Damage assessment of Bemisia tabaci and economic injury level on soybean

Absttract The whitefly Bemisia tabaci is the second most widespread and economically important arthropod pest in the world, with frequent population outbreaks occurring in Brazil and increasing economic damage on soybean crops. High oviposition rate, short life cycle and uneven distribution along the plants’ canopy favour the dissemination of B. tabaci within soybean crops and compromise the efficacy of control measures. The objective of this work was to quantify soybean yield reduction caused by B. tabaci damage and propose an economic injury level (EIL) for this pest in soybean crops. Experimental design was randomized blocks with four replicates. Soybean grain yield and its components (number of pods, number of grains and 1000-grain weight) were quantified in relation to different levels of B. tabaci infestation in two cropping seasons, obtained through insecticide sprays carried out at different growth stages of the soybean plants. The resulting data were submitted to variance analysis, mean separation test and regression analysis. We found that a population density of one whitefly leaflet-1 reduces from 0.88 to 1.79 grains plant-1, 0.16 ± 0.01 g plant-1 or 31.24 ± 4.21 kg ha-1of grain yield, and varies in response for pods plant-1 and 1000-grains weight. Based on this information, we suggest an economic injury level of 1.465 ± 0.195 B. tabaci trifoliate-1, considering a control cost of US$ 20.00 hectare-1 and soybean crop value of US$ 400.00 tonne-1.