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Efficacy of transgenic cotton plant containing the Cry1Ac and Cry2Ab genes of Bacillus thuringiensis against Helicoverpa armigera and Syllepte derogata in cotton cultivation in Burkina Faso
Crop Protection 28 (2009) 205–214
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Efficacy of transgenic cotton plant containing the Cry1Ac and Cry2Ab genes of Bacillus thuringiensis against Helicoverpa armigera and Syllepte derogata in cotton cultivation in Burkina Faso Omer He´ma a, *, Hugues Ninaon Some´ a, Ouola Traore´ a, John Greenplate b,1, Mourad Abdennadher c, 2 a b c
INERA (Institut de l’Environnement et de Recherches Agricoles), 01 BP 208, Bobo-Dioulasso 01, Burkina Faso Monsanto Co, 800 N. Lindbergh Blvd, St Louis, MO 63167, United States Monsanto South Africa, Fourways Office Park, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 June 2008 Received in revised form 24 September 2008 Accepted 25 September 2008
As part of the research into alternatives to pyrethroids, to which lepidopteran cotton pests have begun to develop resistance, transgenic cotton expressing two endotoxins (Cry1Ac and Cry2Ab) of Bacillus thuringiensis Berliner (Bt), in the U.S. germplasms DP50 and Coker 312, was tested under field conditions in Burkina Faso in two contained areas. An untreated (no lepidopteran insecticidal sprays) conventional (non-transgenic) U.S. variety (Coker 312 in 2003; DP50 in 2004 & 2005) and two conventional local varieties (untreated and treated) were utilized in each test as comparators. The experiments conducted in 2003, 2004 and 2005 showed that the transgenic cotton plant significantly reduced larval populations of the cotton bollworm, Helicoverpa armigera, and the cotton leafroller, Syllepte derogata compared to untreated varieties. Plant damage analyses upon maturity revealed significantly higher levels of sound bolls in transgenic cotton plants. Seed cotton yields and lint quality were also higher for the transgenic cotton than for untreated convention varieties. The transgenic variety was always statistically equivalent or superior to the treated conventional one. The transgenic cotton plant expressing two endotoxins (Cry1Ac and Cry2Ab) of B. thuringiensis Berliner (Bt) can therefore be an alternative to the use of pyrethroids and endosulfan in cotton cultivation in Burkina Faso. This will have dual advantage of significantly reducing the quantities of pesticides sprayed in the cotton fields while protecting yields and quality of lint. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Transgenic cotton plant Bacillus thuringiensis Helicoverpa armigera Syllepte derogata Burkina Faso
1. Introduction Cotton is the principal export crop in Burkina Faso, representing over 50% of export earnings (Vognan et al., 2002). Significant economic losses in Burkina Faso cotton are due to feeding damage by caterpillar (Lepidoptera) populations and the cost of pesticides to control them. There are two principal groups of caterpillar pests, distinguished by their feeding preferences: these are bollworms, or fruit-feeders, the most prevalent of which are Helicoverpa armigera (Hu¨bner) (old world bollworm), Diparopsis spp. (red bollworms), and Earias spp. (spiny bollworms), and defoliators, which are primarily, Syllepte derogata (Fabricius) (cotton leafroller), Anomis flava (Fabricius) (looper), and Spodoptera littoralis (Boisduval) (cotton leafworm). * Corresponding author. Tel.: þ226 20 97 21 05; fax: þ226 20 97 01 59. E-mail addresses: [email protected] (O. He´ma), [email protected] (H.N. Some´), [email protected] (O. Traore´), [email protected] (J. Greenplate), [email protected] (M. Abdennadher). 1 Tel.: þ1 314 694 2637; fax: þ1 314 694 6662. 2 Tel.: þ27 11 790 8200; fax: þ27 11 790 8250. 0261-2194/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2008.09.014
For decades, cotton in Burkina Faso was protected from caterpillar damage by chemical pesticides, mainly from two families: pyrethroids and organophosphates often associated in the same treatment. Since 1995, field failure rates of these pesticides have risen, and sensitivity tests in the laboratory have shown a loss of sensitivity to pyrethroids in the larvae of field-collected H. armigera, confirming the presence of resistance (Martin et al., 2000; He´ma, 2004). In a typical year, the Burkina Faso cotton sector uses over $60 million of chemically based pest control products yet a recently conducted study in Burkina Faso found significant pest damage on fields that were protected using a standard regimen of six seasonal sprays (Vitale et al., 2006). The introduction of genetically modified cotton plants expressing the Cry1Ac and Cry2Ab toxins (Perlak et al., 2001; Greenplate et al., 2003), which have a different mode of action to that of pyrethroids, may be an interesting and effective alternative to chemical control. Other studies have shown that transgenic cotton use has greatly reduced pesticide treatments while effectively controlling caterpillar pests (Pray et al., 2002). In this study, we will address the effect of the transgenic cotton expressing Cry1Ac and
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Cry2Ab on Burkina Faso’s principal bollworm pest, H. armigera, and defoliator pest, S. derogata. 2. Materials and methods 2.1. Sites of experimentation Trials were conducted on two research station sites of INERA (Institut de l’Environnement et de Recherches Agricoles), the agricultural research arm of the Burkina Faso government. The research sites, Kouare´, in the East, and Farako-Baˆ, in the West, are 600 km apart. Both are on the 800–1000 mm isohyet with ferruginous soil deficient in organic matter (mainly less than 1%). 2.2. Varieties of cotton plants American (U.S.) and local (Burkina Faso) varieties of cotton plants were used for this study; in 2003, the American variety COKER 312 was used as a conventional control, and DP50 (Deltapine 50, Delta and Pine Land Co., Scott, MS, USA) containing the genes encoding the two endotoxins (Cry1Ac and CryAb) of Bacillus thuringiensis Berliner (Bt) was the test variety. In 2004 and 2005, the conventional version of DP50 and its transgenic counterpart were grown together. Coker 312 was used as a US conventional comparator in 2003 because of the unavailability of conventional DP50 and the fact Coker 312 was the original genetic source of the Cry1Ac component of transgenic
DP50. In 2003, the local conventional variety used was FK37; in 2004 and 2005, FK37 and STAM59 A were used in Farako-Baˆ and Kouare´, respectively. There are some morphological differences between American cotton varieties and local ones: On plant height, the local varieties are larger (120–150 cm on average) whereas the American varieties seldom reach 120 cm. Also, leaf pubescence is more important in the local varieties. The maturity of the two types of cotton plants is the same. 2.3. Treatments compared Four treatments were compared: Bt US: transgenic variety; Tr Conv BF: local conventional variety treated according to national insecticide treatments program: six treatments, beginning at 30 days after plant emergence, one application each 14 days. The two first treatments were done with endosulfan 500 g/ha, treatments number 3 and 4 with association cypermethrin 30 g/ha–profenofos 200 g/ha, the two last ones with association cypermethrin 36 g/ha–acetamiprid 8 g/ha; Un Conv BF: local conventional variety untreated against lepidopteran pests; Un Conv US: American conventional variety untreated against lepidopteran pests.
Fig. 1. a: H. armigera larval counts in Farako-Baˆ, 2003; 27/8/03 (df ¼ 3; F ¼ 1.571; P ¼ 0.248); 3/9/03 (df ¼ 3; F ¼ 2,000; P ¼ 0.168); 10/9/03 (df ¼ 3; F ¼ 5,600; P ¼ 0.012); 17/9/03 (df ¼ 3; F ¼ 9,766; P ¼ 0.002); 24/9/03 (df ¼ 3; F ¼ 9,189; P ¼ 0.002); 8/10/03 (df ¼ 3; F ¼ 2,306; P ¼ 0.129); 15/10/03 (df ¼ 3; F ¼ 7,714; P ¼ 0.004); 22/10/03 (df ¼ 3; F ¼ 1,714; P ¼ 0.217); 29/10/03 (df ¼ 3; F ¼ 2,857; P ¼ 0.032); 5/11/03 (df ¼ 3; F ¼ 1,714; P ¼ 0.217). b: H. armigera larval counts in Kouare´, 2003; 28/08/03 (df ¼ 3; F ¼ 1,895; P ¼ 0.184); 03/09/ 03 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 10/09/03 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 17/09/03 (df ¼ 3; F ¼ 3,412; P ¼ 0.053); 22/09/03 (df ¼ 3; F ¼ 7,062; P ¼ 0.005); 03/10/03 (df ¼ 3; F ¼ 30,327; P < 0.0001); 10/10/03 (df ¼ 3; F ¼ 2,169; P ¼ 0.145); 15/10/03 (df ¼ 3; F ¼ 4,294; P ¼ 0.028).
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2.4. Conducting of the experiment The study design utilized randomized complete blocks with four replicates. Plants were sown at a density of 62,500 plants/ha. The elementary plot varied from year to year, based upon available seed quantities. In 2003 a plot consisted of 4 rows of 15 m; in 2004 it was 8 rows of 10 m, and in 2005 a plot was 10 rows of 15 m. In 2003, insecticide treatments were made to all plots (transgenic and conventional) against Aphis gossypii and Bemisia tabaci (secondary pests not controlled by Bt) on thresholds: 21 of 25 plants heavily infested with A. gossypii and 5 of 25 plants infested by B. tabaci. Two specific treatments with imidacloprid at 30 g/ha were done against aphid and whitefly. In 2004 and 2005, two treatments with the same insecticide were done against these sucking pests at 86 and 100 days after plant emergence corresponding to these pests infestation period. Three types of observations were made: * Direct observations of pests: once a week, beginning at 30 days after emergence of the cotton plant, the number of H. armigera larvae observed on 20 plants and the number of plants infested by the larvae of S. derogata were recorded. * Plant damage analysis at maturity: prior to harvest, a whole middle row of each test plot was carefully analyzed and counts of the number of sound bolls or bolls with no worm damage, the number of worm-damaged bolls, and the number of bolls with discoloured or ‘‘yellow’’ lint caused by the mean boll pests with H. armigera as first were made.
