Effect of Habitat Complexity on Parasitic Efficiency of Romanomermis iyengari1 on Larvae of the Mosquito Culex quinquefasciatus

Indiscriminate use of insecticides to control vectors of malaria, dengue, and yellow fever contaminates the environment and with time, gradually increases insecticide-resistant mosquitoes, making their control increasingly difficult. Use of the parasitic nematode Romanomermis iyengari (Mermithidae) is efficient biological control against mosquitoes, but little is known of the effect of habitat complexity on the success of infection. We determined lethal doses of the nematode on Culex quinquefasciatus (Culicidae) and analyzed the effect of habitat complexity (0, 25, 50, 75, and 100% aquatic debris cover) on successful infection by two lethal loads (10 and 100 parasites per larva). Habitat complexity had no effect on parasitic efficiency of R. iyengari at high concentrations (100 parasites per larva) and significantly decreased parasitic efficiency at low concentrations (10 parasites per larva). Use of combined biological control agents (water bugs (Hemiptera), odonate nymphs (Odonata), and air-breathing fish) of mosquito larvae commonly found in larval habitats should be studied more. Habitat complexity could have a density-dependent effect on parasitic efficiency of R. iyengari on Cx. quinquefasciatus. Complex habitat could affect mobility and ability of a parasite to search for a host. High parasite loads were not affected by habitat complexity and caused high parasite burdens on sampled hosts. Mosquito larvae could reach maturity without being infected by R. iyengari in low parasite loads.