Assessing common bean genotypes for resistance to Diabrotica speciosa (Coleoptera: Chrysomelidae).

Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae) is a major pest of common bean (Phaseolus vulgaris L.; Fabales: Fabaceae), and adults can defoliate plants during the whole crop cycle. This study was conducted to evaluate the resistance to D. speciosa in 16 common bean genotypes (14 landraces and 2 cultivars), through three different experiments. In the laboratory, choice and no-choice feeding tests were performed to evaluate the percentage of leaf consumption. In the greenhouse, plant height, numbers of leaves, percentage of injured leaves, percentage of injury per leaf, weight of seeds, and D. speciosa survival were evaluated. Furthermore, trichome density, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in common bean leaves were assessed. In the laboratory, the genotypes Chumbinho Branco, Dobalde, Manteigado, IPR Tuiuiú, and 90D Mouro were the least consumed by D. speciosa. In the greenhouse, the genotypes Dobalde, Manteigado, and IPR Tuiuiú expressed tolerance to the pest, which was associated with a higher plant height and/or unchanged POD and SOD levels and protein content following insect feeding, and no reduction in seed production. The landrace 90D Mouro exhibited antixenosis and tolerance to D. speciosa, observed as a lower leaf injury, higher trichome density, lower protein contents, higher SOD level and no reduction in seed weight. Overall, we have shown that antixenosis and tolerance can help overcome damages resulting from D. speciosa feeding, with emphasis on four common bean genotypes that may be useful in plant breeding programs aimed at controlling D. speciosa in common bean crops.

Morphological and chemical plant traits associated with feeding non-preference to adult of Diabrotica speciosa (Coleoptera: Chrysomelidae) in soybean genotypes.

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.

Tolerance in Maize Landraces to Diabrotica speciosa (Coleoptera: Chrysomelidae) Larvae and Its Relationship to Plant Pigments, Compatible Osmolytes, and Vigor.

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.

Resistance of Cowpea Genotypes to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Its Relationship to Resistance-Related Enzymes.

Spodoptera frugiperda (J.E. Smith) can attack cowpea plants (Vigna unguiculata [L.] Walp.) (Fabales: Fabaceae) in any growth stage but attacks primarily in the first days after plant emergence, when the plants are more sensitive to defoliation. This study was carried out to evaluate the resistance to S. frugiperda in six cowpea genotypes, of which four were cultivars (BRS Tapahium, BRS Tumucumaque, Fradinho, and Miranda), and two were landraces (Juti and Nioaque), in three different experiments. In the first experiment, adult emergence, adult weight, adult longevity, larva to adult period, numbers of injured leaves per plant canopy (upper, middle, and lower), and reduction in plant dry matter were assessed. In the second experiment, the oviposition preference of S. frugiperda for the different cowpea genotypes was evaluated under free-choice conditions. In the third experiment, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in cowpea leaves were assessed. Insects fed on landrace Juti plants showed low adult emergence, yielded a lower fitness index, and caused less plant dry matter reduction. In addition, plants of landrace Juti were less preferred for oviposition. Overall, Juti plants showed higher resistance levels in all three resistance categories and higher levels of POD and SOD in S. frugiperda injured leaves, in addition to a lower protein content. Juti will be tested in field conditions, followed by molecular characterization. This will provide additional information about its potential as an S. frugiperda resistance source in plant breeding programs.

Antibiosis Levels to Spodoptera frugiperda (Lepidoptera: Noctuidae) in Cowpea Commercial Cultivars and Landrace Varieties.

Spodoptera frugiperda (J.E. Smith) is a major pest of cowpea, (Vigna unguiculata [L] Walp.) (Fabales: Fabaceae), and to date, few tactics are available to control this pest. This study was conducted to evaluate whether cowpea commercial cultivars and landrace varieties express antibiosis to S. frugiperda. The commercial cultivars were developed by the Brazilian Agricultural Research Corporation (Embrapa), and the landrace varieties were obtained from indigenous communities of Mato Grosso do Sul, Brazil. The effects of the cowpea genotypes (commercial cultivars and landrace varieties) were assessed on the development, survival, and reproductive capacity of the insect. Out of six genotypes, the two landraces were the most resistant to the pest. Landrace Juti decreased larval weight and survival, and no larvae reached the pupal phase. Landrace Nioaque adversely affected the larval and pupal weight, the period of development from larva to pupa, adult emergence, and the period of development from larva to adult. The cultivar Fradinho was classified as moderately resistant for reducing the larval and pupal weights, and delaying the period of development from larva to pupa. The cultivar Miranda was susceptible regarding the growth and survival of S. frugiperda, however, females reared on this cultivar laid a lower number of eggs. The resistant genotypes, especially the landrace varieties are promising for future plant breeding programs, with the objective of developing resistant cultivars to S. frugiperda larvae.