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* Estimate of yield: the total seed cotton (lint plus seeds) handharvested from a whole middle row of each plot was weighed. An analysis of variance (ANOVA) was performed using XLSTAT version 6.1.9 software. Percent data are transformed before analyses, using the arcsine square root transformation (asin(sqrt(x/a))). An F test was used, and the averages, where differences were observed, were graded using the Bonferroni test at the threshold of 5% for the biological data; for the data estimating the yield, Fisher’s test was chosen. Within each figure discussed below, means with different letters affixed are significantly different. 3. Results 3.1. H. armigera larval counts in 2003 H. armigera larval densities are shown in Fig. 1a (Farako-Baˆ) and b (Kouare´). On 1st October and 15 October in Farako-Baˆ (1/10/03: df ¼ 3, F ¼ 22.645, P < 0.0001; 15/10/03: df ¼ 3, F ¼ 7.714, P ¼ 0.004) and 10 October in Kouare´ (df ¼ 3, F ¼ 2.169, P ¼ 0.145), the populations of this pest were significantly higher on untreated conventional varieties in comparison to the transgenic variety and conventional treated variety. In fact, while populations averaged well under 1 larva per 20 plants in the transgenic plots, populations of close to 10 larvae per 20 plants were observed on US and/or local conventional varieties.
Fig. 2. a: H. armigera larval counts in Farako-Baˆ, 2004 16/8/04 (df ¼ 3; F ¼ 0.530; P ¼ 0.665); 26/8/04 (df ¼ 3; F ¼ 1,167; P ¼ 0.340); 2/9/04 (df ¼ 3; F ¼ 0.212; P ¼ 0.887); 9/9/04 (df ¼ 3; F ¼ 1,798; P ¼ 0.170); 23/9/04 (df ¼ 3; F ¼ 2,851; P ¼ 0.055); 30/9/04 (df ¼ 3; F ¼ 1,291; P ¼ 0.297); 7/10/04 (df ¼ 3; F ¼ 0.991; P ¼ 0.411); 14/10/04 (df ¼ 3; F ¼ 0.708; P ¼ 0.556); 21/10/04 (df ¼ 3; F ¼ 0.467; P ¼ 0.708). b: H. armigera larval counts in Kouare´, 2004; 16/08/2004 (df ¼ 3; F ¼ 1,167; P ¼ 0.340); 23/08/2004 (df ¼ 3; F ¼ 2,567; P ¼ 0.075); 30/08/2004 (df ¼ 3; F ¼ 1,926; P ¼ 0.148); 06/09/2004 (df ¼ 3; F ¼ 0.970; P ¼ 0.421); 13/09/2004 (df ¼ 3; F ¼ 4,406; P ¼ 0.012); 20/09/2004 (df ¼ 3; F ¼ 4,990; P ¼ 0.007); 27/09/2004 (df ¼ 3; F ¼ 4,330; P ¼ 0.013); 04/10/2004 (df ¼ 3; F ¼ 2,957; P ¼ 0.049); 11/10/2004 (df ¼ 3; F ¼ 1,436; P ¼ 0.253); 18/10/2004 (df ¼ 3; F ¼ 1,167; P ¼ 0.340).
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3.2. H. armigera larval counts in 2004 At the Farako-Baˆ station (Fig. 2a), although no H. armigera larvae were found on transgenic cotton, overall densities were too low to statistically separate treatments (16/8/04: df ¼ 3, F ¼ 0.530, P ¼ 0.665; 26/8/04: df ¼ 3, F ¼ 1.167, P ¼ 0.340; 2/9/04: df ¼ 3, F ¼ 0.212, P ¼ 0.887; 9/9/04: df ¼ 3, F ¼ 1.798, P ¼ 0.170; 23/9/04: df ¼ 3, F ¼ 2.851, P ¼ 0.055; 30/9/04: df ¼ 3, F ¼ 1.291, P ¼ 0.297; 7/ 10/04: df ¼ 3, F ¼ 0.991, P ¼ 0.411; 14/10/04: df ¼ 3, F ¼ 0.708, P ¼ 0.556; 21/10/04: df ¼ 3, F ¼ 0.467, P ¼ 0.708). In Kouare´ (Fig. 2b), on September 27, the transgenic variety had significantly less H. armigera larvae than all the other treatments (df ¼ 3, F ¼ 4.330, P ¼ 0.013). 3.3. H. armigera larval counts in 2005 In Farako-Baˆ (Fig. 3a), the transgenic cotton supported significantly fewer larvae than the conventional varieties (treated and untreated) on September 19 (df ¼ 3, F ¼ 4.000, P ¼ 0.035). In Kouare´ (Fig. 3b), on September 29, the conventional varieties treated and untreated contained significantly more H. armigera larvae than the transgenic cotton (df ¼ 3, F ¼ 4.636, P ¼ 0.022). Densities on transgenics were always well below 0.5 larvae per 20 plants, while
conventional untreated varieties reached 3.5 and 6 larvae per 20 plants in Farako-Baˆ and Kouare´, respectively. Densities on treated conventional variety varied from 0 to 3.5 in Farako-Baˆ and Kouare´. 3.4. S. derogata infestation in 2003 At both sites (Fig. 4a and b), the untreated conventional varieties showed significantly more S. derogata infested plants than did the transgenic cotton plants and the treated conventional variety all the times significant differences were observed, except September 20 in Farako-Baˆ (23/8/03: df ¼ 3, F ¼ 1.571, P ¼ 0.248; 30/8/03: df ¼ 3, F ¼ 0.769, P ¼ 0.533; 7/9/03: df ¼ 3, F ¼ 6.757, P ¼ 0.006; 13/9/03: df ¼ 3, F ¼ 3.447, P ¼ 0.052; 27/9/03: df ¼ 3, F ¼ 11.617, P ¼ 0.001; 4/10/ 03: df ¼ 3, F ¼ 10.222, P ¼ 0.001; 11/10/03: df ¼ 3, F ¼ 32.175, P < 0.0001; 18/10/03: df ¼ 3, F ¼ 10.804, P ¼ 0.001; 25/10/03: df ¼ 3, F ¼ 4.236, P ¼ 0.029; 1/11/03: df ¼ 3, F ¼ 8.200, P ¼ 0.003) and September 11 to September 18 in Kouare´ (4/9/03: df ¼ 3, F ¼ 3.000, P ¼ 0.073; 25/9/03: df ¼ 3, F ¼ 10.169, P ¼ 0.001; 2/10/03: df ¼ 3, F ¼ 28.789, P < 0.0001; 9/10/03: df ¼ 3, F ¼ 17.228, P ¼ 0.000; 16/10/ 03: df ¼ 3, F ¼ 197.343, P < 0.0001; 24/10/03: df ¼ 3, F ¼ 42.571, P < 0.0001; 30/10/03: df ¼ 3, F ¼ 20.877, P < 0.0001). In Farako-Baˆ, in periods of high infestation of this pest we observed more than 6 infested plants out of 20, and in Kouare´ this pest infested around 12
Fig. 3. a: H. armigera larval counts in Farako-Baˆ, 2005; 16/08/2005 (df ¼ 3; F ¼ 0.333; P ¼ 0.802); 23/08/2005 (df ¼ 3; F ¼ 1,222; P ¼ 0.344); 29/08/2005 (df ¼ 3; F ¼ 1,118; P ¼ 0.380); 05/09/2005 (df ¼ 3; F ¼ 4,000; P ¼ 0.035); 12/09/2005 (df ¼ 3; F ¼ 2,889; P ¼ 0.079); 19/09/2005 (df ¼ 3; F ¼ 4,000; P ¼ 0.035); 26/09/2005 (df ¼ 3; F ¼ 6,612; P ¼ 0.007); 03/10/2005 (df ¼ 3; F ¼ 2,684; P ¼ 0.094); 10/10/2005 (df ¼ 3; F ¼ 2,000; P ¼ 0.168); 24/10/2005 (df ¼ 3; F ¼ 3,091; P ¼ 0.068). b: H. armigera larval counts in Kouare´, 2005; 21/08/2005 (df ¼ 3; F ¼ 8,500; P ¼ 0.003); 25/08/2005 (df ¼ 3; F ¼ 3,242; P ¼ 0.060); 01/09/2005 (df ¼ 3; F ¼ 1,571; P ¼ 0.248); 08/09/2005 (df ¼ 3; F ¼ 4,462; P ¼ 0.025); 15/09/2005 (df ¼ 3; F ¼ 4,103; P ¼ 0.032); 22/09/2005 (df ¼ 3; F ¼ 4,171; P ¼ 0.031); 29/09/2005 (df ¼ 3; F ¼ 4,636; P ¼ 0.022); 06/10/2005 (df ¼ 3; F ¼ 0.800; P ¼ 0.517); 13/10/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 20/10/2005 (df ¼ 3; F ¼ 3,000; P ¼ 0.073); 27/10/2005 (df ¼ 3; F ¼ 0.667; P ¼ 0.588).
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Fig. 4. a: S. derogata damage in Farako-Baˆ, 2003; 23/8/03 (df ¼ 3; F ¼ 1,571; P ¼ 0.248); 30/8/03 (df ¼ 3; F ¼ 0.769; P ¼ 0.533); 7/9/03 (df ¼ 3; F ¼ 6,757; P ¼ 0.006); 13/9/03 (df ¼ 3; F ¼ 3,447; P ¼ 0.052); 20/9/03 (df ¼ 3; F ¼ 3,825; P ¼ 0.039); 27/9/03 (df ¼ 3; F ¼ 11,617; P ¼ 0.001); 4/10/03 (df ¼ 3; F ¼ 10,222; P ¼ 0.001); 11/10/03 (df ¼ 3; F ¼ 32,175; P < 0.0001); 18/10/03 (df ¼ 3; F ¼ 10,804; P ¼ 0.001); 25/10/03 (df ¼ 3; F ¼ 4,236; P ¼ 0.029); 1/11/03 (df ¼ 3; F ¼ 8,200; P ¼ 0.003). b: S. derogata damage in Kouare´, 2003; 4/9/03 (df ¼ 3; F ¼ 3,000; P ¼ 0.073); 11/9/03 (df ¼ 3; F ¼ 14,486; P ¼ 0.000); 18/9/03 (df ¼ 3; F ¼ 9,923; P ¼ 0.001); 25/9/03 (df ¼ 3; F ¼ 10,169; P ¼ 0.001); 2/10/03 (df ¼ 3; F ¼ 28,789; P < 0.0001); 9/10/03 (df ¼ 3; F ¼ 17,228; P ¼ 0.000); 16/10/03 (df ¼ 3; F ¼ 197,343; P < 0.0001); 24/10/03 (df ¼ 3; F ¼ 42,571; P < 0.0001); 30/10/03 (df ¼ 3; F ¼ 20,877; P < 0.0001).
