Abstract
Extensive unofficial planting of Bt cotton expressing Cry1Ac toxin has occured for the past two decades in northwestern China, and no mandatory refuge policy has been adopted. The status of Cry1Ac susceptibility of Helicoverpa armigera in this region has not been routinely monitored, nor has the susceptibility to Cry2Ab cotton which has not been released in China. The susceptibility of H. armigera populations to both toxins was assessed in 2014 and 2015 in two contrasting cotton farming systems across the region. Over the 2 years, the response to Cry1Ac of the nine H. armigera field populations sampled ranged from 3.16 to 16.94 μg ml−1 for LC50 and 0.013 to 0.741 μg ml−1 for IC50, and the baseline susceptibility of these strains to Cry2Ab ranged from 3.43 to 19.05 μg ml−1 for LC50 and 0.16 to 3.81 μg ml−1 for IC50. There was no significant difference in susceptibility to either Cry1Ac or Cry2Ab between small-holder and broad-acre farming. The susceptibility to Cry1Ac toxin in northwestern China is higher than that in northern China, while there was no difference for Cry2Ab between northwestern China and northern China. With high levels of adoption of Bt cotton and relatively limited natural refuge for H. armigera, it is important to consider resistance management measures for Bt cotton in northwestern China.
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Key message
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Bt cotton has been cultivated for two decades without official authorization in northwestern China, and the susceptibility of H. armigera to Cry1Ac and Cry2Ab toxic protein has not been well characterized.
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Susceptibility of H. armigera to Cry1Ac and Cry2Ab is still high in northwestern China, and farming type does not influence susceptibility to these Bt toxins.
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IRM (Insect Resistance Management) for Bt cotton should be implemented, and actions to limit dominant resistant individuals spreading from northern China should be taken into consideration.
Introduction
Transgenic crops have been commercially adopted for over 20 years worldwide, and the total area planted annually has reached more than 185 million hectares in 26 countries (James 2016). Economic losses caused by pest Lepidoptera in crops have been greatly reduced by the adoption of Bt crops with concomitant reduction in the use of broad-spectrum insecticide and environmental pollution in cotton production areas (Han et al. 2016; Downes et al. 2010, 2017; Wan et al. 2017; Dively et al. 2018; Wilson et al. 2018). As in the case of insecticides, evolution of resistance to Bt crops threatens the sustainability of this strategy for pest management (Tabashnik et al. 2008, 2013; Huang et al. 2010; Ives et al. 2017). Of the 13 major target pests for Bt crops, field-evolved resistance has been reported in five species at least (Tabashnik et al. 2013; Van Rensburg 2007; Gassmann et al. 2011; Grimi et al. 2018).
The cotton bollworm, Helicoverpa armigera (Hübner), is a highly polyphagous cosmopolitan pest on various crops, particularly on cotton (Cunningham and Zalucki 2014; Downes et al. 2017). In China, Bt cotton expressing a single toxin, Cry1Ac protein, has been widely used to curb this pest in cotton-growing areas (Wu 2007; Zhang et al. 2011; Chen et al. 2017). This situation differs from that in USA, Australia and India, where cotton containing pyramids of two or more Bt genes (mostly expressing Cry1Ac and Cry2Ab) is used (Chen et al. 2017; Liu et al. 2017). The susceptibility of H. armigera to Bt cotton has dramatically decreased over time in northern China (Wu 2007; Li et al. 2007; Liu et al. 2008, 2010; Zhang et al. 2018). Of concern are the presence of diverse resistance alleles and the apparent increasing percentage of dominant resistance in field-selected populations (Zhang et al. 2012; Jin et al. 2013). The percentage of resistant insects with non-recessive resistance reportedly has increased in northern China, from 37% of the 0.93% resistant insects in 2010 to 84% of the 5.5% resistant insects in 2013 (Jin et al. 2015). These trends pose a significant challenge to IRM in China, especially in northwestern China, where Bt cotton has been cultivated intensively for almost two decades although not officially authorized, and now represents more than 70% of the cotton production in China and 8–10% of worldwide cotton production (Wu and Guo 2005; Li et al. 2014; Wang et al. 2018). Even so, the status of H. armigera susceptibility to Cry1Ac Bt cotton has not been routinely monitored in this area of China.
