SUSCETIBILIDADE DE Plutella xylostella A COMBINAÇÕES DE Cepas de Bacillus thuringiensis

Abstract

Diamondback moth (Lepidoptera: Plutellidae), known as the crucifer's moth, is a key plague of cruciferous plants. The use of chemical insecticides in their control resulted in the reduction of the populations of natural enemies and non-target organisms, besides accelerating a development of resistance in populations of this insect. The forms Bioinseticidas such as the entomopathogenic bacterium Bacillus thuringiensis (Bt) are used as an alternative to the chemical control of Diamondback moth, however, reports of resistance of populations of this type. Combinations of Bt strains and/or toxins can be used as resistance management strategies. In this work, we evaluated the susceptibility of Diamondback moth to different combinations of Bt strains using three experimental models: A1 = seven treatments with Bt strains grown on separate plaques (HD2, HD3, HD4, HD7, HD11, HD12 and control), A2 = 16 treatments with Bt strains cultured on the same plate (HD2x3, HD2x7, HD2x11, HD2x12, HD3x7, HD3x7, HD3x7, HD3x11, HD4x7, HD4x11, HD4x11, HD7x11, HD7x12, HD11x12 and control). A = 16 treatments with Bt strains mixed at the time of application (HD2x3, HD2x4, HD2x7, HD2x11, HD2x12, HD3x7, HD3x7, HD3x11, HD3x12, HD4x7, HD4x11, HD4x12 , HD7x11, HD7x12, HD11x12 and control). Our three experimental models required three replicates per treatment with consisted of a suspension division nightclub containing 106

spores/mL and later transferred to Petri dishes with filter paper moistened therein. In each treatment with 60 2nd instar larvae distributed in three replicates. The plates were conditioned in an air-conditioned room with controlled environment and photoperiod. The data were submitted to ANOVA, and to the Scott Knott test (α = 0.05), for data analysis and this was done based on corrected mortality and interaction degree calculations. The relationship between increasing numbers of toxins with increased mortality was not observed in all independent treatments as strains were plated together or mixed at the time of application. There was a better interaction between toxins found in the Bt thunringiensis strain with the strains of Bt finitimus, Bt dendrolimus, and Bt aizawai that demonstrate synergism without A2 model treatment, and additive effect without A3 model. Obtaining synergistic interaction is related to the compatibility of toxins. Strain requirements and with a solution are toxins binding to receptors present on the apical microvilli of the midgut columnar cells of the insect. Combinations of Bt strains have potential to be used as a resistance management strategy of Diamondback moth to Bt bioinsecticide.