Occurrence and pathogenicity of Beauveria bassiana infesting larval Sitona discoideus (Col.: Curculionidae) in the Mediterranean region

Field survey showed that the fungus Beauveria bassiana Vuillemin was the predominant natural enemy of Sitona discoideus Gyllenhal larvae and pupae in the Mediterranean region. The present area of distribution of the disease does not, however, include the parts of North Africa, Cyprus, Syria and Iraq with a Mediterranean climate. At localities regularly investigated in southern France over the period 1973–79, the population dynamics of larval Sitona on volunteer Medicato species appeared to be correlated to some extent with the impact of the fungal disese, which could produce up to 100% mortality on its host larval populations.

Several isolates of the pathogen were tested in laboratory bioassays to determine their potential activity. One accession from southern France proved particularly virulent to S. discoideus larvae and pupae at the relatively low concentration of 10⁵ conidia/g of soil. This accession seemed worth considering for further quarantine testing and introduction into Australia. Differences between isolates were however confounded by varying ages of the cultures involved.