plants out of 20 in the untreated conventional varieties. Very few infested plants were found in transgenic plots; the highest mean value was well below 1 per 20 plants, found on 13 September in Farako-Baˆ. 3.5. S. derogata infestation in 2004 In Farako-Baˆ (Fig. 5a), the infestations of this pest were significantly more important on the local untreated conventional variety than the other treatments from September 26 to October 17 (26/9/04: df ¼ 3, F ¼ 8.520, P ¼ 0.000; 3/10/04: df ¼ 3, F ¼ 24.271, P < 0.0001; 10/10/04: df ¼ 3, F ¼ 15.394, P < 0.0001; 17/10/04: df ¼ 3, F ¼ 17.243, P < 0.0001). In Kouare´ (Fig. 5b), from September 29 to October 13, transgenic plants and treated conventional ones were significantly less infested by S. derogata larvae than the untreated conventional varieties (29/09/ 2004: df ¼ 3, F ¼ 13.040, P < 0.0001; 06/10/2004: df ¼ 3, F ¼ 37.381, P < 0.0001; 13/10/2004: df ¼ 3, F ¼ 19.716, P < 0.0001). As in 2003, infested transgenic plants and infested treated conventional variety were extremely rare or non-existent. 3.6. S. derogata infestations in 2005 In Farako-Baˆ (Fig. 6a), on 30 September, the transgenic cotton plants and the treated conventional variety contained
significantly fewer S. derogata larvae than the untreated conventional variety (df ¼ 3, F ¼ 11.123, P ¼ 0.001). The level of infested plants in untreated conventional varieties reached 8/20. In Kouare´ (Fig. 6b), the phenomenon observed in 2004 happened again; the local untreated conventional variety hosted more larvae of this pest than the other treatments, and again, infested transgenic plants were essentially non-existent on September 28, October 19 and 26 (28/09/2005: df ¼ 3, F ¼ 3.913, P ¼ 0.037; 19/ 10/2005: df ¼ 3, F ¼ 5.781, P ¼ 0.011; 26/10/2005: df ¼ 3, F ¼ 4.236, P ¼ 0.029). 4. Mature bolls analysis 4.1. Sound bolls The analysis of mature bolls in 2003 at Farako-Baˆ and Kouare´ stations (Fig. 7) indicated significantly higher levels of sound bolls in the Bt cotton plants and treated conventional plots than in untreated conventional varieties (Farako-Baˆ: df ¼ 3, F ¼ 32.476, P < 0.0001; Kouare´: df ¼ 3, F ¼ 68.279, P < 0.0001). In fact, we obtained more than 70% sound bolls in the two localities with Bt plants and treated conventional ones, and around 50% or less sound bolls on untreated conventional varieties.
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Fig. 5. a: S. derogata damage in Farako-Baˆ, 2004 10/8/04 (df ¼ 3; F ¼ 0.292; P ¼ 0.831); 17/8/04 (df ¼ 3; F ¼ 1,667; P ¼ 0.197); 29/8/04 (df ¼ 3; F ¼ 1,029; P ¼ 0.395); 5/9/04 (df ¼ 3; F ¼ 2,129; P ¼ 0.119); 12/9/04 (df ¼ 3; F ¼ 4,340; P ¼ 0.012); 19/9/04 (df ¼ 3; F ¼ 4,208; P ¼ 0.014); 26/9/04 (df ¼ 3; F ¼ 8,520; P ¼ 0.000); 3/10/04 (df ¼ 3; F ¼ 24,271; P < 0.0001); 10/10/04 (df ¼ 3; F ¼ 15,394; P < 0.0001); 17/10/04 (df ¼ 3; F ¼ 17,243; P < 0.0001). b: S. derogata damage in Kouare´, 2004 25/08/2004 (df ¼ 3; F ¼ 1,365; P ¼ 0.274); 01/09/2004 (df ¼ 3; F ¼ 1,440; P ¼ 0.252); 08/09/2004 (df ¼ 3; F ¼ 2,690; P ¼ 0.065); 15/09/2004 (df ¼ 3; F ¼ 5,690; P ¼ 0.004);22/09/2004 (df ¼ 3; F ¼ 5,168; P ¼ 0.006); 29/09/2004 (df ¼ 3; F ¼ 13,040; P < 0.0001); 06/10/2004 (df ¼ 3; F ¼ 37,381; P < 0.0001); 13/10/2004 (df ¼ 3; F ¼ 19,716; P < 0.0001); 20/10/2004 (df ¼ 3; F ¼ 9,153; P ¼ 0.0002); 27/10/2004 (df ¼ 3; F ¼ 5,503; P ¼ 0.004).
In 2004 (Fig. 8), we observed a significant difference between the level of sound bolls originating from the Bt cotton plants and the treated conventional ones, and those of the untreated conventional varieties in the two areas (Farako-Baˆ: df ¼ 3, F ¼ 7.159, P ¼ 0.001; Kouare´: df ¼ 3, F ¼ 22.666, P < 0.0001). With the Bt Cotton plants and treated conventional variety, we had more than 80% sound bolls on both sites; in Farako-Baˆ and in Kouare´, the level of sound bolls in the untreated conventional varieties was greater than that of 2003 (over 60%). In 2005, in Farako-Baˆ and Kouare´ (Fig. 9), the Bt cotton plants and the treated conventional plants gave significantly higher levels of sound bolls (more than 70%) than that found in the untreated conventional varieties (60% or less) (Farako-Baˆ: df ¼ 3, F ¼ 14.744, P ¼ 0.0003; Kouare´: df ¼ 3, F ¼ 23.897, P < 0.0001). 4.2. Perforated bolls The Bt cotton plants and the treated conventional ones contained significantly fewer damaged bolls than the conventional varieties treated and untreated on both sites in 2003 (Farako-Baˆ: df ¼ 3, F ¼ 55.322, P < 0.0001; Kouare´: df ¼ 3, F ¼ 39.288, P < 0.0001) (Fig. 7) and 2005 (Farako-Baˆ: df ¼ 3, F ¼ 26.609, P < 0.0001; Kouare´: df ¼ 3, F ¼ 104.167, P < 0.0001) (Fig. 9) and in Kouare´ in 2004 (df ¼ 3, F ¼ 19.727, P < 0.0001). In 2004, at FarakoBaˆ station, transgenic variety was statistically equivalent to treated conventional variety and superior to untreated conventional
varieties as far as the level of perforated bolls is concerned (df ¼ 3, F ¼ 10.946, P < 0.0001) (Fig. 8). In fact, at both sites during the three years of the study, the Bt cotton plants gave fewer than 5% damaged bolls while the conventional varieties contained boll damage levels of 20–40%. The level of perforated bolls in the treated conventional variety varied from 5 to 15%. 4.3. Incidence of yellow cotton On both sites in 2003 (Fig. 10), the transgenic cotton plants and the treated conventional ones produced cotton of significantly better quality than that of the two untreated conventional varieties (Farako-Baˆ: df ¼ 3, F ¼ 16.255, P ¼ 0.0002; Kouare´: df ¼ 3, F ¼ 37.627, P < 0.0001). In 2005 in Farako-Baˆ (Fig. 10), the Bt cotton plants had produced significantly better cotton quality than the treated and the untreated conventional varieties (df ¼ 3, F ¼ 22.232, P < 0.0001). In fact, the Bt cotton plants gave less than 5% yellow cotton on both sites, while the treated conventional ones gave from 4 to 6% yellow cotton and the untreated conventional varieties produced from 7 to 17% yellow cotton. 4.4. Seed cotton yields In 2003 in Farako-Baˆ (Fig. 11), the Bt variety yielded significantly more seed cotton than both conventional varieties (untreated and
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Fig. 6. a: S. derogata damage in Farako-Baˆ, 2005; 20/08/2005 (df ¼ 3; F ¼ 2,571; P ¼ 0.103); 25/08/2005 (df ¼ 3; F ¼ 1,895; P ¼ 0.184); 03/09/2005 (df ¼ 3; F ¼ 0.733; P ¼ 0.552); 09/ 09/2005 (df ¼ 3; F ¼ 1,627; P ¼ 0.235); 16/09/2005 (df ¼ 3; F ¼ 2,862; P ¼ 0.081); 23/09/2005 (df ¼ 3; F ¼ 2,400; P ¼ 0.119); 30/09/2005 (df ¼ 3; F ¼ 11,123; P ¼ 0.001); 07/10/2005 (df ¼ 3; F ¼ 9,571; P ¼ 0.002); 21/10/2005 (df ¼ 3; F ¼ 7,097; P ¼ 0.005); 28/10/2005 (df ¼ 3; F ¼ 2,815; P ¼ 0.084); 04/11/2005 (df ¼ 3; F ¼ 1,714; P ¼ 0.217). b: S. derogata damage in Kouare´, 2005; 31/08/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 07/09/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 14/09/2005 (df ¼ 3; F ¼ 2,652; P ¼ 0.096); 21/09/2005 (df ¼ 3; F ¼ 2,505; P ¼ 0.109); 28/09/2005 (df ¼ 3; F ¼ 3,913; P ¼ 0.037); 05/10/2005 (df ¼ 3; F ¼ 4,184; P ¼ 0.030); 12/10/2005 (df ¼ 3; F ¼ 2,258; P ¼ 0.134); 19/10/2005 (df ¼ 3; F ¼ 5,781; P ¼ 0.011); 26/10/2005 (df ¼ 3; F ¼ 4,236; P ¼ 0.029); 02/11/2005 (df ¼ 3; F ¼ 2,778; P ¼ 0.087); 09/11/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426).
Fig. 7. Mature boll assessment in Farako-Baˆ and Kouare´, 2003; Farako-Baˆ: Sounds bolls (df ¼ 3; F ¼ 32,476; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 55,322; P < 0.0001); (df ¼ 3; F ¼ 16,255; P ¼ 0.0002). Kouare´: Sounds bolls (df ¼ 3; F ¼ 68,279; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 39,288; P < 0.0001).
