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.

Studies on the spatiotemporal dynamics of crop pests enable the determination of their colonization pattern and dispersion in the landscape. Geostatistics is an efficient tool to determine the spatial distribution pattern of the pest in the crops and to visualize them in appropriate maps. Analysis of these maps across the crop developmental stages can be a helpful tool in precision agriculture programs. The aim of this study was to determine the spatiotemporal distribution of Bemisia tabaci whitefly adults and nymphs in commercial soybean crops from planting to harvest. Infestation by the whitefly adults and nymphs started between 30 and 50 days after plant emergence. The maximum population density of ten adults per plant and two nymphs per leaf occurred between 90 and 101 days after plant emergence. In Kriging maps, it was possible to observe the distribution pattern for both adults and nymphs. The colonization of soybean plants by B. tabaci may be divided into three stages: beginning infestation (at the outermost parts of the crop), whole area colonization, and dispersion colonization (when the whole crop area is infested). The density of adult insects was positively correlated with rainfall and relative humidity. Wind speed positively affected the dispersion of adult whiteflies. The distribution pattern of B. tabaci in the soybean crop was aggregated. Climatic factors, such as wind speed, increase the dispersion radius of the whitefly in the crop. Contribution to the field.

O objetivo desta foi identificar genótipos de V. unguiculata sob condição de estresse salino que apresentem menor infestação por Aphis craccivora e maior produtividade. O experimento foi conduzido na área experimental da Fazenda Alvorada, (08º22’28” Sul, 43º51’34” Oeste, altitude de 229 m), em duas safras 2017 e 2018. O plantio foi realizado no mês de agosto e a colheita no mês de novembro. As parcelas foram constituídas por níveis de condutividade elétrica (CE) 0,5; 1,75; 3,0; 4,25 e 5,50 dS m-1, e as subparcelas compostas pelos genótipos: BRS Tumucumaque, BRS Guariba e BRS Imponente. O delineamento experimental foi em blocos casualizados e parcelas subdivididas, com quatro repetições. A ocorrência de A. craccivora diferiu nas duas safras. Na primeira safra, 2017, foi registrado a maior abundancia do afídeo na área, 27,15% das plantas amostradas durante todo o período de avaliação foram infestadas pelo pulgão. O genótipo BRS Guariba apresentou a menor infestação por A. craccivora e maior produtividade. O aumento da condutividade elétrica da solução de irrigação reduziu a área foliar e quantidade de massa seca da parte aérea dos genótipos de feijão, nas duas safras. De acordo com a análise de trilha, a ocorrência de A. craccivora tem correlação direta, e positiva com a variável massa seca e correlação negativa com a variável área foliar. Nas condições estudadas não foi observado efeito do estresse salino na a ocorrência e dinâmica populacional de A. craccivora.

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