Because of superior planting conditions for cotton cultivation, cotton production has greatly increased in Xinjiang Uygur Autonomous Region (called Xinjiang) and cotton makes up a much higher proportion of crop land than provinces in northern China (Fig. 2a; Wu and Guo 2005; Yang et al. 2017a). In contrast, the adoption of Bt cotton in Xinjiang is much lower than other provinces in China (Qiao 2015), partly because its planting does not have official approval. In Xinjiang, Bt cotton was first planted in 1997 and cotton covered about 34% of the total farmland area in 2014 (Li et al. 2013), with the percentage of Bt cotton ca 53% of total cotton in 2012. In comparison, the percentage of Bt cotton planted in six provinces of northern China increased from 11% in 1998 to 50% in 2000, 91% in 2004 and nearly 100% of total cotton by 2014 (Wu et al. 2008; Zhang et al. 2011; Qiao 2015) but comprised less than 10% of total farmland in this cotton area. This suggests that the potential natural refuge for H. armigera in this cotton production region is much higher than that in Xinjiang.
In a desert region such as Xinjiang, the nature of topography and availability of water restricts cotton to a series of relatively small, isolated areas where irrigation is available, effectively islands in a sea of desert and potentially “local” H. armigera populations (Lu and Baker 2013; Lu et al. 2013; Gu et al. 2018). This may restrict the movement and mating of H. armigera among cotton production areas, thus increasing the selection pressure and speeding the evolution of resistance (Ives et al. 2017). Moreover, the pattern of planting systems (i.e., the coexistence of broad-acre and small-holder farming) in Xinjiang might influence the susceptibility of H. armigera due to differences in the amount of natural refuges between the two types of farming (Li et al. 2014). Finally, much of the cotton seed comes from unknown sources (Huang et al. 2014), and the quality of Bt cotton seed being sold is not clear, particularly its toxin protein expression. Thus, it is important to evaluate the susceptibility of H. armigera to Bt toxin in Xinjiang, given the increasing percentage of non-recessive resistance in northern China (Jin et al. 2015). In addition, pyramided Bt cotton expressing both Cry1Ac and Cry2Ab is expected to be commercialized throughout China, including northwestern China (Jin et al. 2015). Therefore, it is necessary to establish and monitor the susceptibility of H. armigera to both Cry2Ab and Cry1Ac in northwestern China.
To aid IRM planning for northwestern China, the susceptibility of H. armigera to Cry1Ac and Cry2Ab was assessed in nine populations across Xinjiang in 2014–2015. We (1) assess the susceptibility of H. armigera to Cry1Ac after two decades of intensive Bt cotton planting without any mandated IRM policy; (2) measure baseline susceptibility to Cry2Ab in H. armigera in the absence of Cry2Ab release in this area; and (3) evaluate the effect of farming system (broad-acre vs. small-holder farming) on the susceptibility H. armigera to Bt toxins. This work provides the first baseline data for cotton bollworm susceptibility to Cry2Ab and updates susceptibility data for Cry1Ac in a situation representing increasing use of Bt crops in this area.
Materials and methods
Collection of insect populations
Larvae (> 3 instar) of H. armigera were collected in fields of different crops locally (mainly tomato and corn, see Tables 1 and 2 for details) adjacent to cotton fields during the cotton-growing season in 2014 and 2015. The sampled sites were selected on the basis of distribution and cropping characteristics (broad-acre vs. small-holder farming) in Xinjiang (Fig. 1). In 2014, fields in each region were chosen in cropping landscapes dominated by cotton, and these fields were revisited in 2015. At least 250 larvae (400 in some cases) were collected from each sampled field or an immediately adjacent field if larval numbers were low (less than 50). Larvae from each sampled crop site were transferred onto fresh artificial diet upon arrival in the laboratory and reared using a standard protocol (Zhang et al. 2011). Consequently, nine populations representing each sampling site were established. For each population, the male and female pupae were separated after larvae pupated. When most of the adults had emerged, 40–50 adults were put together (sex ratio 1:1) for mating in a container covered with a piece of gauze. There were 10–20 containers for each sampled site. Eggs (300–500) were collected from each container and put together based on sampled sites. The neonate larvae were used for bioassays.