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Fig. 8. Mature boll assessment in Farako-Baˆ and Kouare´, 2004; Farako-Baˆ: Sounds bolls (df ¼ 3; F ¼ 7,159; P ¼ 0.001); Perforated bolls (df ¼ 3; F ¼ 10,946; P < 0.0001); Kouare´: Sounds bolls (df ¼ 3; F ¼ 22,666; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 19,727; P < 0.0001).
treated) (df ¼ 3, F ¼ 24.585, P < 0.0001). At Kouare´ station, the Bt cotton plant was statistically equivalent to the treated conventional variety; the untreated varieties yielded significantly less seed cotton (df ¼ 3, F ¼ 21.096, P < 0.0001). The difference between the yield produced by the transgenic variety and the U.S. conventional variety was around 500 kg/ha in Farako-Baˆ and 800 kg/ha in Kouare´. In 2004 at the Farako-Baˆ station (Fig. 11), there were no significant yield differences observed, although there was a numerical difference in favour of the Bt cotton around 200–250 kg/ha (df ¼ 3, F ¼ 1.651, P ¼ 0.230). In Kouare´ (Fig. 11), the transgenic variety produced significantly more seed cotton than the U.S. untreated conventional variety (around 500 kg/ha) (df ¼ 3, F ¼ 33.207, P < 0.0001). In 2005 at the Farako-Baˆ station (Fig. 11), the transgenic cotton produced significantly more seed cotton than the conventional DP50 (around 600 kg/ha) (df ¼ 3, F ¼ 54.447, P < 0.0001). At the Kouare´ station (Fig. 11), the yields on the American varieties were lower by about 200 kg/ha than they were at Farako-Baˆ (difference of 200 kg/ha), but the benefit of the transgenic variety over both conventional varieties was statistically significant, at around 600 kg/ha (df ¼ 3, F ¼ 32.720, P < 0.0001). The treated conventional variety yielded statistically the same level of seed cotton than the transgenic variety. In 2005, we observed an arithmetic difference of
yield between the treated conventional variety and the transgenic one in favour of the treated conventional variety. 5. Discussion The resistance of transgenic cotton plants containing the gene expressing the Cry1Ac of B. thuringiensis to damage by Lepidoptera pest larvae, namely H. armigera (Hu¨bner), Heliothis zea (Boddie), Heliothis virescens (F.), Pectinophora gossypiella (Saunders), and Spodoptera exigua (Hu¨bner), has been demonstrated previously (Wilson et al., 1992; Benedict et al., 1993; Wang et al., 1997; Gore et al., 2001; Chitkowski et al., 2003). This study, which evaluated the efficacy of transgenic cotton plants expressing two deltaendotoxins (Cry1Ac and Cry2Ab) of B. thuringiensis, showed, over three years in two different areas in Burkina Faso, excellent control of the larvae of H. armigera and of S. derogata as well as the treated conventional variety and some times more than this last variety throughout the cotton plant cycle. The analysis of the bolls upon harvest showed that this transgenic cotton produced significantly higher levels of sound bolls than did untreated conventional varieties. The damage caused on bolls by pests in the untreated conventional cotton plots was significantly higher than in the
Fig. 9. Mature boll assessment in Farako-Baˆ and Kouare´, 2005; Farako-Baˆ: Sounds bolls (df ¼ 3; F ¼ 14,744; P ¼ 0.0003); Perforated bolls (df ¼ 3; F ¼ 26,609; P < 0.0001); Kouare´: Sounds bolls (df ¼ 3; F ¼ 23,897; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 104,167; P ; P < 0.0001).
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Fig. 10. Yellow cotton assessment in Farako-Baˆ and Kouare´, 2003: Farako-Baˆ (df ¼ 3; F ¼ 16,255; P ¼ 0.0002); Kouare´ (df ¼ 3; F ¼ 37,627; P < 0.0001). 2004: Farako-Baˆ (df ¼ 3; F ¼ 8,283; P ¼ 0.0004); Kouare´ (df ¼ 3; F ¼ 13,326; P < 0.0001). 2005: Farako-Baˆ (df ¼ 3; F ¼ 22,232; P < 0.0001); Kouare´ (df ¼ 3; F ¼ 3,900; P ¼ 0.037).
transgenic cotton and the treated conventional plots. Insect damage resulted in deterioration in the quality of fiber, with untreated conventional varieties producing more yellow cotton than the transgenic and the treated conventional varieties. In our study, significantly higher seed cotton yields were usually observed in the Bt cotton and the treated conventional one; this is consistent with earlier studies of Bt-expressing cotton (Gore et al., 2000; Wu et al., 2002; Pray et al., 2002). The differences in yield observed between the transgenic and the untreated conventional varieties in Burkina Faso were between 400 and 600 kg/ha. The degree of yield benefit realized with Bt cotton is certainly linked with pest density. In the present study, the only time yield differences were not seen between Bt and conventional varieties was in 2004 in Farako-Baˆ (Fig. 11) where overall H. armigera densities were relatively low (Fig. 2a). Another factor, pertinent to the ultimate value of Bt cotton, is the relative efficacy and cost of the pesticides currently used to control cotton Lepidoptera pests. In Burkina Faso and in West Africa, H. armigera has exhibited various levels of resistance to the pyrethroids commonly used in cotton, with a resistance factor varying from 10 to more than 500 (Martin et al., 2000; He´ma, 2004). Higher pest densities and the reduced efficacy of affordable pesticides may render Bt cotton
a potentially valuable tool to control damaging Lepidopteran pests for several reasons; the use of transgenic Bt cotton may allow an increase in the yield of farmers who actually do 2 to 3 treatments against Lepidopteran pests in steed of 4–5, with concurrent reductions in the cost of pesticides, the time spent spraying dangerous pesticides like endosulfan prohibited by Sahelian Council of Pesticides, and illness due to poisoning (Pray et al., 2002). Because no positive cross-resistance has been observed between the delta-endotoxins of B. thuringiensis and pyrethroids (Wu and Guo, 2004), the use of Bt cotton may also enable an increase in the sensitivity of H. armigera to pyrethroids, an increase in the population of useful insects, and optimization of the natural control of certain pests like sucking ones by beneficials (Wu et al., 2005). Finally, management strategies for Bt cotton must consider the fact that insecticide treatment for Lepidopteran pests can be greatly reduced, but the effective control of sucking pests (aphids, whiteflies), often controlled coincidentally by Lepidoptera sprays in conventional cotton, will have to be addressed in a systematic manner, since the current Bt toxins are not active against these pests. Also, the effectiveness of the Bt toxins on S. littoralis, another Lepidopteran pest in cotton in Burkina Faso, has not been studied
Fig. 11. Seed cotton yield in Farako-Baˆ and Kouare´, 2003: Farako-Baˆ (df ¼ 3; F ¼ 24,585; P < 0.0001); Kouare´ (df ¼ 3; F ¼ 21,096; P < 0.0001); 2004: Farako-Baˆ (df ¼ 3; F ¼ 1,651; P ¼ 0.230); Kouare´ (df ¼ 3; F ¼ 33,207; P < 0.0001); 2005: Farako-Baˆ (df ¼ 3; F ¼ 54,447; P < 0.0001); Kouare´ (df ¼ 3; F ¼ 32.720; P < 0.0001).
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during these three years. These topics will be subjects of future studies. Acknowledgements This research was undertaken with thanks to the government of Burkina Faso, which gave special authorizations for import experimentation of this transgenic cotton, and to the Burkina Faso cotton industry and Monsanto for financial support. References Benedict, J.H., Sachs, E.S., Altman, D.W., Ring, D.R., Stone, T.B., Sims, S.R., 1993. Impact of delta-endotoxin producing transgenic cotton on insect-plant interactions with Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae). Environ. Entomol. 22, 1–9. Chitkowski, R.L., Turnipseed, S.G., Sullivan, M.J., Bridges, W.C., 2003. Field and laboratory evaluations of transgenic cottons expressing one or two Bacillus thuringiensis var. kurstaki Berliner proteins for management of Noctuid (Lepidoptera) pests. J. Econ. Entomol. 03, 0755–0762. Gore, J., Leonard, B.R., Adamaczyk, J.J., 2001. Bollworm (Lepidoptera: Noctuidae) survival on ‘‘Bollgard’’ and ‘‘Bollgard II’’ cotton flower bud and flower components. J. Econ. Entomol. 94 (6), 1445–1451. Gore, J., Leonard, B.R., Church, G.E., Russel, J.S., Hall, T.S., 2000. Cotton boll abscission and yield losses associates with first-instar bollworm (Lepidoptera: Noctuidae) injury to nontransgenic and transgenic Bt cotton. J. Econ. Entomol. 93 (3), 690–696. Greenplate, J.T., Mullins, J.W., Penn, S.R., Dahhm, A., Reich, B.J., Osborn, J.A., Rahn, P.R., Ruschke, L., Shappley, Z.W., 2003. Partial characterization of cotton plants expressing two toxin proteins from Bacillus thuringiensis: relative toxin contribution, toxin interaction, and resistance management. J. Appl. Entomol. 127, 340–347.
