Induction of Nematode-Trapping Organs in the Predacious Fungus Arthrobotrys oligospora (Hyphomycetales) by Infective Larvae of Ostertagia ostertagi (Trichostrongylidae)

Laboratory experiments were designed to study the influence of temperature, concentrations of nematodes, oxygen tension, light, and nutrient levels, on the induction of nematode-trapping hyphal nets in the predacious fungus Arthrobotrys oligospora. When induced by infective Ostertagia ostertagi larvae, a maximum number of nets was produced at 20°C, at which temperature nets in surplus were produced at larval concentrations up to 1,000 larvae per cm2. A. oligospora did not produce nets in an anaerobic atmosphere containing 21 % CO2 (v/v), and net induction was suppressed to a certain degree by exposure to light. The composition of the medium had an important influence on the saprophytic growth and the net-forming capability of A. oligospora as a maximum number of nets was induced at a relatively low concentration of corn meal supporting the relatively sparse mycelium. It was shown that a proportion of trapping nets in A. oligospora maintained their trapping potential for more than 7 weeks when the temperature was below 25°C. Induction of nematodetrapping organs in A. oligospora is discussed in relation to control of infective nematode parasite larvae in cow pats.