Bt proteins
The Cry1Ac and Cry2Ab pro-toxin powders used in bioassays were supplied by Beijing General Pest Biotech Research Co. Ltd. The Bt proteins were separately incorporated into artificial diet for the bioassays (Sims et al. 1996). We chose the test concentrations in our study based on previous similar studies (Wu et al. 1999; Bird and Akhurst 2007; Anilkumar et al. 2008; Brévault et al. 2009). Stock suspensions of Cry1Ac and Cry2Ab were diluted with distilled water to produce six diet concentrations of Cry1Ac (0.005, 0.05, 0.5, 2.5, 5 and 25 μg ml−1) and Cry2Ab (0.05, 0.5, 2.5, 5, 10 and 25 μg ml−1). Distilled water was used as the control in experiments with both Cry1Ac and Cry2Ab.
Bioassays
Two ml of Bt-containing diet was poured into each well of 24-well insect assay trays. Newly hatched (< 24 h) unfed and active larvae were transferred onto the diet with a fine brush (1 larva/well). Trays were covered with plastic ventilated covers and kept in an incubator at 27 ± 1 °C. Twenty-four larvae from each sampled population were used for each concentration and for the untreated control, and the assay was repeated five times with each population of H. armigera.
Based on previous studies on baseline susceptibility of lepidopteran pests to Bt proteins, two parameters were measured in bioassays at 7 days: mortality, defined as individuals showing no reaction to gentle probing (Sims et al. 1996; Avilla et al. 2005; Wu et al. 1999) and larval growth inhibition based on larval weights (Wu et al. 1999; Bird and Akhurst 2007).
Data analysis
Probit analysis of the data was carried out using SPSS 17.0 (SPSS Inc., Chicago, IL, USA) to compute 50% lethal concentrations (LC50) and 50% inhibitory concentrations (IC50). Two populations were considered significantly different in their response if their 95% confidence limits did not overlap (Jalali et al. 2004; Liao et al. 2002; Chandrashekar et al. 2005).
Independent t tests were used to evaluate the effect of farming systems (broad-acre and small-holder farming) and date (2014 and 2015). Pearson correlation analysis was used to estimate the correlation between responses to Cry1Ac and Cry2Ab (Brévault et al. 2009).
Results
Susceptibility of H. armigera to Cry1Ac
The LC50 and IC50 values varied between years as well as among populations. The responses among the nine H. armigera populations to Cry1Ac in 2014 ranged from 5.49 to 16.94 μg ml−1 for LC50 and for IC50 from 0.013 to 0.474 μg ml−1. In 2015, these values ranged from 3.16 to 9.08 μg ml−1 for LC50 and 0.115 to 0.741 μg ml−1 for IC50. The populations in 2014 and 2015 were compared within years based on non-overlap of 95% fiducial limits (Table 1). There were no significant differences among populations in 2014 except for Korla (for LC50) and B86 (for IC50) (Table 1). In 2015, there were no significant differences among populations for LC50, as well as IC50 (Table 1).
Baseline susceptibility of H. armigera to Cry2Ab
Similar to Cry1Ac, there was variability among populations in the susceptibility of H. armigera to Cry2Ab. The responses of nine H. armigera populations to Cry2Ab in 2014 ranged from 3.43 to 8.42 μg ml−1 for LC50 and 0.16 to 1.45 μg ml−1 for IC50. The 95% fiducial limits of the data indicated that there were no significant differences in LC50 and IC50 among different populations (Table 2). In 2015, the responses of nine H. armigera populations to Cry2Ab ranged from 6.19 to 19.05 μg ml−1 for LC50 and from 0.51 to 3.81 μg ml−1 for IC50. The 95% fiducial limits of the data indicated that there were no significant differences in LC50 among the different populations except for Awat, and no significant differences in IC50 except for Alar (Table 2).
Susceptibility of H. armigera to Cry1Ac versus Cry2Ab
Pearson correlation analysis was used to estimate the correlation between Cry1Ac and Cry2Ab responses. Across the nine field populations, there were no significant correlations between Cry1Ac and Cry2Ab susceptibility for any of the two measurements in 2014 (LC50: r = 0.252, p = 0.514; IC50: r = 0.335, p = 0.378) nor in 2015 (LC50: r = 0.097, p = 0.805; IC50: r = 0.558, p = 0.119).
