Control of white grubs (Melolontha melolontha L) by treating adults with the fungus Beauveria brongniartii

Having developed a method to contaminate the breeding sites of the cockchafer with the aid of infected females, two large field trials were carried out, one in 1985 and the other in 1988, Blastospores were applied by helicopter at 26 sites of woodland borders, where the swarming beetles aggregate, The mean dose amounted to 2.0-3.7 X 10(14) spores ha(-1). The infection rates of the treated adults ranged from 30 to 99%. The treatment reduced the average reproduction rate from 5.09 to 2.15 second instar larvae/adult. The development of the treated populations was followed at 15 sites in perennial grassland by examining samples taken in the winter season, Increased infection rates were observed in the generation following the treatment. The population density 6 and 9 years after the treatment, corresponding to two and three generations of the beetle respectively, decreased at 13 sites by more than 50% and at four sites by more than 80%, The population densities remained high at only two sites, although the fungus was present. During this period, the area of heavy feeding damage by the adults at woodland borders decreased from 17.8 to 3.9 km Ar the same time, damage increased outside the treated area from 27 to 31 km. The advantages and disadvantages of this method of breeding site contamination are discussed.