Resistência constitutiva e induzida em plantas forrageiras à cigarrinha-das-pastagens (Hemiptera: Cercopidae)

Abstract

Aspects related to constitutive and induced resistance on forages to spittlebugs (Hemiptera: Cercopidae) were analyzed. Nutrition feasibility of different forages to the main species of spittlebugs that occur in Brazil was assessed. The feasibility of fertilizers and chemical inducers, silicon and nitric oxide, was also verified for the control of that insect pests. The values obtained for D. schach confirmed that B. ruziziensis was the most suitable host plant. Since N. entreriana did not show differences in the evaluated parameters, it was not possible to determine the ideal forage suitability. For M. spectabilis, P. purpureum was found to be the most suitable. The evaluation of the performance of the different spittlebugs within a single forage also showed the identification of which spittlebugs are characterized was a problem. In a monoculture of B. ruziziensis, the species M. spectabilis and D. schach developed better. On P. purpureum, M. spectabilis was a major problem, and on the forages C. dactylon and P. maximum, none of the spittlebugs developed properly, indicating that these plants are less suitable. It was demonstrated M. spectabilis responded differently to fertilization due to genotypes/cultivars provided. Spittlebug attack decreased the characteristics of forage production regardless of soil fertilization and the use of resistance inducers. However, soil fertilization increased the capacity of forage plants in minimizing infestation damage effects of M. spectabilis, but not to the point of avoiding them. On the other hand, chemical inducers were neither able to alter negatively the biological parameters of M. spectabilis nor diminish its population. However, an increase in the contents of phenolic compounds was reported when forages were treated with silicon and when attacked by adult insects. Although there was an increase in the amount of phenolics in silicon-treated forages, that parameter was not useful to detect resistance against the spittlebug. This fact reveals that physiological and biochemical changes brought about by silicon should be further studied.