SEX-PHEROMONE BLEND DISCRIMINATION IN 2 RACES AND HYBRIDS OF THE EUROPEAN CORN-BORER MOTH, OSTRINIA-NUBILALIS

The response specificity of males of two races, and hybrids, of the Eu ropean corn boor moth, to a large series of doses/ratios of E- and Z11 -14:OAc, was determined in a sustained-flight tunnel. For both races a n area of peak response was determined, which included the natural rat io eliciting peak levels of source contact, and other treatments elici ting response profiles over the behavioural sequence not significantly different from the peak, Consistent with studies on other moth specie s response specificity was controlled by two threshold effects, one af fecting locking-on to odour plumes of lower doses and off-ratios conta ining lower proportions of the E or Z isomer than the natural blend, a nd the other resulting in arrestment of upwind flight to higher doses and off-ratios containing higher proportions of the E or Z isomer than the natural blend. A comparison of the size of the areas of peak resp onse showed that males of the univoltine Z race (UZ) using a 3:97 E:Z mix displayed greater specificity and sensitivity than did males of th e bivoltine E race (BE) responding to a 99:1 E:Z pheromone mix. At dos es higher than these eliciting peak response (>100 mu g) response spec ificity was lower for both races, but especially for the BE race, with increased levels of upwind flight and source contact occurring to off -ratios. Finally, consistent with a previous behaviour/genetic study o n this species, F-1 hybrid males displayed peak levels of source conta ct not only to their natural isomer ratio (65:35 E:Z). but also to an expanded range of doses of ratios ranging from 2% to 98% E.