The effect of farming systems and date
For both Cry1Ac and Cry2Ab farming type (small-holder and broad-acre farming) did not affect LC50 and IC50. For years (2014 and 2015), LC50 in 2015 was significantly lower than that in 2014, but there was no difference for IC50 for Cry1Ac. There was no significant difference in LC50 for Cry2Ab susceptibility between years (Table 3).
Discussion
Our work provides the first baseline data on cotton bollworm susceptibility to Cry2Ab and updated information on susceptibility to Cry1Ac following the increasing use of Bt crops in northwestern China. The baseline susceptibility to Cry2Ab in Xinjiang was similar to that in other parts of the world (“Susceptibility baseline of Cry2Ab in northwestern China” section), and the susceptibility to Cry1Ac was higher than in northern China (“Level of susceptibility of H. armigera field populations to Cry1Ac Bt cotton” section).
Level of susceptibility of H. armigera field populations to Cry1Ac Bt cotton
In our study, the lack of a susceptible strain makes it difficult to assess the evolution of resistance of H. armigera to Cry1Ac since the release of Bt cotton in Xinjiang. Our data on susceptibility of cotton bollworm to Cry1Ac can be compared with those from other studies that included a susceptible strain. The two populations in northwestern China described by Zhang et al. (2011) were collected in Shache and Shawan in Xinjiang, which overlap with our sampling areas (Fig. 1). The susceptibility of these two populations was at the same level as that of a susceptible laboratory strain of H. armigera (Zhang et al. 2011). We take the Shache and Shawan populations from Xinjiang to be indicative of a susceptible strain in our study. The median LC50 of Cry1Ac for 13 populations from northern China measured by Zhang et al. (2011) was 2.8 times higher for activated toxin and 3.0 times higher for pro-toxin than for Shache and Shawan populations in Xinjiang. More recently Zhang et al. (2018) found that the susceptibility of H. armigera to Cry1Ac in Xinjiang (as measured by toxin concentration causing 50% inhibition of larval development to the third instar) is higher than that from Huanghe River Valley and Yangtze River Valley cotton areas. This is indirect evidence to suggest that H. armigera in Xinjiang remains relatively susceptible to Cry1Ac but we note that the inference needs to be treated with caution as the two studies used different methods.
The stability of resistance allele frequencies also supports a conclusion of continued Cry1Ac susceptibility of H. armigera in Xinjiang. Li et al. (2010) reported that from 2005 to 2009, the resistance allele frequency in Korla fluctuated between 0.000 and 0.004 and from 0.0000 to 0.0008 in individuals collected from Shache. In 2010–2011, the frequencies of Cry1Ac resistance in H. armigera populations were < 10−3 in both Shihezi and Shache (Wang et al. 2012). These results indicate that resistance allele frequencies in populations of H. armigera in northwestern China were at low levels, which is consistent with the bioassay results in our study.
Possible reasons for continued H. armigera susceptibility to Cry1Ac Bt cotton
Xinjiang has a lower level of alternate host refuge than northern China (Fig. 2b) and the lack of a clear policy on Bt cotton there might, theoretically, lead to rapid resistance evolution. However, the susceptibility of H. armigera to Cry1Ac remains at levels similar to that in northern China.
One possibility is that seed mix refuges might delay or mitigate resistance development to Bt cotton as on other Bt crops (Carroll et al. 2012, 2013; Carrière et al. 2016; Wan et al. 2017). The percentage of non-Bt cotton seed in seed lots was 10–30% in local markets because of poor market management in Xinjiang (Lu, unpublished data). The non-Bt cotton mixed in Bt cotton fields might serve as refuge and delay resistance evolution if larvae of H. armigera have low mobility between Bt cotton and non-Bt cotton and high inherent susceptibility to Bt toxins. The effectiveness of seed mixtures to counter the evolution of resistance is controversial (Brevault et al. 2015; Carrière et al. 2016; Yang et al. 2017b). However, the use of seed mixtures successfully mitigated against the development of resistance at least experimentally, for example the pink bollworm (Pectinophora gossypiella) in China (Wan et al. 2017).
