Preference of Bt‐resistant and susceptible Busseola fusca moths and larvae for Bt and non‐Bt maize

The sustainability of genetically engineered insecticidal Bacillus thuringiensis Berliner (Bt) maize, Zea mays L. (Poaceae), is threatened by the evolution of resistance by target pest species. Several Lepidoptera species have evolved resistance to Cry proteins expressed by Bt maize over the last decade, including the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The insect resistance management (IRM) strategy (i.e., the high‐dose/refuge strategy) deployed to delay resistance evolution is grounded on certain assumptions about the biology and ecology of a pest species, for example, the interactions between the insect pest and crop plants. Should these assumptions be violated, the evolution of resistance within pest populations will be rapid. This study evaluated the assumption that B. fusca adults and larvae select and colonize maize plants at random, and do not show any preference for either Bt or non‐Bt maize. Gravid female B. fusca moths of a resistant and susceptible population were subjected to two‐choice oviposition preference tests using stems of Bt and non‐Bt maize plants. Both the number of egg batches as well as the total number of eggs laid on each stem were recorded. The feeding preference of Bt‐resistant and susceptible neonate B. fusca larvae were evaluated in choice test bioassays with whorl leaf samples of specific maize cultivars. Although no differential oviposition preference was observed for either resistant or susceptible female moths, leaf damage ratings indicated that neonate larvae were able to detect Bt toxins and that they displayed feeding avoidance behaviour on Bt maize leaf samples.     

F2 screen for resistance to a Bacillus thuringiensis-maize hybrid in the sugarcane borer (Lepidoptera: Crambidae)

A novel F2 screening technique was developed for detecting resistance in sugarcane borer, Diatraea saccharalis (F.), to transgenic Bacillus thuringiensis (Bt)-maize expressing the Cry1Ab insecticidal protein. The F2 screening method involved (i) collecting larvae from maize fields; (ii) establishing two-parent families; (iii) screening F2 neonates for survival on Bt-maize leaf tissues; and (iv) confirming resistance on commercial Bt-maize plants. With the F2 screening method, 213 iso-line families of D. saccharalis were established from field collections in northeast Louisiana, USA and were screened for Bt resistance. One family was confirmed to carry a major Bt resistance allele(s). In a laboratory bioassay, larval mortality of the Bt-resistant D. saccharalis on Bt-maize leaf tissues was significantly lower than that of a Bt-susceptible strain. This Bt-resistant D. saccharalis population is the first corn stalk borer species that has completed larval development on commercial Bt-maize. The F2 screening protocol developed in this study could be modified for detecting Bt resistance alleles in other similar corn stalk borers, such as the European corn borer, Ostrinia nubilalis (Hübner), and the southwestern corn borer, D. grandiosella Dyar.     

Sugarcane borer (Lepidoptera: Crambidae) resistance to transgenic Bacillus thuringiensis maize

Transgenic maize, Zea mays L., expressing the Bacillus thuringiensis (Bt) CrylAb toxin has been planted to extensive areas across the United States and several other countries, but no resistance has been documented in field populations oflepidopteran target pests. This article describes the first report of resistance alleles to commercially available Cry1Ab Bt maize in a Louisiana population of sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae). Two hundred thirteen two-parent isolines of D. saccharalis were screened for Cry1Ab resistance on Bt maize leaf tissue using an F2 screening technique. Larvae representing three isolines survived >15 d on Bt tissue in the F2 generation. The second generation backcross progeny (B1F2) derived from isoline 52 completed larval development on Bt maize in the greenhouse. Segregation and resistance frequency analysis associated with isoline 52 suggested that Bt resistance is probably determined by a nearly completely recessive allele at a single locus. With this assumption, the estimated resistance allele frequency in this population is 0.0023, within a 95% confidence interval of 0.0003-0.0064.     

