Associative learning of complex odours in parasitoid host location.

In this paper we address the question how hymenopteran parasitoids deal with complex odour bouquets, using Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) as a model. We examined the capacity of Microplitis croceipes to respond to individual compounds in flight chamber experiments after conditioning parasitoids with a mixture consisting of 2-octanone, methyl jasmonate and beta-caryophyllene. Parasitoids were given a choice between single compounds from the training mixture and beta-ocimene as an unrewarded alternative. When compared with control individuals lacking experience with the odour mixture, parasitoids trained to the odour blend showed an increased preference for 2-octanone and beta-caryophyllene, but not for methyl jasmonate. However, when trained with methyl jasmonate alone, parasitoids were able to respond to this compound. This demonstrates that parasitoids can learn to respond to individual compounds following experience with an odour mixture. However, for certain compounds of a mixture, learning can be blocked by other mixture components. Further experiments in which parasitoids were conditioned and challenged with two compound mixes confirmed that the olfactory background can affect recognition of individual compounds.