Joseph E. Weaver

Histopathology of lecithodendriid trematode infections in stonefly naiads

Abstract Naiads of the perlid stonefly, Acroneuria carolinensis , were experimentally infected with two species of lecithodendriid trematode larvae, Cercaria stenodorya and Cercaria tremaglandis ; naiads of a perlodid stonefly tentatively identified as Isogenus hastatus were infected with C. stenodorya. C. stenodorya entered both host species through articulations or distal gill filaments in relatively large numbers and developed in A. carolinensis without encysting. Host response to this trematode was largely limited to repair of entry lesions, though some hemocyte accumulation and melanin deposition about unencysted larvae was noted in Isogenus. C. tremaglandis entered Acroneuria naiads in much smaller numbers, penetrating leg and body-segment articulations, and becoming encysted in the hemocoel and fat body within 24 hr. Both encysted and unencysted trematodes elicited a host response which consisted of focal hemocytic aggregates, encapsulation, and melanin deposition, and resulted in the death of some of the parasites. Light to moderate C. tremaglandis infections had little or no effect on the total hemocyte counts of A. carolinensis during the first 24 hr of infection. In all instances, damage to the plecopteran hosts was slight, and largely limited to trauma caused by entry and to displacement and lysis of fat body. There was no increase in host mortality.