Extensive use of chemical pesticides poses a great threat to the environment and food safety. The discovery of Bacillus thuringiensis (Bt) toxins with effective insecticidal activity against pests and the development of transgenic technology of plants opened a new era of pest control. Transgenic Bt crops, including maize, cotton and soya bean, have now been produced and commercialized to protect against about 30 major coleopteran and lepidopteran pests, greatly benefiting the environment and the economy. However, with the long-term cultivation of Bt crops, some target pests have gradually developed resistance. Numerous studies have indicated that mutations in genes for toxins activation, toxin-binding and insect immunization are important sources in Bt resistance. An in-depth exploration of the corresponding Bt-resistance mechanisms will aid in the design of new strategies to prevent and control pests. Future research will focus on Bt crops expressing new genes and multiple genes to control a broader range of pests as part of an integrated pest management programme. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.

https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.2018.0316

Recent progress on the interaction between insects and Bacillus thuringiensis crops.

Key message
QTL-M and QTL-E enhance soybean resistance to insects. Pyramiding these QTLs withcry1Ac increases protection against Bt-tolerant pests, presenting an opportunity to effectively deploy Bt with host–plant resistance genes.

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Pyramids of QTLs enhance host-plant resistance and Bt-mediated resistance to leaf-chewing insects in soybean

The Old World bollworm, Helicoverpa armigera (Hubner), was recently introduced into Brazil, where it has caused extensive damage to cotton and soybean crops. MON 87701 × MON 89788 soybean, which expresses the Bt protein Cry1Ac, was recently deployed in Brazil, providing high levels of control against H. armigera. To assess the risk of resistance to the Cry1Ac protein expressed by MON 87701 × MON 89788 soybean in Brazil, we conducted studies to evaluate the baseline susceptibility of H. armigera to Cry1Ac, in planta efficacy including the assessment of the high-dose criterion, and the initial resistance allele frequency based on an F2 screen. The mean Cry1Ac lethal concentration (LC50) ranged from 0.11 to 1.82 μg·mL-1 of diet among all H. armigera field populations collected from crop seasons 2013/14 to 2014/15, which indicated about 16.5-fold variation. MON 87701 × MON 89788 soybean exhibited a high level of efficacy against H. armigera and most likely met the high dose criterion against this target species in leaf tissue dilution bioassays up to 50 times. A total of 212 F2 family lines of H. armigera were established from field collections sampled from seven locations across Brazil and were screened for the presence of MON 87701 × MON 89788 soybean resistance alleles. None of the 212 families survived on MON 87701 × MON 89788 soybean leaf tissue (estimated allele frequency = 0.0011). The responses of H. armigera to Cry1Ac protein, high susceptibility to MON 87701 × MON 89788 soybean, and low frequency of resistance alleles across the main soybean-producing regions support the assumptions of a high-dose/refuge strategy. However, maintenance of reasonable compliance with the refuge recommendation will be essential to delay the evolution of resistance in H. armigera to MON 87701 × MON 89788 soybean in Brazil.

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High Susceptibility to Cry1Ac and Low Resistance Allele Frequency Reduce the Risk of Resistance of Helicoverpa armigers to Bt Soybean in Brazil.

Field evaluation of soybean transgenic event DAS-81419-2 expressing Cry1F and Cry1Ac proteins for the control of secondary lepidopteran pests in Brazil

Soybean looper (SBL), Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae), is an important pest of soybean and cotton in Brazil. The use of insecticides is one of the main control tactics against this pest. To support Integrated Pest Management (IPM) and Insect Resistance Management (IRM) programs, we characterized the susceptibility of Brazilian populations of SBL to insecticides. Field populations were collected from soybean fields during the 2016-2017 and 2017-2018 crop seasons. In the laboratory, late L2/early L3 larvae were exposed to insecticides in diet-overlay or topical bioassays. Field populations of SBL showed high susceptibility to spinetoram (LC50 = 0.074-0.25 μg a.i. per cm2), indoxacarb (LC50 = 0.46-0.94 μg a.i. per cm2), thiodicarb (LC50 = 9.14-36.61 μg a.i. per cm2), chlorantraniliprole (LC50 = 0.15-0.57 μg a.i. per cm2), flubendiamide (LC50 = 0.45-2.01 μg a.i. per cm2), and chlorfenapyr (LC50 = 0.15-0.25 μg a.i. per cm2); the resistance ratios were less than 16-fold. In contrast, SBL populations have reduced susceptibility to lambda-cyhalothrin (LC50 = 3.71-9.54 μg a.i./cm2), methoxyfenozide (LC50 = 0.67-4.23 μg a.i. per cm2), novaluron (LC50 = 27.52-77.63 μg a.i. per cm2), and teflubenzuron (LC50 = 13.41-73.02 μg a.i. per cm2). The resistance ratios relative to a Lab population (susceptible of reference) was up to 38-, 63-, 1,553-, and 5,215-fold, respectively. These high resistance ratios can be associated with resistance evolution. Implications of these findings to IPM and IRM programs are discussed.

https://bioone.org/journals/journal-of-economic-entomology/volume-112/issue-3/toz031/Susceptibility-of-Brazilian-Populations-of-Chrysodeixis-includens-Lepidoptera--Noctuidae/10.1093/jee/toz031.pdf

Susceptibility of Brazilian Populations of Chrysodeixis includens (Lepidoptera: Noctuidae) to Selected Insecticides.

Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) causes economically significant damage to soybeans Glycine max (L.) Merrill (Fabaceae: Phaseoleae). The genetically modified soybean expressing the Cry1Ac protein of Bacillus thuringiensis Berliner, which is toxic to lepidopterans, is a potential alternative tool to manage this pest. Bioassays with H. armigera larval instars were conducted with Bt (Cry1Ac) and non-Bt soybean plants in order to evaluate the efficacy of control with the modified cultivar. Bt soybean affected the mean time of mortality in each larval instar, but its efficacy was not affected by the larval stage. Mortality was 100% in all six instars, indicating that the Bt soybean expressing the Cry 1Ac protein is an efficient control tactic for this pest.

/pdf/effect-of-bt-soybean-on-larvae-of-helicoverpa-armigera-4xqylgt4jj.pdf

Effect of Bt soybean on larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).

The objective of this work was to analyze the faunistic composition of the insect pests that occur during the fallow period in cotton ( Gossypium hirsutum ) crop residues in the state of Mato Grosso do Sul, Brazil. The study sites were the municipalities of Alcinopolis, Chapadao do Sul, Costa Rica, Aral Moreira, Dourados, and Sidrolândia. A sampling design with two replicates per municipality was used. Each replicate comprised 100 random points, and each point corresponded to a cotton plant that was entirely inspected, to count the insect pests on it. The obtained fauna was analyzed and a rarefaction curve of the species was generated. During the evaluation period, a total of 23 species were recorded in the cotton crop residue, and the most frequent and abundant were Bemisia tabaci , Aphis gossypii , Frankliniella schultzei , and Anthonomus grandis . The caterpillars were predominantly found on the non-Bt cotton crops in Dourados, and Chapadao do Sul was the municipality that exhibited the greatest species diversity. Despite being mandatory, the destruction of cotton stalks during the fallow period was not able to completely eliminate the insect pests during the study period; among these insect pests, A. grandis stands out, a species that affects the dynamics of cotton pest control.

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Carlos Eduardo Carducci Gomes

Papers

Effect of Bt soybean on larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).

Insetos fitófagos em restos culturais de algodoeiro durante vazio sanitário em Mato Grosso do Sul