Characterization and virulence of Beauveria bassiana associated with auger beetle (Sinoxylon anale) infesting allspice (Pimenta dioica)

Abstract

The incidence of auger beetle, Sinoxylon anale Lesne (Bostrichidae: Coleoptera), a destructive pest of cosmopolitan occurrence is reported for the first time on allspice trees, Pimenta dioica (L.) Merr. In Kerala, India. The insects bored through the basal region of fresh twigs resulting in dieback symptoms. Morphological characterization and sequencing of a partially amplified fragment of the mitochondrial CO 1 gene (696 bp) revealed the insect to be Sinoxylon anale. An entomopathogenic fungus was isolated from infected cadavers of S. anale that was identified as Beauveria bassiana (Bals.-Criv.) Vuill., sensustricto (s.s.) (Ascomycota: Hypocreales) based on morphological and molecular studies. The partial sequences of the ITS, TUB, TEF and Bloc gene regions were sequenced. The fungus grew well in ambient room temperature conditions (28-32±2°C; 60-70% relative humidity) and the infection process on the insect was documented by scanning electron microscopy. Bioassay studies with the isolate indicated that the fungus was virulent against adult beetles as evidenced by the LC50 (3.6x106 conidia/ml) and ST50 values (6.8 days at a dose of 1 x 107 conidia/ml and 5.8 days at a dose of 1x108 conidia/ml, respectively). This is the first record of B.bassiana naturally infecting S. anale and the fungus holds promise to be developed as a mycoinsecticide.