Susceptibility baseline of Cry2Ab in northwestern China
The baseline susceptibility of Cry2Ab was 3.43–19.05 μg ml−1 (LC50) and 0.16–3.81 μg ml−1 (IC50) over two consecutive years in our study region where Bt cotton expresses single Cry1Ac toxin. Similar variability in the response of H. armigera populations to Cry2Ab toxin has been reported in other areas: 6–28.6 μg ml−1 (India) and 5.12–50.71 μg ml−1 (West Africa) for LC50; 0.14–0.60 μg ml−1 (Australia), 0.31–2.3 μg ml−1 (India) and 0.22–8.72 μg ml−1 (West Africa) for IC50 (Bird and Akhurst 2007; Brévault et al. 2009; Anilkumar et al. 2008).
Zhang et al. (2011) found that the median LC50 of Cry2Ab for 15 populations indicated no significant difference between northern (13 populations) and northwestern China (two populations); the Shache and Shawan populations collected in 2010 from Xinjiang. Moreover, the susceptibility of H. armigera populations to Cry2Ab in Shache and Shawan was not significantly different from that of the susceptible laboratory strains of this species. In our study, the LC50 values of Cry2Ab for nine populations throughout Xinjiang, including Shache and Shawan populations, were not significantly different from each other except for Awat in 2015 (Table 2). These results indicate that the susceptibility of H. armigera to Cry2Ab in northwestern China is still higher in the Bt cotton areas as expected.
Lack of cross-resistance between Cry2Ab and Cry1Ac
The high susceptibility to Cry2Ab across populations in northwestern China and the lack of correlation between Cry2Ab and Cry1Ac susceptibility indicate that any resistance to Cry1Ac that may be present has not conferred cross-resistance to Cry2Ab. Our results are consistent with many studies across a range of target pests that includes H. armigera and other Helicoverpa species, including studies of H. armigera in Australia and western Africa (Brévault et al. 2009), but not with the cross-resistance found between Cry1Ac and Cry2Ab in one study from northern China (Gao et al. 2009). Our results indicate that Bt cotton containing Cry2Ab could be very useful against populations with resistance to Cry1Ac, at least in Xinjiang.
Rational IRM to Bt cotton in northwestern China
Even though H. armigera still exhibits a high level of susceptibility to Bt cotton in Xinjiang, a policy on Bt cotton adoption and IRM should be developed to manage seed markets in this region. Actions need to be considered to restrict dominant resistant individuals increasing locally or moving from northern China to northwestern China.
Cotton only makes up 4–10% of the sown area in northern China of which 98% is Bt cotton without a mandatory refuge (Fig. 2 and Huang et al. 2010). Although there are large areas of natural refuge including corn, soybean and vegetables in northern China (Ye et al. 2015), resistance appears to be on the rise, particularly the frequency of individuals with dominant resistance (Jin et al. 2015). The significant concern is how long can one avoid mandatory refuges in northwestern China and a policy for their implementation? Mandatory refuges are considered one of the key contributors to successful IRM in Australia (Downes et al. 2017; Wilson et al. 2018). An active IRM program should be developed for Xinjiang as far less natural refuge is available, particularly in broad-acre farming districts (Lu et al. 2013). The optimization of multiple refuge hosts temporally and spatially across landscapes is crucial for the production of susceptible moths that are likely to mate with resistant moths (Baker et al. 2008; Baker and Tann 2013; Lu et al. 2013; Li et al. 2017), thus improving the efficacy of IRM. Moreover, after a careful risk assessment, pyramided Bt cotton should be released to provide an additional tool to combat potential Bt resistance issues in northern China (Chen et al. 2017; Liu et al. 2017).
Author contribution statement
ZZL and MPZ designed research, PPW, JHM and DPX conducted bioassays, JL, HQW collected samples, ZMX and GPH analyzed data, and MPZ and ZZL wrote this manuscript. All authors read and approved the manuscript.
