Field-evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India.
TL;DR: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non-Bt cotton in the Amreli district of Gujarat in western India, providing the first evidence of field-evolved resistance of pink bollworm toCry1Ac.
Abstract: BACKGROUND: The pink bollworm is one of the most destructive pests of cotton. Transgenic cotton producing Bt toxin Cry1Ac or a combination of Cry1Ac and Cry2Ab2 has been used effectively against this pest. However, some other insects have evolved resistance to Bt toxins in the field. During the 2007–2008 and 2008–2009 seasons, pink bollworm populations in India were surveyed to evaluate their responses to Cry1Ac and seed powder containing Cry1Ac and Cry2Ab2.
RESULTS: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non-Bt cotton in the Amreli district of Gujarat in western India. The median lethal concentration of Cry1Ac for five-day-old larvae (LC50) was significantly higher for insects derived in 2008 from Amreli than for any of the other field populations tested from four locations in India. For Cry1Ac, the mean LC50 for the strain derived from Amreli in 2008 was 44 times higher than for the most susceptible population. However, for seed powder of Bollgard II containing primarily Cry2Ab2, the 2008 Amreli population was only slightly less susceptible than the most susceptible population.
CONCLUSIONS: The data reported here constitute the first evidence of field-evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009–2010 growing season, which confirmed field-evolved resistance to Cry1Ac in Amreli. The lack of cross-resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac. Copyright © 2011 Society of Chemical Industry
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TL;DR: Field outcomes support theoretical predictions that factors delaying resistance include recessive inheritance of resistance, low initial frequency of resistance alleles, abundant refuges of non-Bt host plants and two-toxin Bt crops deployed separately from one-t toxin BT crops.
Abstract: Evolution of resistance in pests can reduce the effectiveness of insecticidal proteins from Bacillus thuringiensis (Bt) produced by transgenic crops We analyzed results of 77 studies from five continents reporting field monitoring data for resistance to Bt crops, empirical evaluation of factors affecting resistance or both Although most pest populations remained susceptible, reduced efficacy of Bt crops caused by field-evolved resistance has been reported now for some populations of 5 of 13 major pest species examined, compared with resistant populations of only one pest species in 2005 Field outcomes support theoretical predictions that factors delaying resistance include recessive inheritance of resistance, low initial frequency of resistance alleles, abundant refuges of non-Bt host plants and two-toxin Bt crops deployed separately from one-toxin Bt crops The results imply that proactive evaluation of the inheritance and initial frequency of resistance are useful for predicting the risk of resistance and improving strategies to sustain the effectiveness of Bt crops
838 citations
TL;DR: This is the first report of field-evolved resistance to a Bt toxin by the western corn rootworm and by any species of Coleoptera, and suggests that improvements in resistance management and a more integrated approach to the use of Bt crops may be necessary.
Abstract: Background
Crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are planted on millions of hectares annually, reducing the use of conventional insecticides and suppressing pests. However, the evolution of resistance could cut short these benefits. A primary pest targeted by Bt maize in the United States is the western corn rootworm Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae).
601 citations
TL;DR: Activity of Cry1AMod toxins, which are able to form toxin oligomers in the absence of receptors, against different resistant populations, supports the hypothesis that toxin oligomerization is a limiting step in the Cry insecticidal activity.
Abstract: Bacillus thuringiensis bacteria are insect pathogens that produce different Cry and Cyt toxins to kill their hosts. Here we review the group of three-domain Cry (3d-Cry) toxins. Expression of these 3d-Cry toxins in transgenic crops has contributed to efficient control of insect pests and a reduction in the use of chemical insecticides. The mode of action of 3d-Cry toxins involves sequential interactions with several insect midgut proteins that facilitate the formation of an oligomeric structure and induce its insertion into the membrane, forming a pore that kills midgut cells. We review recent progress in our understanding of the mechanism of action of these Cry toxins and focus our attention on the different mechanisms of resistance that insects have evolved to counter their action, such as mutations in cadherin, APN and ABC transporter genes. Activity of Cry1AMod toxins, which are able to form toxin oligomers in the absence of receptors, against different resistant populations, including those affected in the ABC transporter and the role of dominant negative mutants as antitoxins, supports the hypothesis that toxin oligomerization is a limiting step in the Cry insecticidal activity. Knowledge of the action of 3d-Cry toxin and the resistance mechanisms to these toxins will set the basis for a rational design of novel toxins to overcome insect resistance, extending the useful lifespan of Cry toxins in insect control programs.
581 citations
Cites background from "Field-evolved resistance to Bt toxi..."
...It has been shown that insects can develop resistance to Bt toxins in the laboratory and to Bt sprays in the field (Ferré & Van Rie, 2002; Janmaat & Myers, 2003; Tabashnik et al., 2008; Kruger et al., 2009; Storer et al., 2010; Dhurua & Gujar, 2011; Gassmann et al., 2011; Zhang et al., 2011)....
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TL;DR: Global monitoring data reported during the first two decades of transgenic crops was analyzed, with each case representing the responses of one pest species in one country to one insecticidal protein from Bacillus thuringiensis (Bt).
