Semiochemicals of Ostrinia nubilalis: Diel response to sex pheromone and phenylacetaldehyde in open field

Ostrinia nubilalis (European corn borer, ECB) is a widely recognized pest of several crops over much of the northern hemisphere. Diel flight rhythms of this moth in response to the attractants phenylacetaldehyde (PAA) and sex pheromones were studied in field conditions. Trapping experiments during three seasons (2008, 2009, 2010) were conducted in an area of the Po valley (northern Italy) where maize cultivation is widespread and O. nubilalis E and Z strains live in sympatry. Both ECB males and females were captured by water pan traps baited with PAA and males alone with Z/E pheromone isomers (11-tetradecenyl acetate). Moths caught by traps were counted every three hours, from 18.00 to 06.00 h. Both ECB males and females showed no crepuscular habits. Adults were caught by traps before 21.00 h only at the end of August, when light values were almost zero. Most of females attracted by PAA were trapped early in the night (21.00-24.00 h). Almost all of those females had mated, suggesting that PAA attraction could be related to oviposition. Unlike females, males did not show a diurnal rhythm in response to PAA, i.e. male captures maintained a steady level all night long. Males behaved differently in response to both Z and E pheromone blends; captures were mainly recorded after 24.00 h. This finding is consistent with previous data that demonstrated a gradual increase of pheromone titer and calling behaviour by females during the scotophase, following a decrease of temperature and an increase of relative humidity.