Effect of learning on the oviposition preference of field-collected and laboratory-reared Chilo partellus (Lepidoptera: Crambidae) populations

Recent studies show that Vetiver grass, (Vetiveria zizanioides (L.) Nash), may have potential as a dead-end trap crop in an overall habitat management strategy for the spotted stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). Vetiver grass is highly preferred for oviposition, in spite of the fact that larval survival is extremely low on this grass. The oviposition behaviour of female Chilo partellus moths was investigated by determining the amount and size of egg batches allocated to maize and Vetiver plants and studying the effect of rearing conditions and oviposition experience on host plant selection. Two-choice preference tests were used to examine the effect of experience of maize (a suitable host plant) and Vetiver plants on the oviposition choice of C. partellus. For both field-collected and laboratory-reared moths, no significant differences were found in the preference distributions between the experienced groups. It is concluded that females do not learn, i.e. that they do not change their preference for Vetiver grass after having experienced oviposition on either maize or this grass, which supports the idea that trap cropping could have potential as a control method for C. partellus. Differences observed between field-collected and laboratory-reared moths in the amount and size of egg batches laid on maize and Vetiver grass indicate that data obtained from experiments with laboratory-reared insects should be treated with caution.     

Growth and development of Bacillus thuringiensis Cry1Ab-susceptible and Cry1Ab-resistant sugarcane borer on diet and conventional maize plants

The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), is a dominant maize borer pest and a major target of Bacillus thuringiensis (Bt)‐maize in Louisiana and the Gulf Coast area of Texas (USA). Growth and development of D. saccharalis on non‐toxic diet, diet treated with three low concentrations (0.01, 0.05, and 0.1 μg g^?1) of Cry1Ab toxin, and on non‐Bt maize plants were compared for five insect genotypes: a Bt‐susceptible strain (BT‐SS), a Cry1Ab‐resistant strain (BT‐RR), a back‐crossed and re‐selected resistant strain (BT‐R’R’), and two F₁ progeny of the BT‐SS and BT‐R’R’ strains. Fitness of the five genotypes was examined by infesting neonates on diet with/without Cry1Ab toxin in the laboratory and on intact non‐Bt maize plants in the greenhouse. Biological parameters measured were neonate‐to‐pupa development time and pupation rate, larval survival, larval and pupal weight, and sex ratio. Larvae of BT‐SS and BT‐R’R’ on non‐toxic diet and non‐Bt maize plants grew normally and there were no significant differences between the two strains in all measured parameters, suggesting a lack‐of‐fitness cost of the Cry1Ab resistance in D. saccharalis. Except for the development time on non‐Bt diet, all other parameters on both non‐Bt diet and non‐Bt maize plants were similar among the five genotypes. Larval development of BT‐SS was significantly affected on diet treated with Cry1Ab toxin at 0.05 and 0.1 μg g^?1, whereas the effect to BT‐RR and BT‐R’R’ was not significant. Pupal weight and sex ratio reared on Cry1Ab‐diet were similar and there were no significant differences among the five genotypes. Neonate‐to‐pupation rate decreased as Cry1Ab concentrations increased but the decrease was more significant for BT‐SS than for the other four genotypes. The lack‐of‐fitness costs of Bt resistance in D. saccharalis imply a greater challenge in managing Bt resistance for this maize borer species.     

Performance of Bt-susceptible and -heterozygous dual-gene resistant genotypes of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in seed blends of non-Bt and pyramided Bt maize

A seed blend refuge has been implemented in the U.S. Corn Belt for Bt maize resistance management. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a target pest of Bt maize in the Americas. The larvae of this pest are mobile, which may affect the efficacy of seed blend refuges. In this study, field and greenhouse trials were conducted to determine the performance of Bt-susceptible (aabb) and -heterozygous dual-gene-resistant (AaBb) genotypes of S. frugiperda in seed blends of non-Bt and pyramided Bt maize. Three field trials evaluated larval survival, larval growth, and plant injury with aabb in seed blends of Bt maize expressing Cry1A.105/Cry2Ab2/Vip3A with 0–30% non-Bt seeds. Greenhouse tests investigated the performance of aabb and AaBb in seed blends of Cry1A.105/Cry2Ab2 with 0–30% non-Bt seeds. In pure non-Bt maize plots, after 9–13 d of neonates being released on the plants, 0.39 and 0.65 larvae/plant survived with leaf injury ratings of 4.7 and 5.9 (Davis's 1–9 scale) in the field and greenhouse, respectively. In contrast, live larvae and plant injury were virtually not observed on Bt plants across all planting patterns. Larval occurrence and plant injury by aabb on non-Bt plants were similar between seed blends and pure non-Bt plantings, suggesting that the blended refuges could provide an equivalent susceptible population as structured refuge under the test conditions. In the greenhouse, the two insect genotypes in seed blends performed similarly, indicating that the seed blends did not provide more favorable conditions for AaBb over aabb. The information generated from this study should be useful in managing S. frugiperda and evaluating if send blends could be suitable refuge options for Bt resistance management in the regions where the insect is a primary target pest.     

