Fall Armyworm Resistance Research Articles

Exploratory comparative transcriptomic analysis reveals potential gene targets associated with Cry1A.105 and Cry2Ab2 resistance in fall armyworm (Spodoptera frugiperda).

Genetically modified (GM) crops, expressing Bacillus thuringiensis (Bt) insecticidal toxins, have substantially transformed agriculture. Despite rapid adoption, their environmental and economic benefits face scrutiny due to unsustainable agricultural practices and the emergence of resistant pests like Spodoptera frugiperda, known as the fall armyworm (FAW). FAW's adaptation to Bt technology in corn and cotton compromises the long-term efficacy of Bt crops. To advance the understanding of the genetic foundations of resistance mechanisms, we conducted an exploratory comparative transcriptomic analysis of two divergent FAW populations. One population exhibited practical resistance to the Bt insecticidal proteins Cry1A.105 and Cry2Ab2, expressed in the genetically engineered MON-89Ø34 - 3 maize, while the other population remained susceptible to these proteins. Differential expression analysis supported that Cry1A.105 and Cry2Ab2 significantly affect the FAW physiology. A total of 247 and 254 differentially expressed genes were identified in the Cry-resistant and susceptible populations, respectively. By integrating our findings with established literature and databases, we underscored 53 gene targets potentially involved in FAW's resistance to Cry1A.105 and Cry2Ab2. In particular, we considered and discussed the potential roles of the differentially expressed genes encoding ABC transporters, G protein-coupled receptors, the P450 enzymatic system, and other Bt-related detoxification genes. Based on these findings, we emphasize the importance of exploratory transcriptomic analyses to uncover potential gene targets involved with Bt insecticidal proteins resistance, and to support the advantages of GM crops in the face of emerging challenges.

Field Evaluation of Experimental Maize Hybrids for Resistance to the Fall Armyworm (Lepidoptera: Noctuidae) in a Warm Temperate Climate.

The polyphagous fall armyworm (FAW), Spodoptera frugiperda, has become an invasive pest worldwide in recent years. To develop maize germplasm with multiple pest resistance and understand genetic inheritance, 12 experimental hybrids (six pairs of reciprocal crosses) with diverse genetic backgrounds and four commercial checks were examined for FAW resistance in 2013 and 2014. The experiment utilized a randomized complete block design with four replications as the block factor. FAW injury on maize plants was assessed at 7 and 14 d after the artificial infestation at the V6 stage, and predatory arthropod taxa and abundance on maize seedlings were recorded 7 d after the infestation. Spodoptera frugiperda resistance varied significantly among the 16 hybrids. Two reciprocal crosses ('FAW1430' × 'Oh43' and 'CML333' × 'NC358') showed the least FAW injury. Eleven arthropod predators [i.e., six coleopterans, three hemipterans, earwigs (dermapterans), and spiders (or arachnids)] were also recorded; the two most common predators were the pink spotted ladybeetle, Coleomegilla maculata, and the insidious flower (or minute pirate) bug, Orius spp. Predator abundance was not correlated to FAW injury but varied greatly between 2013 and 2014. Principal component analysis demonstrated that, when compared with FAW resistant (or Bt-transgenic) checks ('DKC69-71', 'DKC67-88', and 'P31P42'), five pairs of the reciprocal crosses had moderate FAW resistance, whereas a pair of reciprocal crosses ('NC350' × 'NC358' and NC358 × NC350) showed the same FAW susceptibility as the non-Bt susceptible check 'DKC69-72'. Both parents contributed similarly to FAW resistance, or no maternal/cytoplasmic effect was detected in the experimental hybrids.

Toxicity of Cry- and Vip3Aa-Class Proteins and Their Interactions against Spodoptera frugiperda (Lepidoptera: Noctuidae).

