Biological efficacy of the entomopathogenic fungus Beauveria bassiana for controlling the European spruce bark beetle Ips typographus (Coleoptera: Curculionidae) in semi-controlled laboratory conditions
Abstract: The epidemic desiccation of mainly autochthonous spruce stands, as the modern phenomenon, is present in the most countries of Southeastern and Central Europe, and in the Republic of Serbia, due to the very unfavourable, extreme climatic conditions over the last twenty-year period. The changes in the trees induced by the desiccation, the reduction of the transpiration, of the carbon assimilation, have significanly reduced their natural, mainly chemical resistance to the attacks of the various xylophagous insects, such as European spruce bark beetle (Ips typographus), which is one of the most dangerous pests of spruce. It is mostly a secondary biotic agent, affecting trees that are already weakened. When the population level of it is significantly increased, it attacks the healthy plants, and it becomes the primary biotic agent. In Serbia it very frequently occurs in the outbreaks and occupy great areas. In the semi-controlled laboratory conditions (Institute of Forestry in Belgrade), studies of the biological efficacy in the control of I. typographus, three concentrations (1 %, 2 % and 3 %) of bioinsecticide Naturalis Biogard® (concentrated suspension of a least 2.3 × 107 living spores/ml of Beauveria bassiana strain ATCC 74040 in vegetal oil), were conducted. Bark samples approximately 20 × 10 cm in size, were taken from freshly cut healthy spruces, and placed individually in plastic boxes together with 30 I. typographus adults from natural population. Samples were treated with insecticide diluted in water and stored in the laboratory and controlled at seven-day intervals. Experiments was established in the complete random block pattern in three repetitions, where the blocks for each variant present 3 samples. The percentage of I. typographus individuals infected with B. bassiana on bark samples treated with Naturalis® 1 % was 18.3 %, 2 % – 25.94 % and for Naturalis® 3 % – 42.87 %. With the preliminary results it can be concluded that the mycoinsecticide Naturalis Biogard® can be used to control European spruce bark beetle, as a part of integrated pest management strategy.