Search

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−2; 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. [ABSTRACT FROM AUTHOR]

This study aimed at evaluating organic by-products vinasse and cassava wastewater on the sanitary and physiological quality of soybean seeds. Sanity tests, phytoalexin induction and physiological qualities were performed, conducted in a completely randomized design. The sanity test was carried out in a 3 × 5 factorial scheme (two by-products: vinasse – V, cassava wastewater – C and the junction between them – V + C, in five concentrations: 0, 25, 50, 75 and 100%), with 8 repetitions/treatment. In the induction of phytoalexin, a factorial scheme (3 × 4) + 1 – two by-products and their junction, was adopted, with 4 concentrations (25, 50, 75 and 100%), plus an additional witness – with 5 repetitions/treatment, and for the physiological qualities 3 × 5 factorial scheme, described above, with four replicates/treatment. Cassava wastewater has large amounts of sugars, which may have favored the development of pathogens in this treatment. Vinasse had the highest capacity of inhibiting the genera Aspergillus, Cladosporium, and Penicillium, which was explained by the positive relationship between its concentrations and the induction of phytoalexin, being the most effective by-product in fungus control, at concentrations of 75 and 100% and without changing the physiological quality of seeds. [ABSTRACT FROM AUTHOR]

Simple Summary: Lepidopteran species commonly interact in the same niches in multiple crops. Interspecific competition has been neglected as a pressure selection agent in insecticide resistance studies. Our results showed that competition may act as an agent to speed up the evolution of diamide resistance in Spodoptera frugiperda and Helicoverpa armigera. Intra- and interspecific competition is considered a fundamental phenomenon in ecology. It acts as one of the most powerful selective forces that drives ecological diversity, the spatiotemporal distribution of organisms, fitness, and evolutionary aspects. Spodoptera frugiperda and Helicoverpa armigera are devastating pests and can co-occur in systems consisting of multiple agricultural crops and compete for food resources. Insecticide resistance in populations of these species has been a major threat to the sustainability of agroecosystems. No study to date has shown the effect of intra- and interspecific competition as a selective pressure agent on the evolution of insecticide resistance in lepidopteran pests in an experimental and theoretical way. Our study developed a parameterized computational model with experimental results for S. frugiperda and H. armigera competition. We simulated the behavior of heterozygous individuals with a competition capacity 100% equal to homozygous individuals resistant (100 RR) or susceptible to insecticides (00 RR), and intermediate between them (50 RR). Competition involving strains of these insect species can accelerate the evolution of their resistance to insecticides in agricultural crops. We found that competitive processes can result in a high probability of competitive exclusion for individuals with the susceptibility allele of these lepidopteran species. The results of this study are of paramount importance for understanding the impact of ecological factor competition on the evolution of insecticide resistance in lepidopteran pests, which until now has been neglected in these types of evolutionary dynamics studies. [ABSTRACT FROM AUTHOR]

BACKGROUND Beans from cowpea cultivars fertilized with mineral N or inoculated with various rhizobium strains may contain different nitrogen concentrations and nitrogen metabolite composition, which affects the beans' defense mechanisms against pests. In this study, the population growth of Callosobruchus maculatus reared on beans from four cowpea cultivars fertilized with different nitrogen sources was evaluated. The factors tested were beans from four cowpea cultivars and seven different nitrogen sources: mineral N fertilization, inoculation with five strains of symbiotic diazotrophic bacteria, and soil nitrogen (absolute control). RESULTS BRS Tapaihum and BRS Acauã cultivars had lower cumulative emergence and instantaneous rate of population growth of the insects compared with other cultivars, indicating antixenosis resistance against C. maculatus. Inoculation of BRS Acauã cultivar with the diazotrophic bacteria strain BR 3299 resulted in higher mortality of C. maculatus. For BRS Tapaihum cultivar, inoculation with diazotrophic bacteria strains BR3267, BR 3262 and BR 3299, and nitrogen fertilization resulted in higher mortality among C. maculatus. CONCLUSION BRS Tapaihum and BRS Acauã cultivars showed the lowest cumulative insect emergence and instantaneous rates of population growth, and the highest insect mortality, mainly when the grains were obtained from plants inoculated with rhizobial strains. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]