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is one of the most important insect pests affecting corn crops worldwide. Although planting transgenic corn expressing Bacillus thuringiensis (Bt) toxins has been approved as being effective against FAW, its populations' resistance to Bt crops has emerged in different locations around the world. Therefore, it is important to understand the interaction between different Bt proteins, thereby delaying the development of resistance. In this study, we performed diet-overlay bioassays to evaluate the toxicity of Cry1Ab, Cry1Ac, Cry1B, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, Vip3Aa11, Vip3Aa19, and Vip3Aa20, as well as the interaction between Cry1Ab-, Cry1F-, Cry2Ab-, and Vip3Aa-class proteins against FAW. According to our results, the LC50 values of Bt proteins varied from 12.62 ng/cm2 to >9000 ng/cm2 (protein/diet), among which the Vip3Aa class had the best insecticidal effect. The combination of Cry1Ab and Vip3Aa11 exhibited additive effects at a 5:1 ratio. Cry1F and Vip3Aa11 combinations exhibited additive effects at 1:1, 1:2, and 5:1 ratios. The combination of Cry1F and Vip3Aa19 showed an antagonistic effect when the ratio was 1:1 and an additive effect when the ratio was 1:2, 2:1, 1:5, and 5:1. Additionally, the combinations of Cry1F and Vip3Aa20 showed antagonistic effects at 1:2 and 5:1 ratios and additive effects at 1:1 and 2:1 ratios. In addition to the above combinations, which had additive or antagonistic effects, other combinations exhibited synergistic effects, with variations in synergistic factors (SFs). These results can be applied to the establishment of new pyramided transgenic crops with suitable candidates, providing a basis for FAW control and resistance management strategies.

A ScWIP5 gene confers fall armyworm resistance by reducing digestive enzyme activities in sugarcane.

The fall armyworm, Spodoptera frugiperda, is one of the most dangerous pests to various crops. As the most crucial sugar crop, sugarcane is also constantly threatened by these pests. Plant wound-induced proteinase inhibitors (WIP) are natural defense proteins that play important roles in the defense system against insect attack. Breeding for resistance would be the best way to improve the variety characteristics and productivity of sugarcane. Screening and verification for potential plant endogenous insect-resistant genes would greatly improve the insect-resistant breeding progress of sugarcane. A sugarcane WIP5 gene (ScWIP5) was up-regulated 536 times after insect feeding treatment on previous published transcriptome databases. ScWIP5 was then cloned and its potential role in sugarcane resistance to fall armyworm evaluated by construction of transgenic Nicotiana benthamiana. The toxicity of ScWIP5 transgenic N. benthamiana to fall armyworm showed lower weight gain and higher mortality compared to wild-type N. benthamiana feeding group. Furthermore, the concentration of JA and NbAOC, NbAOS, and NbLOX from the Jasmin acid biosynthesis pathway was significantly induced in ScWIP5 transgenic N. benthamiana compared to the control. In addition, digestive enzyme actives from the insect gut were also evaluated, and trypsin and cathepsin were significantly lower in insects fed with ScWIP5 transgenic N. benthamiana. These results indicate that ScWIP5 might enhance insect resistance by increasing JA signal transduction processes and reducing insect digestive enzyme activities, thus impacting insect growth and development. © 2023 Society of Chemical Industry.

Hybrid breeding for fall armyworm resistance: Combining ability and hybrid prediction

AbstractFall armyworm (FAW, Spodoptera frugiperda) emerged as a major lepidopteran pest destroying maize in sub‐Saharan Africa. A diallel mating design was used to generate 210 experimental hybrids from 21 lines. Experimental hybrids and four checks were evaluated in two locations. Commercial checks suffered higher foliar and ear damage compared to the top 15 hybrids. Mean squares associated with the genotypic variation were higher than genotype‐by‐environment interactions for foliar and ear damage traits. Heritabilities were moderate to high. Significant correlations were observed between grain yield (GY) with ear rot (−0.54) and ear damage (−0.45). Positive and significant GCA effects were observed for GY in seven parental lines, which were developed from multiple insect resistance breeding programmes. CKSBL10153 has the highest GCA value for GY and shows significant GCA effects for foliar and ear damage traits. These lines were identified as the ideal combiners for GY and FAW resistance and are therefore recommended for utilization as testers in the development of FAW‐resistant three‐way cross‐hybrid maize with correlated response for increased GY. GCA and marker‐based prediction correlations of GY were 0.79 and 0.96, respectively. Both GCA effects and marker‐based models were effective in predicting hybrid performance for FAW resistance.