References
Anilkumar KJ, Rodrigo-Simón A, Ferré J, Pusztai-Carey M, Sivasupramaniam S, Moar WJ (2008) Production and characterization of Bacillus thuringiensis Cry1Ac-resistant cotton bollworm Helicoverpa zea (Boddie). Appl Environ Microbiol 74:462–469
Avilla C, Vargas-Osuna E, González-Cabrera J, Ferré J, González-Zamora JE (2005) Toxicity of several δ-endotoxins of Bacillus thuringiensis against Helicoverpa armigera (Lepidoptera: Noctuidae) from Spain. J Invertebr Pathol 90:51–54
Baker G, Tann CR (2013) Mating of Helicoverpa armigera (Lepidoptera: Noctuidae) moths and their host plant origins as larvae within Australian cotton farming systems. Bull Entomol Res 103:171–181
Baker GH, Tann CR, Fitt GP (2008) Production of Helicoverpa spp. (Lepidoptera, Noctuidae) from different refuge crops to accompany transgenic cotton plantings in eastern Australia. Aust J Agric Res 59:723–732
Bird LJ, Akhurst RJ (2007) Variation in susceptibility of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) in Australia to two Bacillus thuringiensis toxins. J Invertebr Pathol 94(2):84–94
Brevault T, Tabashnik BE, Carriere Y et al (2015) A seed mixture increases dominance of resistance to Bt cotton in Helicoverpa zea. Sci Rep 5(1):9807
Brévault T, Prudent P, Vaissayre M, Carrière Y (2009) Susceptibility of Helicoverpa armigera (Lepidoptera: Noctuidae) to Cry1Ac and Cry2Ab2 insecticidal proteins in four countries of the West African cotton belt. J Econ Entomol 102:2301–2309
Carrière Y, Fabrick JA, Tabashnik BE (2016) Can pyramids and seed mixtures delay resistance to Bt crops? Trends Biotechnol 34:291–302
Carroll MW, Head G, Caprio M (2012) When and where a seed mix refuge makes sense for managing insect resistance to Bt plants. Crop Prot 38:74–79
Carroll MW, Head G, Caprio M, Stork L (2013) Theoretical and empirical assessment of a seed mix refuge in corn for southwestern corn borer. Crop Prot 49:58–65
Chandrashekar K, Kumari A, Kalia V, Gujar GT (2005) Baseline susceptibility of the American bollworm, Helicoverpa armigera (Hübner) to Bacillus thuringiensis Berl var. kurstaki and its endotoxins in India. Curr Sci India 88:167–175
Chen W, Lu G, Cheng H et al (2017) Transgenic cotton co-expressing chimeric Vip3AcAa and Cry1Ac confers effective protection against Cry1Ac-resistant cotton bollworm. Transgenic Res 26(6):763–774
Cunningham JP, Zalucki MP (2014) Understanding heliothine (Lepidoptera: Heliothinae) pests: what is a host plant? J Econ Entomol 107:881–896
Dively GP, Venugopal PD, Bean D et al (2018) Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growers. Proc Natl Acad Sci USA 115(13):3320–3325
Downes S, Parker T, Mahon R (2010) Incipient resistance of Helicoverpa punctigera to the Cry2Ab Bt toxin in Bollgard II® cotton. PLoS ONE 5:e12567
Downes S, Kriticos D, Parry H, Paull C, Schellhorn N, Zalucki MP (2017) A perspective on management of Helicoverpa armigera: transgenic Bt cotton, IPM, and landscapes. Pest Manag Sci 73:485–492
Gao YL, Wu KM, Gould F, Shen ZC (2009) Cry2Ab tolerance response of Helicoverpa armigera (Lepidoptera: Noctuidae) populations from Cry1Ac cotton planting region. J Econ Entomol 102:1217–1223
Gassmann AJ, Petzold-Maxwell JL, Keweshan RS, Dunbar MW (2011) Field-evolved resistance to Bt maize by western corn rootworm. PLoS ONE 6:e22629
Grimi DA, Parody B, Ramos ML et al (2018) Field-evolved resistance to Bt maize in sugarcane borer (Diatraea saccharalis) in Argentina. Pest Manag Sci 74(4):905–913
Gu S, Han P, Ye Z et al (2018) Climate change favours a destructive agricultural pest in temperate regions: late spring cold matters. J Pest Sci 91(4):1191–1198
Han P, Velascohernandez MC, Ramirezromero R et al (2016) Behavioral effects of insect-resistant genetically modified crops on phytophagous and beneficial arthropods: a review. J Pest Sci 89(4):859–883
