Efeito do nitrogênio na mediação da tolerância de Brachiaria ruziziensis à Mahanarva spectabilis (Distant, 1909) (Hemiptera: Cercopidae)

Abstract

Mahanarva spectabilis (Hemiptera: Cercopidae) (Distant, 1909) has been compromising the production of milk and meat because the damages caused to the forage and control methods of this insect pest, that have been researched. The objective of this study was to evaluate the effect of nitrogen on the tolerance mediation of Brachiaria ruziziensis Germain and Everard, Mahanarva spectabilis. Pots containing soil and plants of B.ruziziensis were fertilized with nitrogen at doses 0, 50, 100, 200 and 400 kg/ha, divided into three applications. After twelve days of the last fertilization, the plants received nymphs of M. spectabilis at densities 0, 5, 10, and 15. After 10 days, chlorophyll content, leaf area damage, plant height, and forage bromatological quality were evaluated. Posteriorly the percentage of tiller emission (10 and 28 days after withdrawl of the nymphs) was evaluated. The experiment were conducted in a randomized complete block design in a factorial scheme. There was no interaction between the studied components (nitrogen x nymph density) for any of the variables. Nitrogen mediated tolerance, promoting reduction in the injuries caused by M. spectabilis in B. ruziziensis plants, with an increase in the chlorophyll index as nitrogen doses increased; reducing leaf area damage at doses 50 and 100 kg/N/ha; increase in the height of the plants and also increase in the percentage of shoots responding to the increase of the doses. It was also found alteration in forage quality, with reduction of the cellulose, increase the percentage of crude protein, reduce the levels of neutral detergent fiber and consequently elevation of IVDMD. In contrast the increase of the nymph density of M. spectabilis promoted reduction in chlorophyll content, in the emission of tillers, as well as increase of leaf area damage. Also altered forage quality, with reduced lignin, crude protein, digestibility in vitro dry matter and increased neutral detergent fiber. So the nitrogen acted as a tolerance mediator in B. ruziziensis plants submitted to different nymph densities of M. spectabilis.