title: Histopathological effects of Aspergillus clavatus (Ascomycota: Trichocomaceae) on larvae of the southern house mosquito, Culex quinquefasciatus (Diptera: Culicidae).
abstract: Aspergillus clavatus (Ascomycota: Trichocomaceae) was previously found to be an opportunistic pathogen of mosquitoes (Diptera: Culicidae). In the present study, the mechanism leading to its insecticidal activity was investigated regarding histological damages on Culex quinquefasciatus larvae exposed to A. clavatus spores. Multiple concentration assays using spore suspensions (0.5-2.5 × 10(8) spores ml(-1)) revealed 17.0-74.3 % corrected mortalities after 48 h exposure. Heat-deactivated spores induced a lower mortality compared to nonheated spores suggesting that insecticidal effects are actively exerted. Spore-treated and untreated larvae were prepared for light microscopy as well as for scanning and transmission electron microscopy. Spores failed to adhere to the external body surface (except the mouth parts) of these aquatic immature stages but progressively filled the digestive tract where their metabolism seemed to activate. In parallel, the internal tissues of the larvae, i.e. the midgut wall, the skeletal muscles, and the cuticle-secreting epidermis, were progressively destroyed between 8 and 24 h of exposure. These observations suggest that toxins secreted by active germinating spores of A. clavatus in the digestive tract altered the larval tissues, leading to their necrosis and causing larval death. Fungal proliferation and sporulation then occurred during a saprophytic phase. A. clavatus enzymes or toxins responsible for these pathogenic effects need to be identified in further studies before any use of this fungus in mosquito control.
authors.affiliation: Functional and Evolutionary Entomology, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium. Electronic address: entomologie.gembloux@ulg.ac.be.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bawin
authors.affiliation: Functional and Evolutionary Entomology, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium; Laboratory of Reproductive Biology, Department of Animal Biology, Faculty of Science and Technology, University Cheikh Anta Diop, B-5005 Dakar Fann, Senegal. Electronic address: fawrou@yahoo.fr.
authors.forename: Fawrou
authors.initials: F
authors.lastname: Seye
authors.affiliation: Functional and Evolutionary Entomology, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium. Electronic address: s.boukraa@doct.ulg.ac.be.
authors.forename: Slimane
authors.initials: S
authors.lastname: Boukraa
authors.affiliation: Functional and Evolutionary Entomology, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium. Electronic address: jean-yves.zimmer@alumni.ulg.ac.be.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Zimmer
authors.affiliation: Functional and Evolutionary Entomology, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium; Medical Entomology, Pasteur Institute, Ambatofotsikely, 101, Antananarivo, Madagascar. Electronic address: rfaranantenaina@pasteur.mg.
authors.forename: Fara Nantenaina
authors.initials: FN
authors.lastname: Raharimalala
authors.affiliation: Laboratory of Reproductive Biology, Department of Animal Biology, Faculty of Science and Technology, University Cheikh Anta Diop, B-5005 Dakar Fann, Senegal. Electronic address: mydya2001@yahoo.fr.
authors.forename: Mady
authors.initials: M
authors.lastname: Ndiaye
authors.affiliation: Functional and Evolutionary Morphology, Department of Biology, Ecology and Evolution, Faculty of Sciences, University of Liege, Allée de la Chimie 3, B-4000 Liège, Belgium. Electronic address: pcompere@ulg.ac.be.
authors.forename: Philippe
authors.initials: P
authors.lastname: Compere
authors.affiliation: Microbial Processes and Interactions, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium. Electronic address: f.delvigne@ulg.ac.be.
authors.forename: Frank
authors.initials: F
authors.lastname: Delvigne
authors.affiliation: Functional and Evolutionary Entomology, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés 2, B-5030 Gembloux, Belgium. Electronic address: frederic.francis@ulg.ac.be.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Francis
mesh_terms: D000825:Animal Structures / Q000473:pathology; D000818:Animals; D001230:Aspergillus / Q000254:growth & development* / Q000472:pathogenicity*; D003465:Culex / Q000382:microbiology* / Q000502:physiology; D006651:Histocytochemistry; D007814:Larva / Q000382:microbiology / Q000502:physiology; D008853:Microscopy; D013172:Spores, Fungal / Q000254:growth & development* / Q000472:pathogenicity*; D016019:Survival Analysis; D013997:Time Factors
keywords: Aspergillosis; Bioassay; Electron microscopy; Entomopathogenic fungi; Histopathology; Microbial control