Entomopathogenic nematodes (EPNs) have been used successfully to control a variety of economically important insect pests. Their pathogenic effect is mostly due to the symbiotic bacteria of the genera Xenorhabdus Thomas & Poinar and Photorhabdus Boemare, Akhurst & Mourant (Enterobacteriales: Enterobacteriaceae), located in the intestine of the infective juveniles (IJs) (Poinar, 1990; Lacey & Shapiro-Ilan, 2008). The bacto–helminthic complexes of Heterorhabditis–Photorhabdus and Steinernema–Xenorhabdus have high potential as effective biological control agents against many soil dwelling insect pests or those in cryptic habitats such as galleries in plants (Burnell & Stock, 2000; Koppenhöfer, 2007). Within 30–60 min after entering the host’s haemocoel through natural openings (mouth, anus, and spiracles) or directly through the cuticle, nematodes release their bacterial symbionts, which multiply and cause septicaemia by producing toxins and kill the insect host within 24–48 h (Grewal, Ehlers, & Shapiro- Ilan, 2005).