Bioatividade de extratos vegetais no controle de pulgão preto Toxoptera citricida Kirk.,1907 (Hemiptera: Aphididae) na cultura dos citros e sobrevivência de joaninhas e abelhas

Abstract

The use of plant extracts has been an alternative in substitution to chemical insecticides that throughout the years has caused many unbalances in the environment and human health. The objective of the present work was to evaluate the bioactivity of plant extracts in the control of the black aphid in citrus and the selectivity on natural enemies and beneficial insects using three forms of extraction. Leaves and branches containing aphids collected in the field were tied to seedlings so that artificial infestation could occur in such a way that the pest-insects transfer would occur gradually and without causing damage to its mouth or any other type of stress. For the preparation of the aqueous extracts, rhizomes, leaves and in natura fruits of the plants were used. A scale with 500g capacity for weighing plant parts and a blender containing a determined volume with distilled water to facilitate trituration was used, and the material was filtered using a voil type fabric. The in natura parts of the plants were weighed and deposited in a beaker covered with aluminum foil and closed with a Petri dish in order to retain the vapor and therefore avoid loss of the active principle and heated up to 100 C for three minutes in a magnetic heater. Afterwards, the extract was cooled in room temperature, filtered and applied over the target insect. For the field experiment, 100 x 70 x 70 cm cages, covered at the bottom with the voil fabric were built. The recipients with the aphid infested seedlings were placed over white polypropiline and at the base of the bag of the seedlings a white polypropiline disc was placed in order to facilitate the visualization of the dead aphids fallen after the application of the extracts. The extracts were applied directly to the insects from top to bottom in the abaxial side of citrus leaves and in the infested buds up to a distance of 10 cm using a small polyethylene pulverizer with 10 mL capacity. The application was carried out until dripping occurred, in a total of 5 mL per seedling. Ladybugs were raised in pumpkin from the Jacarezinho cultivar, infested with Planococcus citri Risso coccides as food (pray) for the predator. The raising methodology was adapted aiming to increase the number of insects for the experiments. The adaptation consisted simply in supplying food to the predator directly in vases and therefore the C. montrouzieri adults were stimulated to consume greater quantities of coccides (prays) and still use the place as substrate for oviposition facilitating the management of raising due to easy obtainment of a greater number of eggs and larvae of the predator. The bees were collected and placed in transparent polyethylene jars with holes in the lid and taken to the apiculture lab where the experiment was carried out. The bees were maintained for 3 minutes in the freezer in order to facilitate handling. Using tweezers, the bees were taken away from the jars and placed in Petri dishes with filter paper in the bottom, previously humidified with aqueous ginger or mastruz extract. Test tubes containing sweet water at 30% and tamponated with cotton were placed Inside the Petri dish. The cold ginger extract after 48 hours of application, demonstrated that the survival indice in the concentrations 0.4, 0.5 and 0.6 g/mL-1, respectively, decreased to 17%, 23% and 11% which from the practical point of view, its concentrated use should be in the first 48 hours after the preparation. The aqueous mastruz extract promoted significant death in the concentrations of 0.5 g.mL-1 (12,6%) and 0.7 g.mL-1 (19,2 %) and 0.6 g.mL-1 (27,4 %). Despite the lesser impact caused by the plant extracts for being biodegradable and for staying for lesser periods in the environment, it can be observed in the evaluation of the selectivity of the plant extracts studied in thiswork, it promoted toxicity of adult insects of Apis mellifera and Cryptolaemus montrouzieri. Therefore, we can conclude that the ginger and matruz extracts can be used to control the black aphid in citrus; however, it should be observed if these pest-insects are causing economic damage and avoid applying them during the reproduction season in citrus when bees visit the flowers.