Possibly similar genetic basis of resistance to Bacillus thuringiensis Cry1Ab protein in 3 resistant colonies of the sugarcane borer collected from Louisiana,USA

The sugarcane borer, Diatraea saccharalis (F.), is a major maize borer pest and a target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the mid‐southern region of the United States. Evolution of resistance in target pest populations is a great threat to the long‐term efficacy of Bt crops. In this study, we compared the genetic basis of resistance to Cry1Ab protein in 3 resistant colonies of sugarcane borer established from field populations in Louisiana, USA. Responses of larvae to the Cry1Ab protein for the parental and 10 other cross colonies were assayed in a diet‐incorporated bioassay. All 3 resistant colonies were highly resistant to the Cry1Ab protein with a resistance ratio of >555.6 fold. No maternal effect or sex linkage was evident for the resistance in the 3 colonies; and the resistance was functionally nonrecessive at the Cry1Ab concentrations of ≤ 3.16 μg/g, but it became recessive at ≥10 μg/g. In an interstrain complementation test for allelism, the F₁ progeny from crosses between any 2 of the 3 resistant colonies exhibited the similar resistance levels as their parental colonies, indicating that the 3 colonies most likely shared a locus of Cry1Ab resistance. Results generated from this study should provide useful information in developing effective strategies for managing Bt resistance in the insect.     

Evaluation of adult emergence and larval root injury for Cry3Bb1‐resistant populations of the western corn rootworm

The transgenic maize (Zea mays L.) event MON 88017 produces the Bacillus thuringiensis Berliner (Bt) toxin Cry3Bb1 to provide protection from western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding. In response to reports of reduced performance of Cry3Bb1‐expressing maize at two locations in Illinois, we conducted a two‐year experiment at these sites to characterize suspected resistance, as well as to evaluate root injury and adult emergence. Single‐plant bioassays were performed on larvae from each population that was suspected to be resistant. Results indicate that these populations had reduced mortality on Cry3Bb1‐expressing maize relative to susceptible control populations. No evidence of cross‐resistance between Cry3Bb1 and Cry34/35Ab1 was documented for the Cry3Bb1‐resistant populations. Field studies were conducted that included treatments with commercially available rootworm Bt hybrids and their corresponding non‐Bt near‐isolines. When compared with their near‐isolines, larval root injury and adult emergence were typically reduced for hybrids expressing Cry34/35Ab1 either alone or in a pyramid. In many instances, larval root injury and adult emergence were not significantly different for hybrids expressing mCry3A or Cry3Bb1 alone when compared with their non‐Bt near‐isolines. These findings suggest that Cry34/35Ab1‐expressing Bt maize may represent a valuable option for maize growers where Cry3Bb1 resistance is either confirmed or suspected. Consistent trends in adult size (head capsule width and dry mass) for individuals recovered from emergence cages were not detected during either year of this experiment. Because of the global importance of transgenic crops for managing insect pests, these results suggest that improved decision‐making for insect resistance management is needed to ensure the durability of Bt maize.     

