Infection of Aedes aegypti (Diptera: Culicidae) larvae and Adults by the Entomopathogenic Fungus Metarhizium anisopliae (Metschn.) Sorokin

Abstract

Aims: The dengue vector Aedes aegypti is currently a target for control by entomopathogenic fungi. We have previously shown the susceptibility of both larvae and adult A. aegypti to fungal infection by Metarhizium anisopliae and strategies are being developed for control of both stages in the field. Study Design: Few studies have been carried out on the early stages of the infection process of entomopathogenic fungi in mosquitoes, especially in the case of adult infection. Place and Duration of Study: Department of Entomology and Plant Pathology and the Department of Cell Biology at the State University of North Fluminense. May 2010 – July 2011. Methodology: Conidia were obtained for all experiments by culturing M. anisopliae in SDA. Conidial suspensions were standardized by serial dilution following quantification using a hemocytometer. Larvae were infected by addition of conidial suspensions to the water in which they were being maintained. Larvae were removed at specific time intervals for observation using a scanning electron microscope. Adult A. aegypti were infected by spraying with conidial suspensions at a concentration previously established. Following inoculation, mosquitoes were maintained in cages and cohorts were removed for observation using a scanning electron microscopy at specific time intervals. Results: The initial stage of the infection process of larvae and adults (females) was described here. Conidia were found to attach to specific regions of the larvae, associated with thoracic hairs. Saprophytic fungal development was observed on the integument of larvae 36 hours after exposure to the fungus. For infection of adults, adhesion and germination of conidia were only observed on the thorax. Conclusion: The pattern of fungal infection of mosquito larvae was different to that previously documented in the literature. The integument of the larvae was found to be a favorable environment for fungal development. This did not appear to be the case in colonization of the adult integument, which was a more hostile environment for the fungus. However, the microbial control of adult mosquitoes is thought to be more promising than that of larvae due to reduced half-life of the conidia in aqueous environments.