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Pathogenesis of infection by the hyphomycetous fungus,Tolypocladium cylindrosporum inAedes sierrensis andCulex tarsalis [Dip.: Culicidae]

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Abstract

The mode of infection and cycle of development ofTolypocladium cylindrosporum Gams was examined inAedes sierrensis andCulex tarsalis. Larvae were found to be infected through the external cuticle, the pharynx and the midgut. Blastospores and conidia were both infective although for equal numerical concentrations blastospores proved more virulent causing high mortality within the first 48 h after inoculation (80 % for L2 larvae exposed to 5×105 spores/ml), while conidia generally took 7–10 days to produce the same results. Sporulation did not occur on submerged cadavers. Conidia were produced only on floating cadavers in contact with air. Conidial production on floating 4th instar larvae was found to average 1.8×107 conidia/larva.

Invasion of the haemocoele and fairly extensive growth of the fungus almost invariably occurred before larvae were killed. This was particularly true forAedes sierrensis larvae. Details are presented of growth within the host and post-mortem penetration of the fungus out of the cadaver.

AdultA. sierrensis sprayed with a conidial suspension proved susceptible to infection with 100 % mortality being recorded at 10 days. Infections originated in the thorax, suggesting, the integument or possibly the thoracic spiracles to be the most probable site of infection.

Résumé

Le mode d'infection et le cycle de développement deTolypocladium cylindrosporum Gams chezAedes sierrensis etCulex tarsalis sont observés.

Les larves sont intectées à travers la cuticule externe, le pharynx et le mésenteron. Les blastospores et les conidiospores sont infectieuses, mais à concentration égale les blastospores sont plus virulentes puisqu'en 48 h, 80% des larves L2 traitées à 5.105 spores/ml sont mortes, tandis qu'avec les conidies le même résultat est obtenu en 7 à 10 j.

Les cadavres immergés ne sporulent pas, seuls les cadavres à la surface de l'eau produisent des conidies. Il y a environ 1,8.107 conidies par cadavre du 4e stade. L'invasion de l'hémocoele et une croissance importante du champignon interviennent toujours avant la mort de la larve. Ceci est particulièrement vrai pour les larves d'Aedes sierrensis. Des détails de croissance du champignon dans l'hôte et de sa sortie du cadavre sont montrés.

Les adultes d'Ae. sierrensis pulvérisés avec une suspension conidienne à 5.106 spores/ml meurent en 10 j.

L'infection a pour origine le thorax, ce qui laisse à penser que les spiracles thoraciques sont les sites préférentiels d'infection.

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  1. George G. Soarés Jr.

    Present address: Mycogen Corp., 5451 Oberlin Dr, 92121, San Diego, CA, USA

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  1. Station de recherches de lutte biologique, INRA, La Minière, 78280, Guyancourt, France

    George G. Soarés Jr.

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Soarés, G.G. Pathogenesis of infection by the hyphomycetous fungus,Tolypocladium cylindrosporum inAedes sierrensis andCulex tarsalis [Dip.: Culicidae] . Entomophaga 27, 283–299 (1982). https://doi.org/10.1007/BF02374812

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