More than 10 years after commercialization, Vip3A-expressing MIR162 remains highly efficacious in controlling major Lepidopteran maize pests: laboratory resistance selection versus field reality

MIR162, a maize event that expresses Vip3Aa20 (Vip3A) approved for commercial cultivation around 2010, has been excellent for control of major Lepidopteran pests. However, development of fall armyworm (FAW) resistance to Vip3A is a serious concern. Resistant colonies selected in the laboratory can serve as valuable tools not only for better understanding of Vip3A's mode of action (MOA) and mechanism of resistance (MOR) but also for screening novel leads of new MOA that will help control FAW in case resistance to Vip3A in the field becomes a reality. We selected a Vip3A-resistant FAW strain, FAWVip3AR, by subjecting a FAW founder population containing field genetics to Vip3A exposure. FAWVip3AR had >9800-fold resistance to Vip3A by diet surface overlay bioassays and resistance was stable. Feeding bioassays using detached leaf tissues or whole plants indicated that FAWVip3AR larvae readily fed and completed the full life cycle on Vip3A-expressing MIR162 maize plants and leaf tissues that killed 100% of susceptible larvae. Yet, FAWVip3AR faced at least two challenges. First, FAWVip3AR suffered an apparent disadvantage (incomplete resistance) when feeding on MIR162 in comparison to FAWVip3AR feeding on Vip3A-free isoline AX5707 maize; and second, FAWVip3AR showed a fitness costs in comparison to a Vip3A-susceptible strain when both fed on AX5707. We also demonstrated that, >10 years after commercialization, MIR162 and Vip3A remain highly efficacious against field populations of three major Lepidopteran pests from different geographic locations and FAW strains resistant to other Bacillus thuringiensis (Bt) toxins that are currently on the market.

Screening of maize inbred lines and evaluation of hybrids for their resistance to fall armyworm

Maize yield losses due to fall armyworm (FAW) infestation is in the range of 22–67%, amounting to millions of US dollars in sub-Saharan Africa (SSA). Identifying new sources of maize genotypes with resistance to insects and a better understanding of resistance mechanisms have opened the avenue for the exploration of host-plant resistance (HPR). The present study was carried out to assess the resistance of maize inbred lines and hybrids to FAW foliar feeding damage through natural and artificial screening. Thirty-five (35) maize inbred lines obtained from the International Maize and Wheat Improvement center (CIMMYT) and the United State Department of Agriculture – Agricultural Research Services (USDA–ARS) were screened for fall armyworm resistance in Ghana in 2019. In addition, sixty (60) single-cross hybrids and twenty (20) double-crosses developed from 17 desirable inbred lines were evaluated for resistance to fall armyworm using artificial and natural infestations in 2020 and 2021. Significant differences were recorded among the inbred lines, F1 hybrids, and the double-crosses. The cluster and principal component analysis classified the thirty-five inbred lines into four groups suggesting the presence of wide variability. Hybrids (CML343*CML 346)//(CML124*MP 713), (MP713*MP705)//(CML123*MP713), (CML331*MP701)//(MP702*MP705), (CML330*MP702)//(CML123*MP706), (CML122*MP713)//(CML330*MP701), (OBT*MP708)//(MP713*MP705),MP704*CML122)//(CML123*MP713), (CML123*MP708)//(CML122*MP713) and (CML330*MP701)//(MP713*MP705) were found to be promising. These hybrids should be recommended for further testing and commercialization in SSA.

Genes and genetic mechanisms contributing to fall armyworm resistance in maize.

Maize (Zea mays L.) is a crop of major economic and food security importance globally. The fall armyworm (FAW), Spodoptera frugiperda, can devastate entire maize crops, especially in countries or markets that do not allow the use of transgenic crops. Host-plant insect resistance is an economical and environmentally benign way to control FAW, and this study sought to identify maize lines, genes, and pathways that contribute to resistance to FAW. Of the 289 maize lines phenotyped for FAW damage in artificially infested, replicated field trials over 3 years, 31 were identified with good levels of resistance that could donate FAW resistance into elite but susceptible hybrid parents. The 289 lines were genotyped by sequencing to provide singlenucleotidepolymorphism(SNP) markers for a genome-wide association study (GWAS), followed by a metabolic pathway analysis using the Pathway Association Study Tool (PAST). GWAS identified 15 SNPs linked to 7 genes, and PAST identified multiple pathways, associated with FAW damage. Top pathways, and thus useful resistance mechanisms for further study, include hormone signaling pathways and the biosynthesis of carotenoids (particularly zeaxanthin), chlorophyll compounds, cuticular wax, known antibiosis agents, and 1,4-dihydroxy-2-naphthoate. Targeted metabolite analysis confirmed that maize genotypes with lower levels of FAW damage tend to have higher levels of chlorophyll a than genotypes with high FAW damage, which tend to have lower levels of pheophytin, lutein, chlorophyll b and β-carotene. The list of resistant genotypes, and the results from the genetic, pathway, and metabolic study, can all contribute to efficient creation of FAW resistant cultivars.