He´ma S.A.O., 2004. Contribution a` la caracte´risation biochimique de la re´sistance de Helicoverpa armigera (Hu¨bner, 1808) (Lepidoptera, Noctuidae) aux pyre´thrinoı¨des au Burkina Faso. Me´moire de D.E.A., Ecole Doctorale Re´gionale de Biotechnologie, Universite´ de Ouagadougou, 37 p. Martin, T., Ochou, G.O., Hala, N.F., Vassal, J.M., Vaissayre, M., 2000. Pyrethroid resistance in the cotton bollworm, Helicoverpa armigera (Hu¨bner), in West Africa. Pest Manag. Sci. 56, 549–554. Perlak, F.J., Oppenhuizen, M., Gustafson, K., Voth, R., Sivasupramaniam, S., Heering, D., Carey, B., Ihrig, R.A., Roberts, J.K., 2001. Development and commercial use of Bollgard cotton in the USA – early promises versus today’s reality. Plant J. 27 (6), 489–501. Pray, C.E., Huang, J., Hu, R., Rozelle, S., 2002. Five years of Bt cotton in China-the benefits continue. Plant J. 31 (4), 423–430. Vitale, J., Glick, H., Greenplate, J., 2006. The Economic Impacts of Monsanto’s Bollgard II in West Africa: Emprirical Evidence from Burkina Faso. A paper accepted for presentation at the 10th ICABR Conference, Ravello, Italy. Vognan, G., Oue´draogo, M., et Oue´draogo, S., 2002. Description de la filie`re cotonnie`re au Burkina Faso. Rapport interme´diaire, INERA, 34 p. Wang, W., Jiang, Y., Yang, X., Guo, S., Ni, W., Chen, Z., Tian, Y., 1997. Study on evaluation and utilization of transgenic Bt cotton to cotton bollworm. Sci. Agri. Sin. 30, 7–12. Wilson, F.D., Flint, H.M., Deaton, W.R., Fischhoff, D.A., Perlak, F.J., Armotrong, T.A., Fuchs, R.L., Berberich, S.A., Parks, N.J., Stapp, B.R., 1992. Resistance of cotton lines containing a Bacillus thuringiensis toxin to pink bollworm (Lepidoptera: Gelechidae) and other insects. J. Econ. Entomol. 85, 1516–1521. Wu, K., Guo, Y., Greenplate, J.T., Deaton, R., 2002. Resistance monitoring of Helicoverpa armigera (Lepidoptera Noctuidae) to Bacillus thuringiensis insecticidal protein in China. J. Econ. Entomol 95 (4), 826–831. Wu, K., Guo, Y., 2004. Changes in susceptibility to conventional insecticides of a Cry1Ac-selected population of Helicoverpa armigera (Hu¨bner) (Lepidoptera: Noctuidae). Pest. Manag. Sci. 60, 680–684. Wu, K., Mu, W., Liaang, G., Guo, Y., 2005. Re´gionale reversion of insecticide resistance in Heliocoverpa armigera (Lepidoptera: Noctuidae) is associated with the use of Bt cotton in northern China. Pest Manag. Sci. 61, 491–498.
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Crop Protection journal homepage: www.elsevier.com/locate/cropro
Efficacy of transgenic cotton plant containing the Cry1Ac and Cry2Ab genes of Bacillus thuringiensis against Helicoverpa armigera and Syllepte derogata in cotton cultivation in Burkina Faso Omer He´ma a, *, Hugues Ninaon Some´ a, Ouola Traore´ a, John Greenplate b,1, Mourad Abdennadher c, 2 a b c
INERA (Institut de l’Environnement et de Recherches Agricoles), 01 BP 208, Bobo-Dioulasso 01, Burkina Faso Monsanto Co, 800 N. Lindbergh Blvd, St Louis, MO 63167, United States Monsanto South Africa, Fourways Office Park, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 June 2008 Received in revised form 24 September 2008 Accepted 25 September 2008
As part of the research into alternatives to pyrethroids, to which lepidopteran cotton pests have begun to develop resistance, transgenic cotton expressing two endotoxins (Cry1Ac and Cry2Ab) of Bacillus thuringiensis Berliner (Bt), in the U.S. germplasms DP50 and Coker 312, was tested under field conditions in Burkina Faso in two contained areas. An untreated (no lepidopteran insecticidal sprays) conventional (non-transgenic) U.S. variety (Coker 312 in 2003; DP50 in 2004 & 2005) and two conventional local varieties (untreated and treated) were utilized in each test as comparators. The experiments conducted in 2003, 2004 and 2005 showed that the transgenic cotton plant significantly reduced larval populations of the cotton bollworm, Helicoverpa armigera, and the cotton leafroller, Syllepte derogata compared to untreated varieties. Plant damage analyses upon maturity revealed significantly higher levels of sound bolls in transgenic cotton plants. Seed cotton yields and lint quality were also higher for the transgenic cotton than for untreated convention varieties. The transgenic variety was always statistically equivalent or superior to the treated conventional one. The transgenic cotton plant expressing two endotoxins (Cry1Ac and Cry2Ab) of B. thuringiensis Berliner (Bt) can therefore be an alternative to the use of pyrethroids and endosulfan in cotton cultivation in Burkina Faso. This will have dual advantage of significantly reducing the quantities of pesticides sprayed in the cotton fields while protecting yields and quality of lint. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Transgenic cotton plant Bacillus thuringiensis Helicoverpa armigera Syllepte derogata Burkina Faso
1. Introduction Cotton is the principal export crop in Burkina Faso, representing over 50% of export earnings (Vognan et al., 2002). Significant economic losses in Burkina Faso cotton are due to feeding damage by caterpillar (Lepidoptera) populations and the cost of pesticides to control them. There are two principal groups of caterpillar pests, distinguished by their feeding preferences: these are bollworms, or fruit-feeders, the most prevalent of which are Helicoverpa armigera (Hu¨bner) (old world bollworm), Diparopsis spp. (red bollworms), and Earias spp. (spiny bollworms), and defoliators, which are primarily, Syllepte derogata (Fabricius) (cotton leafroller), Anomis flava (Fabricius) (looper), and Spodoptera littoralis (Boisduval) (cotton leafworm). * Corresponding author. Tel.: þ226 20 97 21 05; fax: þ226 20 97 01 59. E-mail addresses: [email protected] (O. He´ma), [email protected] (H.N. Some´), [email protected] (O. Traore´), [email protected] (J. Greenplate), [email protected] (M. Abdennadher). 1 Tel.: þ1 314 694 2637; fax: þ1 314 694 6662. 2 Tel.: þ27 11 790 8200; fax: þ27 11 790 8250. 0261-2194/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2008.09.014
For decades, cotton in Burkina Faso was protected from caterpillar damage by chemical pesticides, mainly from two families: pyrethroids and organophosphates often associated in the same treatment. Since 1995, field failure rates of these pesticides have risen, and sensitivity tests in the laboratory have shown a loss of sensitivity to pyrethroids in the larvae of field-collected H. armigera, confirming the presence of resistance (Martin et al., 2000; He´ma, 2004). In a typical year, the Burkina Faso cotton sector uses over $60 million of chemically based pest control products yet a recently conducted study in Burkina Faso found significant pest damage on fields that were protected using a standard regimen of six seasonal sprays (Vitale et al., 2006). The introduction of genetically modified cotton plants expressing the Cry1Ac and Cry2Ab toxins (Perlak et al., 2001; Greenplate et al., 2003), which have a different mode of action to that of pyrethroids, may be an interesting and effective alternative to chemical control. Other studies have shown that transgenic cotton use has greatly reduced pesticide treatments while effectively controlling caterpillar pests (Pray et al., 2002). In this study, we will address the effect of the transgenic cotton expressing Cry1Ac and
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Cry2Ab on Burkina Faso’s principal bollworm pest, H. armigera, and defoliator pest, S. derogata. 2. Materials and methods 2.1. Sites of experimentation Trials were conducted on two research station sites of INERA (Institut de l’Environnement et de Recherches Agricoles), the agricultural research arm of the Burkina Faso government. The research sites, Kouare´, in the East, and Farako-Baˆ, in the West, are 600 km apart. Both are on the 800–1000 mm isohyet with ferruginous soil deficient in organic matter (mainly less than 1%). 2.2. Varieties of cotton plants American (U.S.) and local (Burkina Faso) varieties of cotton plants were used for this study; in 2003, the American variety COKER 312 was used as a conventional control, and DP50 (Deltapine 50, Delta and Pine Land Co., Scott, MS, USA) containing the genes encoding the two endotoxins (Cry1Ac and CryAb) of Bacillus thuringiensis Berliner (Bt) was the test variety. In 2004 and 2005, the conventional version of DP50 and its transgenic counterpart were grown together. Coker 312 was used as a US conventional comparator in 2003 because of the unavailability of conventional DP50 and the fact Coker 312 was the original genetic source of the Cry1Ac component of transgenic
DP50. In 2003, the local conventional variety used was FK37; in 2004 and 2005, FK37 and STAM59 A were used in Farako-Baˆ and Kouare´, respectively. There are some morphological differences between American cotton varieties and local ones: On plant height, the local varieties are larger (120–150 cm on average) whereas the American varieties seldom reach 120 cm. Also, leaf pubescence is more important in the local varieties. The maturity of the two types of cotton plants is the same. 2.3. Treatments compared Four treatments were compared: Bt US: transgenic variety; Tr Conv BF: local conventional variety treated according to national insecticide treatments program: six treatments, beginning at 30 days after plant emergence, one application each 14 days. The two first treatments were done with endosulfan 500 g/ha, treatments number 3 and 4 with association cypermethrin 30 g/ha–profenofos 200 g/ha, the two last ones with association cypermethrin 36 g/ha–acetamiprid 8 g/ha; Un Conv BF: local conventional variety untreated against lepidopteran pests; Un Conv US: American conventional variety untreated against lepidopteran pests.
Fig. 1. a: H. armigera larval counts in Farako-Baˆ, 2003; 27/8/03 (df ¼ 3; F ¼ 1.571; P ¼ 0.248); 3/9/03 (df ¼ 3; F ¼ 2,000; P ¼ 0.168); 10/9/03 (df ¼ 3; F ¼ 5,600; P ¼ 0.012); 17/9/03 (df ¼ 3; F ¼ 9,766; P ¼ 0.002); 24/9/03 (df ¼ 3; F ¼ 9,189; P ¼ 0.002); 8/10/03 (df ¼ 3; F ¼ 2,306; P ¼ 0.129); 15/10/03 (df ¼ 3; F ¼ 7,714; P ¼ 0.004); 22/10/03 (df ¼ 3; F ¼ 1,714; P ¼ 0.217); 29/10/03 (df ¼ 3; F ¼ 2,857; P ¼ 0.032); 5/11/03 (df ¼ 3; F ¼ 1,714; P ¼ 0.217). b: H. armigera larval counts in Kouare´, 2003; 28/08/03 (df ¼ 3; F ¼ 1,895; P ¼ 0.184); 03/09/ 03 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 10/09/03 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 17/09/03 (df ¼ 3; F ¼ 3,412; P ¼ 0.053); 22/09/03 (df ¼ 3; F ¼ 7,062; P ¼ 0.005); 03/10/03 (df ¼ 3; F ¼ 30,327; P < 0.0001); 10/10/03 (df ¼ 3; F ¼ 2,169; P ¼ 0.145); 15/10/03 (df ¼ 3; F ¼ 4,294; P ¼ 0.028).
