Pathogenicity of bacterium, Xenorhabdus nematophila isolated from entomopathogenic nematode (Steinernema carpocapsae) and its secretion against Galleria mellonella larvae

Abstract

The entomopathogenic bacterium, Xenorhabdus nematophila was isolated from the hemolymph of Galleria mellonella infected with Steinernema carpocapsae. The bacterial cells and its metabolic secretions have been found lethal to the Galleria larvae. Toxic secretion in broth caused 95% mortality within 4 d of application whereas the bacterial cells caused 93% mortality after 6 d. When filter and sand substrates were compared, the later one was observed as appropriate. Similarly, bacterial cells and secretion in broth were more effective at 14% moisture and 25 degrees C temperature treatments. Maximum insect mortality (100%) was observed when bacterial concentration of 4x10(6) cells/ml was used. Similarly, maximum bacterial cells in broth (95%) were penetrated into the insect body within 2 h of their application. However, when stored bacterial toxic secretion was applied to the insects its efficacy declined. On the other hand, when the same toxic secretion was dried and then dissolved either in broth or water was proved to be effective. The present study showed that the bacterium, X. nematophila or its toxic secretion can be used as an important component of integrated pest management against Galleria.

Fig. 1

Mortality response of Galleria larvae to Xenorhabdus cells in broth (◦) and water (•), Xenorhabdus secretion in broth (▫) and water (▪), broth alone (∆) and water alone (▲) after different time intervals. The data were fitted on polynomial model (at 6 d.f.) excluding control treatments whereas vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 2

Effect of Xenorhabdus cells in broth (checker bars) and water (brick bars), Xenorhabdus secretion in broth (dotted bars) and water (zebra lines bars), broth alone (black bars) and water alone (white bars) on mortality of Galleria larvae using filter and sand substrates. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 3

Effect of Xenorhabdus cells in broth (checker bars) and water (brick bars), Xenorhabdus secretion in broth (dotted bars) and water (zebra lines bars), broth alone (black bars) and water alone (white bars) on mortality of Galleria larvae at three moisture contents. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 4

Effect of Xenorhabdus cells in broth (checker bars) and water (brick bars), Xenorhabdus secretion in broth (dotted bars) and water (zebra lines bars), broth alone (black bars) and water alone (white bars) on mortality of Galleria larvae at three temperature regimes. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 5

Effect of different bacterial cell concentrations (4×10², 4×10³, 4×10⁴, 4×10⁵, 4×10⁶ and 4×10⁷ cells/ml) in broth (◦) and water (•) on mortality percentage of Galleria larvae. The data were fitted on polynomial model (at 5 d.f.) whereas vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 6

Percent penetration of Xenorhabdus cells in broth (◦) and water (•), on primary axis and mortality of Galleria larvae caused by Xenorhabdus cells in broth (▫) and water (▪), on secondary axis after different time intervals. The data were fitted on polynomial model (at 7 d.f.) whereas vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 7

Effect of stored bacterial secretion in broth (◦) and water (•), broth alone (▫) and water alone (▪) on mortality percentage of Galleria larvae after different time intervals. The data were fitted on linear model (at 4 d.f.) excluding control treatments whereas vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates

Fig. 8

Effect of Xenorhabdus dried secretion in broth (XDSB) and water (XDSW), broth alone (B-alone) and water alone (W-alone) on mortality percentage of Galleria larvae. Vertical bars (where larger than the points) represent the standard error (s.e.) of variability of replicates