Ação de Metarhizium anisopliae (Metschnikoff, 1879) Sorokin, 1883 e Beauveria bassiana (Balsamo) Vuilllemin, 1912 sobre Ctenocephalides felis felis (Boúche, 1835) (Siphonaptera: Pulicidae)

Abstract

Fleas are ectoparasites commonly found in dogs and cats and the species Ctenocephalides felis (Bouché, 1835) are the most found in these animals. Ctenocephalides felis felis life cycle is influenced by temperature and humidity. This haematophagous insect feeds for approximately 30 days; its bite can cause allergic dermatitis and also can transmit several etiologic agents to domestic animals and humans. The objectives of the work were verifying the in vitro pathogenicity of the fungi Metarhizium anisopliae and Beauveria bassiana on eggs and adults of C. felis felis and investigated by scanning electron microscopy the development of entomopathogenic fungi on flea cuticle. Fleas were exposed to conidia (108 ml 1) of Metarhizium anisopliae (isolate 959) or Beauveria bassiana (isolate 986). The eggs and the adults used in the experiments were obtained from the colony, and were aspirated for the tubes (10 each). In the tests of effectiveness, the bioassays were constituted of two groups control and four groups treated with the suspensions in the concentrations 105, 106, 107 and 108 conidia.mL-1, and for each treatment they were made ten repetitions. Each group received a milliliter of the suspension to be tested, staying immersed by three minutes. The observations were done on each 12 hours and during the experimental phase the tubes were conditioned in acclimatized chamber in 25 1 C e = 75 % of relative humidity. The results demonstrated that the concentration 108 conidia.mL-1 of the two species inhibited the larval eclosion and caused the mortality of adults. Following standard protocols for electron microscopy, the specimens were prepared 2, 15, 26 and 96 h after infection. Glutaraldehyde 2.5% was used as a fixative. The electromicrography revealed that 2 h after fungus exposure, conidia attachments encompassed the entire flea cuticle, especially on abdominal intersegmental membranes. The emergence of germ tubes and appressoria formation occurred at 15 h, thickening and branching of hyphae on the flea cuticle was noted at 26 h. Therefore, both of these fungal isolates were able to develop on cuticular surfaces of Ctenocephalides felis felis.