An accidental release of 336 fertile Laspeyresia pomonella (L.) (168 ♂, 168 ♀) into an infestation-free orchard in the Wenas Valley near Yakima, Washington, provided valuable information concerning female dispersal and population suppression by the subsequent release of sterile males. The fertile × fertile matings occurring prior to the release of sterile males resulted in approximately 2030 entries in the orchard. About 90% of all infestation was within 1000 ft of the release area, and some infestation was observed as far away as 2000 ft. The release of 5425 sterile males within 24 hours of the fertile release and a followup release of 5000 sterile males 24 hours later, in addition to regular daily releases of about 1850 sterile moths (males and females) in the valley, are credited with limiting the fertile × fertile matings among the remaining estimated 90 unmated females to 0–4.