conclusions
• Pigeon pea, corn and okra are found as the
most cost effective natural refuges.
• Sunflower is found as the least cost effective
natural refuge.
• Efficient refuge size varied significantly under
various cropping patterns
Implications
• The framework developed by this study can be
used to assess the structured refuge
requirements in a specific crop-mix.
• The assessment can help in making suggestions
to farmers on type of and acreage under a
natural refuge crop they may plant.
• The framework developed by this study will help
in evaluating the role of natural refuges for Bt
crops in other countries.
Thanks!