Determination of volatile nematode exudates and their effects on a nematode-trapping fungus.

Volatile compounds exuded from axenically grown free-living nematodes were determined with gas chromatographic and mass spectrometric techniques. Carbon dioxide evolved from 5-200 nematodes was determined with an ampoule technique, whereas total ammonia (NH3 + NH4 (+)) and acetic and propionic acids were determined by direct injection of water in which nematodes had been suspended for 1-3 days. CO2 amounted to about 80 ng nematode(-1) d(-1), total ammonia to 1-5 ng, and acetic and propionic acids to 0.5 and 1.0 pg nematode(-1) d(-1).The effects of these compounds on induction of trap formation in the nematodetrapping fungusArthrobotrys oligospora were tested. CO2 inhibited trap formation at 5-10% CO2 in air (v/v), whereas ammonia stimulated trap formation in a certain concentration range. No effects of acetic and propionic acids were noted for the concentrations tested. The combined effects of these volatiles in the aqueous environment are discussed on the basis of stoichiometric considerations.