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Spodoptera frugiperda (J.E. Smith) is a major pest of maize [Zea mays L. (Poales: Poaceae)] in tropical and subtropical regions. We aimed to evaluate the oviposition preference, growth, and survival of S. frugiperda on maize landraces and assess the nutritional quality of the leaves of different Brazilian maize landraces through evaluation of consumption indices. The oviposition preference was assayed using free and no-choice tests, and antibiosis by evaluating insect growth parameters, including weight, development time, survival in different stages of the life cycle, and nutritional indices. Landrace Pérola and cultivar BRS-Caatingueiro were the least preferred for S. frugiperda oviposition. Larvae fed with landrace Pérola consumed a lower amount of leaves and showed longer development time and lower survival until the end of the pupal stage. Larvae fed with the leaves of landrace Pérola and cultivar BRS-Caatingueiro displayed the lowest nutritional indices. Overall, Pérola was the most promising source of resistance to S. frugiperda. Identification of resistance in maize landraces may support breeding programs aimed at developing cultivars and hybrids resistant to S. frugiperda and other agricultural pests and inform growers regarding resistance of their landraces for integrated pest management.

Diabrotica speciosa is an important pest of several crops in South America, including soybeans. Adults cause severe defoliation in soybean plants, and damage is significant when cotyledons are attacked. This study evaluated feeding non-preference to D. speciosa adults using 10 soybean genotypes, testing (i) 15-day-old whole plants and (ii) leaf disks of 60-day-old plants, through assessments of soybean attractiveness and leaf area consumed (LAC). Foliar contents of flavonoids and nutrients, and leaf trichome density were quantified for potential correlations with soybean resistance to adult of D. speciosa. In the whole young-plant experiment, under free-choice conditions, the lowest LAC was observed in IAC 100 and PI 227687. In no-choice, PI 227687 and IGRA RA 626 RR showed lower LAC than the other genotypes. In the leaf disk test, in free-choice, the genotypes IAC 100, PI 274454, PI 227687, DM 339, and BR 16 were the least preferred by adult of D. speciosa. In no-choice, PI 274454 was one of the least preferred, similarly to IGRA RA 626 RR, Dowling, and PI 227687. In the whole plant experiment, a high rutin content and low amounts of zinc, calcium, sulfur and manganese were associated with less consumption of D. speciosa on leaves of resistant genotypes. In contrast, in the leaf disk test there was a significant influence of trichomes in soybean resistance to the pest. In conclusion, the PI lines herein assessed are also promising sources for developing cultivars resistant to D. speciosa.

Resistance to insect pests can be found in several native, landrace plants and can be an important alternative to conventional control methods. Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae) larvae are important maize (Zea mays L.) (Cyperales: Poaceae) root pests and finding native resistance in landraces would greatly contribute to maize-breeding programs aimed at controlling this pest. This study investigated whether the growth, survival, oviposition rhythm, fecundity, and fertility of D. speciosa are negatively influenced by specific maize landraces, and the existence of any morphological barriers in the roots that may correlate with plant resistance to the larval attack. Nineteen genotypes (17 landraces and 2 cultivars) were screened for antibiosis in assays that were conducted in the laboratory using seedling maize plants where the development time, longevity, weight, total survival, and sex ratio of adults were evaluated. Out of nineteen genotypes, eight were selected according to their resistance levels for an additional rearing study evaluating oviposition and fecundity. Landrace Pérola and cultivar SCS 154-Fortuna were classified as resistant because they increased the maturation period from larva to adult and decreased survivorship; and the landrace Palha Roxa was also classified as resistant for showing a lower fertility rate than other landraces. Resistant landraces that were infested by D. speciosa larvae showed greater amounts of some morphological barriers comparing with uninfested plants. The landraces classified as resistant may be considered in future plant-breeding programs, aiming to develop resistant maize cultivars to D. speciosa larval attack.

This study aimed to evaluate some factors that influence the expression of antixenosis in soybean genotypes against Anticarsia gemmatalis Hübner and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Free-choice and no-choice feeding assays were performed with the resistant soybean genotype IAC 100 and the susceptible genotype BRSGO 8360 using A. gemmatalis and S. frugiperda larvae. The following factors that may affect expression of resistance were evaluated: one larva versus two larvae per leaf disc; use of larvae without prior feeding suspension versus larvae starved for 3 h prior to the assay; leaf discs versus entire leaflets; upper part versus lower part of the plant; and, vegetative versus reproductive growth stages. The level of resistance exhibited by the genotype IAC 100 was high enough to not be obscured by the effects of all factors assayed in the present study upon the feeding preference of A. gemmatalis and S. frugiperda larvae. However, our results demonstrate the importance of knowing the optimal conditions for conducting an assay for evaluating resistance of genotypes for specialist and generalist insect species. Utilization of two larvae of A. gemmatalis per leaf disc, not starved before the assays, with leaf discs from the upper part of plants at the reproductive growth stage provided better discrimination of differences in antixenosis expression in soybean genotypes. For S. frugiperda, use of one larva per leaf disc, not starved before the assays, with leaf discs from the lower part of plants at the reproductive growth stage gave more satisfactory results for feeding preference tests.

