SUSCEPTIBILITY OF LEATHERJACKETS (TIPULA-PALUDOSA AND TIPULA-OLERACEA, TIPULIDAE, NEMATOCERA) TO THE ENTOMOPATHOGENIC NEMATODE STEINERNEMA FELTIAE

The susceptibility of Tipula paludosa and Tipula oleracea larvae to St einernema feltiae was examinated in laboratory bioassays. Dauer juveni les (DJs) entered the larval hemocoel mainly by direct penetration of the cuticle. All instars except L1 encapsulated nematodes in the hemoc oel. However, the prevention of larval death by encapsulation was depe ndent on the number of invading nematodes. Larval mortality was correl ated with the number of invading nematodes, indicating that DJ penetra tion is the limiting step during pathogenesis. In contrast to other in stars, the dosage-mortality response of young L1 was less pronounced. T. paludosa was less susceptible to S. feltiae than T. oleracea. In bo th Tipula species highest mortality was recorded for the L1 approachin g the first molt, while young L1 were less susceptible. Susceptibility of L2 to L4 larvae decreased with their age. For T. oleracea, LC(50) values ranged from 7 DJs per insect for the L1 approaching the first m olt, to 56 for the L4. CO2 release of the different larval stages was not correlated to nematode invasion. It is therefore concluded that pe netration is not triggered by CO2, but by other more specific stimuli. (C) 1994 Academic Press, Inc.