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2.4. Conducting of the experiment The study design utilized randomized complete blocks with four replicates. Plants were sown at a density of 62,500 plants/ha. The elementary plot varied from year to year, based upon available seed quantities. In 2003 a plot consisted of 4 rows of 15 m; in 2004 it was 8 rows of 10 m, and in 2005 a plot was 10 rows of 15 m. In 2003, insecticide treatments were made to all plots (transgenic and conventional) against Aphis gossypii and Bemisia tabaci (secondary pests not controlled by Bt) on thresholds: 21 of 25 plants heavily infested with A. gossypii and 5 of 25 plants infested by B. tabaci. Two specific treatments with imidacloprid at 30 g/ha were done against aphid and whitefly. In 2004 and 2005, two treatments with the same insecticide were done against these sucking pests at 86 and 100 days after plant emergence corresponding to these pests infestation period. Three types of observations were made: * Direct observations of pests: once a week, beginning at 30 days after emergence of the cotton plant, the number of H. armigera larvae observed on 20 plants and the number of plants infested by the larvae of S. derogata were recorded. * Plant damage analysis at maturity: prior to harvest, a whole middle row of each test plot was carefully analyzed and counts of the number of sound bolls or bolls with no worm damage, the number of worm-damaged bolls, and the number of bolls with discoloured or ‘‘yellow’’ lint caused by the mean boll pests with H. armigera as first were made.
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* Estimate of yield: the total seed cotton (lint plus seeds) handharvested from a whole middle row of each plot was weighed. An analysis of variance (ANOVA) was performed using XLSTAT version 6.1.9 software. Percent data are transformed before analyses, using the arcsine square root transformation (asin(sqrt(x/a))). An F test was used, and the averages, where differences were observed, were graded using the Bonferroni test at the threshold of 5% for the biological data; for the data estimating the yield, Fisher’s test was chosen. Within each figure discussed below, means with different letters affixed are significantly different. 3. Results 3.1. H. armigera larval counts in 2003 H. armigera larval densities are shown in Fig. 1a (Farako-Baˆ) and b (Kouare´). On 1st October and 15 October in Farako-Baˆ (1/10/03: df ¼ 3, F ¼ 22.645, P < 0.0001; 15/10/03: df ¼ 3, F ¼ 7.714, P ¼ 0.004) and 10 October in Kouare´ (df ¼ 3, F ¼ 2.169, P ¼ 0.145), the populations of this pest were significantly higher on untreated conventional varieties in comparison to the transgenic variety and conventional treated variety. In fact, while populations averaged well under 1 larva per 20 plants in the transgenic plots, populations of close to 10 larvae per 20 plants were observed on US and/or local conventional varieties.
Fig. 2. a: H. armigera larval counts in Farako-Baˆ, 2004 16/8/04 (df ¼ 3; F ¼ 0.530; P ¼ 0.665); 26/8/04 (df ¼ 3; F ¼ 1,167; P ¼ 0.340); 2/9/04 (df ¼ 3; F ¼ 0.212; P ¼ 0.887); 9/9/04 (df ¼ 3; F ¼ 1,798; P ¼ 0.170); 23/9/04 (df ¼ 3; F ¼ 2,851; P ¼ 0.055); 30/9/04 (df ¼ 3; F ¼ 1,291; P ¼ 0.297); 7/10/04 (df ¼ 3; F ¼ 0.991; P ¼ 0.411); 14/10/04 (df ¼ 3; F ¼ 0.708; P ¼ 0.556); 21/10/04 (df ¼ 3; F ¼ 0.467; P ¼ 0.708). b: H. armigera larval counts in Kouare´, 2004; 16/08/2004 (df ¼ 3; F ¼ 1,167; P ¼ 0.340); 23/08/2004 (df ¼ 3; F ¼ 2,567; P ¼ 0.075); 30/08/2004 (df ¼ 3; F ¼ 1,926; P ¼ 0.148); 06/09/2004 (df ¼ 3; F ¼ 0.970; P ¼ 0.421); 13/09/2004 (df ¼ 3; F ¼ 4,406; P ¼ 0.012); 20/09/2004 (df ¼ 3; F ¼ 4,990; P ¼ 0.007); 27/09/2004 (df ¼ 3; F ¼ 4,330; P ¼ 0.013); 04/10/2004 (df ¼ 3; F ¼ 2,957; P ¼ 0.049); 11/10/2004 (df ¼ 3; F ¼ 1,436; P ¼ 0.253); 18/10/2004 (df ¼ 3; F ¼ 1,167; P ¼ 0.340).
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3.2. H. armigera larval counts in 2004 At the Farako-Baˆ station (Fig. 2a), although no H. armigera larvae were found on transgenic cotton, overall densities were too low to statistically separate treatments (16/8/04: df ¼ 3, F ¼ 0.530, P ¼ 0.665; 26/8/04: df ¼ 3, F ¼ 1.167, P ¼ 0.340; 2/9/04: df ¼ 3, F ¼ 0.212, P ¼ 0.887; 9/9/04: df ¼ 3, F ¼ 1.798, P ¼ 0.170; 23/9/04: df ¼ 3, F ¼ 2.851, P ¼ 0.055; 30/9/04: df ¼ 3, F ¼ 1.291, P ¼ 0.297; 7/ 10/04: df ¼ 3, F ¼ 0.991, P ¼ 0.411; 14/10/04: df ¼ 3, F ¼ 0.708, P ¼ 0.556; 21/10/04: df ¼ 3, F ¼ 0.467, P ¼ 0.708). In Kouare´ (Fig. 2b), on September 27, the transgenic variety had significantly less H. armigera larvae than all the other treatments (df ¼ 3, F ¼ 4.330, P ¼ 0.013). 3.3. H. armigera larval counts in 2005 In Farako-Baˆ (Fig. 3a), the transgenic cotton supported significantly fewer larvae than the conventional varieties (treated and untreated) on September 19 (df ¼ 3, F ¼ 4.000, P ¼ 0.035). In Kouare´ (Fig. 3b), on September 29, the conventional varieties treated and untreated contained significantly more H. armigera larvae than the transgenic cotton (df ¼ 3, F ¼ 4.636, P ¼ 0.022). Densities on transgenics were always well below 0.5 larvae per 20 plants, while
conventional untreated varieties reached 3.5 and 6 larvae per 20 plants in Farako-Baˆ and Kouare´, respectively. Densities on treated conventional variety varied from 0 to 3.5 in Farako-Baˆ and Kouare´. 3.4. S. derogata infestation in 2003 At both sites (Fig. 4a and b), the untreated conventional varieties showed significantly more S. derogata infested plants than did the transgenic cotton plants and the treated conventional variety all the times significant differences were observed, except September 20 in Farako-Baˆ (23/8/03: df ¼ 3, F ¼ 1.571, P ¼ 0.248; 30/8/03: df ¼ 3, F ¼ 0.769, P ¼ 0.533; 7/9/03: df ¼ 3, F ¼ 6.757, P ¼ 0.006; 13/9/03: df ¼ 3, F ¼ 3.447, P ¼ 0.052; 27/9/03: df ¼ 3, F ¼ 11.617, P ¼ 0.001; 4/10/ 03: df ¼ 3, F ¼ 10.222, P ¼ 0.001; 11/10/03: df ¼ 3, F ¼ 32.175, P < 0.0001; 18/10/03: df ¼ 3, F ¼ 10.804, P ¼ 0.001; 25/10/03: df ¼ 3, F ¼ 4.236, P ¼ 0.029; 1/11/03: df ¼ 3, F ¼ 8.200, P ¼ 0.003) and September 11 to September 18 in Kouare´ (4/9/03: df ¼ 3, F ¼ 3.000, P ¼ 0.073; 25/9/03: df ¼ 3, F ¼ 10.169, P ¼ 0.001; 2/10/03: df ¼ 3, F ¼ 28.789, P < 0.0001; 9/10/03: df ¼ 3, F ¼ 17.228, P ¼ 0.000; 16/10/ 03: df ¼ 3, F ¼ 197.343, P < 0.0001; 24/10/03: df ¼ 3, F ¼ 42.571, P < 0.0001; 30/10/03: df ¼ 3, F ¼ 20.877, P < 0.0001). In Farako-Baˆ, in periods of high infestation of this pest we observed more than 6 infested plants out of 20, and in Kouare´ this pest infested around 12
Fig. 3. a: H. armigera larval counts in Farako-Baˆ, 2005; 16/08/2005 (df ¼ 3; F ¼ 0.333; P ¼ 0.802); 23/08/2005 (df ¼ 3; F ¼ 1,222; P ¼ 0.344); 29/08/2005 (df ¼ 3; F ¼ 1,118; P ¼ 0.380); 05/09/2005 (df ¼ 3; F ¼ 4,000; P ¼ 0.035); 12/09/2005 (df ¼ 3; F ¼ 2,889; P ¼ 0.079); 19/09/2005 (df ¼ 3; F ¼ 4,000; P ¼ 0.035); 26/09/2005 (df ¼ 3; F ¼ 6,612; P ¼ 0.007); 03/10/2005 (df ¼ 3; F ¼ 2,684; P ¼ 0.094); 10/10/2005 (df ¼ 3; F ¼ 2,000; P ¼ 0.168); 24/10/2005 (df ¼ 3; F ¼ 3,091; P ¼ 0.068). b: H. armigera larval counts in Kouare´, 2005; 21/08/2005 (df ¼ 3; F ¼ 8,500; P ¼ 0.003); 25/08/2005 (df ¼ 3; F ¼ 3,242; P ¼ 0.060); 01/09/2005 (df ¼ 3; F ¼ 1,571; P ¼ 0.248); 08/09/2005 (df ¼ 3; F ¼ 4,462; P ¼ 0.025); 15/09/2005 (df ¼ 3; F ¼ 4,103; P ¼ 0.032); 22/09/2005 (df ¼ 3; F ¼ 4,171; P ¼ 0.031); 29/09/2005 (df ¼ 3; F ¼ 4,636; P ¼ 0.022); 06/10/2005 (df ¼ 3; F ¼ 0.800; P ¼ 0.517); 13/10/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 20/10/2005 (df ¼ 3; F ¼ 3,000; P ¼ 0.073); 27/10/2005 (df ¼ 3; F ¼ 0.667; P ¼ 0.588).
