INDIVIDUAL VARIABILITY OF THE FLIGHT POTENTIAL OF IPS-SEXDENTATUS BOERN (COLEOPTERA, SCOLYTIDAE) IN RELATION TO DAY OF EMERGENCE, SEX, SIZE, AND LIPID-CONTENT

Individual variability in the flight potential of Ips sexdentatus Boer n. was investigated using flight mill experiments. Non-flyer status an d flight durations were studied in relation to day of emergence. sex, pronotum width, dried body weight (after lipid ether extraction). and lipid content estimate. Lipid content estimation was determined in bee tles reared on the same trees and under identical conditions as the fl ight test insects. The four flight-tested cohorts showed that approxim ately one-third were non-flyers. The distribution of individual flight durations was described by a log-normal curve. Consequently. the disp ersal variability within the population could be fitted to a linear mo del on a log-probit scale. The concept of FD50 (flight duration 50). d efined as the flight duration of 50% of a sample population. was used to describe population flight potential. There was no significant corr elation between the individual flight duration and the day of emergenc e. sex. body size or weight, or lipid content estimate. A significant positive correlation was recorded between the different classes of fly er (i.e. non-, short, long, and very long flyers) and the average lipi d content estimate. It was hypothesized that (1) a mininium threshold fuel supply was necessary to initiate the dispersal flight and (2) fue l supply could result in dispersal tendencies representing a specific response to habitat constraints.