Encapsulation of the entomopathogenic nematode Steinernema feltiae in Tipula 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 without the symbiotic bacteria Xenorhabdus bovienii. The encapsulation response varied considerably between individual insect larvae. The variation could not be attributed to a more or less scattered nematode invasion over time since it was also recorded after simultaneous injection of a fixed DJ dose. The proportion of encapsulated nematodes declined with 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 encapsulating nematodes with and without symbionts inside the hemocoel; however, at doses of 10 and 20 DJ/larva, axenic nematodes were encapsulated less frequently than monoxenic nematodes. Injected axenic nematodes that were not encapsulated did not develop in T. oleracea larvae but disappeared from the insect's hemocoel. Coinjection of symbiotic bacteria increased encapsulation of axenic nematodes, showing that X. bovienii is triggering the encapsulation response of T. oleracea against S. feltiae.