Pheromone trap monitoring of Z-strain European corn borer (Lepidoptera: Pyralidae): Optimum pheromone blend, comparison with blacklight traps, and trap number requirements

Commercial pheromone lures for monitoring European corn borer, Ostrinia nubilalis (Hubner), captured significantly fewer moths and indicated a delayed peak emergence compared with blacklight traps in Minnesota. Pheromone trap studies were therefore conducted during 1992-1994 at Rosemount and Le Sueur, MN, to determine the relative attractiveness of different ratios of (Z)- and (E)-11-tetradecenyl acetate isomers to O. nubilalis male moths. Isomer ratios in the pheromone lures tested ranged in percentage of concentration from 99.5:0.5 to 95.0:5.0 (Z:E). In addition to overall catch, the timing of O. nubilalis flights based on pheromone and blacklight traps catches was compared. The variance to mean relationship in pheromone trap catch data was used to estimate the optimum number of traps needed. Analysis of the proportion of total moths captured indicated that moths were highly attracted to lures with a ratio of isomers near 98:2 (Z:E). A significant decline in attractiveness occurred with lures in the 95:5 (Z:E) isomer range. Although the 1st moth catch in pheromone traps usually coincided with blacklight traps, the timing of 2nd-generation cumulative emergence (e.g., 50% peak catch) was significantly different between pheromone and blacklight traps. Despite an aggregated distribution of moth catches, the expected optimum trap number ranged from 2 to 5 at the 25% precision level. Results of this study confirm the increased response of O. nubilalis males to limited concentrations of (E) isomer (1-3%) in the pheromone blend. To ensure optimum performance of O. nubilalis pheromone lures, a renewed emphasis must be placed on quality control protocols during commercial pheromone lure preparation.