Preliminary field trials with Culicinomyces clavosporus against some Egyptian mosquitoes in selected habitats.

Culicinomyces clavosporus was isolated from diseased larvae of Culex pipiens collected from brackish water habitat. Pure cultures of the fungus were grown on nutrient agar media. In the laboratory, the Egyptian isolate of the fungus was bioassayed against first instar larvae of Aedes caspius, Cx. antennatus and Cx. pipiens. The estimated LC50's for Ae. caspius, Cx. antennatus and Cx. pipiens were 4.4 x 10(2), 7.6 x 10(2) and 11.8 x 10(2) conidia/ml, respectively. Field studies were undertaken in a variety of habitats supporting populations of mosquitoes in Mahalet Marhoom, El-Gharbia Governorate, in the summer of 1999. Evaluations included artificial pool studies and field trials. The fungus was applied once to 3 different natural breeding habitats of mosquitoes at a dose rate of 10(10) conidia/m2. Cx. clavosporus introduction into unpolluted rice field that had high densities of Cx. antennatus and low densities of Anopheles tenebrosus Doenitz and Cx. perexiguus resulted in 100% control of the larvae 5 days post treatment. Introduction of the fungus into brackish water habitat supporting large brood of Ae. caspius, and few numbers of Culiseta longiareolata (Macquart), Cx. Pusillus, Cx. perexiguus and Cx. pipiens was equally effective. Dissection and examinations of larvae from both sites confirmed infection by the fungus. However, introduction of the fungus into a drain supporting high population density of Cx. pipiens was not effective. Microscopic examination of larvae removed from this site revealed that the conidia failed to germinate and penetrate the host cuticle. The presence of organic pollution in the breeding site drastically reduced the infectivity of the fungus. Thus, the fungus appears promising as a possible limiting factor for mosquito populations, and eventually its use in control of mosquitoes merits further investigations.