ENCAPSULATION OF THE ENTOMOPATHOGENIC NEMATODE STEINERNEMA-FELTIAE INTIPULA-OLERACEA

The encapsulation response of Tipula oleracea to the entomopathogenic nematode Steinernema feltiae was investigated by exposing the insects to nematode dauer juveniles (DJs) and by injecting DJs with and withou t the symbiotic bacteria Xenorhabdus bovienii. The encapsulation respo nse varied considerably between individual insect larvae. The variatio n could not be attributed to a more or less scattered nematode invasio n over time since it was also recorded after simultaneous injection of a fixed DJ dose. The proportion of encapsulated nematodes declined wi th increasing dose (injected DJs/larva) from approx 80% for 1 DJ/larva to 33-34% for 20 DJ/larva. Tipula oleracea larvae were capable of enc apsulating nematodes with and without symbionts inside the hemocoel; h owever, at doses of 10 and 20 DJ/larva, axenic nematodes were encapsul ated less frequently than monoxenic nematodes. Injected axenic nematod es that were not encapsulated did not develop in T. oleracea larvae bu t disappeared from the insect's hemocoel. Coinjection of symbiotic bac teria increased encapsulation of axenic nematodes, showing that X. bov ienii is triggering the encapsulation response of T. oleracea against S. feltiae. (C) 1997 Academic Press.