New Site for the Eradication of a White Grub Population (Melolontha Vulgaris Fabr. and Melolontha Hippocastani Fabr.) by Release of Irradiated Adults

The area considered (about 1100 ha) is situated on the Swiss shore of Lake Constance and is infested with two cockchafer species (Melolontha vulgaris Fabr. and M. hippocastani Fabr.). The dynamics of the cockchafer population were followed from 1955 to 1967, Estimates of the cockchafer population were obtained by: (1) soil sampling for adults; (2) soil sampling for white grubs; (3) observation of flight, activity and assessing damage on preferred food trees; (4) capture-recapture method with the aid of marked adults in spring 1967. Estimates were made several limes with the isotopic dilution technique. Throughout the flight period 1967 the occurrence of adults was observed along the border of the Güttingerwald. Preferred food trees were regularly inspected and changes of preference with season were noted. Crepuscular flight activity of adults was watched at exposed comers of the wood. Changes in the flight direction during the period of observation were related to sex ratios in samples taken the following morning and compared with the developmental stage of the ovaries. Beetles were collected by shaking the host trees at dawn, and weight and volume of the samples were registered. Four therapeutical X-ray units potentially utilizable for irradiating beetles are available within 35 km. The nearest facility, 5 km away, was tested for its daily capacity. (author)