Inheritance of resistance to Bacillus thuringiensis Cry1Ab protein in the sugarcane borer (Lepidoptera: Crambidae)

Inheritance traits of a Cry1Ab-resistant strain of the sugarcane borer, Diatraea saccharalis (F.) were analyzed using various genetic crosses. Reciprocal parental crosses between Cry1Ab-susceptible and Cry1Ab-resistant populations, F₁ by F₁ crosses, and backcrosses of F₁ with the Cry1Ab-resistant population were successfully completed. Larval mortality of the parental and cross-populations were assayed on Cry1Ab diet and Bacillus thuringiensis (Bt)-corn leaf tissue. Maternal effects and sex linkage were examined by comparing the larval mortality between the two F₁ populations. Dominance levels of resistance were measured by comparing the larval mortality of the Cry1Ab-resistant, -susceptible, and -heterozygous populations. Number of genes associated with the resistance was evaluated by fitting the observed mortality of F₂ and backcross populations with a Mendelian monogenic inheritance model. Cry1Ab resistance in D. saccharalis was likely inherited as a single or a few tightly linked autosomal genes. The resistance was incompletely recessive on Bt corn leaf tissue, while the effective dominance levels (D_ML) of resistance increased as Cry1Ab concentrations decreased with Cry1Ab-treated diet. D_ML estimated based on larval mortality on intact Bt corn plants reported in a previous study ranged from 0.08 to 0.26. This variability in D_ML levels of Cry1Ab resistance in D. saccharalis suggests that Bt corn hybrids must express a sufficient dose of Bt proteins to make the resistance genes functionally recessive. Thus, Bt resistant heterozygous individuals can be killed as desired in the “high/dose refuge” resistance management strategy for Bt corn.     

Development of Transgenic Sugarcane Resistant to Sugarcane Borer

Sugarcane borer (Diatraea saccharalis) is a major pest of sugarcane (Saccharum spp. hybrids), across the Americas. The insect is partially controlled by biological and chemical means, but still causes significant economic losses to sugarcane growers and processors. Proteins derived from Bacillus thuringiensis, Bt proteins, have been used to control sugarcane borer in maize (Zea mays) for the past decade. In sugarcane, the expression of individual Bt proteins has been reported several times. However practical use of Bt proteins requires their use as part of an Integrated Pest Management (IPM) system that includes the delivery of high doses of protein and the use of a refuge to slow the evolution of insect resistance to the protein. Here we demonstrate the feasibility of using Bt proteins to protect sugarcane from sugarcane borer in a commercial setting. We have expressed two Bt proteins with differing modes of action (Cry1Ab and Cry2Ab) in commercial sugarcane varieties, demonstrated efficacy against sugarcane borer in the field and describe a strategy for trait deployment in this tropical crop with complex genetics that limits trait introgression by backcrossing.     

Extended monitoring of resistance to Bacillus thuringiensis Cry1Ab maize in Diatraea saccharalis (Lepidoptera: Crambidae)

The sugarcane borer, Diatraea saccharalis (F.), is a major target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the mid-Southern region of the United States. During 2007-2009, a total of 986 feral individuals of D. saccharalis were collected from maize fields in six locations of Louisiana and Mississippi and examined for resistance to Cry1Ab maize using F 1/F 2 screens. Major resistance alleles to Cry1Ab maize in the populations sampled from non-Bt maize plants during 2007 and 2008 in Louisiana and 2009 in Mississippi were rare. From a total of 487 individuals collected from three locations in Louisiana in 2007 and 2008, only one individual was identified with major resistance alleles. In addition, no major resistance alleles were detected in 242 individuals collected from three locations in Mississippi in 2009. The frequency of major resistance alleles was estimated to be 0.002 with a 95% CI of 0.00025-0.0057 for the Louisiana populations and < 0.0061, with 95% probability, for the Mississippi populations. The resistance frequency estimated for the Louisiana populations in 2007 and 2008 was not significantly different from those reported previously for populations sampled in 2004-2006. However, among 200 individuals sampled from non-Bt maize plants in 2009 in Louisiana, six individuals were identified to possess major resistance alleles. The estimated major resistance allele frequency for the populations sampled from non-Bt maize plants in 2009 in Louisiana was 0.0176 with a 95% CI of 0.0072 to 0.0328, which was significantly greater than those estimated for the populations collected in 2004-2008. Similarly, the frequency of minor resistance alleles to Cry1Ab maize for the Louisiana populations collected in 2009 was also significantly greater than those estimated for the populations sampled before. In addition, two out of 57 feral individuals collected from Bt maize plants in Louisiana in 2009 were identified to carry major resistance alleles to Cry1Ab maize. Since 2010, transgenic maize expressing pyramided Bt genes has been planted in the US mid-Southern region and by 2011, pyramided Bt maize has replaced Cry1Ab maize as the dominant Bt maize for managing lepidopteran pests including D. saccharalis. The timely switching from single-gene Cry1Ab maize to the pyramided Bt maize should prevent further increases in Cry1Ab resistance allele frequency and thus ensure the continued success of Bt maize for managing D. saccharalis in the region.     

