The Dispersal of Sterilized Codling Moths1 Released in the Wenas Valley, Washington

Traps baited with virgin female Laspeyresia pomonella (L.) were distributed inside of each commercial orchard plus 47 noncommercial sites throughout 32 square miles of the Wenas Valley, WA, to monitor the inter- and intra-orchard dispersion of sterile marked males. The males dispersed to all points within the orchards; migrated from backyard and abandoned trees located throughout the area into the orchards, and from orchards into these locations, frequently 1.5 miles and occasionally as much as 5.4 miles; and entered the valley from an adjacent orchard to the south of the Wenas Valley, or entered this orchard from the valley. Trap placement and numbers, female density, and wind were important factors that influenced intra-orchard dispersal. In open terrain, behavioral changes were noted in flight and searching, and the host plant was more attractive than pheromone traps. From this study, we can conclude that long-distance dispersal is not unusual but involves a small percentage of the population, and that codling moth populations tend to remain localized.