Interaction ofCatenaria anguillulaewithRomanomermis culicivorax

The development ofCatenaria anguillulae,at 27°C, in live and heat-immobilizedRomanomermis culicivoraxwas studied at the ultrastructural level.C. anguillulaezoospores infected eggs, preparasites, and postparasites. The zoospores attached predominately to the head of preparasites but in postparasites attachment was primarily on the attenuated tail region. Zoospore attachment usually occurred within 4 h but at high zoospore densities attachment occurred within 30 min. Infection hyphae penetrated the cuticle and developed sporangial swellings within the nematode tissues and pseudocoelom. Sporangia produced exit tubes within 48 h. Those regions of the J3 and J4 nematodes infected byC. anguillulaebecame immobile whereas uninfected regions remained mobile. The J2 infected nematodes usually died within 1–2 days. Tissues adjacent toC. anguillulaehyphae or developing sporangia appeared to be relatively unaffected and ultrastructurally normal. The lack of an apparent host response in the nematode suggested either a lack of hypersensitivity or a long evolutionary host–parasite relationship.