Effects of Bt maize expressing Cry1Ab and Bt spray on Spodoptera littoralis

Various studies have been conducted to assess the damage caused by secondary lepidopteran pests to transgenic Bt maize expressing Cry1Ab. However, to date little is known on the effects of transgenic maize on Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), a polyphagous herbivore which is considered a pest in Mediterranean maize growing areas. Here we present results on the effects of Bt maize (Bt‐11) and Bt spray (Dipel) on the various life stage parameters of this herbivore. We further assess the expression of Cry1Ab in different leaves and leaf parts in maize at a given plant growth stage, and determine whether the feeding damage of 3rd instar S. littoralis is influenced by Bt toxin expression. Contrary to previous literature reporting that S. littoralis is not sensitive to Bt Cry1Ab toxin, our results show that insects fed on either transgenic or Bt sprayed plants were negatively affected. Young S. littoralis larvae (1st and 2nd instars) were found to be the most sensitive to the Bt toxin. This was represented by a higher mortality and a slower developmental time of larvae maintained on transgenic or sprayed plants when compared to insects maintained on control plants. Moreover, Bt maize had a stronger and prolonged detrimental effect on insects when compared to Bt spray in maize. This was revealed by the fact that insects maintained on transgenic plants from 3rd instar to pupation took longer to reach adult emergence compared to insects that were maintained on sprayed plants. This was likely due to the continuous exposure of insects to the toxin when kept on transgenic maize. ELISA results showed a variation in the amount of Bt toxin among different leaf sections in transgenic maize at a given plant growth stage. These differences in Bt toxin were primarily found in the youngest leaf of growing plants. Although the lowest amounts of Bt toxin were detected in the growing leaf section of young leaves, this difference did not appear to influence the feeding behavior of 3rd instar S. littoralis.     

Bt Crops Producing Cry1Ac,Cry2Ab and Cry1F Do Not Harm the Green Lacewing,Chrysoperla rufilabris

The biological control function provided by natural enemies is regarded as a protection goal that should not be harmed by the application of any new pest management tool. Plants producing Cry proteins from the bacterium, Bacillus thuringiensis (Bt), have become a major tactic for controlling pest Lepidoptera on cotton and maize and risk assessment studies are needed to ensure they do not harm important natural enemies. However, using Cry protein susceptible hosts as prey often compromises such studies. To avoid this problem we utilized pest Lepidoptera, cabbage looper (Trichoplusia ni) and fall armyworm (Spodoptera frugiperda), that were resistant to Cry1Ac produced in Bt broccoli (T. ni), Cry1Ac/Cry2Ab produced in Bt cotton (T. ni), and Cry1F produced in Bt maize (S. frugiperda). Larvae of these species were fed Bt plants or non-Bt plants and then exposed to predaceous larvae of the green lacewing Chrysoperla rufilabris. Fitness parameters (larval survival, development time, fecundity and egg hatch) of C. rufilabris were assessed over two generations. There were no differences in any of the fitness parameters regardless if C. rufilabris consumed prey (T. ni or S. frugiperda) that had consumed Bt or non-Bt plants. Additional studies confirmed that the prey contained bioactive Cry proteins when they were consumed by the predator. These studies confirm that Cry1Ac, Cry2Ab and Cry1F do not pose a hazard to the important predator C. rufilabris. This study also demonstrates the power of using resistant hosts when assessing the risk of genetically modified plants on non-target organisms.     

