Vertical distribution of Bemisia tabaci on soybean and attractiveness of cultivars
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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.