Mass production of entomopathogenic nematodes for plant protection

Entomopathogenic nematodes of the genera Heterorhabditis and Steinernema ar e commercially used to control pest insects. They are symbiotically associa ted with bacteria of the genera Photorhabdus and Xenorhabdus, respectively, which are the major food source for the nematodes. The biology of the nema tode-bacterium complex is described, a historical review of the development of in vitro cultivation techniques is given and the current use in agricul ture is summarised. Cultures of the complex are pre-incubated with the symb iotic bacteria before the nematodes are inoculated. Whereas the inoculum pr eparation and preservation of bacterial stocks follow standard rules, nemat odes need special treatment. Media development is mainly directed towards c ost reduction, as the bacteria are able to metabolise a variety of protein sources to provide optimal conditions for nematode reproduction. The proces s technology is described, discussing the influence of bioreactor design an d process parameters required to obtain high nematode yields. As two organi sms are grown in one vessel and one of them is a multicellular organism, th e population dynamics and symbiotic interactions need to be understood in o rder to improve process management. Major problems can originate from the d elayed or slow development of the nematode inoculum and from phase variants of the symbiotic bacteria that have negative effects on nematode developme nt and reproduction. Recent scientific progress has helped to understand th e biological and technical parameters that influence the process, thus enab ling transfer to an industrial scale. As a consequence, costs for nematode- based products could be significantly reduced.