Bioatividade de extratos botânicos sobre Plutella xylostella L. 1758 (Lepidoptera: Plutellidae)

Abstract

The diamondback moth (Plutella xylostella L. 1758) is, economically, the most important pest that affects brassica plantations. Its control is carried out mainly with applications of synthetic insecticides, which, when used constantly and incorrectly, lead to a series of environmental and human health problems. Therefore, there is a need for control methods that minimize impacts on the environment and are selective for target organisms. In this case, the bioactive compounds present in botanical extracts become a promising option in the management of harmful insects, as they cause different reactions on them. Therefore, the present work aimed to review which botanical species had their extracts tested on the biological and behavioral parameters of P. xylostella in the last 15 years (Chapter I). As well as, to analyze the effects of extracts from Fabaceae and Rubiaceae on feeding and oviposition of P. xylostella (Chapter II), the toxicity of extracts from Psychotria sp., prepared by maceration and infusion, on eggs, pupae and larvae of the insect (Chapter III) and the bioactivity of Rubiaceae and Fabaceae extracts, prepared by maceration and infusion, on the biological parameters of P. xylostella (Chapter IV). In the literature review, a methodical search was carried out through databases and websites related to the theme, articles written in English, Portuguese or Spanish were selected. Couples of newly emerged adults and third instar larvae of P. xylostella were submitted to oviposition and feeding preference tests, respectively, with two options of choice, using aqueous extract of Psychotria sp., Alibertia sp., Acosmium subelegans, Vatairea macrocarpa, prepared by maceration, and distilled water as options. While contact toxicity was verified by applying aqueous extracts of Psychotria sp, prepared by maceration and infusion, on eggs, pupae and third-instar larvae of P. xylostella. Toxicity in the insect's biological parameters was tested by feeding newly hatched larvae with cabbage disks submerged in botanical extracts of Psychotria sp., Acosmium subelegans and Vatairea macrocarpa, evaluating the lethal and sub-lethal effects of the extract. The bibliographic review pointed out 117 botanical species that had their extracts tested on the biological and behavioral parameters of P. xylostella in the last 15 years. The most studied families were Asteraceae, Euphorbiaceae, Fabaceae, Piperaceae, Rubiaceae, Lamiaceae, Myrtaceae and Solanaceaea. Water and leaves were the most used solvent and botanical structure in the preparation of extracts, respectively. Alibertia sp., Psychotria sp., Acosmium subelegans and Vatairea macrocarpa extracts caused oviposition deterrence and reduced egg viability, with A. sessilis extract being the most efficient among them. The aqueous extract of A. intermedia and A. subelegans stimulated the feeding of the third instar larvae of P. xylostella, while the other extracts acted as deterrents. Psychotria extracts did not demonstrate contact toxicity in larvae and pupae. However, they were toxic to P. xylostella eggs. The lowest egg survival was observed in the treatment with aqueous extract of P. deflexa. The bioactivity of the extracts on the biological parameters of P. xylostella, showed that the aqueous extracts of P. leiocarpa, P. deflexa, A. subelegans and V. macrocarpa reduced the duration and survival of the eggs, in addition to causing larval mortality greater than 70%. P. leiocarpa extracts prolonged pupal duration and significantly reduced female fecundity, while V. macrocarpa extracts reduced pupal survival. It was observed that extracts prepared by infusion were more effective in reducing egg survival when compared to extracts prepared by maceration. We emphasize that the experiments were carried out under controlled conditions of temperature, humidity and photoperiod, which is why there is a need for additional work aimed at elucidating the bioactivity of the extracts under field conditions, as well as its mechanism of action on the target insect and its toxicity on natural enemies. In the present work, we concluded that the studied species have great potential in the control of P. xylostella and that the extraction method did not interfere in the degree of toxicity of the plant. We hope that the bibliographic review can deepen knowledge on the subject and collaborate to strengthen future research.