**1.3.3 Genetic diversity maintenance**

Maintaining genetic stability and diversity of wild parasitic nematodes collection is vital for research on parasite-host interactions, drug resistance and their applications. For example, prolonged passage of insecticidal nematodes (i.e. entomopathogenic nematodes) can cause a reduction of traits beneficial to pest control (Shapiro et al., 1996; Stuart & Gaugler, 1996; Wang & Grewal, 2002). Three continuous passages of *Galleria mellonella in vitro* resulted in a significant reduction in reproductive potential, and attenuated tolerance to heat, UV and desiccation (Wang & Grewal, 2002). These observations suggest that a selective pressure had been exerted on an isolated population that experienced continuous passages. The original genetic diversity in an isolated population will thus be largely reduced if cryopreservation is not practiced immediately after collection, before experimental analysis is performed.
