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.

Oviposition behavior of Helicoverpa armigera in soybean / Comportamento de oviposição de Helicoverpa armigera em soja

The objective of this study was to evaluate the oviposition behavior of Helicoverpa armigera confined in different adult pair density and growth stages of soybean plants, and the resistance of soybean genotypes to H. armigera in the category nonpreference for oviposition. The oviposition behavior of H. armigera was assessed using one, two, and four adult pairs per soybean plant of the cultivar BR-16 at the growth stages: vegetative V8 (eighth unrolled trifoliate leaf), reproductive R2 (full bloom) and reproductive R5.2 (beginning seed). The nonpreference for oviposition was evaluated using eight soybean genotypes and an oviposition preference index was calculated. The number of trichomes in leaflets was quantified for being correlated to H. armigera oviposition. One adult pair and soybean plants stage at pod-set affected and showed the best results oviposition preference on soybean plants. The genotypes M8230-RR and W711-RR presented resistance characteristics, and PI-227687 was preferred for oviposition. The trichome density positively affects the female oviposition behavior.(AU)

O objetivo deste trabalho foi avaliar o comportamento de oviposição de Helicoverpa armigera confinadas em diferentes densidades de casais e estádios fenológicos de plantas de soja, e a resistência de genótipos de soja na categoria não preferência para oviposição para H. armigera. Para o comportamento de oviposição de H. armigera, foram avaliadas as densidades de um, dois e quatro casais por planta, e os estádios fenológicos vegetativo, de florescimento e reprodutivo de plantas de soja do cultivar BR 16. Para o teste de não preferência para oviposição, oito genótipos de soja foram utilizados e um índice de preferência para oviposição foi calculado. A densidade de tricomas nos folíolos foi quantificada para ser correlacionada com a oviposição de H. armigera. A densidade de um casal e plantas de soja em estádio reprodutivo proporcionaram os melhores resultados quanto à preferência para oviposição de H. armigera em soja. Os genótipos M8230 RR e W711 RR apresentaram características de resistência, enquanto o PI 227687 foi o mais preferido para oviposição. A quantidade de tricomas influenciou positivamente no comportamento de oviposição das fêmeas.(AU)

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.

Genomic analysis of a cypovirus isolated from the eucalyptus brown looper, Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae).

The eucalyptus brown looper, Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae), is the main lepidopteran defoliator of eucalyptus plantations in Brazil. Outbreaks of this insect pest are common in Brazil and can affect the productivity of planted forests severely. T. arnobia caterpillars from a laboratory colony with viral infection symptoms were analyzed by electron microscopy that revealed polyhedral occlusion bodies (OBs) with several icosahedral virus particles embedded. Analysis of its genetic material showed ten segments of dsRNA, which confirmed this virus as a possible member of the genus Cypovirus. Phylogenetic analysis of the whole genome sequence revealed its close relationship with other isolates of Cypovirus 14 species and according to these results we proposed the name Thyrinteina arnobia cypovirus 14 (TharCPV-14) for this new virus isolate. Further research will be necessary in order to analyze the potential of this virus as a biopesticide.

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.

Attractiveness, non-preference for feeding and oviposition to Ascia monuste orseis Godart (Lepidoptera: Pieridae) in collard greens / Atratividade, não-preferência para alimentação e oviposição de Ascia monuste orseis Godart (Lepidoptera: Pieridae) em couve comum

Collard greens Brassica oleracea var. acephala is one of the most important horticultural grown in Brazil for human feeding. The caterpillar Ascia monuste orseis (Lepidoptera: Pieridae) stands out among the important pest in Brassicaceae causing severe plant defoliation. The objective of this study was to identify resistant genotypes (antixenosis) in 26 collard greens genotypes to A. monuste orseis. In free-choice test, randomized blocks were used; and in the non-choice test we adopted a completely randomized design. Manteiga de Jundiaí, crespa de Capão Bonito, couve de Arthur Nogueira 1, manteiga I-1811, manteiga de Ribeirão Pires I-1811, orelha-de-elefante and Pires 1 de Campinas presented antixenosis (non-preference for oviposition). Pires 1 de Campinas, manteiga I-1811, manteiga de São José, verde-escura and manteiga de Monte Alegre presented antixenosis (non-preference for feeding). These collard greens genotypes can be directly used by farmers for cultivation or by breeders as donor sources in breeding programs for resistance to A. monuste orseis.(AU)

Brassica oleracea var. acephala (couve comum) é uma das mais importantes olerícolas cultivadas no Brasil para alimentação humana. A lagarta Ascia monuste orseis (Lepidoptera: Pieridae) destaca-se entre as pragas mais significativas no cultivo de Brassicaceae por causar severa desfolha na planta. O objetivo deste trabalho foi identificar, em 26 genótipos de couve comum, fontes de resistência (antixenose) a A. monuste orseis. No teste de livre escolha, adotou-se o esquema casualizado de blocos; e no teste sem chance de escolha o esquema foi inteiramente casualizado. Manteiga de Jundiaí, crespa de Capão Bonito, couve de Arthur Nogueira 1, manteiga I-1811, manteiga de Ribeirão Pires I-1811, orelha-de-elefante e Pires 1 de Campinas apresentaram antixenose (não preferência para oviposição). Pires 1 de Campinas, manteiga I-1811, manteiga de São José, verde-escura e manteiga de Monte Alegre apresentaram antixenose (não preferência para alimentação). Esses genótipos de couve comum podem ser cultivados diretamente por agricultores ou ser usados por melhoristas em programas de melhoramento genético para resistência a A. monuste orseis.(AU)

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.