A field study was conducted, 1971–72, in central Iowa, to determine whether females of several strains of the European corn borer,Ostrinia nubilalis(Hübner) and 2 preparations of synthetic lure could successfully compete in attracting feral male European corn borer adults. Females were from Georgia, Iowa, Minnesota, New York, and Quebec. The synthetic lures used werecis-11-tetradecenyl acetate (Z-11-tda) isomerically pure and Z-11-tda containing 8.5%trans(E) isomer. A large segment of the male Eureopean corn borer population in central Iowa is attracted to a source that emits pure or relatively pure Z-11-tda and responds to Georgia (southern ecotype), Minnesota, and Quebec (northern ecotype), as well as Iowa (central ecotype) females, but shows little response to New York females. Nightly drops of 6–12°C after 1700 h and temperature plateaus of 2 or more consecutive h, and high relative humidity, should usually occur to produce searching and attraction activities of the Iowa male and the Georgia, Iowa, Minnesota, and Quebec females, respectively. Wind direction was partially responsible for interaction between attractive sources and males at 28 m. A field by attractant interaction showed that the corn borer moths inhabiting the edge of each experimental cornfield were in a contagious (clumped) distribution.