Huang JK, Mi JW, Lin H, Wang ZJ, Chen RJ, Hu RF, Rozelle S, Pray C (2010) A decade of Bt cotton in Chinese fields: assessing the direct effects and indirect externalities of Bt cotton adoption in China. Sci China Life Sci 53:981–991
Huang JK, Mi JW, Chen RJ, Su HH, Wu KM, Qiao FB, Hu RF (2014) Effect of farm management practices in the Bt toxin production by Bt cotton: evidence from farm fields in China. Transgenic Res 23:397–406
Ives A, Paull C, Hulthen A, Downes S, Andow D, Haygood R, Zalucki MP, Schellhorn N (2017) Spatio-temporal variation in landscape composition may speed resistance evolution of pests to Bt crops. PLoS ONE 12(1):e0169167
Jalali SK, Mohan KS, Singh SP, Manjunath TM, Lalitha Y (2004) Baseline-susceptibility of the old-world bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) populations from India to Bacillus thuringiensis Cry1Ac insecticidal protein. Crop Prot 23:53–59
James C (2016) Global status of commercialized biotech/GM crops: 2016. ISAAA Brief No. 52. ISAAA, Ithaca, NY
Jin L, Wei YY, Zhang L, Yang YH, Tabashnik BE, Wu YD (2013) Dominant resistance to Bt cotton and minor cross-resistance to Bt toxin Cry2Ab in cotton bollworm from China. Evol Appl 6:1222–1235
Jin L, Zhang HN, Lu YH, Yang YH, Wu KM, Tabashnik BE, Wu YD (2015) Large-scale test of the natural refuge strategy for delaying insect resistance to transgenic Bt crops. Nat Biotechnol 33:169–174
Li GP, Wu KM, Gould F, Wang JK, Miao J, Gao XW, Guo YY (2007) Increasing tolerance to Cry1Ac cotton from cotton bollworm, Helicoverpa armigera, was confirmed in Bt cotton farming area of China. Ecol Entomol 32:366–375
Li GP, Feng HQ, Gao YL, Wyckhuys KAG, Wu KM (2010) Frequency of Bt resistance alleles in Helicoverpa armigera in the Xinjiang cotton-planting region of China. Environ Entomol 39:1698–1704
Li XY, Gong ZL, Wang JD (2013) Planting status and policy advices of transgenic cotton in Xinjiang, China. In: Proceeding of China cotton association 2013 annual meeting, pp 10–15
Li HM, Ma JH, Wang P (2014) Cotton bollworm resistance to the Bt cotton and management strategy in Xinjiang, China. Egypt J Biol Pest Control 24:533–541
Li Y, Gao Y, Wu K et al (2017) Function and effectiveness of natural refuge in IRM strategies for Bt crops. Curr Opin Insect Sci 21:1–6
Liao C, Heckel DG, Akhurst R (2002) Toxicity of Bacillus thuringiensis insecticidal proteins for Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae), major pests of cotton. J Invertebr Pathol 80:55–63
Liu F, Xu Z, Chang J, Chen J, Meng F, Zhu Y, Shen J (2008) Resistance allele frequency to Bt cotton in field populations of Helicoverpa armigera (Lepidoptera: Noctuidae) in China. J Econ Entomol 101:933–943
Liu F, Xu Z, Zhu YC, Huang F, Wang Y, Li H, Li H, Gao C, Zhou W, Shen J (2010) Evidence of field-evolved resistance to Cry1Ac-expressing Bt cotton in Helicoverpa armigera (Lepidoptera: Noctuidae) in northern China. Pest Manag Sci 66:155–161
Liu L, Gao M, Yang S, Liu S, Wu Y, Carriere Y, Yang Y (2017) Resistance to Bacillus thuringiensis toxin Cry2Ab and survival on single-toxin and pyramided cotton in cotton bollworm from China. Evolut Appl 10(2):170–179
Lu ZZ, Baker G (2013) Spatial and temporal dynamics of Helicoverpa armigera (Lepidoptera, Noctuidae) in contrasting agricultural landscapes in northwestern China. Int J Pest Manag 59:25–34
Lu ZZ, Zalucki MP, Perkins LE, Wang DY, Wu LL (2013) Towards a resistance management strategy for Helicoverpa armigera in Bt cotton in northwestern China: an assessment of potential refuge crops. J Pest Sci 86:695–703
Qiao FB (2015) Fifteen years of Bt cotton in China: the economic impact and its dynamics. World Dev 70:177–185
