Evaluation of lethal and repellent action of aqueous vegetable extracts for the control of spittlebugs (Hemiptera: Cercopidae)

Abstract

Spittlebugs (Hemiptera: Cercopidae) are species considered to be the main pests of forage grasses throughout Tropical America. In Brazil, Mahanarva spectabilis (Distant) is the main and most limiting pest associated with elephant grass (Pennisetum purpureum Schum.). These insects have the potential to generate great economic losses for the milk and meat production chain, harming producers. Among the spittlebugs control tactics, the use of resistant grasses, biological control and the application of synthetic insecticides in adults are the best known methods. The use of synthetic insecticides is economically viable only when combined with other spittlebugs control strategies, but they are environmentally unsafe products, so it is necessary to research tactics that are less aggressive to the environment, socially viable and of low cost for mainly small farmers. In this context, the insecticidal and repellent action that plant compounds have against different insect-pest species stands out. Thus, the objectives of this research were to evaluate whether aqueous extracts of the aromatic plants A. sativum, R. graveolens, C. verum, C. citratus, S. aromaticum, I. verum, E. globulus, N. tabacum and T. vulgaris have an insecticidal effect on spittlebug nymphs and the choice of spittlebugs adults can be altered for elephant grass, by attraction or non-attraction, in olfactometry tests. In the first stage of the research, the insecticidal effect of the extracts on nymphs of M. spectabilis was evaluated. The results indicated that the tobacco extract was the most effective among all nine tested. At a concentration of 20%, after 48 hours, it reached an efficiency of 76%. Then, bioassays were carried out comparing 5 concentrations of tobacco extract (5%, 10%, 15%, 20% and, 25%), where the extract in the concentration of 25% reached an efficiency greater than 92%. As for the extraction methods, the infusion and decoction methods were shown to be equivalent to the standard extraction method (UAE). Tobacco extract is recommended as a strategy to control M. spectabilis, at a concentration of 25%, with its extraction by infusion and decoction. In the second stage, olfactometry bioassays were performed. The combinations of aqueous extracts applied to the host plant were tested against fresh air and against the host plant without the extract. The aqueous vegetable extracts of tobacco, star anise and eucalyptus were not attractive for the M. spectabilis, and can be used as a management tactic in the case of elephant grass.