Species Richness and Community Composition of Ants and Beetles in Bt and non-Bt Maize Fields.

Insect-resistant genetically modified (GM) plants have been cultivated in several countries on a large scale. These plants express the Cry toxins from the bacterium Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) (Bt), which confers target-pest resistance to plants. Studies on the effects of GM plants on nontarget organisms are important to assess the technology's impact on biodiversity. The objective of this study was to determine whether there are differences in the species richness and composition of ants and ground beetles in Bt maize (four different toxins: Cry1Ab, Cry1F, and Cry1A.105/Cry2Ab2) and conventional isoline (non-Bt) fields, in the first (summer) and second (winter) cropping seasons in 13 localities of Mato Grosso do Sul State, Brazil, over a 2-yr period (2009-2011). The assessment of Coleoptera and Formicidae species was performed using pitfall traps placed in fields throughout the period of vegetative growth and maturation of plants. Data were analyzed using faunistic indices of species richness, ordination by nonmetric multidimensional scaling, and multivariate analysis of variance. No statistically significant difference was found in the species richness of ant and ground beetle communities when comparing sites of Bt with those of non-Bt maize. Overall, Bt technology did not affect the composition of ant and ground beetles; however, municipality and cropping season exerted influence on the beetle composition. Some species were only observed in the first crop, whereas others were only observed in the second crop. This research suggests that Bt maize does not affect ant and ground beetle populations differently from its isoline.

Oviposition Preference and Antibiosis to Spodoptera frugiperda (Lepidoptera: Noctuidae) in Brazilian Maize Landraces.

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.

Characterization of Antibiosis to Diabrotica speciosa (Coleoptera: Chrysomelidae) in Brazilian Maize Landraces.

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.

Factors Influencing Expression of Antixenosis in Soybean to Anticarsia gemmatalis and Spodoptera frugiperda (Lepidoptera: Noctuidae).

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.

Infestation of Caliothrips phaseoli (Thysanoptera: Thripidae) on Bean Cultivars Grown in the Winter, Rainy, and Dry Seasons in Brazil.

The present study aimed to identify common bean (Phaseolus vulgaris L.) cultivars less susceptible to Caliothrips phaseoli (Hood) in different growing seasons, to evaluate whether climatic conditions influence plant resistance to C. phaseoli infestation, and to investigate the preferred plant part for insect feeding. Eighteen common bean cultivars were evaluated in the winter season, and 19 cultivars were assessed in the rainy and dry seasons, under field conditions in the municipality of Jaboticabal, state of São Paulo, Brazil. Infestation of C. phaseoli nymphs in the upper and lower parts of the beans plants was recorded at weekly intervals from 25 days after plant emergence (DAE) to 60 DAE. In the winter season, the cultivars 'IAC Galante,' 'IAC Centauro,' 'IAC Carioca Eté,' and 'IAC Formoso' had significantly lower number of thrips than the cultivar 'IAC Diplomata.' In the rainy season, the cultivars 'IAC Harmonia' and 'IPR Siriri' had the lowest thrips infestation, differing from the cultivars 'BRS Pontal' and 'IAC Una.' The bean cultivars were equally susceptible to C. phaseoli in the dry season. The results suggest that C. phaseoli nymphs prefer to infest leaves of the lower part of bean plants, like most generalist herbivorous insects. In the winter and dry seasons, the highest thrips infestation was observed at 60 DAE, while in the rainy season, it was recorded from 32 to 46 DAE. Overall, C. phaseoli infestation on bean cultivars was not influenced by either temperature, relative humidity, or rainfall.