Effect of temperature on the pathogenicity of entomopathogenic nematodes (Steinernema and Heterorhabditis spp.) to Delia radicum

Susceptibility of last instar larvae of Delia radicum to Steinernema feltiae, S. carpocapsae, S. arenarium, Heterorhabditis megidis and H. bacteriophora was evaluated in the laboratory at 10degreesC, 15degreesC and 20degreesC. S. feltiae was the only species that killed the larvae at 10degreesC; S. carpocapsae, S. arenarium and H. megidis were effective at 15 - 20degreesC whereas H. bacteriophora killed the maggot only at 20degreesC. The temperature significantly affected the host searching ability of all tested species. Mobility was reduced at low temperatures. Significant effects of the host presence on nematode mobility were found for S. feltiae, S. arenarium and H. megidis but not for S. carpocapsae and H. bacteriophora. The dynamics of the attachment to and penetration into the host were monitored for S. feltiae at 10degreesC, 15degreesC or 20degreesC and for S. carpocapsae at 20degreesC. In the period of 6 - 30 hours after inoculation, S. carpocapsae attached in higher number at 20degreesC than did S. feltiae at all temperatures. At 20degreesC, S. carpocapsae penetrated the host only after 30 hours while S. feltiae penetrated already after 15, 9, 6 hours at 10degreesC, 15degreesC and 20degreesC, respectively.