Abstract: Transgenic crops have revolutionized insect pest control, but their effectiveness has been reduced by evolution of resistance in pests. We analyzed global monitoring data reported during the first two decades of transgenic crops, with each case representing the responses of one pest species in one country to one insecticidal protein from Bacillus thuringiensis (Bt). The cases of pest resistance to Bt crystalline (Cry) proteins produced by transgenic crops increased from 3 in 2005 to 16 in 2016. By contrast, in 17 other cases there was no decrease in pest susceptibility to Bt crops, including the recently introduced transgenic corn that produces a Bt vegetative insecticidal protein (Vip). Recessive inheritance of pest resistance has favored sustained susceptibility, but even when inheritance is not recessive, abundant refuges of non-Bt host plants have substantially delayed resistance. These insights may inform resistance management strategies to increase the durability of current and future transgenic crops.
404 citations
TL;DR: Cry1F resistant S. frugiperda showed a recessive autosomal inheritance for alleles involved in resistance to Cry1F protein, indicating that implementation of resistance management strategies is urgent to prolong the lifetime of Cry1f for controlling S.frug Piperda in Brazil.
366 citations
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TL;DR: A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed, consisting of 133 crystal proteins comprising 24 primary ranks are systematically arranged.
Abstract: The crystal proteins of Bacillus thuringiensis have been extensively studied because of their pesticidal properties and their high natural levels of production. The increasingly rapid characterization of new crystal protein genes, triggered by an effort to discover proteins with new pesticidal properties, has resulted in a variety of sequences and activities that no longer fit the original nomenclature system proposed in 1989. Bacillus thuringiensis pesticidal crystal protein (Cry and Cyt) nomenclature was initially based on insecticidal activity for the primary ranking criterion. Many exceptions to this systematic arrangement have become apparent, however, making the nomenclature system inconsistent. Additionally, the original nomenclature, with four activity-based primary ranks for 13 genes, did not anticipate the current 73 holotype sequences that form many more than the original four subgroups. A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed. Roman numerals have been exchanged for Arabic numerals in the primary rank (e.g., Cry1Aa) to better accommodate the large number of expected new sequences. In this proposal, 133 crystal proteins comprising 24 primary ranks are systematically arranged.
1,167 citations
TL;DR: The understanding of the biochemical and genetic basis of resistance to Bt can help design appropriate management tactics to delay or reduce the evolution of resistance in insect populations.
Abstract: Bacillus thuringiensis (Bt) is a valuable source of insecticidal proteins for use in conventional sprayable formulations and in transgenic crops, and it is the most promising alternative to synthetic insecticides. However, evolution of resistance in insect populations is a serious threat to this technology. So far, only one insect species has evolved significant levels of resistance in the field, but laboratory selection experiments have shown the high potential of other species to evolve resistance against Bt. We have reviewed the current knowledge on the biochemical mechanisms and genetics of resistance to Bt products and insecticidal crystal proteins. The understanding of the biochemical and genetic basis of resistance to Bt can help design appropriate management tactics to delay or reduce the evolution of resistance in insect populations.
907 citations
TL;DR: The results suggest that the potential for resistance development in pest populations is an important consideration for deployment of B. thuringiensis toxin genes in genetically-engineered crop plants and use in related tactics.
Abstract: Foliar applications of commercial formulations of the insecticidal spore-crystal protein complex of Bacillus thuringiensis subsp. kurstaki caused development of resistance in field populations of a major lepidopteran pest of vegetables, diamondback moth, Plutella xylostella (L.). Laboratory bioassays of larvae showed that the LC50 and LC95 for a field population of diamondback moth treated repeatedly with B. thuringiensis were 25 to 33 times greater than the respective LC50’s and LC95’s for two susceptible laboratory colonies. Mortality at the field rate of B. thuringiensis was 34-35% in two resistant populations compared with 90-100% in two susceptible laboratory colonies. The results suggest that the potential for resistance development in pest populations is an important consideration for deployment of B. thuringiensis toxin genes in genetically-engineered crop plants and use of B. thuringiensis in related tactics.
765 citations
TL;DR: Onfarm field trials carried out with Bacillus thuringiensis (Bt) cotton in different states of India show that the technology substantially reduces pest damage and increases yields.
Abstract: Onfarm field trials carried out with Bacillus thuringiensis (Bt) cotton in different states of India show that the technology substantially reduces pest damage and increases yields. The yield gains are much higher than what has been reported for other countries where genetically modified crops were used mostly to replace and enhance chemical pest control. In many developing countries, small-scale farmers especially suffer big pest-related yield losses because of technical and economic constraints. Pest-resistant genetically modified crops can contribute to increased yields and agricultural growth in those situations, as the case of Bt cotton in India demonstrates.
762 citations
01 Jan 2009
TL;DR: In the period 1996 to 2012, millions of farmers in ~30 countries worldwide, made more than 100 million independent decisions to plant an accumulated hectarage of more than 1.5 billion hectares – 50% more than the land mass of the US or China; this demonstrates the trust and confidence of millions of risk-averse farmers in biotech crops which deliver sustainable and substantial socioeconomic and environmental benefits.
Abstract: In the period 1996 to 2012, millions of farmers in ~30 countries worldwide, made more than 100 million independent decisions to plant an accumulated hectarage of more than 1.5 billion hectares – 50% more than the land mass of the US or China; this demonstrates the trust and confidence of millions of risk-averse farmers in biotech crops which deliver sustainable and substantial, socioeconomic and environmental benefits.
734 citations