POPULATION-STRUCTURE IN THE SMALL ERMINE MOTH YPONOMEUTA-PADELLUS - AN ESTIMATE OF MALE DISPERSAL

1. An extensive investigation was carried out into the structure of a large, effectively continuous population of Yponomeuta padellus Latrei lle, feeding on hawthorn, Crataegus monogyna, and blackthorn, Prunus s pinosa. 2. Mark-recapture studies were used to obtain direct estimates of the male dispersal rate, sigma, in two successive years. 3. Disper sal was found to be extremely localized with respect to the total area of the study population. Estimates of sigma ranged from a minimum of 2.47 m to a maximum of 12.5 m. 4. Limited dispersal could be an import ant factor governing the genetic differentiation of Y.padellus populat ions, and its implications for the supposed existence of host races in this species are discussed.