External Development of the Entomopathogenic Fungus Beauveria bassiana on the Housefly (Musca domestica)

Abstract

Light and scanning electron microscopy were used to view the external development, mode of penetration and to establish comparisons between three strains (strains 7320, 7569 and 7771) of the entomopathogenic fungus Beauveria bassiana (Balsamo) (Hypocreales: Clavicipitaceae) on the surface of the common housefly (Musca domestica L.) (Diptera: Muscidae). The host was sprayed with 1 ml conidial suspension of B. bassiana (108 conidia ml−1). The specimens used in the investigation were collected at specific periods after spraying and prepared for viewing using standard methods. Beauveria bassiana conidia attached to the host cuticle after 6 h and germination tubes developed 12–48 h after applying B. bassiana conidia to the host. Densities of B. bassiana conidia varied considerably on the body regions of the host, with the highest densities occurring on the inter-segmental regions, the legs and the base of setae, with observable lower densities of conidia on body regions without setae. Penetration of the cuticle was affected after formation of appressoria. Extensive growth of mycelium on the surface of the insect’s integument was followed by colonization of the host. After 72–120 h post colonization, the first sporulation was observed on the cuticle. After 144 h post-spraying with B. bassiana, the cuticle of the host had completely degraded. Although all three B. bassiana strains killed the flies within 24 h, strain 7771 colonized the cadavers faster than strains 7320 and 7569. Thus, the results of the present study showed potential of B. bassiana as a biological control agent of the housefly.