Location: Fruit and Nut ResearchTitle: Biocontrol potential of Steinernema thermophilum and its symbiont Xenorhabdus indica against lepidopteran pests: virulence to egg and larval stages Author
|Shapiro Ilan, David|
Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2014
Publication Date: 3/1/2014
Citation: Kalia, V., Sharma, G., Shapiro Ilan, D.I., Ganguly, S. 2014. Biocontrol potential of Steinernema thermophilum and its symbiont Xenorhabdus indica against lepidopteran pests: virulence to egg and larval stages . Journal of Nematology. 46,18-26. Interpretive Summary: Due to environmental and regulatory pressures, environmentally safe alternatives to broad spectrum chemical insecticides are needed. Entomopathogenic nematodes (also called beneficial nematodes) are safe environmentally friendly natural insecticides. These small round worms are commercially produced and applied to control a variety of insect pests. The nematodes kill their insect hosts with the help of a symbiotic bacterium that they carry with them. When new beneficial nematode species are discovered, it is important to characterize their ability to control various insect pests. If the nematode shows promise in controlling insects then it might be developed commercially to expand the use of biological pest suppression. In this study, a relatively newly discovered nematode species called Steinernema thermophilum was tested against eggs and larval stages of two important caterpillar pests called Helicoverpa armigera and Spodoptera litura. Results indicated that both the nematodes (with bacteria) and the bacteria alone were able to kill the caterpillars effectively in the laboratory. Both larval and egg stages of the caterpillars were susceptible. To our knowledge this is the first report of an entomopathogenic nematode’s ability to kill caterpillar eggs. We conclude that S. thermophilum as well as the nematode’s symbiotic bacteria applied separately have the potential to be developed as biocontrol agents for key caterpillar pests.
Technical Abstract: Under laboratory conditions, the biocontrol potential of Steinernema thermophilum was tested against eggs and larval stages of two important lepidopteran insect pests, Helicoverpa armigera and Spodoptera litura (polyphagous pests), as well as Galleria mellonella (used as a model host) . In terms of host susceptibility of lepidopteran larvae to S. thermophilum, based on the LC5036 hr after treatment, G. mellonella (LC50 =16.28 IJ/larvae) was found to be more susceptible than S. litura (LC50 =85 IJ/larvae) while neither host was found to be significantly different from H. armigera (LC50 =54.68 IJ/larvae). In addition to virulence to the larval stages, ovicidal activity up to 84 % was observed at 200 IJ/50 and 100 eggs of H. armigera and S. litura respectively. To our knowledge this is the first report of entomopathogenic nematode pathogenicity to lepidopteran eggs. Production of infective juvenile nematodes/insect larva was also measured and found to be positively correlated with rate of IJ for H. armigera (r = 0.990), S. litura (r = 0.892) as well as G. mellonella (r = 0.834). Both Phase I and phase II of symbiotic bacteria Xenorhabdus indica were tested separately against neonates of H. armigera and S. litura by feeding assays, and found to be virulent to the target pests; phase variation did not affect the level of virulence. Thus S. thermophilum as well as the nematode’s symbiotic bacteria applied separately have the potential to be developed as biocontrol agents for key lepidopteran pests.