The rootworm Diabrotica speciosa (Germar) is native to South America and causes severe economic losses to several crops due to root feeding and disease spread. In maize (Zea mays L.), losses in production come from larval rootworm attack on plant roots resulting in plant health problems, including stalk lodging. More options for controlling this pest are needed to create well balanced, integrated pest management programs for farmers in this region. Natural sources of tolerance in maize genotypes are important for maize breeding programs, and this study investigated the expression of tolerance in several Brazilian maize landraces to D. speciosa. Plant vigor and compounds associated with plant health, including chlorophylls, carotenoids, glycine betaine, and proline were assessed for each landrace. Five landraces and one maize cultivar were selected based on their levels of antibiosis-resistance to D. speciosa that were determined in a prior screening. The percent reduction in plant growth was used as the measure of tolerance. The landrace Azteca was classified as tolerant to D. speciosa larval feeding, displaying less reduction in plant matter despite having lower plant vigor. This landrace also had higher amounts of chlorophyl and carotenoid pigments, suggesting a positive correlation between tolerance to D. speciosa and higher contents of these photosynthetic pigments. The compatible osmolytes glycine betaine and proline do not seem to be associated with tolerance in maize landraces to D. speciosa larvae. Landrace Azteca seems promising for plant breeding, and repeated field studies are needed to confirm its suitability in maize integrated pest management.

Plants have evolved a diverse array of defensive mechanisms against biotic and abiotic stresses, which can be either constitutive or inducible. Variation in plant-intrinsic factors such as the genotype and the leaf position coupled with insect herbivory can affect the expression of resistance to insects. We investigated if soybean defense induction triggered by Spodoptera cosmioides herbivory varies in function of the genotype and leaf position. This hypothesis was tested in two bioassays using leaf discs or entire leaflets collected from the upper and lower trifoliates of S. cosmioides -injured and uninjured V3-V4 soybean plants. We used one genotype that was constitutively resistant and one that was constitutively susceptible to S. cosmioides based on previous screening. Third-instar larvae were fed one of the treatments and assayed for leaf consumption, larval growth, and efficiency of conversion of ingested food. Genotype and leaf position significantly interacted with herbivory and affected soybean-induced resistance to S. cosmioides . Negative responses on S. cosmioides larvae consumption and growth rates were only observed when leaf material was originated from the upper soybean trifoliate. The susceptible soybean genotype did not exhibit induced resistance characteristics. Food offered as leaf disc was better at demonstrating induced resistance in previously injured soybean, whereas offering entire leaflet the induced effects were less pronounced. Here we provide new findings on soybean resistance by demonstrating that resistance induction to S. cosmioides herbivory is dependent on the plant genotype and leaf position where injury took place, with negative effects better evinced in bioassays using leaf discs than entire leaflets.

Soybean crop is regulated by abiotic and biotic stresses with great potential in reducing grain yield and quality. The selection of resistant cultivars is a promising approach for mitigating these damages. We evaluated the chemical profile of Glycine max leaves from different cultivars in order to explore their defense mechanisms against Spodoptera cosmioides caterpillars. We optimized solid–liquid extraction techniques using ultrasound bath and static headspace extraction. Additionally, we developed an approach based on liquid and gas chromatography for analyzing the chemical profile of G. max cultivars. The principal component analysis allowed the classification of transgenic cultivars, which are classified as susceptible to S. cosmioides , from those obtained by genetic improvement and resistant to the insect. Differences were observed in the abundance of phenolic glycosides, lipids, aldehydes, and alcohols. More specifically, S. cosmioides resistant cultivars presented molecules related to the jasmonic and salicylic acid pathways. Such data can contribute to a molecular understanding of phenotypic diversity in soybean cultivars, from plant quality to resistance mechanisms and adaptation, to environmental stress and herbivory.

