Microbial control of diamondback moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae) using bacteria (Xenorhabdus nematophila) and its metabolites from the entomopathogenic nematode Steinernema carpocapsae

Abstract

Cells and cell-free solutions of the culture filtrate of the bacterial symbiont, Xenorhabdus nematophila taken from the entomopathogenic nematode Steinernema carpocapsae in aqueous broth suspensions were lethal to larvae of the diamondback moth Plutella xylostella. Their application on leaves of Chinese cabbage indicated that the cells can penetrate into the insects in the absence of the nematode vector. Cell-free solutions containing metabolites were also proved as effective as bacterial cells suspension. The application of aqueous suspensions of cells of X. nematophila or solutions containing its toxic metabolites to the leaves represents a possible new strategy for controlling insect pests on foliage.

Fig. 1

Effects of broth (△), cells suspension (▽) and cell-free metabolites (□) of X. nematophila on mortality percentage of different diamondback moth larvae instars. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability at 5% level of probability

Fig. 2

Mortality response of diamondback moth larvae to bacterial treatments, cells suspension (▽) and cell-free metabolites (□) of X. nematophila and broth (△) at 20, 25 and 30 °C temperature. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability at 5% level of probability

Fig. 3

Mortality response of diamondback moth larvae to cells suspension (▽) and cell-free metabolites (□) of Xenorhabdus nematophila and broth (△) after different time intervals. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability at 5% level of probability

Fig. 4

Effect of different bacterial cell concentrations (4×10², 4×10³, 4×10⁴, 4×10⁵, 4×10⁶ and 4×10⁷ cells/ml) on mortality percentage of diamondback moth larvae. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability at 5% level of probability

Fig. 5

Effect of moist and dry condition of Chinese cabbage leaves on mortality of diamondback moth larvae treated with cells suspension (▽), cell-free solutions (□) of Xenorhabdus nematophila and broth control (△). Vertical bars (where larger than the points) represent the standard error (s.e.) of variability at 5% level of probability

Fig. 6

Response of diamondback moth larvae to different bacterial treatments, cells suspension and cell-free metabolites and broth control when infected an intact Chinese cabbage plants. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability at 5% level of probability