Avaliação de agentes biológicos e nim sobre Plutella xylostella (Lepidoptera: Plutellidae) em couve

Abstract

Plutella xylostella (Lepidoptera: Plutellidae) is an important insect pest of the Brásicas, especially of cabbage. Among its management methods the control with synthetic insecticides is the most used, however there are other forms of control, such as the use of entomopathogenic bacteria, botanical insecticides and parasitoid insects. Among itsnatural enemies, the larval-pupa parasitoid Tetrastichus howardi (Hymenoptera: Eulophidae) stands out. The objective of this work was to evaluate the parasitism and the development of T. howardi in P. xylostella larvae of the fourth instar in semi-field, as a function of the density of this parasitoid, to verify the mortality of P. xylostella using Bacillus thuringiensis, Azadirachta indica and T. howardi and to observe if the use of T. howardi parasitoid in conjunction with the other controls, has a synergistic effect or may negatively affect the development of this natural enemy. The experiments were carried out in the Laboratory of Biological Control of Insects (LECOBIOL) and greenhouse (-22.19806 °, -54.93389 °) of the Faculty of Biological and Environmental Sciences, Federal University of Grande Dourados, Mato Grosso do Sul, Brazil. The experiments were conducted in a completely randomized design (DIC), the first consisting of seven treatments and one control, in which each treatment contained ten replicates. Twenty-four-hour-old T. howardi females were released in pots with cabbage seedlings in greenhouse at different densities of parasitoid by 4th instar caterpillar (1:1, 3:1, 6:1, 9:1, 12:1, 15:1 and 18:1 host). The second experiment was composed of six treatments, each treatment contained ten replicates with one disc of cabbage and five caterpillars of 3rd instar. The treatments 1, 3 and 5 were composed by immersion of the leaf disc in water, neem solution and solution with Bt respectively. Treatments 2,4 and 6 were composed by the combination of treatments 1, 3 and 5 with 24-hour old females of T. howardi, already fed and mated. T. howardi females parasitized and developed on P. xylostella 4° instar larvae in cabbage plants, under semi-field conditions, at all evaluated densities, with a higher parasitism of 84% obtained at a density of 9: 1. In general, T. howardi, B. thuringiensis, Neem, isolated or associated, caused mortality of P. xylostella 3° instar larvae above 65%, and the bacterium and the botanical insecticide when associated with the parasitoid were more effective in control.