Uso de Lithothamnium calcareum (Pallas) Areschoug, 1852 (Florideophyceae, Corallinales, Corallinaceae) e guar-guar associado à nanotecnologia para controle de Plutella xylostella (Linneus, 1758) (Lepidoptera, Plutellidae)

Abstract

The diamondback moth – Plutella xylostella (Linnaeus, 1758) (Lepidoptera, Plutellidae), is a cosmopolitan micro-moth, considered one of the most important pests of brassica cultivars worldwide, such as cabbage, broccoli, cauliflower, among others. The damage is caused by the larval stages which, when consuming the leaves of the host plants, reduces the quality, devaluing or making the product unfeasible for sale. The damage potential of this species is due to the short life cycle combined with a high reproductive rate, which allows the occurrence of several generations throughout the year. In Brazil, the losses caused by this species reach one billion dollars a year. Despite the existence of natural control methods such as products made from plant extracts, biological control agents such as entomopathogenic fungi and bacteria, the use of synthetic pesticides is still the main mechanism used to control diamondback moth, since these products have high efficiency in a short period of time. However, an increasing number of studies have shown that when used incorrectly, these compounds cause numerous harms to the health and environment, in addition to promoting resistance in populations to such products. In this sense, the use of new technologies combined with the use of natural products such as seaweed flour and natural biopolymers become an increasingly and necessary practice. In this scenario, nanotechnology emerges as a promising tool for the formulation of new natural insecticides that are less harmful to the environment and human health, which can act in the control of pests and diseases that compete with cultivars. Given the above and allied to the need for research related to new technologies for pest control, especially those that are less harmful to the environment and human health, the main objective of this study was to develop a natural nanotechnological insecticide based on Lithothamnion calcareum, a red alga belonging to the Corallinaceae family (Florideophyceae: Corallinales) associated with guar-guar, a natural biopolymer, to combat or to control individuals of Plutella xylostella. Initially, the complexation of the seaweed flour solution with the miniaturized natural biopolymer solution in a time of three minutes at an amplitude of 100%, was carried out forming the solution used in the experiments, called alga-biopolymer solution. This solution was subjected to DLS analysis, which indicated a decrease in particle size, and UV-vis, which demonstrated that there was the formation of a new compound after the interaction between the products. The algabiopolymer solution and its respective controls (acetic acid solution, seaweed flour solution, biopolymer solution and distilled water) at different concentrations (5,0%, 2,5% and 1,25%) were subjected to tests of insecticidal viability by contact and ingestion using second instar larvae of P. xylostella. For each treatment, three Petri dishes containing 10 larvae in each were used, which were made in triplicate. In the contact test, the larvae were sprayed with the aforementioned solutions and evaluated every hour. It was observed that after 13 hours of larvae exposure to the alga-biopolymer solution, 100% of the individuals were dead, with the solutions showing statistically significative difference among the control solutions. In the ingestion test, the larvae were fed with cabbage leaves treated with the above-mentioned solutions. Changes were observed in biological aspects such as decrease in pupal biomass and number of eggs layed. For both experiments, the solutions at concentrations of 2,5% and 1,25% proved to be efficient to control P. xylostella, indicating that the solution algabiopolymer can be used as a new strategy to control and minimize the damage caused by P. xylostella to their host plants. In this way, this product is less harmful to human health and environment when compared to traditional control methods, in addition to presenting low production costs, easy application and handling when compared to traditional control methods.