Quantitative genetic analysis of Cry1Ab tolerance in Ostrinia nubilalis Spanish populations 2

Abstract 2 Tolerance to Bacillus thuringiensis Cry1Ab toxin in Spanish Ostrinia nubilalis 3 populations was analyzed by quantitative genetic techniques, using isolines established 4 from field-derived insects. F1 offspring was tested for susceptibility to trypsin activated 5 Cry1Ab using a concentration that caused a mean larval mortality of 87% (± 17% SD). 6 The progeny of the most tolerant isolines (that had shown mortalities lower than 60%) 7 was crossed to obtain the F2 generation that was exposed to the same Cry1Ab 8 concentration. A clear reduction in mortality (62% ± 17% SD) was observed. The upper 9 limit for heritability was estimated to range between 0.82 and 0.90, suggesting that a 1

Recent trends in management strategies for two major maize borers: Ostrinia nubilalis and Sesamia nonagrioides

23 p.-2 tab.Stem borers (Lepidoptera) are common cereal pests. In many parts of the world, the species Ostrinia nubilalis and Sesamia nonagrioides stand out as important insect pests of economically important crops such as maize. Their management relied mainly on transgenic host plant resistance over the last 25 years. Technologies based on the insecticidal properties of Bacillus thuringiensis-derived proteins allowed widespread pest population suppression, especially for O. nubilalis. However, the recent discovery of Bt resistance, which has revitalized interest in both pests’ biology and management, may jeopardize the effectiveness of such transgenic technologies. Historical information on O. nubilalis bionomy may need to be reassessed in light of changing climate conditions and changing agricultural practices, as well as increased production of alternate host crops across its distribution range. The current paper examines the bioecology and historical research that has been conducted to manage these two important maize-boring pests.N

El uso de la biotecnología en el control de plagas: los cultivos resistentes a insectos en la Unión Europea

3 p.-2 fig.Peer reviewe

Sensitivity of buff-tailed bumblebee (Bombus terrestris L.) to insecticides with different mode of action

17 p.-3 fig.-2 tab. This article belongs to the Special Issue Impact of Environmental Factors and Management Practices on Bee HealthSystemic insecticides are recognized as one of the drivers of the worldwide bee decline as they are exposed to them through multiple pathways. Specifically, neonicotinoids, some of which are banned for outdoor use in the European Union (EU), have been pointed out as a major cause of bee collapse. Thus, farmers have had to look for alternatives for pest control and use known insecticides or new substances reportedly less harmful to bees. We evaluated the oral acute toxicity of six insecticides (three of them systemic: imidacloprid, thiacloprid and sulfoxaflor) with four different modes of action on buff-tailed bumblebee workers (Bombus terrestris): two banned neonicotinoids (imidacloprid, thiacloprid), two pyrethroids (deltamethrin, esfenvalerate), one sulfoximine (sulfoxaflor) and a microbial insecticide based on Bacillus thuringiensis toxins, present in genetically modified (Bt) maize. The microbial insecticide only caused mortality to bumblebee workers at extremely high concentrations, so it is expected that Bt maize does not pose a risk to them. The toxicity of the other five insecticides on bumblebees was, from highest to lowest: imidacloprid, sulfoxaflor, deltamethrin, esfenvalerate and thiacloprid. This outcome suggests that certain insecticides in use are more toxic to B. terrestris than some banned neonicotinoids. Further chronic toxicity studies, under realistic conditions, are necessary for a proper risk assessment.This research was funded by the Spanish Ministry of Science and Innovation (grant number PID2019-104578RB-I00) and the Spanish Ministry of Economy and Competitiveness (grant number AGL2015-64825-R). G.C. was funded by a predoc fellowship (BES-2016-077782) by the Spanish Ministry of Economy, Industry and Competitiveness.Peer reviewe

Susceptibility to the Cry1F toxin of field populations of Sesamia nonagrioides (Lepidoptera: Noctuidae) in Mediterranean maize cultivation regions

9 páginas, 3 figuras, 3 tablas -- PAGS nros. 214-221Maize hybrids expressing the Cry1F toxin provide efficient control of lepidopteran pests. The Mediterranean corn borer, Sesamia nonagrioides (Lefèvre), is one of the most damaging pests of maize in the Mediterranean basin. In this work we firstly determined the efficacy of maize hybrids expressing the Cry1F toxin (event TC1507) to control neonates of S. nonagrioides. Leaf tissue feeding bioassays revealed that TC1507 maize is highly effective against this pest, and the percentage mortality obtained was comparable to that obtained with a Cry1Ab-expressing maize hybrid (Compa CB, event 176), which is known to be highly efficacious against S. nonagrioides. Secondly, interpopulation variation in the susceptibility to the Cry1F insecticidal protein was established for nine field-collected populations of S. nonagrioides (three Spanish, two French, two Italian, one Greek, and one Turkish). Estimates of the susceptibility of larvae to the Cry1F toxin showed low variability in lethal concentrations and growth inhibition concentrations among field populations. Moreover, no significant differences were found when they were grouped by geographical areas [Western Mediterranean (Spain and France) versus Eastern Mediterranean (Italy, Greece and Turkey)] or by history of exposure to Bt plants (Spanish vs. other populations). Therefore, the minor differences found in field populations can be attributed to natural variation in sensitivity to Cry1F. The importance of establishing baselines of susceptibility for resistance detection is discussed. Future changes in susceptibility of S. nonagrioides populations to Cry1F could be documented based on this baseline dataPeer reviewe

