The effects of parasitism by Romanomermis culicivorax (Nematoda: Mermithidae) on growth and development of Aedes vexans (Diptera: Culicidae) in laboratory and field tests

Parasitism by Romanomermis culicivorax caused symptoms typical of starvation in Aedes vexans larvae in both field and laboratory experiments. Infected larvae were reduced in size, moulting at each instar was delayed, there was a failure to develop significant fat body, and secondary pigmentation occurred in later instars. Excluding samples taken after the onset of pupation of uninfected larvae, mean percent infection ranged from 7.2 to 18.8, 12.4 to 24.8, 9.2 to 23.2, and 38.0 to 49.0% when preparasites were applied at 10 000, 20 000, 50 000, and 100 000 m−2 to artificial field pools, respectively. Of 2786 parasitic juvenile nematodes encountered in dissected larvae during the field trial, 2.0% were melanized.