Evaluation of commercial and non-commercial strains of entomopathogenic fungi against large raspberry aphid Amphorophora idaei

The European large raspberry aphid, Amphorophora idaei (Borner) (Hemiptera: Aphididae), is one of the most important pests of the raspberry, causing significant economic damage due to its high mobility and its role as a vector of various viral plant pathogens. In the absence of effective control solutions, 16 strains of entomopathogenic fungi comprising six genera, i.e. Isaria fumosorosea, Lecanicillium longisporum, Lecanicillium muscarium, Beauveria bassiana, Metarhizium anisopliae and Metarhizium brunneum (formally known as Metarhizium anisopliae var. anisopliae) were screened for their comparative virulence against A. idaei. Three different concentrations of fungal conidial suspensions (1 × 105, 1 × 106 and 1 × 108 ml−1) of M. brunneum, I. fumosorosea and L. longisporum were sprayed on detached raspberry leaves infested with A. idaei under laboratory conditions, and further trials were conducted in the glasshouse. The results showed that these entomopathogenic fungal strains were able to reduce the number of A. idaei. However, virulence varied significantly between different fungal strains/species. The most virulent species were L. longisporum and I. fumosorosea, followed by M. brunneum. All species of B. bassiana showed least virulence. The virulence of three selected strains M. brunneum BNL102, I. fumosorosea FE 9901 and L. longisporum Vertalec were dependent on dose and insect life stage. LT50 values of A. idaei exposed to pre-treated leaves with entomopathogenic fungi were relatively lower than those of aphids that received direct inocula by spraying. Similarly, significant reduction in A. idaei populations were observed in the glasshouse. Overall, this study demonstrates the effectiveness of fungal strains that could be commercially exploited against A. idaei.