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Fig. 4. a: S. derogata damage in Farako-Baˆ, 2003; 23/8/03 (df ¼ 3; F ¼ 1,571; P ¼ 0.248); 30/8/03 (df ¼ 3; F ¼ 0.769; P ¼ 0.533); 7/9/03 (df ¼ 3; F ¼ 6,757; P ¼ 0.006); 13/9/03 (df ¼ 3; F ¼ 3,447; P ¼ 0.052); 20/9/03 (df ¼ 3; F ¼ 3,825; P ¼ 0.039); 27/9/03 (df ¼ 3; F ¼ 11,617; P ¼ 0.001); 4/10/03 (df ¼ 3; F ¼ 10,222; P ¼ 0.001); 11/10/03 (df ¼ 3; F ¼ 32,175; P < 0.0001); 18/10/03 (df ¼ 3; F ¼ 10,804; P ¼ 0.001); 25/10/03 (df ¼ 3; F ¼ 4,236; P ¼ 0.029); 1/11/03 (df ¼ 3; F ¼ 8,200; P ¼ 0.003). b: S. derogata damage in Kouare´, 2003; 4/9/03 (df ¼ 3; F ¼ 3,000; P ¼ 0.073); 11/9/03 (df ¼ 3; F ¼ 14,486; P ¼ 0.000); 18/9/03 (df ¼ 3; F ¼ 9,923; P ¼ 0.001); 25/9/03 (df ¼ 3; F ¼ 10,169; P ¼ 0.001); 2/10/03 (df ¼ 3; F ¼ 28,789; P < 0.0001); 9/10/03 (df ¼ 3; F ¼ 17,228; P ¼ 0.000); 16/10/03 (df ¼ 3; F ¼ 197,343; P < 0.0001); 24/10/03 (df ¼ 3; F ¼ 42,571; P < 0.0001); 30/10/03 (df ¼ 3; F ¼ 20,877; P < 0.0001).
plants out of 20 in the untreated conventional varieties. Very few infested plants were found in transgenic plots; the highest mean value was well below 1 per 20 plants, found on 13 September in Farako-Baˆ. 3.5. S. derogata infestation in 2004 In Farako-Baˆ (Fig. 5a), the infestations of this pest were significantly more important on the local untreated conventional variety than the other treatments from September 26 to October 17 (26/9/04: df ¼ 3, F ¼ 8.520, P ¼ 0.000; 3/10/04: df ¼ 3, F ¼ 24.271, P < 0.0001; 10/10/04: df ¼ 3, F ¼ 15.394, P < 0.0001; 17/10/04: df ¼ 3, F ¼ 17.243, P < 0.0001). In Kouare´ (Fig. 5b), from September 29 to October 13, transgenic plants and treated conventional ones were significantly less infested by S. derogata larvae than the untreated conventional varieties (29/09/ 2004: df ¼ 3, F ¼ 13.040, P < 0.0001; 06/10/2004: df ¼ 3, F ¼ 37.381, P < 0.0001; 13/10/2004: df ¼ 3, F ¼ 19.716, P < 0.0001). As in 2003, infested transgenic plants and infested treated conventional variety were extremely rare or non-existent. 3.6. S. derogata infestations in 2005 In Farako-Baˆ (Fig. 6a), on 30 September, the transgenic cotton plants and the treated conventional variety contained
significantly fewer S. derogata larvae than the untreated conventional variety (df ¼ 3, F ¼ 11.123, P ¼ 0.001). The level of infested plants in untreated conventional varieties reached 8/20. In Kouare´ (Fig. 6b), the phenomenon observed in 2004 happened again; the local untreated conventional variety hosted more larvae of this pest than the other treatments, and again, infested transgenic plants were essentially non-existent on September 28, October 19 and 26 (28/09/2005: df ¼ 3, F ¼ 3.913, P ¼ 0.037; 19/ 10/2005: df ¼ 3, F ¼ 5.781, P ¼ 0.011; 26/10/2005: df ¼ 3, F ¼ 4.236, P ¼ 0.029). 4. Mature bolls analysis 4.1. Sound bolls The analysis of mature bolls in 2003 at Farako-Baˆ and Kouare´ stations (Fig. 7) indicated significantly higher levels of sound bolls in the Bt cotton plants and treated conventional plots than in untreated conventional varieties (Farako-Baˆ: df ¼ 3, F ¼ 32.476, P < 0.0001; Kouare´: df ¼ 3, F ¼ 68.279, P < 0.0001). In fact, we obtained more than 70% sound bolls in the two localities with Bt plants and treated conventional ones, and around 50% or less sound bolls on untreated conventional varieties.
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Fig. 5. a: S. derogata damage in Farako-Baˆ, 2004 10/8/04 (df ¼ 3; F ¼ 0.292; P ¼ 0.831); 17/8/04 (df ¼ 3; F ¼ 1,667; P ¼ 0.197); 29/8/04 (df ¼ 3; F ¼ 1,029; P ¼ 0.395); 5/9/04 (df ¼ 3; F ¼ 2,129; P ¼ 0.119); 12/9/04 (df ¼ 3; F ¼ 4,340; P ¼ 0.012); 19/9/04 (df ¼ 3; F ¼ 4,208; P ¼ 0.014); 26/9/04 (df ¼ 3; F ¼ 8,520; P ¼ 0.000); 3/10/04 (df ¼ 3; F ¼ 24,271; P < 0.0001); 10/10/04 (df ¼ 3; F ¼ 15,394; P < 0.0001); 17/10/04 (df ¼ 3; F ¼ 17,243; P < 0.0001). b: S. derogata damage in Kouare´, 2004 25/08/2004 (df ¼ 3; F ¼ 1,365; P ¼ 0.274); 01/09/2004 (df ¼ 3; F ¼ 1,440; P ¼ 0.252); 08/09/2004 (df ¼ 3; F ¼ 2,690; P ¼ 0.065); 15/09/2004 (df ¼ 3; F ¼ 5,690; P ¼ 0.004);22/09/2004 (df ¼ 3; F ¼ 5,168; P ¼ 0.006); 29/09/2004 (df ¼ 3; F ¼ 13,040; P < 0.0001); 06/10/2004 (df ¼ 3; F ¼ 37,381; P < 0.0001); 13/10/2004 (df ¼ 3; F ¼ 19,716; P < 0.0001); 20/10/2004 (df ¼ 3; F ¼ 9,153; P ¼ 0.0002); 27/10/2004 (df ¼ 3; F ¼ 5,503; P ¼ 0.004).
In 2004 (Fig. 8), we observed a significant difference between the level of sound bolls originating from the Bt cotton plants and the treated conventional ones, and those of the untreated conventional varieties in the two areas (Farako-Baˆ: df ¼ 3, F ¼ 7.159, P ¼ 0.001; Kouare´: df ¼ 3, F ¼ 22.666, P < 0.0001). With the Bt Cotton plants and treated conventional variety, we had more than 80% sound bolls on both sites; in Farako-Baˆ and in Kouare´, the level of sound bolls in the untreated conventional varieties was greater than that of 2003 (over 60%). In 2005, in Farako-Baˆ and Kouare´ (Fig. 9), the Bt cotton plants and the treated conventional plants gave significantly higher levels of sound bolls (more than 70%) than that found in the untreated conventional varieties (60% or less) (Farako-Baˆ: df ¼ 3, F ¼ 14.744, P ¼ 0.0003; Kouare´: df ¼ 3, F ¼ 23.897, P < 0.0001). 4.2. Perforated bolls The Bt cotton plants and the treated conventional ones contained significantly fewer damaged bolls than the conventional varieties treated and untreated on both sites in 2003 (Farako-Baˆ: df ¼ 3, F ¼ 55.322, P < 0.0001; Kouare´: df ¼ 3, F ¼ 39.288, P < 0.0001) (Fig. 7) and 2005 (Farako-Baˆ: df ¼ 3, F ¼ 26.609, P < 0.0001; Kouare´: df ¼ 3, F ¼ 104.167, P < 0.0001) (Fig. 9) and in Kouare´ in 2004 (df ¼ 3, F ¼ 19.727, P < 0.0001). In 2004, at FarakoBaˆ station, transgenic variety was statistically equivalent to treated conventional variety and superior to untreated conventional
varieties as far as the level of perforated bolls is concerned (df ¼ 3, F ¼ 10.946, P < 0.0001) (Fig. 8). In fact, at both sites during the three years of the study, the Bt cotton plants gave fewer than 5% damaged bolls while the conventional varieties contained boll damage levels of 20–40%. The level of perforated bolls in the treated conventional variety varied from 5 to 15%. 4.3. Incidence of yellow cotton On both sites in 2003 (Fig. 10), the transgenic cotton plants and the treated conventional ones produced cotton of significantly better quality than that of the two untreated conventional varieties (Farako-Baˆ: df ¼ 3, F ¼ 16.255, P ¼ 0.0002; Kouare´: df ¼ 3, F ¼ 37.627, P < 0.0001). In 2005 in Farako-Baˆ (Fig. 10), the Bt cotton plants had produced significantly better cotton quality than the treated and the untreated conventional varieties (df ¼ 3, F ¼ 22.232, P < 0.0001). In fact, the Bt cotton plants gave less than 5% yellow cotton on both sites, while the treated conventional ones gave from 4 to 6% yellow cotton and the untreated conventional varieties produced from 7 to 17% yellow cotton. 4.4. Seed cotton yields In 2003 in Farako-Baˆ (Fig. 11), the Bt variety yielded significantly more seed cotton than both conventional varieties (untreated and
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Fig. 6. a: S. derogata damage in Farako-Baˆ, 2005; 20/08/2005 (df ¼ 3; F ¼ 2,571; P ¼ 0.103); 25/08/2005 (df ¼ 3; F ¼ 1,895; P ¼ 0.184); 03/09/2005 (df ¼ 3; F ¼ 0.733; P ¼ 0.552); 09/ 09/2005 (df ¼ 3; F ¼ 1,627; P ¼ 0.235); 16/09/2005 (df ¼ 3; F ¼ 2,862; P ¼ 0.081); 23/09/2005 (df ¼ 3; F ¼ 2,400; P ¼ 0.119); 30/09/2005 (df ¼ 3; F ¼ 11,123; P ¼ 0.001); 07/10/2005 (df ¼ 3; F ¼ 9,571; P ¼ 0.002); 21/10/2005 (df ¼ 3; F ¼ 7,097; P ¼ 0.005); 28/10/2005 (df ¼ 3; F ¼ 2,815; P ¼ 0.084); 04/11/2005 (df ¼ 3; F ¼ 1,714; P ¼ 0.217). b: S. derogata damage in Kouare´, 2005; 31/08/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 07/09/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426); 14/09/2005 (df ¼ 3; F ¼ 2,652; P ¼ 0.096); 21/09/2005 (df ¼ 3; F ¼ 2,505; P ¼ 0.109); 28/09/2005 (df ¼ 3; F ¼ 3,913; P ¼ 0.037); 05/10/2005 (df ¼ 3; F ¼ 4,184; P ¼ 0.030); 12/10/2005 (df ¼ 3; F ¼ 2,258; P ¼ 0.134); 19/10/2005 (df ¼ 3; F ¼ 5,781; P ¼ 0.011); 26/10/2005 (df ¼ 3; F ¼ 4,236; P ¼ 0.029); 02/11/2005 (df ¼ 3; F ¼ 2,778; P ¼ 0.087); 09/11/2005 (df ¼ 3; F ¼ 1,000; P ¼ 0.426).
