Atividade inseticida de compostos de origem vegetal em mahanarva spectabilis (distant, 1909) (hemiptera: cercopidae)

Abstract

Spittlebug Mahanarva spectabilis (Distant, 1909) (Hemiptera: Cercopidae) can limit forage production. The use of resistant grasses and application of synthetic insecticides in adults are some of the recommended methods for the control of this insect pest. Botanical insecticides are considered as alternatives to synthetic chemical insecticides in pest management because they are of low toxicity to the environment and human health. In this context, the present thesis is structured to develop and evaluate an alternative method, less laborious and reliable, to investigate the insecticidal activity using pure constituents of plant origin and, from these results, to evaluate the insecticidal activities of thymol, carvacrol, eugenol, cinnamaldehyde and trans-anethole on M. spectabilis eggs, nymphs and adults under laboratory conditions. The alterative method proposed in the research for bioinsecticide testing was not ideal due to the high mortality of adults in the control treatment. After establishing the efficient methodology, it was found that the most effective thymol concentrations were 1.2; 2.5 and 5.0% leading, respectively, to 97, 86 and 98% of egg unviability and mortality of nymphs and adults. Eugenol, carvacrol and thymol showed efficiencies higher than 85% in the evaluation performed 48 hours after the application of solutions in M. spectabilis eggs. In the tests with insect pests, 2.5% thymol and carvacrol and 2.0 and 2.5% eugenol showed intermediate efficiencies, with values above 61%. The highest efficiency (95%) was found with 2.5% trans-anethole. In adult tests, only 2.5% trans-anethole treatment was effective up to 90%, while in other treatments the efficiency rates did not exceed 51%. Thus, in this study we were able to define a methodology for testing bioinserted products on M. spectabilis, using thymol as a model and highlighting its potential to control this insect pest. And considering that the control of this insect should focus on reducing the number of nymphs and adults and that only insecticides that achieve an average mortality of 90% (± 10%) are considered efficient, we recommend trans-anethole as a natural insecticide potential for the control of M. spectabilis nymphs and adults due to the high rate of insecticide activity demonstrated. Moreover, these compounds may be an alternative to synthetic insecticides and lead to the development of new classes of bioinsecticides.