Genetic analyses of tropical maize lines under artificial infestation of fall armyworm and foliar diseases under optimum conditions.

Development and deployment of high-yielding maize varieties with native resistance to Fall armyworm (FAW), turcicum leaf blight (TLB), and gray leaf spot (GLS) infestation is critical for addressing the food insecurity in sub-Saharan Africa. The objectives of this study were to determine the inheritance of resistance for FAW, identity hybrids which in addition to FAW resistance, also show resistance to TLB and GLS, and investigate the usefulness of models based on general combining ability (GCA) and SNP markers in predicting the performance of new untested hybrids. Half-diallel mating scheme was used to generate 105 F1 hybrids from 15 parents and another 55 F1 hybrids from 11 parents. These were evaluated in two experiments, each with commercial checks in multiple locations under FAW artificial infestation and optimum management in Kenya. Under artificial FAW infestation, significant mean squares among hybrids and hybrids x environment were observed for most traits in both experiments, including at least one of the three assessments carried out for foliar damage caused by FAW. Interaction of GCA x environment and specific combining ability (SCA) x environment interactions were significant for all traits under FAW infestation and optimal conditions. Moderate to high heritability estimates were observed for GY under both management conditions. Correlation between GY and two of the three scorings (one and three weeks after infestation) for foliar damage caused by FAW were negative (-0.27 and -0.38) and significant. Positive and significant correlation (0.84) was observed between FAW-inflicted ear damage and the percentage of rotten ears. We identified many superior-performing hybrids compared to the best commercial checks for both GY and FAW resistance associated traits. Inbred lines CML312, CML567, CML488, DTPYC9-F46-1-2-1-2, CKDHL164288, CKDHL166062, and CLRCY039 had significant and positive GCA for GY (positive) and FAW resistance-associated traits (negative). CML567 was a parent in four of the top ten hybrids under optimum and FAW conditions. Both additive and non-additive gene action were important in the inheritance of FAW resistance. Both GCA and marker-based models showed high correlation with field performance, but marker-based models exhibited considerably higher correlation. The best performing hybrids identified in this study could be used as potential single cross testers in the development of three-way FAW resistance hybrids. Overall, our results provide insights that help breeders to design effective breeding strategies to develop FAW resistant hybrids that are high yielding under FAW and optimum conditions.

MAIZE RESPONSE TO FALL ARMYWORM (SPODOPTERA FRUGIPERDA) AND ASIAN CORN BORER (OSTRINIA FURNACALIS) IN THE PHILIPPINES

Philippine traditional maize has long existed for hundreds of years, facing and coping with continuous threats of different pests and diseases, with Asian corn borer and fall armyworm as the most damaging insect pests. Developing resistant varieties can employ rich genetic resources, as these varieties may have likely adapted to these biotic stresses. The development of ACB-resistant varieties proved successful with the Bt corn introduction; however, the attempt to breed for resistance to FAW is still underway. The two insect pests belong under the same Order, and cross-resistance between these pests may be possible. In this study, several traditional maize varieties underwent screening for resistance to ACB and FAW through larval survival on leaf-feeding assay. Among the accessions observed, three variants of APN 0120 (Silangan) and three other traditional maize (APN 0397, APN 0913, APN 0938) showed intermediate to high resistance toward FAW leaf damage. Few of these resistant varieties showed negative to Bt introgression. The most notable is the variant SI of APN 0120, with high resistance to ACB and FAW and low larval weight, without the presence of Bt. A previous report stated the original collection of this accession have potential ACB resistance, although Bt-introgressed. On the other hand, APN 0397 (Lagkitan), introgressed with Bt Cry1Ab, expressed dual resistance to ACB and FAW, too. It elucidates the reaction and potential of previously screened ACB-resistant varieties against FAW and the efficiency of Cry1Ab against FAW. It also demonstrates the potential of the traditional maize as source of germplasm to be explored to promote the utilization of open-pollinated varieties with inherent insect resistance. Moreover, this paper establishes massrearing procedures and laboratory techniques for effective fall armyworm-resistance screening using excised leaf method.

