Abstract
There are many species and strains of Steinernema and Heterorhabditis and of their respective symbionts, Xenorhabdus and Photorhabdus. Selective use of the most appropriate nematode species/strain and/or selective utilization of the differing characters of these species and strains can temporarily decrease target insect populations. Genetic improvement and the exchange of bacterial symbionts may lead to improved biological control of insects. Enormous advances have occurred in the in vitro, mass production of entomopathogenic nematodes, utilizing industrial fermentation technology, which has enabled the production of the very large numbers of nematodes required for field applications. As well, improved storage, transport and application methods for the nematodes have ensured more consistent insect control. Nevertheless, understanding of the biology of Steinernema and Heterorhabditis in the soil is very incomplete. The attraction of Steinernema spp. to their target hosts is complex, and secretions of plants and the microflora, in particular, appear to change the nematode's behaviour.
The beneficial characteristics of this nematode-bacterium complex to agroforestry are not limited to that of controlling insects. Many secondary metabolites produced by the bacterial symbionts have significant bioactive properties. Some of these compounds are antimycotic (e.g., xenocoumacins, xenorhabdins, nematophin), antibiotic (e.g., xenorxides, indoles), nematicidal (e.g., stilbenes) and insecticidal. The effective field use of some of these substances or of their derivatives can now be realized, and may play a key role when integrated in pest management strategies in the agroforestry industries.
