BARK BEETLE CONTROL - CONTRIBUTION OF PHEROMONE METEOROLOGY AND POPULATION-DYNAMICS

The use of semiochemicals in pest management systems of bark beetles is viewed in relation to optimization of resources investment, comparing beetle numbers in univoltine, requisite-governed woodboring Trypodendron lineatum (Oliv.) with multigeneration bark inhabiting Ips typographus (L.). The efficiency of different numbers of and distance between traps and pheromone load of dispensers was analysed using steady state models and comparing results with published and own field data. Competition between traps and beetle-infested logs, attractive distance and overlap of pheromone plume was compared for lineatum using models which assume a GAUSS distribution of concentration decrease around a pheromone source. For (+)-lineatin (reaction threshold 0.1 ng/m3, production 6.43 ng/female/d, duration of production 3 d/ female), 100,000 females/ha and a flight period of 2 weeks, daily mean production is 128.6-mu-g/ha. Attractive distance x(max) is 20-40 cm for 1 T. lineatum-female and 13-16 m for a trap with 1 CONREL-dispenser (mean release rate 10-mu-g/d (+)-lineatin). A 10-fold increase of attractive distance x(max) needs a 100-fold increase of pheromone release rate according to the model, and 200-fold according to field experiments. In field experiments, Coleoptera (esp. Staphylinidae and Rhizophagidae) were the most abundant non-target trap catches. Insecticide-treated trap logs had the widest range of non-target insects including orders that were not affected by the non-insecticide trapping systems. Mass trapping can be successful in logging areas and/or forests. However, the exclusion of non-target insects still is an unsolved problem and we still have only limited knowledge on potential population increase of beetles and maximum reduction that can be achieved by trapping. Also, population levels reduced by mass trapping can be compensated by increasing reproductive effort of the succeeding generation and/or competitive displacement by secondary bark beetle species.