Nematodes as multitrophic organisms: the good, the bad and the unexpected

Nematodes are cosmopolitan metazoans that occupy all possible ecological niches from the equator to the poles and have even been sent into space. As a group they live a largely unobserved life feeding on fungi and bacteria, but some groups can be predatory, feeding on other nematodes while others can be parasitic either on animals or on plants. Within the agricultural context they can be either good or bad, acting as biological control agents of insect pests and parasites of crops respectively. Firstly, and the good, using entomopathogenic nematodes, that carry a symbiotic bacterium and can parasitize insects and shown to successfully control white grubs in the field, in recent experiments we have been able to increase their rate of reproduction in a fermentation system by the addition of fecundity enhancing peptides. Secondly, and the bad, using root-exudates from a series of crops that are parasitized by the sedentary endoparasitic cyst and root-knot nematodes, we have been able to show that root-exudates from a host plant alter the way the nematode ages and makes it increasingly susceptible to hyperparasitic bacteria from endospore forming Pasteuria group of parasites, whereas root exudates from a non-host plant do not. Both these sets of results, although perhaps not necessarily counterintuitive, were certainly unexpected.