Caracterização da bioatividade de óleos essenciais e seus constituintes majoritários no manejo de resistência de Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Abstract

The intensive use of synthetic insecticides to control the diamondback moth (Plutella xylostella) has caused problems such as: overdosing in the application due to the inefficiency of the active ingredient and contamination of the water table, among others. A possible strategy to minimize economic and ecological damage would be the search for plants with active secondary metabolites acting as natural insecticides for the management of this pest in the cultivation of leafy vegetables. Thus, this thesis aimed to investigate the phytochemical mechanisms of the bioactivity of major constituents Eugenol and Limonene belonging to the essential oils of Eugenia caryophyllata (Tumb) and Citrus aurantium L. var. amara (Engl), respectively, in P. xylostella. Therefore, the susceptibility of P. xylostella to essential oils and their major constituents was evaluated using a lethal average concentration (LC50) on third instar larvae, also based on the toxicity ratio (TR50) of LC50 between generations and under selective pressure in the laboratory. The evaluation of metabolic variation between successive generations of P. xylostella was performed using extracts of P. xylostella insects and was performed by the comparative method of Principal Component Analysis (PCA). Furthermore, adaptive survival requirements was evaluated based on the biological parameters of P. xylostella after successive generations and under selective pressure in the laboratory. A greater tolerance of P. xylostella was verified in susceptibility from the toxicity ratio of CL50S, [E. caryophyllata (1.63-2.59 mg/l) and TR50=1.6]; [Limonene-(R) (14.86-29.67 mg/l) and TR50=2.0]; [Decis® 25 EC (3.25-14.01 mg/l) and TR50=4.31] and [Lufenuron (0.45-2.9 mg/l) and TR50=6.4]. The analyzes of metabolic variations indicated the presence in a greater proportion of fatty acids, dipeptides, phenolic compounds, among others, which are considered as metabolizers of active compounds, with emphasis on the selective pressure of P. xylostella with Decis® 25 EC, Lufenuron and Limonene. The bioassays carried out in the laboratory showed that those formulated based on essential oils and commercial insecticides negatively interfered with the pupae weight, on the duration of the larval period, on the duration of the pupal period, fecundity, fertility and longevity in the female’s life. In the experiment on biological factors of population growth, it was observed that there were differences in the net reproduction rate (Ro) and in the average time between generations (T). Thus, the results showed that the susceptibility of P. xylostella to major constituents of essential oils can vary after consecutive generations and under selective pressure in the laboratory.