Quantitative genetic analysis of Cry1Ab tolerance in Ostrinia nubilalis Spanish populations

30 p.-2 fig.-3 tab.Tolerance to Bacillus thuringiensis Cry1Ab toxin in Spanish Ostrinia nubilalis populations was analyzed by quantitative genetic techniques, using isolines established from field-derived insects. F1 offspring was tested for susceptibility to trypsin activated Cry1Ab using a concentration that caused a mean larval mortality of 87% (±17% SD). The progeny of the most tolerant isolines (that had shown mortalities lower than 60%) was crossed to obtain the F2 generation that was exposed to the same Cry1Ab concentration. A clear reduction in mortality (62 ± 17% SD) was observed. The upper limit for heritability was estimated to range between 0.82 and 0.90, suggesting that a high part of phenotypic variation in tolerance to Cry1Ab was attributable to genetic differences. An estimate of the minimum number of segregating factors indicated that the loci involved in tolerance to Cry1Ab were at least two. The role of the cadherin gene, which is a B. thuringiensis resistance gene in Lepidoptera, was assessed in the most tolerant isolines by using an EPIC-PCR marker specifically developed for this study. Association between cadherin and tolerance was obtained in one tolerant isoline; however it could be not confirmed by segregation analysis in the F2 progeny because F2 offspring was not viable. Our results indicate that the tolerance trait is common in Spanish field populations. Quantitative genetic techniques may be helpful for estimating the influence of genetic factors to Cry1Ab tolerance in O. nubilalis.Support for this project was provided by the EU Fifth Framework Project ‘‘ProBenBt’’ (Ref. QLK3-CT-2002-01969), by the Spanish Ministerio de Educación y Ciencia (project Ref. at the University of Valencia AGL2006-11914) and by the Spanish Ministerio de Ciencia e Innovación (project Ref. at the Centro de Investigaciones Biológicas of Madrid AGL 2009-08813). Cristina Crava was funded by a V Segles grant from the University of Valencia (Ref. UV-BVS- 07-2083).Peer reviewe

Ten years of MON 810 resistance monitoring of field populations of Ostrinia nubilalis in Europe

9 p.-2 fig.-1 tab.From 2005 to 2015, Ostrinia nubilalis were collected in the most important maize-growing areas in Europe where MON 810 was cultivated. The susceptibility of these O. nubilalis collections to the Cry1Ab protein was determined using overlay bioassays and compared to that of reference (control) strains. Larvae that died or did not moult after 7 days were used to calculate a moulting inhibition concentration (MIC). Two different batches of Cry1Ab protein were used over the course of this study. Between 2005 and 2015, 145 collections of O. nubilalis from 14 areas were analysed. The Cry1Ab susceptibility of populations from different geographic regions differed only slightly across years. The greatest variability in the MIC50 for field samples collected from 2005 to 2011 and tested with batch 1 was 6.6-fold in 2006. For field-collected O. nubilalis, the difference between MIC50 values of the most susceptible and most tolerant samples was 13.1-fold for this period. For samples collected in 2012–2015 and tested with batch 2, the greatest variability was 4.1-fold in 2014. A diagnostic concentration (MIC99) was calculated for batch 1 (48 ng/cm2) using the results from all the collections in 2005–2012. Bridging experiments indicated that the diagnostic concentration for batch 2 was 28 ng/cm2. From 2006 onwards, no O. nubilalis reached the 2nd larval stage when the diagnostic concentration of either batch of Cry1Ab was used. Only one insect collected from Romania in 2012 and two insects collected as reference strain from Spain in 2015 survived exposure to a dosage of 20 ng/cm2, and none of these larvae survived on MON 810 maize. Our results indicate that there has been no significant change in susceptibility to Cry1Ab in European populations of O. nubilalis over the period 2005–2015.This report presents the results of laboratory-based research and would not have been possible without the kind help of all those who supplied insects: M. Hoenig (Herbolzheim, G), U. Hoffmann(BTL, Keindorf, G), Dr. G. Langenbruch (Darmstadt, G), K.Lindner (Müncheberg, G), A. Schier (Nürtingen, G), D. Proff (Ansbach, G), A.Weissenberger (Wiwersheim, F), A. Mesas and N. Eychenne (Castanet Tolosan, F), I. Rami and N. Daste (Fredon Aquitaine, Villenave d’Ornon,F), K. Koubaïti (Biard, F), Prof. F. Kocourek and V. Falta (Prague, CZ),P. Beres and A. Maslanka (Rzeszow and Warsaw, PL), M. Czepo(Budapest, HU) and Prof. L. Cagan (Nitra, SK), Prof. I. Rosca, I. Sabau(Bucharest, RO), M. Gatti (Repros, Alonte, I) and the laboratory and field technicians of the Spanish group of Plant-Insect Interactions(CIB, CSIC, Madrid, ES). Thanks are also extended to field technicians of Monsanto and Pioneer in Spain and Portugal. Thanks to Monsanto Europe SA for commissioning this study and for providing the Cry1Ab protein.We wish to thank Prof AFG Dixon (UEA Norwich, UK) and Graham Head (Monsanto Company, St Louis, MO, USA) for language correction.Peer reviewe

