Screening of a highly pathogenic strain against hazelnut weevil and microscopic observation on its infection process

Hazelnut weevil is the primary pest causing yield loss of hazelnut orchard in China. In practice, chemical spray is the major method of controlling hazelnut weevil. However, frequent chemical spray may cause excessive residual of hazelnut products. The aim of present study is to screen a highly pathogenic strain against nut weevil and provide scientific evidence for its biocontrol. Metarhizium anisopliae var. acridum 3.7986, M. anisopliae 3.4607 and Beauveria bassiana subsp. palomenae (CGMCC No. 12108) were used to infect nut weevil adults, and the time course of accumulated lethal ratio of nut weevil adults was analyzed after inoculation. It was shown that, after inoculated with B. bassiana 12108, the accumulated lethal ratio of nut weevil adults reached 91.67% and 100% on the fourth and sixth day, respectively, which was much higher than in inoculated with M. anisopliae 3.4607 (6.67% and 17.5%), and M. anisopliae 3.4607 (10.0% and 22.5%). LT₅₀ and LT₉₀ of B.bassiana 12108 were 2.56 and 4.42 days, respectively, which were much shorter than that of M. anisopliae 3.7986 (11.40 and 17.70 days) and M. anisopliae 3.4607 (8.80 and 12.80 days). Moreover, the process of B. bassiana infecting nut weevil adults was observed using dissecting microscope and scanning electronic microscope. We found that, at the early stage of infection, B. bassiana 12108 began to grow from joint of mouthparts, antennae, legs and joint base of chest foot. On the 10th day after inoculation, the hazelnut weevil was covered by dense hyphae, and its chest cavity was filled with dense hyphae as well. Simultaneously, a large amount of spores were formed on the body surface.Taken together, our results indicate that B. bassiana 12108 is highly virulence against hazelnut weevil, and provides scientific evidence for further developing of biological pesticide controlling hazelnut weevil.