Fig. 7. Mature boll assessment in Farako-Baˆ and Kouare´, 2003; Farako-Baˆ: Sounds bolls (df ¼ 3; F ¼ 32,476; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 55,322; P < 0.0001); (df ¼ 3; F ¼ 16,255; P ¼ 0.0002). Kouare´: Sounds bolls (df ¼ 3; F ¼ 68,279; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 39,288; P < 0.0001).
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Fig. 8. Mature boll assessment in Farako-Baˆ and Kouare´, 2004; Farako-Baˆ: Sounds bolls (df ¼ 3; F ¼ 7,159; P ¼ 0.001); Perforated bolls (df ¼ 3; F ¼ 10,946; P < 0.0001); Kouare´: Sounds bolls (df ¼ 3; F ¼ 22,666; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 19,727; P < 0.0001).
treated) (df ¼ 3, F ¼ 24.585, P < 0.0001). At Kouare´ station, the Bt cotton plant was statistically equivalent to the treated conventional variety; the untreated varieties yielded significantly less seed cotton (df ¼ 3, F ¼ 21.096, P < 0.0001). The difference between the yield produced by the transgenic variety and the U.S. conventional variety was around 500 kg/ha in Farako-Baˆ and 800 kg/ha in Kouare´. In 2004 at the Farako-Baˆ station (Fig. 11), there were no significant yield differences observed, although there was a numerical difference in favour of the Bt cotton around 200–250 kg/ha (df ¼ 3, F ¼ 1.651, P ¼ 0.230). In Kouare´ (Fig. 11), the transgenic variety produced significantly more seed cotton than the U.S. untreated conventional variety (around 500 kg/ha) (df ¼ 3, F ¼ 33.207, P < 0.0001). In 2005 at the Farako-Baˆ station (Fig. 11), the transgenic cotton produced significantly more seed cotton than the conventional DP50 (around 600 kg/ha) (df ¼ 3, F ¼ 54.447, P < 0.0001). At the Kouare´ station (Fig. 11), the yields on the American varieties were lower by about 200 kg/ha than they were at Farako-Baˆ (difference of 200 kg/ha), but the benefit of the transgenic variety over both conventional varieties was statistically significant, at around 600 kg/ha (df ¼ 3, F ¼ 32.720, P < 0.0001). The treated conventional variety yielded statistically the same level of seed cotton than the transgenic variety. In 2005, we observed an arithmetic difference of
yield between the treated conventional variety and the transgenic one in favour of the treated conventional variety. 5. Discussion The resistance of transgenic cotton plants containing the gene expressing the Cry1Ac of B. thuringiensis to damage by Lepidoptera pest larvae, namely H. armigera (Hu¨bner), Heliothis zea (Boddie), Heliothis virescens (F.), Pectinophora gossypiella (Saunders), and Spodoptera exigua (Hu¨bner), has been demonstrated previously (Wilson et al., 1992; Benedict et al., 1993; Wang et al., 1997; Gore et al., 2001; Chitkowski et al., 2003). This study, which evaluated the efficacy of transgenic cotton plants expressing two deltaendotoxins (Cry1Ac and Cry2Ab) of B. thuringiensis, showed, over three years in two different areas in Burkina Faso, excellent control of the larvae of H. armigera and of S. derogata as well as the treated conventional variety and some times more than this last variety throughout the cotton plant cycle. The analysis of the bolls upon harvest showed that this transgenic cotton produced significantly higher levels of sound bolls than did untreated conventional varieties. The damage caused on bolls by pests in the untreated conventional cotton plots was significantly higher than in the
Fig. 9. Mature boll assessment in Farako-Baˆ and Kouare´, 2005; Farako-Baˆ: Sounds bolls (df ¼ 3; F ¼ 14,744; P ¼ 0.0003); Perforated bolls (df ¼ 3; F ¼ 26,609; P < 0.0001); Kouare´: Sounds bolls (df ¼ 3; F ¼ 23,897; P < 0.0001); Perforated bolls (df ¼ 3; F ¼ 104,167; P ; P < 0.0001).
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Fig. 10. Yellow cotton assessment in Farako-Baˆ and Kouare´, 2003: Farako-Baˆ (df ¼ 3; F ¼ 16,255; P ¼ 0.0002); Kouare´ (df ¼ 3; F ¼ 37,627; P < 0.0001). 2004: Farako-Baˆ (df ¼ 3; F ¼ 8,283; P ¼ 0.0004); Kouare´ (df ¼ 3; F ¼ 13,326; P < 0.0001). 2005: Farako-Baˆ (df ¼ 3; F ¼ 22,232; P < 0.0001); Kouare´ (df ¼ 3; F ¼ 3,900; P ¼ 0.037).
transgenic cotton and the treated conventional plots. Insect damage resulted in deterioration in the quality of fiber, with untreated conventional varieties producing more yellow cotton than the transgenic and the treated conventional varieties. In our study, significantly higher seed cotton yields were usually observed in the Bt cotton and the treated conventional one; this is consistent with earlier studies of Bt-expressing cotton (Gore et al., 2000; Wu et al., 2002; Pray et al., 2002). The differences in yield observed between the transgenic and the untreated conventional varieties in Burkina Faso were between 400 and 600 kg/ha. The degree of yield benefit realized with Bt cotton is certainly linked with pest density. In the present study, the only time yield differences were not seen between Bt and conventional varieties was in 2004 in Farako-Baˆ (Fig. 11) where overall H. armigera densities were relatively low (Fig. 2a). Another factor, pertinent to the ultimate value of Bt cotton, is the relative efficacy and cost of the pesticides currently used to control cotton Lepidoptera pests. In Burkina Faso and in West Africa, H. armigera has exhibited various levels of resistance to the pyrethroids commonly used in cotton, with a resistance factor varying from 10 to more than 500 (Martin et al., 2000; He´ma, 2004). Higher pest densities and the reduced efficacy of affordable pesticides may render Bt cotton
a potentially valuable tool to control damaging Lepidopteran pests for several reasons; the use of transgenic Bt cotton may allow an increase in the yield of farmers who actually do 2 to 3 treatments against Lepidopteran pests in steed of 4–5, with concurrent reductions in the cost of pesticides, the time spent spraying dangerous pesticides like endosulfan prohibited by Sahelian Council of Pesticides, and illness due to poisoning (Pray et al., 2002). Because no positive cross-resistance has been observed between the delta-endotoxins of B. thuringiensis and pyrethroids (Wu and Guo, 2004), the use of Bt cotton may also enable an increase in the sensitivity of H. armigera to pyrethroids, an increase in the population of useful insects, and optimization of the natural control of certain pests like sucking ones by beneficials (Wu et al., 2005). Finally, management strategies for Bt cotton must consider the fact that insecticide treatment for Lepidopteran pests can be greatly reduced, but the effective control of sucking pests (aphids, whiteflies), often controlled coincidentally by Lepidoptera sprays in conventional cotton, will have to be addressed in a systematic manner, since the current Bt toxins are not active against these pests. Also, the effectiveness of the Bt toxins on S. littoralis, another Lepidopteran pest in cotton in Burkina Faso, has not been studied
Fig. 11. Seed cotton yield in Farako-Baˆ and Kouare´, 2003: Farako-Baˆ (df ¼ 3; F ¼ 24,585; P < 0.0001); Kouare´ (df ¼ 3; F ¼ 21,096; P < 0.0001); 2004: Farako-Baˆ (df ¼ 3; F ¼ 1,651; P ¼ 0.230); Kouare´ (df ¼ 3; F ¼ 33,207; P < 0.0001); 2005: Farako-Baˆ (df ¼ 3; F ¼ 54,447; P < 0.0001); Kouare´ (df ¼ 3; F ¼ 32.720; P < 0.0001).
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during these three years. These topics will be subjects of future studies. Acknowledgements This research was undertaken with thanks to the government of Burkina Faso, which gave special authorizations for import experimentation of this transgenic cotton, and to the Burkina Faso cotton industry and Monsanto for financial support. References Benedict, J.H., Sachs, E.S., Altman, D.W., Ring, D.R., Stone, T.B., Sims, S.R., 1993. Impact of delta-endotoxin producing transgenic cotton on insect-plant interactions with Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae). Environ. Entomol. 22, 1–9. Chitkowski, R.L., Turnipseed, S.G., Sullivan, M.J., Bridges, W.C., 2003. Field and laboratory evaluations of transgenic cottons expressing one or two Bacillus thuringiensis var. kurstaki Berliner proteins for management of Noctuid (Lepidoptera) pests. J. Econ. Entomol. 03, 0755–0762. Gore, J., Leonard, B.R., Adamaczyk, J.J., 2001. Bollworm (Lepidoptera: Noctuidae) survival on ‘‘Bollgard’’ and ‘‘Bollgard II’’ cotton flower bud and flower components. J. Econ. Entomol. 94 (6), 1445–1451. Gore, J., Leonard, B.R., Church, G.E., Russel, J.S., Hall, T.S., 2000. Cotton boll abscission and yield losses associates with first-instar bollworm (Lepidoptera: Noctuidae) injury to nontransgenic and transgenic Bt cotton. J. Econ. Entomol. 93 (3), 690–696. Greenplate, J.T., Mullins, J.W., Penn, S.R., Dahhm, A., Reich, B.J., Osborn, J.A., Rahn, P.R., Ruschke, L., Shappley, Z.W., 2003. Partial characterization of cotton plants expressing two toxin proteins from Bacillus thuringiensis: relative toxin contribution, toxin interaction, and resistance management. J. Appl. Entomol. 127, 340–347.
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