Ecological Effects of Transgenic
Crops: Non-target Effects in Bt
Cotton
This presents the results of research only. Mention of a proprietary
product does not constitute endorsement or recommendation for its use by USDA.
Steven E. Naranjo
USDA-ARS Phoenix, Arizona
&
Peter C. Ellsworth
University of Arizona, Maricopa, Arizona
Pest Complex - Western U.S. Cotton
Key Pests
Pectinophora
gossypiella
Bemisia tabaci
Lygus hesperus
Sporadic and Minor Pests
Cotton bollworm
Tobacco budworm
Armyworms
Loopers
Cotton leafperforator
Saltmarsh caterpillar
Cutworms
Fleahoppers
Plant bugs
Stink bugs
Cotton aphid
Thrips
Spider mites
Insecticide Use Patterns
Arizona Cotton
Bt cotton
Insect growth regulators
Mean applications per acre
14
14
Pink bollworm
Whitefly
Lygus
Other
12
10
12
10
8
8
6
6
4
4
2
2
0
1
990
1
991
Ellsworth and Jones 2000
1
992
1
993
1
994
1
995
1
996
1
997
1
998
1
999
2
000
0
Selective Insecticide Use
Arizona Cotton
Bt cotton
Pyriproxyfen
Buprofezin
80
% Acreage treated
70
60
50
40
30
20
10
0
1996
1997
1998
1999
2000
Natural Enemy Complex -Western U.S.
Parasitoids
Predators
30+ species
50+ species
Hyposter
Copidosoma
Microplitis
Lysiphlebus
Chelonus
Lespesia
Eretmocerus
Encarsia
Anaphes
Leiophron
Geocoris
Orius
Nabis
Zelus
Collops
Hippodamia
Drapetis
Chrysoperla
Labidura
Misumenops
Natural Enemies – Pectinophora gossypiella
Predators
23 species described
9 species (immunological ID)
Parasitoids
4 native species described (rare)
16 exotic species introduced
(0 established)
Non-Target Effects
(Arthropods)
Function
Abundance
Diversity
General Methods
Non-target abundance/diversity

Replicated experimental studies at MAC

Treatments:

Bt cotton / conventional cotton

Unsprayed for any pest

Insecticides for all pests as needed

Sampling by sweep nets, beat buckets,
whole plants, pitfall traps

ANOVA, EstimatorS V. 5 (Colwell) for
diversity analyses
Natural Enemy Abundance
Natural Enemy Abundance
No Insecticides
4530
5611
2400
Cum. arthropod-days (50 sweeps)
2000
1999
0.28
0.40
1600
1200
0.34
800
400
0.98
0.03
0.37
0.08
0.24
0.57
0
Misum
Collops Geocoris
Orius
Nabis
Zelus
Chrysop Drapetis Hymen
1600
1200
Bt cotton
2000
0.39
0.89
800
400
Non-Bt
0.18
0.70
0.66
0.23
0.16
0.16
0.51
0
Misum
Collops Geocoris
Orius
Nabis
Zelus
Chrysop Drapetis Hymen
Natural Enemy Abundance
No Insecticides
Cum. arthropod-days (50 sweeps)
1999
2000
16000
12000
8000
Bt cotton
Non-Bt
P = 0.18
P = 0.29
6000
8000
4000
4000
2000
0
n
n
ul Aug Aug
Sep
9 Ju 29 Ju 19 J
7
8
8
1
2
0
g
p
n
n
g
ul
9 Ju 29 Ju 19 J 8 Au 28 Au 17 Se
Natural Enemy Abundance
Insecticides as Needed (e.g. 1999)
Cum arthropod-days (50 sweeps)
Cultivar
Insecticides
6000
Bt cotton
Non-Bt
5000
Unsprayed
Sprayed
4000
3000
P = 0.001
2000
1000
P = 0.92
0
29 Jun
8 Aug
17 Sep
29 Jun
8 Aug
17 Sep
Arthropod Community Structure
Community Structure – Pitfall Traps
(Bt vs. Non-Bt)
Diversity
Evenness
(Fisher's alpha)
(Shannon)
20
0.8
68
15
70
57
0.6
57
*
10
0.4
5
0.2
0
0.0
1999
2000
Non-Bt
1999
Bt cotton
2000
Community Structure – Pitfall Traps
(Sprayed vs. Unsprayed)
Diversity
Evenness
(Fisher's alpha)
(Shannon)
20
0.7
69
68
15
0.6
*
74
40
*
*
0.5
0.4
10
0.3
0.2
5
0.1
0
0.0
1999
2000
1999
Unspray
Spray
2000
Natural Enemy Function
Methods
Natural Enemy Function




Replicated experimental studies at MAC
No insecticides
Estimate rates of predation and parasitism
Sentinel pink bollworm
egg masses (20 per plot)

Life tables for whitefly
nymphs (50 per plot)
Natural Enemy Function
Predation on Pink Bollworm Eggs
1.0
19 July 2001
1 August 2001
30 August 2001
1.0
Proportion eaten
Bt cotton
Non Bt
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
Natural Enemy Function
Mortality of Whitefly Nymphs
12 July 2001
20 August 2001
Marginal rate of mortality
0.7
0.7
Bt cotton
Non Bt
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.0
Predation
Parasitism
Predation
Parasitism
Conservation Biological Control
An Example
Whitefly IPM in Cotton
Natural Enemies
Bt Cotton
IGRs
Impact of Conservation
1997
Thanks to
Virginia Barkley
Kim Beimfohr
Becci Burke
Melanie Charney
Scott Davis
Ghislaine Majeau
Ruben Marchosky
Greg Owens
Jeffrey Rivas
Doug Sieglaff