Effect of Volatile Compounds of the Entomopathogenic Fungi Beauveria bassiana (Bals.-Criv.) Vuill. and Lecanicillium muscarium R. Zare et W. Gams on the Behavior of Sitophilus granarius (L.) (Coleoptera, Dryophthoridae) and Evaluation of the Virulence of Different Strains of These Fungi

Abstract

Adult granary weevils feeding on grain responded selectively to the volatile compounds of different strains of the entomopathogenic fungi Beauveria bassiana and Lecanicillium muscarium. The mycelium of B. bassiana strains had a repellent effect or a neutral effect with a tendency toward repellency. The response to L. muscarium strains varied from weak repellent (G-033) and neutral (Vl 49) to attractive one (Vl 21). Beauveria bassiana strain Bb 17 showed the highest virulence after beetles were sprayed with conidial suspension containing 1.0 × 108 spores / ml: the mortality of the beetles on the 7th day reached 74% with extensive mycelial growth over the dead beetles, LT50 was 5.6 days for this strain and 23 days for strain Bb 13. The L. muscarium strains showed low virulence, with the exception of strain G-033 (LT50 15.3 days), and they also formed mycelium on the dead insects. The granary weevil response should be considered when assessing the potential of entomopathogenic fungi. Beauveria bassiana strain Bb 17 was selected as a promising pest control agent, since neutral reaction of the granary weevil to its mycelium facilitates the spreading of fungal infection.