Sims SB, Greenplate JT, Stone TB, Caprio MA, Gould FL (1996) Monitoring strategies for early detection of Lepidoptera resistance to Bacillus thuringiensis insecticidal proteins. In: ACS symposium series No. 645, pp 229–242
Tabashnik BE, Gassmann AJ, Crowder DW, Carrière Y (2008) Insect resistance to Bt crops: evidence versus theory. Nat Biotechnol 26:199–202
Tabashnik BE, Brévault T, Carrière Y (2013) Insect resistance to Bt crops: lessons from the first billion acres. Nat Biotechnol 31:510–521
Van Rensburg JBJ (2007) First report of field resistance by the stem borer, Busseola fusca (Fuller) to Bt-transgenic maize. S Afr J Plant Soil 24:147–151
Wan P, Xu D, Cong S et al (2017) Hybridizing transgenic Bt cotton with non-Bt cotton counters resistance in pink bollworm. Proc Natl Acad Sci USA 114(21):5413–5418
Wang DM, Li HQ, Ding RF, Li HB, Liu J, Xu Y (2012) Frequency of resistance to Bacillus thuringiensis toxin CrylAc in Xinjiang field population of Helicoverpa armigera. J Plant Prot 39:518–522
Wang D, Yang X, Li H et al (2018) Genetic homogeneity between populations of cotton bollworm from Xinjiang, China. J Asia-Pac Entomol 21(1):309–315
Wilson LJ, Whitehouse ME, Herron GA et al (2018) The management of insect pests in Australian cotton: an evolving story. Annu Rev Entomol 63(1):215–237
Wu KM (2007) Monitoring and management strategy for Helicoverpa armigera resistance to Bt cotton in China. J Invertebr Pathol 95:220–223
Wu KM, Guo YY (2005) The evolution of cotton pest management practices in China. Annu Rev Entomol 50:31–52
Wu KM, Guo YY, Lv N (1999) Geographic variation in susceptibility of Helicoverpa armigera (Lepidoptera: Noctuidae) to Bacillus thuringiensis insecticidal protein in China. J Econ Entomol 92:273–278
Wu KM, Lu YH, Feng HQ, Jiang YY, Zhao JZ (2008) Suppression of cotton bollworm in multiple crops in China in areas with Bt toxin-containing cotton. Science 321:1676–1678
Yang F, Kerns DL, Brown S et al (2017a) Pollen contamination in seed mixture increases the dominance of resistance to Bt maize in Spodoptera frugiperda (Lepidoptera: Noctuidae). Pest Manag Sci 73(11):2379–2385
Yang X, Zhang Z, Niu Y et al (2017b) Cotton root morphology and dry matter accumulation at different film removal times. Agron J 109(6):2586–2597
Ye L, Fu X, Ouyang F et al (2015) Determining the major Bt refuge crops for cotton bollworm in North China. Insect Sci 22(6):829–839
Zhang HN, Yin W, Zhao J, Jin L, Yang YH, Wu SW, Tabashnik BE, Wu YD (2011) Early warning of cotton bollworm resistance associated with intensive planting of Bt cotton in China. PLoS ONE 6:e22874
Zhang H, Tian W, Zhao J et al (2012) Diverse genetic basis of field-evolved resistance to Bt cotton in cotton bollworm from China. Proc Natl Acad Sci USA 109:10275–10280
Zhang D, Xiao Y, Chen W et al (2018) Field monitoring of Helicoverpa armigera (Lepidoptera: Noctuidae) Cry1Ac insecticidal protein resistance in China (2005–2017). Pest Manag Sci. https://doi.org/10.1002/ps.5175
Acknowledgements
We gratefully thank all of the staff at the Plant Protection stations for helping to collect larvae. This work was supported by the International S&T Cooperation Program of China (2011DFA33170), the CAS President’s International Fellowship Initiative (PIFI) in 2018, Xinjiang Production and Construction Groups’ Science & Technology Aid Project (No.2014AB009) and First Class Discipline construction (NXYLXK2017A01) in Ningxia Hui Autonomous Region.
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Wang, P., Ma, J., Head, G.P. et al. Susceptibility of Helicoverpa armigera to two Bt toxins, Cry1Ac and Cry2Ab, in northwestern China: toward developing an IRM strategy. J Pest Sci 92, 923–931 (2019). https://doi.org/10.1007/s10340-018-1047-0
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DOI: https://doi.org/10.1007/s10340-018-1047-0