An improved method for nematode infection assays in Drosophila larvae

The infective juveniles (IJs) of entomopathogenic nematodes (EPNs) seek out host insects and release their symbiotic bacteria into their body cavity causing septicaemia, which eventually leads to host death. The interaction between EPNs and their hosts are only partially understood, in particular the host immune responses appears to involve pathways other than phagocytosis and the canonical transcriptional induction pathways. These pathways are genetically tractable and include for example clotting factors and lipid mediators. The aim of this study was to optimize the nematode infections in Drosophila melanogaster larvae, a well-studied and genetically tractable model organism. Here we show that two nematode species namely Steinernema feltiae and Heterorhabditis bacteriophora display different infectivity toward Drosophila larvae with the latter being less pathogenic. The effects of supporting media and IJ dosage on the mortality of the hosts were assessed and optimized. Using optimum conditions, a faster and efficient setup for nematode infections was developed. This newly established infection model in Drosophila larvae will be applicable in large scale screens aimed at identifying novel genes/pathways involved in innate immune responses.