Mortality of the Nut-Leaf Weevil Strophosoma Melanogrammum (Forster) and Damage Rate of Needles After Treatment with Entomopathogenic Fungi

Abstract

The susceptibility of the nut-leaf weevil, Strophosoma melanogrammum (Forster) (Coleoptera; Curculionidae) to the select- ed strains of Beauveria bassiana (Bals.-Criv.) Vuillemin, Isaria farinosa (Holm) Brown & Smith, I. fumosorosea (Wize) Brown & Smith, Metarhizium anisopliae (Metschnikoff) Sorokin and M. flavoviride Gams & Rozsypal, was tested under laboratory conditions. Two ways of insect exposure to fungus were studied; direct inoculation of weevils and indirect by contact with inoculated A. procera twigs that served as food for S. melanogrammum. All of the tested isolates were pathogenic to S. melanogrammum. Direct inoculation of adult weevils in fungal spore suspensions resulted in the greatest mortality compared to indirect inoculation where A. procera twigs were immersed in spore suspensions. Direct inoculation with B. bassiana and Metarhizium spp. isolates caused over 80% mortality after 28 days at 20°C, while LT 50 values ranged from 15.0 to 21.6 days. Indirect inoculation with the most effective isolate M. anisopliae (275) resulted in 72% mortality after 28 days with a LT 50 value of 22.1 days. Both direct and indirect spore application failed to reduce needle damage compared with the control. However, significant differences between particular isolates have appeared.