Metabarcoding versus mapping unassembled shotgun reads for identification of prey consumed by arthropod epigeal predators.

BACKGROUND: A central challenge of DNA gut content analysis is to identify prey in a highly degraded DNA community. In this study, we evaluated prey detection using metabarcoding and a method of mapping unassembled shotgun reads (Lazaro). RESULTS: In a mock prey community, metabarcoding did not detect any prey, probably owing to primer choice and/or preferential predator DNA amplification, while Lazaro detected prey with accuracy 43-71%. Gut content analysis of field-collected arthropod epigeal predators (3 ants, 1 dermapteran, and 1 carabid) from agricultural habitats in Brazil (27 samples, 46-273 individuals per sample) revealed that 64% of the prey species detections by either method were not confirmed by melting curve analysis and 87% of the true prey were detected in common. We hypothesized that Lazaro would detect fewer true- and false-positive and more false-negative prey with greater taxonomic resolution than metabarcoding but found that the methods were similar in sensitivity, specificity, false discovery rate, false omission rate, and accuracy. There was a positive correlation between the relative prey DNA concentration in the samples and the number of prey reads detected by Lazaro, while this was inconsistent for metabarcoding. CONCLUSIONS: Metabarcoding and Lazaro had similar, but partially complementary, detection of prey in arthropod predator guts. However, while Lazaro was almost 2× more expensive, the number of reads was related to the amount of prey DNA, suggesting that Lazaro may provide quantitative prey information while metabarcoding did not.

Ethological aspects of Helicoverpa armigera in the reproductive phase of cotton

Pest behavior studies are important to inform the periods when the pest is more exposed to pesticide. This study aimed to evaluate the movement and feeding of Helicoverpa armigera larvae in the first three instars during the reproductive phase of cotton. First, larval behavior was evaluated with a completely randomized design in a 3 × 5 factorial design with eight replications. The treatments were the instars versus behaviors (crawling, resting, waving, eating and dropping-off). In addition, another 3 × 6 factorial design with eight replications was performed to evaluate the plant region most preferred by the caterpillars. The treatments were the instars versus six parts of the plant (abaxial surface, adaxial surface, on floral bud, internal surface of bract, petiole, and terminal growth). Then, the period of the day when caterpillars are more active was also evaluated by a 3 × 2 factorial essay. The treatments were the instars versus periods of the day. Eating and resting are the most frequent behaviors for all instars. The plant regions preferred by the caterpillars for crawling are on the floral bud and the adaxial face of the leaf. There is no preferred period of the day for eating, resting, waving or dropping-off. Caterpillars (until the third instar) prefer to walk in the morning and other behaviors can occur at any period. Therefore, sprays should preferably occur in the morning, and the insecticide drops/spray should reach the flower buds and the adaxial surface of the leaves to contaminate the larvae.

Field Efficacy of Metarhizium rileyi Applications Against Spodoptera frugiperda (Lepidoptera: Noctuidae) in Maize.

The efficacy of the fungus Metarhizium rileyi (Farlow) Kepler, S. A. Rehner & Humber (Hypocreales: Clavicipitaceae) against the fall armyworm Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and the impact on the community of epigeans predators as well as the natural occurrence of native fungal strains were evaluated after sequential sprays in maize. In the first season, the infestation was lower than 0.2 larvae per plant throughout the three fungal sprays and no significant difference was observed in the number of infected larvae among treatments. In the second season, insect population reached an average of 0.8 larvae per plant between the second and third sprays and the number of larvae succumbed by M. rileyi was higher in fungal-treated plots in the following weeks. Molecular characterization of the collected isolates on mummified larvae revealed the introduction of a new isolate did not eliminate the native strain on the fungal-treated plots. In both seasons, the diversity and abundance of predator species in the plots were not affected by any of the treatments. We showed that applications of selected strains of M. rileyi early in the season have no significant impact on the occurrence of natural enemies in maize.

Susceptibility of soybean looper to lufenuron and spinosad / Susceptibilidade da lagarta falsa-medideira a lufenuron e espinosade

The soybean looper (Chrysodeixis includens) is an important defoliation pest in crops such as soybean and cotton in Brazil. Its main control tactic is chemical insecticides. Considering the importance of chemical control for this pest, monitoring the susceptibility of C. includens populations is strategic for an efficient Insect Resistance Management. Therefore, the objective of this study was to evaluate the susceptibility levels of C. includens populations in the state of Mato Grosso - Brazil to lufenuron and spinosad. Seven populations were collected in soybean fields around the state. For the bioassays, early L3 larvae were exposed to insecticides using the diet-overlay method. Although the compounds have distinct modes of action, Tangará da Serra population had the highest resistance ratios for lufenuron (11.62) and spinosad (7.84), compared to laboratory population (susceptibility reference). Even with low resistance levels, it is necessary to maintain regional monitoring of C. includens susceptibility to the evaluated insecticides, as well as to extend the range of molecules monitored.(AU)

A lagarta falsa-medideira (Chrysodeixis includens) é uma importante praga desfolhadora em culturas como soja e algodão no Brasil e seu principal método de controle é o uso de inseticidas químicos. Considerando a importância do controle químico para essa praga, o monitoramento da suscetibilidade de populações de C. includens é estratégico para um eficiente programa de Manejo da Resistência de Insetos. Portanto, objetivou-se com este estudo avaliar os níveis de suscetibilidade de populações de C. includens no estado de Mato Grosso, Brasil, aos inseticidas lufenurom e espinosade. Sete populações foram coletadas em cultivos de soja ao longo do estado. Para os bioensaios, lagartas em terceiro ínstar foram expostas aos inseticidas utilizando o método de contaminação superficial de dieta. Embora os compostos apresentem modos de ação distintos, a população de Tangará da Serra obteve as maiores razões de resistência para lufenurom (11,62) e espinosade (7,84) em relação à população de laboratório (referência de suscetibilidade). Apesar dos níveis de resistência terem sido baixos, é necessário manter a manutenção do monitoramento dos níveis de suscetibilidade aos inseticidas avaliados, assim como ampliar a gama de moléculas monitoradas.(AU)