Genetic Analysis of Agronomic and Fall Armyworm-Resistance Traits in Maize Hybrids with Varying Levels of Resistance to Stem Borers

Stem borer (SB) and more recently, fall armyworm (FAW) are serious economic pests in maize production in sub-Saharan Africa. It is hypothesized that SB-resistant germplasm may confer resistance against FAW. However, the performance of SB-resistant lines in hybrid combinations and the inheritance of FAW-resistant traits under variable FAW infestations have not been reported. This study was conducted to (i) obtain information on the inheritance of agronomic and FAW-resistant traits under variable FAW infestations; (ii) identify hybrids combining high grain yield (GYLD) and stability under FAW infestations; and (iii) determine the effects of FAW damage on GYLD. Three SB-resistant lines (1393, CKSBL10060 and CML 331) as testers and six open-pollinated varieties (OPVs) as lines were crossed in a line tester scheme to generate eighteen test crosses. The test crosses together with two tester × tester crosses and two checks were evaluated under artificial FAW infestation (AI), natural infestation (NI) and pesticide-protected condition (PC) in Nigeria. Additive and non-additive effects were significant for GYLD, most agronomic and FAW-resistant traits under AI and NI, except ear damage (EDAM) scores under NI, whereas only the non-additive effect was significant for GYLD under PC. Two testers (1393 and CKSBL10060) combined significant and positive GCA effects for GYLD with desirable GCA effects for FAW-resistant traits under AI and NI, whereas CML 331 combined significant and negative GCA effects of GYLD with undesirable GCA effects of FAW resistance under the test conditions. Three OPVs (AWR SYN-W2, AMATZBR-WC4 and TZB-SR) had a significantly positive GCA effect for GYLD and a desirable GCA effect for either leaf damage (LDAM) or EDAM score under AI. The FAW LDAM and EDAM significantly reduced GYLD under AI but not under NI. Three test crosses (AMATZBR-WC4 x CKSBL10060, TZB-SR x CKSBL10060 and TZBR Comp 1-WC2 × 1393) combined high yield with stability and FAW tolerance across the test conditions and thus were recommended for further testing.

Maize genotype selection resistance to fall armyworm (Spodoptera frugiperda J.E. Smith) based on the degree of damaged leaf

Corn as one of the world’s staple food sources has become one of the most important commodities in the world. Indonesia as one of the maize producer countries also strives to improve the quality and quantity of production by genotype varieties that are resistant to specific conditions and are resistant to various pests and diseases. At present, the very high pressure and attack of fall armyworm (FAW) that exceed the economic threshold in maize cultivation is one of the problems that need integrated management, one of which is the formation of varieties that are resistant to FAW. The purpose of this selection test was to obtain the maize genotype resistance of FAW (Spodoptera frugiperda). The research was carried out in Agricultural Technology Research and Assessment Installation, Bajeng, Gowa Regency, South Sulawesi. The total of genetic materials in this test was 13 genotypes (POP 02, POP 03, POP 05, POP 10, POP 11, POP 15, POP 18, POP 21, POP 23, POP 24, POP 26, POP 27, and POP 28) and 2 check varieties (BISI 18 and JH 37). The treatments were arranged in a randomized block design with 3 replicates. The FAW as the test insects was obtained from the environment that had been exposed to it. Observations started 4 weeks after planting (WAP) by observing the total number of damaged plants, the percentage of attacks according to the Davis scale, and the level of plant resistance. All tested genetic materials showed moderate resistance to tolerance to FAW. The highest damage percentage was in the line Pop.18 (46.26%) and the lowest was in POP 11 (7-24%) and POP. 26 (14-26%). The moderate resistant strains obtained were Pop 10, Pop 11, Pop 21, Pop 23, Pop 24, Pop 26, Pop 27, and Pop 28. The results of this study can be continued for the formation of the next generation to obtain resistant strains and can be tested for plant morphology and physiology that trigger the resistance to FAW.

