Evaluation of insecticidal activity of entomopathogenic bacteria Photorhabdus and Xenorhabdus against shoot and fruit borer Earias vittella (Lepidoptera: Noctuidae) of vegetable crops

Abstract

The shoot and fruit borer, Earias vittella is one of the major polyphagous pest prefer various host plants attacking almost 38 plant species and causes yield loss of 15-45% in vegetable crops annually in India. In this study Entomopathogenic bacteria (EPB) were used for biocontrol larvae of Earias vittella under in vitro condition. Whole cell culture and cell supernatant of EPB was screened for insecticidal activity against the larvae and results has shown that the lethality of larvae started after 12-24h of treatment. The percent mortality treated with intact cell was significantly higher in larvae treated with EPB3 with 90% mortality at 72h followed by EPB1 and EPB3. The larvae treated with cell supernatant of EPB had shown lethality in the range of the mortality of larvae where in the range of 50-70% at 72h of treatment and there was no significant difference among the bacteria treated. The LD50 value represent the concentration of cells required for the 50% population to be lethal and EPB3 had expressed significantly lower concentration of 4.28x104 CFU / ml followed by EPB9 and EPB8. The LD50 value for the larvae treated with cell supernatant were in the range of 1010 to 1012 CFU / ml. The larvae treated with EPB3 cell culture has taken significantly less time for mortality of fifty percent of population with a media lethal time (LT50) of 24h followed by EPB1 (30h) and EPB8 (32h). Among all the isolates EPB3 (Xenorhabdus nematophila) and EPB1 (Photorhabdus luminescens) had more virulence against the Earias vittella and can be further tested for biocontrol efficiency under greenhouse and field conditions.