PARASITE-INDUCED CHANGES IN CHIRONOMUS-DECORUS (DIPTERA, CHIRONOMIDAE)

The midge Chironomus decorus is common and abundant in the western basin of Lake Erie. Adult midges were found to be parasitized by the mermithid nematode Limnomermis bathybia from May through October 1985, with a seasonal prevalence of about 37%. Parasitic juvenile worms leave the host after the midge emerges from the pupa to the flying adult stage. Gross changes induced in C decorus by the parasite were as follows. Parasitized males had wider wings than normal and antennae lacked the plumose condition and also exhibited a reduction of flagellomeres. The eighth tergite of males was altered from a rounded to a squared condition and the eighth sternite exhibited bristle pads characteristic of the female. In parasitized females, the posterior edge of the ninth sternite was fully sclerotized and the genital opening and spermathecae were lacking.