New techniques for breeding maize (Zea mays) varieties with fall armyworm resistance and market‐preferred traits for sub‐Saharan Africa

AbstractDeploying maize varieties with fall armyworm (Spodoptera frugiperda [J.E. Smith]; FAW) resistance, desirable product profiles (PPs) and climate resilience is fundamental for food and economic security in sub‐Saharan Africa (SSA). This study reviewed and identified challenges and opportunities for effective and accelerated breeding of demand‐led maize hybrids with FAW resistance and adaptation to the diverse agro‐ecologies of SSA. Lessons were drawn on improving breeding efficiency through adequate genetic variation delivered via prebreeding programmes, speed breeding and a reduced breeding stage plan. Appropriate PPs aligned with demand‐led breeding approaches were highlighted as foundations for variety design and commercialization. Challenges to accelerated FAW resistance breeding in maize included inadequate funds and modern tools; poor adaptation of some exotic donor parental lines; lack of information on FAW resistance among local varieties; lack of integration of molecular markers associated with FAW resistance and agronomic traits into selection plans; and limited infrastructure for FAW rearing and germplasm screening. Integration of modern breeding tools and scientific innovations were recommended for accelerated development and release of FAW resistant and market‐preferred maize varieties.

Effects of Elevated CO2 Concentration on Host Adaptability and Chlorantraniliprole Susceptibility in Spodoptera frugiperda.

Elevated atmospheric carbon dioxide concentrations (eCO2) can affect both herbivorous insects and their host plants. The fall armyworm (FAW), Spodoptera frugiperda, is a highly polyphagous agricultural pest that may attack more than 350 host plant species and has developed resistance to both conventional and novel-action insecticides. However, the effects of eCO2 on host adaptability and insecticide resistance of FAW are unclear. We hypothesized that eCO2 might affect insecticide resistance of FAW by affecting its host plants. To test this hypothesis, we investigated the effect of eCO2 on (1) FAW's susceptibility to chlorantraniliprole after feeding on wheat, (2) FAW's population performance traits (including the growth and reproduction), and (3) changes in gene expression in the FAW by transcriptome sequencing. The toxicity of chlorantraniliprole against the FAW under eCO2 (800 µL/L) stress showed that the LC50 values were 2.40, 2.06, and 1.46 times the values at the ambient CO2 concentration (400 µL/L, aCO2) for the three generations, respectively. Under eCO2, the life span of pupae and adults and the total number of generations were significantly shorter than the FAW under aCO2. Compared to the aCO2 treatment, the weights of the 3rd and 4th instar larvae and pupae of FAW under eCO2 were significantly heavier. Transcriptome sequencing results showed that more than 79 detoxification enzyme genes in FAW were upregulated under eCO2 treatment, including 40 P450, 5 CarE, 17 ABC, and 7 UGT genes. Our results showed that eCO2 increased the population performance of FAW on wheat and reduced its susceptibility to chlorantraniliprole by inducing the expression of detoxification enzyme genes. This study has important implications for assessing the damage of FAW in the future under the environment of increasing atmospheric CO2 concentration.

Fall Armyworm Infestation and Development: Screening Tropical Maize Genotypes for Resistance in Zambia.

Knowledge of fall armyworm (FAW) (Spodoptera frugiperda J.E. Smith) rearing, infestation and development and precision screening protocols are preconditions for the successful introgression of resistance genes into farmer-preferred varieties. We aimed to determine FAW developmental stages, screen tropical maize and select resistant lines under controlled conditions in Zambia. Field-collected FAW samples constituting 30 egg masses and 60 larvae were reared using maize leaf- and stalk-based and soy- and wheat flour-based diets at 27 ± 1 °C, 60 ± 5% relative humidity and 12 h day length. The resulting neonates were separated into sets A and B. The life cycles of set A and field-collected larvae were monitored to document the FAW developmental features. Set B neonates were used to infest the seedlings of 63 diverse tropical maize genotypes. Egg, larva, pupa and adult stages had mean durations of 2, 24, 20 and 12 days, respectively. Test maize genotypes revealed significant differences (p < 0.05) based on FAW reaction types, with lines TL13159, TL02562, TL142151, VL050120 and CML548-B exhibiting resistance reactions, while CML545-B, CZL1310c, CZL16095, EBL169550, ZM4236 and Pool 16 displayed moderate resistance. These genotypes are candidate sources of FAW resistance for further breeding. This study will facilitate controlled FAW rearing for host screening in the integration of FAW resistance into market-preferred maize lines.

