A densidade de plantas tem influência direta na morfofisiologia, nos componentes de produção e no rendimento do feijão-caupi. Com o objetivo de avaliar o comportamento morfoagronômico de uma cultivar moderna de feijão-caupi [Vigna unguiculata (L.) Walp.] submetida a diferentes densidades de plantas, foi conduzido um experimento no município de Alvorada do Gurgueia-PI, em sistema irrigado por aspersão no ano agrícola de 2009/2010. Avaliaram-se cinco populações de plantas (100, 200, 300, 400 e 500 mil plantas ha-1) pelo delineamento de blocos completos casualizados com quatro repetições. O aumento da população de 100 para 500 mil plantas ha-1 provocou reduções de 30,19% no diâmetro do caule, 96,5% no número de ramos, 63,8% no número de vagens por planta e de 67,6% na produção de grãos por planta. O comprimento do epicótilo aumentou linearmente com o aumento da população de plantas. O peso de cem grãos não foi influenciado significativamente pelas diferentes populações de plantas. As diferentes densidades de plantas promoveram mudanças significativas na morfologia e nos componentes de produção da cultivar.

Insecticides from different chemical groups were tested by laboratory bioassay to verify the percentage mortality of Helicoverpa armigera (Hubner 1808) (Lepidoptera: Noctuidae). The experiment was conducted in the Crop Science laboratory-Prof. CinobelinaElvas Campus-UFPI, Bom Jesus, PI, from January to June, 2013. The populations utilized came from the University's own insect breeding laboratories. Third instar larvae of H. armigera were used to conduct the bioassay. The experimental design was fully randomized, with 13 treatments and four replications. Five larvae were used per replication, with 12 insecticides from 9 different chemical groups and a control. Each treatment consisted of three doses. The methods of application used were topical contact and ingestion in artificial diet. According to the results the percentage mortality of H. armigera larvae varied among the treatments. The results demonstrated that chlorpyrifos and spinosad were effective against third instar H. armigera larvae both on contact and by ingestion. Flubendiamide, acephate, methomyl, Bacillus thuringiensis, dimethoate, chlorantraniliprole and fipronil had good responses to control of H. armigera.

No abstract

This study aimed to assess the resistance of grain from two varieties of maize landraces in initial breeding in Bom Jesus-PI, with respect to S. zeamais attack. Seeds of two maize landraces were used: purple straw maize from two different origins (São Paulo (SP) and Espírito Santo (ES)) and Peruvian purple maize. The experimental design was completely randomized with four replications. The data for each response variable were subjected to analysis of variance, applying the F-test (p ≤ 0.05), and when significant differences were found, there was a comparison of means by Tukey test (p ≤ 0.05). The statistical analyses were performed using the software SAS ® . In a free-choice test and bioassay for evaluating the nutritional index (no choice test), maize varieties differed significantly by Tukey test and the cultivar SP was considered resistant, while the cultivars purple and ES were considered susceptible.

The reduction in the number and frequency of insecticide applications in transgenic crops has favored population outbreaks of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in various Bt (Bacillus thuringiensis Berliner) soybean cultivars [Glycine max (L.) Merrill; Fabaceae], reflecting the fact that plants have different levels of attractiveness to insects. The identification of Bt soybean cultivars resistant to whitefly represents a viable and effective control alternative. The objective of this study was to characterize the vertical distribution of insects on the plant and to identify Bt soybean cultivars less attractive to B. tabaci. The insects used were collected in tomato crops, and the whitefly population was maintained on leaf cabbage plants. Fifteen soybean cultivars were evaluated to determine attractiveness to whitefly. Soybean plants were stratified into upper, middle, and lower thirds. Multiple-choice and no-choice bioassays were carried out with the 15 cultivars. Subsequently, 10 cultivars were selected for a new multiple-choice assay. The parameters evaluated were the number of adults per leaflet and number of eggs cm À2 ; the degree of colonization by nymphs was determined only in the multiple-choice assay. The density and length of trichomes of the 15 cultivars were also characterized. It was shown that the upper third of the plant was the most attractive, having the largest number of adults and colonizing nymphs. The cultivars BRS 9280RR, M 8808, and M 8644IPRO showed low levels of B. tabaci infestation by adults, eggs, and nymphs in the bioassays performed. There was a negative correlation between trichome length and density with the number of adults, eggs, and degree of colonization by nymphs. The vertical distribution and attractiveness of soybean cultivars to whitefly are discussed.

No abstract

The selection pressure generated by the incorrect use of Bt maize might result in Spodoptera frugiperda individuals resistant to the toxins synthesized by the plant. In this study was evaluated the nutritional parameters of Spodoptera frugiperda submitted to the maize that synthesize the toxins Cry1F, Cry1A105-Cry2Ab2 and Vip3Aa20, during five subsequent generations of selection pressure. The caterpillars were submitted to the treatments: Non-Bt maize (CONV), Cry1F (Bt1), Cry1A105/Cry2Ab (Bt2) and Vip3Aa20 (VIP1, VIP2 and VIP3) and exposed for a period of four days in each cycle, for five successive generations. The larval survival of S. frugiperda was evaluated in five generations. The consumed leaf area was quantified in the second generation and the nutritional indexes in the latter ones. The results indicate that caterpillars of S. frugiperda from VIPs lineage presented the lowest percentage of survival, with a high Metabolic Cost and a considerable efficiency reduction in the conversion of the digested and ingested food. The lineage maintained in VIP2 showed the lowest leaf consumption (83.13%). However, the action of Vip3Aa20 toxin on S. frugiperda resulted in a higher Metabolic Cost in reduction of leaf area consumption. However, from the third generation on there is a survival of insects exposed to Bt toxins, suggesting the surviving potential of this species in Bt maize subjected to continuous exposure to this technology. Sobrevivência e índices nutricionais de Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) mantida em milho Bt por cinco gerações RESUMO: A pressão de seleção gerada pelo uso incorreto do milho Bt pode resultar em indivíduos de Spodoptera frugiperda resistentes às toxinas expressadas pela planta. Neste trabalho foi determinado os parâmetros nutricionais de Spodoptera frugiperda submetida aos milhos que sintetizam as toxinas Cry1F, Cry1A105-Cry2Ab2 e Vip3Aa20, durante cinco gerações. As lagartas foram submetidas aos tratamentos: Milho não-Bt (CONV), Cry1F (Bt1), Cry1A105/Cry2Ab (Bt2) e Vip3Aa20 (VIP1, VIP2 e VIP3) e expostas por um período de quatro dias em cada ciclo, por cinco gerações sucessivas. Foi avaliada a sobrevivência larval de S. frugiperda em cinco gerações. A área foliar consumida foi quantificada na segunda geração e nas posteriores foram determinados os índices nutricionais. As lagartas de S. frugiperda, da geração mantida no milho VIPs, apresentaram menor porcentagem de sobrevivência, com um alto Custo Metabólico e considerável redução na Eficiência na conversão do alimento digerido e Eficiência na conversão do alimento ingerido. A geração mantida no Hibrido VIP2 apresentou o menor consumo foliar (83,13%). Contudo a ação da toxina Vip3Aa20 sobre S. frugiperda resultou no maior Custo Metabólico em redução no consumo de área foliar. Contudo a partir da terceira geração observa-se uma sobrevivência de insetos expostos as toxinas Bt, sugerindo o potencial desta espécie em sobreviver aos milhos Bt quando submetidas a exposição contínua a esta tecnologia. Palavra...