A. Peters et Ru. Ehlers, SUSCEPTIBILITY OF LEATHERJACKETS (TIPULA-PALUDOSA AND TIPULA-OLERACEA, TIPULIDAE, NEMATOCERA) TO THE ENTOMOPATHOGENIC NEMATODE STEINERNEMA FELTIAE, Journal of invertebrate pathology, 63(2), 1994, pp. 163-171
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.