Differential susceptibility of two Melolontha populations to infections bythe fungus Beauveria brongniartii

The susceptibility of second-instar larvae of the European cockchafer, Melo lontha melolontha L., originating from two different geographical locations was investigated with eight isolates of the insect pathogenic fungus Beauv eria brongniartii (Sacc.) Petch. 77-94% of larvae from northern Italy (Auer , South Tyrolia) succumbed to mycosis with an average survival time (AST) o f 22.9-40.1 days. Infections in larvae from south-western Switzerland (Bram ois, Valais) were 28-72% and the ASTs varied between 34.7-56.4 days. Differ ences in susceptibility between the two host populations rr;ray be explaine d by the historical ages of the two populations and the presence of B. bron gniartii resulting in a coevolution of tolerance between the host and patho gen. The Italian population is occasionally infected by B. brongniartii; in comparison, the Swiss population has existed for at least 50 years and reg ular infections by the pathogen are observed Coevolution between B. brongni artii and M. melolontha from Switzerland may explain the apparent resistanc e of the host towards this pathogen in laboratory assays.