Effect of melanization of entomopathogenic nematodes on the potential of Steinernema feltiae and Heterorhabditis bacteriophora for the control of Aedes albopictus and Aedes aegypti

The effect of melanization of entomopathogenic nematodes (EPNs) on their potential for the control of Aedes albopictus (Skuse) (Diptera: Culicidae) and A. aegypti (Linnaeus) (Diptera: Culicidae) were analyzed in the laboratory. Different concentrations (10, 50, 100, 300, 600, 1200, and 2400 infective juveniles per larva) of Steinernema feltiae Filipjev (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) were applied on third instar larvae of both species of mosquitoes. Nematodes were melanized by parasitized larvae and this led to the death of the mosquito in all cases. A higher nematode concentration resulted in an increase in the number of larvae with melanizated nematode, mosquito mortality and the mean number of melanized nematodes per larva. The LT₅₀ was 24 h for H. bacteriophora in both mosquito species and 43 and 62 h for S. feltiae in A. aegypti and A. albopictus, respectively. H. bacteriophora was more lethal than S. feltiae and A. aegypti was more susceptible than A. albopictus to both nematode species. Mosquito mortality mainly occurred in the larval stage (96.7%), and the parasitized larvae that survived underwent metamorphosis and died as pupae (2.7%) or adults (0.6%). Mosquito larvae (A. albopictus and A. aegypti) parasitized with H. bacteriophora and S. feltiae reached the adult stage with melanized nematodes inside. Melanization was related to a reduction in the developmental time of A. albopictus parasitized by H. bacteriophora and A. aegypti parasitized by S. feltiae. The present study demonstrates that the innate immunological defense of mosquito larvae does not limit the lethality of EPNs as control agents.