In Brazil, Phaseolus vulgaris L. constitutes one of the main food substrates for human consumption due to its high nutritional features and its affordable cost. Despite the extensive bean production in the country, Spodoptera frugiperda (Lepidoptera: Noctuidae), a polyphagous chewing pest, uses bean plants as alternative hosts, thereby reducing its productivity. The objective of this study was to screen and characterize different bean genotypes for their resistance against S. frugiperda. From 22 genotypes screened on antixenosis experiments, ten genotypes were selected for detailed study on their influence on S. frugiperda biology through antibiosis experiments. The genotypes selected for characterization were IPR Celeiro, IAC Tigre, IAC Nuance, IPR Curió, IAC Una, IAC Sintonia, IAPAR 65, BRS Esplendor, IAC Formoso and IPR Eldorado. For antibiosis analysis, insects since neonates, were kept feeding on leaves during whole larval cycle. The genotype IAC Nuance was the least harmed by S. frugiperda in both free-choice (F9,90 = 3.96; p < 0.001) and no-choice (F9,90 = 8.21; p < 0.001) antixenosis tests. In antibiosis tests, the insects fed on the genotype IAC Tigre had the highest mortality rate (F9,40 = 7.52; p < 0.001). In addition, IAC Nuance negatively influenced the larval weight (F9,229 = 6.59; p < 0.001), larval viability (F9,40 = 7.52; p < 0.001), pupal period (F8,114 = 4.93; p < 0.001) and total cycle duration (F8,96 = 4.34; p < 0.001) of S. frugiperda. Finally, using a multivariate clustering analysis, the genotypes were sorted as: Highly resistant- IAC Tigre; Moderately resistant- IAC Nuance; Susceptible- IPR Curió, IAC Una and IPR Celeiro; Highly susceptible- IAC Sintonia, IAPAR 65, BRS Esplendor, IAC-Formoso and IPR Eldorado. This study provides a scientific basis for selecting a genotype that can mitigate the attack of fall armyworm S. frugiperda in bean crops, which can be essential for the integrated pest management (IPM) of this key pest.

Information on Phaseolus vulgaris L. resistance categories and mechanisms to the Mexican bean weevil Zabrotes subfasciatus Boheman (Coleoptera: Chrysomelidae: Bruchinae) is important for breeding and subsequent commercialization of improved P. vulgaris genotypes. Using resistant genotypes in the bruchid beetles control may reduce insecticide applications, environmental risks, and production costs. Therefore, the objective of this study was to evaluate antixenosis and antibiosis of P. vulgaris genotypes to Z. subfasciatus and the relation of bromatological components on resistance. Free- and no-choice tests were carried out in a climate-controlled room (temperature 25 ± 1 °C, relative humidity 70 ± 10%, and 12:12 h light:dark photoperiod). Host selection for oviposition, total and viable numbers of eggs, emerged adults, egg to adult period (life cycle), adult longevity, and dry mass consumed of Z. subfasciatus were evaluated on 10 P. vulgaris genotypes. Bean samples of P. vulgaris genotypes were subjected to a bromatological analysis to determine possible resistance mechanisms. In the oviposition antixenosis, none of the P. vulgaris genotypes showed resistance to Z. subfasciatus. Contrastingly, the genotypes Raz 59, 173, 177, 179, 283, 284, 361, and 364 showed resistance in the categories of feeding antixenosis and/or antibiosis to Z. subfasciatus. On average, these genotypes reduced the number of emerged adults in 95.9%, the dry mass consumed in 88.3%, and increased the Z. subfasciatus life cycle in 40.3% compared to susceptible genotypes (IAC Alvorada and 178). Crude protein content in the resistant genotypes was on average 10.9% higher than in the susceptible genotypes. Some proteins, such as arcelin, have antibiotic effects on bruchid beetles, indicating that a higher protein content in resistant genotypes may have been one of the mechanisms responsible for antibiosis of these genotypes to Z. subfasciatus.

Several secondary metabolites are associated with plant resistance against herbivores. Cassava genotypes present a wide variety of metabolites with insecticidal potential, but little is known about the identity of these compounds. The present work was conducted for the identification of insecticidal molecules present in cassava genotypes. To this purpose, we firstly evaluated the development of the generalist herbivore Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) fed with leaves from six cassava genotypes (IAC-14, IAC-90, IAC-12, IAC-Caapora, Baianinha and MEcu 72). Following bioassays, we measured the levels of two anti-herbivory related groups of compounds (phenolics and steroidal saponins) in all genotypes using colorimetric methods. The metabolic fingerprinting (GC–MS) of three contrasting cassava genotypes selected by their biological interferences over S. frugiperda was performed. The most unsuitable nutritional indices were observed for larvae fed with MEcu 72. Lower reproductive indices were observed for adults in which larval stages were fed with Baianinha or MEcu 72. Steroidal saponin content was similar in all genotypes, but phenolic content was 25% higher in MEcu 72. GC–MS metabolite fingerprinting of MEcu 72, Baianinha and IAC-Caapora resulted in the annotation of 53 metabolites in which 20 presented different relative abundance among the evaluated genotypes. Molecules such as myo -inositol-2-monophosphate, p -coumaric acid, chlorogenic acid, p -hydroxybenzoic acid, octadecadienoic acid and n -hexacosane were more abundant in MEcu 72 or Baianinha than in IAC-Caapora. The possible roles of these molecules in the development of S. frugiperda are discussed.