Assessment of prey-mediated effects of the coleopteran-specific toxin Cry3Bb1 on the generalist predator Atheta coriaria (Coleoptera: Staphylinidae)

10 páginas, 3 figuras, 5 tablas -- PAGS nros. 293-302A laboratory study was carried out to assess the potential prey-mediated effects of Cry3Bb1-expressing Bt maize on the fitness and predatory ability of Atheta coriaria Kraatz (Coleoptera: Staphylinidae), using Tetranychus urticae Koch (Acari: Tetranychidae) as prey. The concentration of Cry3Bb1 toxin through the trophic chain significantly decreased from Bt maize (21.7 μg g−1 FW) to mites (5.6 μg g−1 FW) and then to A. coriaria adults (1.4 μg g−1 FW), but not from mites to A. coriaria L1–L3 larvae (4.1–4.6 μg g−1 FW). Interestingly, the toxin levels detected in A. coriaria larvae represent more than 20% of the concentration found in Bt maize, and the toxin was detected up to 48 h after exposure. To our knowledge, this is the highest level of exposure ever reported in a predatory beetle to the Cry3Bb1 protein. When A. coriaria larvae were reared on Bt-fed mites, Bt-free mites or rearing food, no significant differences among treatments were observed in development, morphological measurements of sclerotized structures and body weight. Moreover, no negative effects on reproductive parameters were reported in adults feeding on Bt-fed prey after 30 days of treatment, and survival was not affected after 60 days of exposure. Similarly, predatory ability and prey consumption of A. coriaria larvae and adults were not affected by exposure to the toxin. All together, these results indicate a lack of adverse effects on A. coriaria, a species commonly used as a biological control agent. The use of A. coriaria as a surrogate species for risk assessment of GM crops that express insecticidal proteins is discussedThis work received financial support from the Spanish Ministry of Environment (MMA) and CICYT (AGL2009-08813). Matías García's research was supported by a contract from the Science and Innovation Ministry (JAE-Doc)Peer reviewe

Correction: Sixteen Years of Bt Maize in the EU Hotspot: Why Has Resistance Not Evolved?

[This corrects the article DOI: 10.1371/journal.pone.0154200.]

Monitoring insect resistance to Bt maize in the European Union: update, challenges, and future prospects

14 p.-6 fig.-1 tab.Transgenic maize producing the Cry1Ab toxin of Bacillus thuringiensis (Bt maize) was approved for cultivation in the European Union (EU) in 1998 to control the corn borers Sesamia nonagrioides (Lefèbvre) and Ostrinia nubilalis (Hübner). In the EU since then, Cry1Ab is the only Bt toxin produced by Bt maize and Spain is the only country where Bt maize has been planted every year. In 2021, about 100,000 hectares of Bt maize producing Cry1Ab were cultivated in the EU, with Spain accounting for 96% and Portugal 4% of this area. In both countries, Bt maize represented less than 25% of all maize planted in 2021, with a maximum regional adoption of 64% Bt maize in northeastern Spain. Insect resistance management based on the high-dose/refuge strategy has been implemented in the EU since 1998. This has been accompanied by monitoring to enable early detection of resistance. The monitoring data from laboratory bioassays show no decrease in susceptibility to Cry1Ab had occurred in either pest as of 2021. Also, control failures have not been reported, confirming that Bt maize producing Cry1Ab remains effective against both pests. Conditions in the EU preventing approval of new genetically modified crops, including maize producing two or more Bt toxins targeting corn borers, may limit the future effectiveness of resistance management strategies.This review includes the revision of data obtained by our group in the frame of various R&D contracts of technological support funded by private companies: Monsanto Europe SA (2016–2019) and Bayer CropScience Schweiz AG (since 2020).Peer reviewe