Controle da mosca-branca, Bemisia tabaci (Gennadius, 1889) (Hemiptera: Aleyrodidae) com extratos botânicos em Brassica oleracea var. acephala

Abstract

Cabbage (Brassica oleracea) is among the main vegetables grown in Brazil and worldwide. Its production faces the attack of several pests, including the whitefly (Bemisia tabaci), especially the B biotype, capable of using more than 500 plants as hosts, attacking crops of economic importance and causing damage that can reach up to 100 %. The use of plant extracts with toxic properties is presented as an alternative management for this pest. The objective of this work was to evaluate the effectiveness of biodefensives in the form of plant extracts and nanoemulsions in controlling whiteflies under semi-field conditions. The bioassays were carried out in the laboratory and in the greenhouse where the B. tabaci stock creation was installed. Healthy cabbage seedlings were produced continuously to replace the stock rearing and for bioassays. The botanical materials collected were dried in a forced air oven (40 C°) and crushed to prepare aqueous (water) and organic (hexane, dichloromethane and methanol) extracts. Andiroba oils were purchased from local producers. Cabbage seedlings were infested with B. tabaci nymphs, selecting two leaves per plant, with at least 50 nymphs for extract applications. LC50 tests, modes of action (topical, translaminar and systemic) and the test with nanoemulsions of hexane extract of biribá and andiroba oil were carried out. The experimental design adopted was completely randomized. Mortality percentages were submitted to ANOVA and means compared by Tukey's test (p<0.05). The aqueous extract of timbó Deguelia amazonica obtained an estimated LC50 of 2.12%. The LC50 of the timbó hexane extract was 1.03%. The mode of action with the best performance for timbó was the topical route, however the systemic route also obtained promising results. The aqueous extract of Annona mucosa seeds obtained an estimated LC50 of 4.95%. The LC50 of the biriba hexane extract was 1.3%. The mode of action with the best performance for biribá was the topical route, however, its systemic route also obtained promising results. The LC50 of andiroba oil (Carapa guianensis) diluted in hexane was 1.77%. The mode of action with the best performance for biribá was the topical route. Among the nanoemulsions, C. guianensis 2% and A. mucosa 1 and 2% achieved very positive mortality results. The analyzes by APCI-MS found fatty acids in the hexanic extract of A. mucosa, while for that of D. amazonica the presence of rotenone and deguelin was identified. The three tested species are presented as an alternative control for the whitefly.