Evaluation of Maize Varieties for Resistance to Field Pests: Fall Armyworm (Spodoptera frugiperda JE Smith) and Stem Borer in a Tropical Rainforest Agro-Ecology

Aims: To evaluate newly improved maize varieties for fall armyworm and stem borer resistance and determine the relationship among traits for increased productivity in a rainforest location in Nigeria.&#x0D; Study Design: The experiments were laid out in a 10 x 10 triple lattice design with three replications and Randomized Complete Block Design (RCBD) in four replicates.&#x0D; Place and Duration of Study: Field experiments were conducted during the late seasons of 2018 and 2019 at Obafemi Awolowo University Teaching and Research Farm, Ile Ife, Osun State, Nigeria.&#x0D; Methodology: Hundred newly improved maize varieties were evaluated during the late season of 2018 for fall armyworm resistance, while ten stem borers resistant varieties were evaluated during the late season of 2019. Data were collected on emergence, flowering, vegetative, armyworm, and grain yield traits. Data collected were subjected to analysis of variance (ANOVA), descriptive statistics, correlation and cluster Analysis.&#x0D; Results: Differential responses for resistance to fall armyworm traits were observed for all the varieties evaluated. Fall armyworm trait was observed to be negatively correlated with emergence percentage and ear number and positively correlated with flowering traits and moisture content. Furthermore, the results from the stem borer varieties evaluation indicated varietal differences for emergence percentage, plant height, ear height and kernel number. Stand count, ear number and weight per plot, moisture content had a significant positive correlation with yield while days to tasseling and silking and kernel row number had a significant negative correlation with yield.&#x0D; Conclusion: The best resistant varieties to fall armyworm were F2SCA 1413-36, ACR. 06 TZL COMP. 3C4 and 2013 TZEE-W POP STR with 6.01 tons/ha, 5.11 tons/ha, and 4.87 tons/ha of yield respectively while that of stem borer were TZBR Comp 1 –W C2 and Ama TZBR-W C4 with grain yield of 3.7 tons/hectare and 3.5 tons/hectare respectively.

Evaluation of Maize Varieties for Resistance to Field Pests: Fall Armyworm (Spodoptera frugiperda JE Smith) and Stem Borer in a Tropical Rainforest Agro-Ecology

Aims: To evaluate newly improved maize varieties for fall armyworm and stem borer resistance and determine the relationship among traits for increased productivity in a rainforest location in Nigeria.&#x0D; Study Design: The experiments were laid out in a 10 x 10 triple lattice design with three replications and Randomized Complete Block Design (RCBD) in four replicates.&#x0D; Place and Duration of Study: Field experiments were conducted during the late seasons of 2018 and 2019 at Obafemi Awolowo University Teaching and Research Farm, Ile Ife, Osun State, Nigeria.&#x0D; Methodology: Hundred newly improved maize varieties were evaluated during the late season of 2018 for fall armyworm resistance, while ten stem borers resistant varieties were evaluated during the late season of 2019. Data were collected on emergence, flowering, vegetative, armyworm, and grain yield traits. Data collected were subjected to analysis of variance (ANOVA), descriptive statistics, correlation and cluster Analysis.&#x0D; Results: Differential responses for resistance to fall armyworm traits were observed for all the varieties evaluated. Fall armyworm trait was observed to be negatively correlated with emergence percentage and ear number and positively correlated with flowering traits and moisture content. Furthermore, the results from the stem borer varieties evaluation indicated varietal differences for emergence percentage, plant height, ear height and kernel number. Stand count, ear number and weight per plot, moisture content had a significant positive correlation with yield while days to tasseling and silking and kernel row number had a significant negative correlation with yield.&#x0D; Conclusion: The best resistant varieties to fall armyworm were F2SCA 1413-36, ACR. 06 TZL COMP. 3C4 and 2013 TZEE-W POP STR with 6.01 tons/ha, 5.11 tons/ha, and 4.87 tons/ha of yield respectively while that of stem borer were TZBR Comp 1 –W C2 and Ama TZBR-W C4 with grain yield of 3.7 tons/hectare and 3.5 tons/hectare respectively.

