Virulence of entomopathogenic nematodes against developmental stages of Plutella xylostella (Lepidoptera: Plutellidae) — effect of exposure time

Abstract

Summary The virulence of entomopathogenic nematodes (EPN) Steinernema carpocapsae, S. feltiae and Heterorhabditis bacteriophora was evaluated against the diamondback moth, Plutella xylostella. The results revealed that diamondback moth mortality was affected by its developmental stage. For both Steinernema species, diamondback moth larval mortality peaked at 18 infective juveniles (IJ) larva−1; similar results were recorded for H. bacteriophora, with mortality peaking at 20 IJ larva−1. Mortality of pre-pupa exposed to Steinernema species increased up to 35 IJ pre-pupa−1; in S. feltiae a decreasing trend was recorded at higher concentrations of IJ. A negative correlation was recorded between LC50 and ln ET values; S. carpocapsae appeared as the most virulent EPN against larvae (6.5 IJ larva−1) and H. bacteriophora was an effective EPN against pre-pupae (6.5 IJ pre-pupa−1). EPN virulence at dose levels was evaluated by plotting LC50 against ln exposure time, and in the majority of data sets deviations from a linear model were observed and data were statistically fitted by a two-stage phase.