Virulência de bactérias associadas a Azadirachta indica sobre Spodoptera frugiperda

Abstract

The armyworm the corn, Spodoptera frugiperda (JE Smith), is considered a pest insect of large economic importance for agriculture, due to damage to different cultures. This study aimed to evaluate the virulence of bacteria isolated from the neem plant, Azadirachta indica A. Juss, on the biology of S. frugiperda. The evaluated bacterial isolates were 1 Epi, Epi 7, 9 Epi, Epi 11, Epi 12, Epi 13, 5 Nim, Nim 8, 10 Nim, Nim 11, Nim 12, Nim 14 and Nim 15 which were obtained from fermented neem extracts (Neem) and the surface of the leaves of that plant (epiphytic Epi). These isolates were sub cultured in TSA solid medium (40 g Tryptic Soy Agar in 1000 mL of water). Bacterial suspensions were prepared from the addition of saline solution (0.85% NaCl) to plates containing bacteria multiplied. These suspensions were centrifuged for 15 minutes at 10,000 rpm rotation. The supernatants obtained were reserved and stored in new flasks and a varying volume of saline solution was added to bacterial cells, depending on the assay to be performed and the isolate assessed, to adjust the concentrations. This procedure was performed in a spectrophotometer calibrated for 540 nm optical density. Initially, the effect of ingesting anti contaminated, component of the artificial diet of parental of larvae of S. frugiperda on the pathogenicity of the isolates Epi 7. Epi 11, Epi 13 and Nim 11. The bacterial suspensions were adjusted in a spectrophotometer to 0.1 absorbance, and they were used to treat fragments of new maize leaves. These fragments were offered individually for newly hatched caterpillars of S. frugiperda, from parents reared under an artificial diet or maize leaves. As caterpillars control were also from parental fed artificial diet or maize leaves and fed untreated maize leaves in the test. The duration and larval and pupal mortality, weight of male and female pupae and deformation of pupae and adults were evaluated. The intake of maize leaves or artificial diet by parents of S. frugiperda did not affect the pathogenicity of the bacterial isolates. After that, it was determined the number of bacterial cells present in each of the bacterial suspensions assessed aiming at standardization of the concentration of these pathogens in the assays were evaluated. These two components were used for the immersion of pieces of maize leaves in two assays individually carried out. For both assays, the fragments of treated leaves were transferred to glass tubes together with a newly hatched caterpillar of S. frugiperda. The caterpillars of the control received untreated maize leaves. The duration and mortality of larval and pupae, weight of male and female pupae, and deformation of pupae and adults were evaluated. All the evaluated bacterial isolates affected the survival and biology of newly-hatched larvae of S. frugiperda, however, Epi 13 and Nim 14 were the most virulent to that insect. The supernatants of Epi 1. Epi 7. Epi 12, Epi 13. Nim 11, Nim 12, Nim 14 and Nim 15 isolates reduced the survival of larvae of S. frugiperda. Bacteria isolated from the neem plant are promising for use in caterpillars of S. frugiperda management programs.