Influência de genótipos de couve (Brassica oleracea L. var. acephala DC.) na biologia de Plutella xylostella (L., 1758) (Lepidoptera: Plutellidae) / Influence of cabbage genotypes (Brassica oleracea L. var. acephala DC.) on the biology of Plutella xylostella (L., 1758) (Lepidoptera: Plutellidae)

Objetivou-se, com este trabalho, avaliar a influência de alguns genótipos de couve (Brassica oleracea L. var. acephala DC.) no desenvolvimento de Plutella xylostella (L., 1758) (Lepidoptera: Plutellidae). Os genótipos avaliados foram: Manteiga de Ribeirão Pires I-2620, Roxa I-919, Manteiga de São José, Manteiga de Monte Alegre, Pires 2 de Campinas, Couve Comum, Couve de Arthur Nogueira 2, Couve de Arthur Nogueira 1. Lagartas recém-eclodidas foram mantida em discos foliares de 8 cm de diâmetro para cada genótipo. Foram analisados os seguintes parâmetros: duração e viabilidade das fases larval e pupal, longevidade e fecundidade de adultos, utilizando análises paramétricas e de agrupamentos para interpretação dos dados. Observou-se um prolongamento em dias no ciclo de P. xylostella, aumento no peso de pupa e maiores valores de viabilidade e fecundidade, durante a segunda geração. O genótipo Couve de Arthur Nogueira 2 foi menos favorável ao desenvolvimento de P. xylostella nas duas gerações, e Couve Comum demonstrou maior influência negativa ao inseto na segunda geração. Manteiga de Ribeirão Pires I-2620 foi o mais suscetível nas duas gerações, agrupando com este na segunda geração Pires 2 de Campinas e Manteiga de São José.

The purpose of this study was to evaluate the effect of cabbage genotypes (Brassica oleracea L. var. acephala DC.) on growth of Plutella xylostella (Lepidoptera: Plutellidae). The genotypes evaluated were: Manteiga of Ribeirão Pires I-2620, Roxa I919, Manteiga of São José, Manteiga of Monte Alegre, Pires 2 of Campinas, Couve Comum, Couve of Arthur Nogueira 2, Couve of Arthur Nogueira 1. Neonate larvae were reared in 8 cm leaf discs of each genotype. The parameters evaluated were: period and viability of the larval and pupal stages, sex ratio, longevity and fecundity of adults. Parametric and Cluster analyses were used for data analysis. Overall, it was observed a developmental delay in the P. xylostella cicle, larger pupal, higher viability and fecundity during the second generation. Couve of Arthur Nogueira 2 was less favorable to the development of P. xylostella in the two generations, and Couve Comum was not an appropriate host for the insect in the second generation. Manteiga of Ribeirão Pires I-2620 was the most susceptible in both generations belonging to the same cluster with Pires 2 of Campinas and Manteiga of São José in the second generation.

Fatores que afetam a oviposição de Bemisia tabaci (Genn. ) Biótipo B (Hemiptera: aleyrodidae) em feijoeiro / Factors acting on Bemisia tabaci (Genn. ) biotype B (Hemiptera: aleyrodidae) oviposition in common bean

Este trabalho teve por objetivo avaliar o comportamento de oviposição de Bemisia tabaci (Genn.) biótipo B, em relação à idade da planta, densidade de adultos e regiões da planta de feijoeiro, sendo utilizado o genótipo Pérola. No teste com chance de escolha foram utilizadas plantas com 20, 30 e 40 dias de idade para avaliar a preferência de oviposição do inseto. Para o teste sem chance de escolha, referentes às diferentes densidades de adultos, foram utilizadas plantas com 30 dias de idade, liberando-se 50, 100 e 150 adultos por planta. Quanto ao teste sem chance de escolha para a posição da planta (ápice, mediana e basal), adotou-se a idade de 40 dias para a liberação dos adultos. As plantas com 30 dias de idade foram preferidas para oviposição. A densidade de 100 adultos por planta propiciou oviposição adequada para discriminar genótipos quanto aos graus de resistência enquanto a região apical da planta foi a preferida para postura, portanto a mais adequada para as amostragens de ovos de B. tabaci biótipo B em plantas de feijoeiro, visando um manejo adequado da praga.

The objective of this work was to evaluate the oviposition behavior of the whitefly Bemisia tabaci (Genn.) biotype B in relation to plant age, adult density and plant region on common beans plants. The genotype Perola was used to do the test. In free-choice tests 20, 30 and 40 day-old plants were used where evaluated the oviposition Fatores que afetam... JESUS, F. G. et al. Biosci. J., Uberlândia, v. 27, n. 2, p. 190-195, Mar./Apr. 2011 194 preference of the insect. In no-choice test, 30 day-old plants were used to evaluate densities of 50, 100 and 150 adults per plants. No-choice test for plant position (apex, median, base) 40 day-old plants were adopted for liberation of adults. The 30 and 40 day-old plants were preferred for oviposition, the densities of 100 adults per plants ensured the number of eggs enough to discriminate common beans genotypes with different whitefly resistance degrees, and apical region of plant were preferred for whitefly egg laying and therefore more suitable for egg sampling in common bean plants.