Identification of compounds from the eggs of Ostrinia nubilalis and Mamestra brassicae having kairomone activity on Trichogramma brassicae

In the presence of an extract of Ostrinia nubilalis or Mamestra brassicae eggs, female Trichogramma brassicae exhibited increased rates of upwind locomotion in the tubes of a linear olfactometer. GC and GC-MS analyses of O. nubilalis and M. brassicae egg extracts revealed the presence of fatty acids, their ethyl esters, and various hydrocarbons. Exposing the wasps to a mixture of the five main saturated hydrocarbons (heneicosane, tricosane, pentacosane, heptacosane and nonacosane) increased the upwind progression in the olfactometer. Single hydrocarbons elicited reduced or no activity. Ethyl palmitate and palmitic acid were also effective in increasing upwind locomotion. Z11-14:Ac, the main component of the female sex pheromone of O. nubilalis was inactive, regardless of its concentration. It is concluded that various compounds present on the surface of the O. nubilalis egg masses may play a role in the orientation of T. brassicae to its host.