Preliminary investigations on the use of Beauveria bassiana (Bals.) Vuill. and other control methods against the bark beetle Ips typographus (Col., Scolytidae) in the field.

The bark beetle, Ips typographus (Coleoptera, Scolytidae), is considered to be one of the most important insect pests of spruce in Europe. Effective and environmentally safe, longterm biological control methods are still lacking. Our work describes investigations to assess the suitability of the entomopathogenic fungus Beauveria bassiana (Hyphomycetes, Moniliales) for its integration into an autodissemination technique by which I. typographus is attracted to a pheromone lure and dosed subsequently with conidia in a specially designed trap. Contaminated bark beetles leave the trap and carry the pathogen into the pest population. With respect to a combination of B. bassiana, also other control methods, such as the mineral dust silicic acid, the plant extract Neem Azal T/S(R) and the insecticides Karate WG Forst(R) and Fastac(R) were tested. In lab experiments, ail tested reisolates of B. bassiana showed a high virulence against I. typographus. However, the mortality and mycosis of the beetles varied depending on the bioassay method. Therefore, a suitable, standardised method was developed. The best reisolates causing the highest mortality within one week were Bba Z, originally isolated from I. typographus, and the strain from the industrial product Boverol(R)(Bba 138). The mineral dust and insecticide Karate WG Forst(R) induced a 100% beetle mortality within three days at 25 degrees C, the plant extract Neem Azal T/S(R) suppressed the beetle fertility. Based on these laboratory investigations, preliminary field experiments on the treatment of nuptial chambers and on the combination of pheromone traps with B. bassiana were conducted. In the nuptial chamber test, the pathogen induced a high beetle mortality within one week and a mycosis rate of 91%. In the first tests with pheromone traps and B. bassiana a high mortality up to 100% within six days and a mycosis rate of 70-96% were noted. In the last experiment, traps were located on flight cages with spruce trunks in order to study the behaviour of the infected beetles. Beetles contaminated with Boverol(R) died before reaching the spruce trunks or formed only reduced brood systems.