Cry1Ie毒素胁迫下亚洲玉米螟的抗性发展及汰选种群对其他Bt毒素的交互抗性

亚洲玉米螟Ostrinia furnacalis (Guenée) 是危害玉米的重要害虫之一, 转Bt基因抗虫玉米为其防治提供了新的途径。然而, 靶标害虫产生抗性将严重阻碍Bt制剂及转Bt基因抗虫玉米的持续应用。明确害虫对转Bt基因玉米表达的毒素蛋白的抗性演化, 对于制定科学有效的抗性治理策略具有重要的理论和实际意义。本实验通过人工饲料汰选法研究了Bt Cry1Ie毒素胁迫下亚洲玉米螟的抗性发展及汰选14代的种群对其他Bt毒素（Cry1Ab, Cry1Ac和Cry1Fa）的交互抗性, 并观察了Cry1Ie蛋白胁迫对亚洲玉米螟生物学的影响。结果表明： 随着汰选压不断提高, 亚洲玉米螟种群对Cry1Ie毒素的敏感性逐渐下降。汰选14代后, 种群对Cry1Ie毒素的抗性水平提高了23倍。然而, Cry1Ab, Cry1Ac和Cry1Fa对所获Cry1Ie汰选种群的毒力与对敏感种群的毒力相比没有显著差异, 说明Cry1Ie汰选没有引起亚洲玉米螟对Cry1Ab, Cry1Ac和Cry1Fa毒素产生交互抗性。同时, 与敏感种群相比, Cry1Ie汰选14代的种群幼虫平均发育历期延长5.7 d, 蛹重减轻13.7%, 单雌产卵量下降40.0%。本研究结果说明, 大面积单一种植转cry1Ie基因抗虫玉米, 可能引起亚洲玉米螟产生抗性; 亚洲玉米螟Cry1Ie抗性种群对Cry1Ab, Cry1Ac和Cry1Fa没有交互抗性, 含有cry1Ie和cry1Ab, cry1Ac或cry1F双/多基因抗虫玉米, 可作为靶标害虫抗性治理的重要策略。     

Susceptibility of field populations of sugarcane borer from non‐Bt and Bt maize plants to five individual Cry toxins

Abstract Sugarcane borer, Diatraea saccharalis (F.), is a major target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the US mid‐south region. Resistance development in target pest populations is a major threat to the sustainable use of Bt crops. In our field trials in 2009, a significant number of live borers and plant injury from D. saccharalis were observed in an experimental SmartStax? maize line. The objective of this study was to assess the relative susceptibility of two field populations of D. saccharalis collected from non‐Bt and Bt maize plants containing SmartStax? traits to five individual Cry proteins. The five Bt proteins included two proteins (Cry1A.105 and Cry2Ab2) that were expressed in SmartStax? maize plants and three other common Bt proteins (Cry1Aa, Cry1Ab and Cry1Ac) that were not produced in SmartStax?. Larval mortality and growth inhibition on Bt diet of the fourth generation after field collections were evaluated 7 days after release of neonates on the diet surface. The laboratory bioassays showed that 50% lethal concentration (LC₅₀) values for Cry1A.105 and Cry2Ab2 for the population originated from Bt plants were 3.55‐ and 1.34‐fold greater, respectively, than those of the population collected from non‐Bt plants. In contrast, relative to the population from non‐Bt plants, the LC₅₀ of the population sampled from Bt plants were 3.85‐, 2.5‐ and 1.64‐fold more sensitive to Cry1Aa, Cry1Ab and Cry1Ac, respectively. The results did not provide clear evidence to conclude that the observed field survival of D. saccharalis on Bt plants was associated with increased levels of resistance.     