Modeling fall armyworm resistance in Bt-maize areas during crop and off-seasons

Entomologists have often used computational modeling to study the dynamics of insects in agricultural landscapes. Recently, important issues such as the movement of adults and immatures associated with insect resistance to GMO (genetically modified organism) crops have been addressed using computational models. We developed an individual-based model using the cellular automata approach (CA) to investigate how an intercropping system composed of maize engineered with Bacillus thuringiensis (Bt) gene, refuge areas (non-Bt maize), and grasses combined with off-season periods might influence the evolution of resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae), one of the leading agricultural pests targeted by GMOs. We designed the Bt and non-Bt plants in two different arrangements: (a) a seed mixture and (b) strips rows, adding grasses in areas adjacent to the field. We added the seasonal planting dynamics (crop season and off-season), to evaluate a total of six agricultural scenarios. We followed a crop calendar from the United States to create simulations close to agricultural practice. The results showed that the frequency of the resistance allele was strongly related to the landscape arrangements and their dynamics. Since the adult insects are mobile, the seed-mixture scenario increased the frequency of the resistance the most (95.86%), followed by strips (82.10%), without grass fields. The maize harvest made it possible to reduce the frequency of resistance allele below 1%. Based on our results, we can expect that the maintenance of pasture areas, for instance next to the corn crops, will act as a reservoir of susceptible insects during off-season periods.

PERSPECTIVA ACTUAL DEL GUSANO COGOLLERO Spodoptera frugiperda (Lepidoptera: Noctuidae) Y SU RESISTENCIA DESARROLLADA A INSECTI

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; Fall Armyworm (FAW) is one of the most damaging agricultural pests found in Western Hemisphere, and it is now one of the key pests on several crops on America, Africa, Oceania, and Asia; becoming a major threat to food safety in many countries, due to losses caused to farmers.&lt;strong&gt; Objective.&lt;/strong&gt; Review current knowledge of FAW resistance to active ingredients in the world. &lt;strong&gt;Methodology. &lt;/strong&gt;A systematic study was carried out by collecting information from scientific writings, from first reports of resistance of fall armyworm to the more current ones, which included different national and international databases. &lt;strong&gt;Main finding&lt;/strong&gt;. FAW control for decades has been based on the use of chemical insecticides; this has generated applications increase without control and therefore, resistance of the pest. FAW resistance has been reported since 1965; today, FAW has been reported to be resistant to 33 active ingredients in different parts of the world. &lt;strong&gt;Implications. &lt;/strong&gt;The knowledge generated is essential to plan control strategies. &lt;strong&gt;Conclusion.&lt;/strong&gt; The development of new chemical insecticide molecules and the emergence of Bt technology have not achieved good control of FAW. Management strategies for FAW need to be implemented not only in Mexico, but in all places where FAW is present, to avoid further increase FAW resistance to of insecticides and Bt crops; otherwise, the FAW will be present in more places in the world, putting the food safety in more countries at risk.&lt;/p&gt;

Strong Fitness Costs of Fall Armyworm Resistance to Dual-Gene Bt Maize Are Magnified on Less-Suitable Host-Crop Cultivars

We examined the fitness costs of resistance to transgenic Cry1A.105+Cry2Ab2 Bacillus thuringiensis (Bt) maize in the fall armyworm, Spodoptera frugiperda, a globally invasive pest species. Using Bt-resistant and -susceptible populations of similar genetic backgrounds, we compared insect life-history traits and population growth rates on the foliage of Bt or non-Bt cultivars of maize, soybean, and cotton. We found that (i) the resistance alleles led to a major reduction in insect fitness on seven of the eight cultivars of three host crops studied; (ii) developmental time was the life-history trait that accounted for most of the fitness variation of the armyworm, and (iii) the magnitude of fitness reduction of the resistant individuals was stronger on cotton foliage, on which the insects did not pass the resistance alleles to subsequent generations. These results show that fall armyworm resistance to Cry1A.105+Cry2Ab2-expressing Bt maize comes with strong fitness costs, which were magnified on less-suitable host plants for the insects. Thus, natural selection may help maintain or even restore the insect susceptibility to the pesticidal proteins and perhaps is a significant factor helping manage fall armyworm resistance to Cry1A.105+Cry2Ab2 Bt maize. These findings indicate that fitness costs of insect resistance to multi-toxin Bt crops can be strong, and host plants or conditions that magnify the fitness differential of susceptible insects could be specifically deployed with refuge to improve resistance management to Bt crops.