Patogenicidade de bactérias isoladas de nim à Spodoptera frugiperda (J. E. Smith)

Abstract

The fall armyworm Spodoptera frugiperda (JE Smith) is considered an insect- pest of great economic importance for agriculture, due to damage and to emergence of resistant populations to pesticides. In order to avoid these problems, this study aimed to evaluate the pathogenicity of microorganisms isolated from the neem, Azadirachta indica A. Juss plast, on the biology of S frugiperda. We evaluated 33 bacterial isolates, obtained from fermented extracts of neem (Nim), from the surface of the leaves (epiphytics - Epi) and mesophyll (endophytics-Endo). The bacterial suspensions were prepared from the addition of 10 ml of a solution of sterile Nacl (0.85%), that were homogenized and taken to spectrophotometer to be adjusted to absorbance 0.6 or 0.8 in optical density 540 nm depending on the evaluated experiment. These suspensions were used to treat by immersing the pieces of maize leaves. These pieces of leaf were air-dried and transferred to glass tubes, together with a S. frugiperda caterpillar 10 days old. The caterpillars of control received maize leaves without treatment. We assessed the duration and mortality of larvae and pupae, weight of male and female pupae and deformation of pupae and adults, and the percentage of viable adults. They were assessed the colony forming units (UFC) of each one of the isolates evaluated in suspensions calibrated in spectrophotometer for 0.6 or 0.8 of absorbance. The ingestion of bacterial isolates by S. frugiperda caterpillars 10 days old have increased duration and mortality of larval phase, duration and pupae mortality, decreased weights of males and females pupae, increased adult deformation, and reduced percentage of viable adult. We found 11 isolates that increased duration of the larval stage of S. frugiperda, and 10 which increased the mortality of that phase. For pupae stage, we found 19 isolates that increased the duration, 14 which increased mortality, 23 which reduced weight of male pupac and 19 which decreased weight of female pupae. To adulthood, 13 isolates were increased percentage of deformation and 12 ones that reduced the percentage of viable adults. The intake of isolates Endo 01 e Epi 14 did not affect any stage of the insect. Thus, it is concluded that all of the isolates were pathogenic to S. frugterda except for Endo 01 e Em 14.