Prevalence of Four Nematode Species : First Comments Since Infection/Parasitism in Fourth-Instar Larvae

We examined the infective capacity of the mermithid nematodes, Romanomermis iyengari, Romanomermis culicivorax, Romanomermis wuchangensis, and Strelkovimermis spiculatus in fourth-instar mosquito larvae nearing pupation of Aedes aegypti, Aedes sierrensis, and Culex pipiens to determine their prevalence in the adults of these mosquitoes. We exposed 100 fourth-instar larvae to pre-parasitic nematodes (juvenile 2 stages) at a ratio of 10:1 (10 nematodes per mosquito larvae). Two days after the nematode applications, a sample of 20 pupae was taken and placed into transparent plastic cups with distilled water to observe the development and growth of pupae until they reached the adult phase with nematodes inside. The four species of nematodes showed the highest prevalence of infection on the Cx. pipiens mosquito, exceeding 55% parasitism, while R. wuchangensis and R. iyengari surpassed this value on Ae. sierrensis by 61.11% and 57.89%. Aedes aegypti was the least susceptible to nematodes, with parasitism values between 30% and 40%. In laboratory settings, we obtained high rates (26.32–77.78%) of parasitized adults when the three-mosquito species in fourth-instar larvae nearing pupation were exposed to infective nematodes. R. wuchangensis (1.86) and S. spiculatus (1.80) were infected Cx. pipiens with greater intensity and R. iyengari (1.33) and R. culicivorax (1.09) with less intensity. This evaluation offers valuable insights into the variability of nematode prevalence of infection and infectivity in fourth-instar larvae, which host mermithids capable of progressing through the pupal stage to adulthood.