Bt maize can provide non-chemical pest control and enhance food safety in China

China is the world's second-largest maize producer and consumer. In recent years, the invasive fall armyworm Spodoptera frugiperda (J.E. Smith) has adversely affected maize productivity and compromised food security. To mitigate pest-inflicted food shortages, China's Government issued biosafety certificates for two genetically modified (GM) Bt maize hybrids, Bt-Cry1Ab DBN9936 and Bt-Cry1Ab/Cry2Aj Ruifeng 125, in 2019. Here, we quantitatively assess the impact of both Bt maize hybrids on pest feeding damage, crop yield and food safety throughout China's maize belt. Without a need to resort to synthetic insecticides, Bt maize could mitigate lepidopteran pest pressure by 61.9–97.3%, avoid yield loss by 16.4–21.3% (range −11.9–99.2%) and lower mycotoxin contamination by 85.5–95.5% as compared to the prevailing non-Bt hybrids. Yield loss avoidance varied considerably between experimental sites and years, as mediated by on-site infestation pressure and pest identity. For either seed mixtures or block refuge arrangements, pest pressure was kept below established thresholds at 90% Bt maize coverage in Yunnan (where S. frugiperda was the dominant species) and 70% Bt maize coverage in other sites dominated by Helicoverpa armigera (Hübner) and Ostrinia furnacalis (Guenée). Drawing on experiences from other crop/pest systems, Bt maize in se can provide area-wide pest management and thus, contribute to a progressive phase-down of chemical pesticide use. Hence, when consciously paired with agroecological and biodiversity-based measures, GM insecticidal crops can ensure food and nutrition security, contribute to the sustainable intensification of China's agriculture and reduce food systems' environmental footprint.     

Cross-Resistance between Cry1 Proteins in Fall Armyworm (Spodoptera frugiperda) May Affect the Durability of Current Pyramided Bt Maize Hybrids in Brazil

Genetically modified plants expressing insecticidal proteins from Bacillus thuringiensis (Bt) offer valuable options for managing insect pests with considerable environmental and economic benefits. Despite the benefits provided by Bt crops, the continuous expression of these insecticidal proteins imposes strong selection for resistance in target pest populations. Bt maize (Zea mays) hybrids have been successful in controlling fall armyworm (Spodoptera frugiperda), the main maize pest in Brazil since 2008; however, field-evolved resistance to the protein Cry1F has recently been reported. Therefore it is important to assess the possibility of cross-resistance between Cry1F and other Cry proteins expressed in Bt maize hybrids. In this study, an F₂ screen followed by subsequent selection on MON 89034 maize was used to select an S. frugiperda strain (RR) able to survive on the Bt maize event MON 89034, which expresses the Cry1A.105 and Cry2Ab2 proteins. Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found. The RR strain showed high levels of resistance to Cry1F, which apparently also conferred high levels of cross resistance to Cry1A.105 and Cry1Ab, but had only low-level (10-fold) resistance to Cry2Ab2. Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively. Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil. Nevertheless, the occurrence of Cry1F resistance in S. frugiperda across Brazil, and the cross-resistance to Cry1Ab and Cry1A.105, indicates that current Cry1-based maize hybrids face a challenge in managing S. frugiperda in Brazil and highlights the importance of effective insect resistance management for these technologies.     

Bacillus thuringiensis plants expressing Cry1Ac,Cry2Ab and Cry1F are not toxic to the assassin bug,Zelus renardii

Cotton‐ and maize‐producing insecticidal crystal (Cry) proteins from the bacterium, Bacillus thuringiensis (Bt), have been commercialized since 1996. Bt plants are subjected to environmental risk assessments for non‐target organisms, including natural enemies that suppress pest populations. Here, we used Cry1F‐resistant Spodoptera frugiperda (J.E. Smith) and Cry1Ac and Cry2Ab‐resistant Trichoplusia ni (Hübner) as prey for the assassin bug, Zelus renardii (Kolenati), a common predator in maize and cotton fields. In tritrophic studies, we assessed several fitness parameters of Z. renardii when it fed on resistant S. frugiperda that had fed on Bt maize expressing Cry1F or on resistant T. ni that had fed on Bt cotton expressing Cry1Ac and Cry2Ab. Survival, nymphal duration, adult weight, adult longevity and female fecundity of Z. renardii were not different when they were fed resistant‐prey larvae (S. frugiperda or T. ni) reared on either a Bt crop or respective non‐Bt crops. ELISA tests demonstrated that the Cry proteins were present in the plant at the highest levels, at lower levels in the prey and at the lowest levels in the predator. While Z. renardii was exposed to Cry1F and Cry1Ac and Cry2Ab when it fed on hosts that consumed Bt‐transgenic plants, the proteins did not affect important fitness parameters in this common and important predator.