Learning parasitoid

In Alloxysta victrix, 6-methylhept-5-en-2-one 16, which is produced by both males and females, was identified as potentially attractive to the males and slightly repellent to the females in Y-tube olfactometer assays [60]. In this study, the activity was also dependent on prior exposure of the insects to the compound. Naive insects responded more strongly than previously exposed ones. This underscores a second difficulty in the bioassay-guided identification of parasitoid hymenopteran pheromones the responses are very dependent on the context and on prior exposure. Learning has been demonstrated in several species of parasitic hymenoptera [61-65]. 

Learning is not required for the aphid parasitoid Aphidius ervi to recognize pea plants that are damaged by its specific host, the pea aphid Acyrthosiphon pisum (Du et al, 1998 Powell et al., 1998). This parasitoid is far more attracted by pea plants infested by this host than by pea plants infested by a non-host, Aphis fabae. Implicated in the specificity of the signal is 6-methyl-5-hepten-2-one, a substance that was only detected in the odor profile of plants infested by A. pisum (Wadhams et al., 1999) the pure compound was found to be highly attractive to A. ervi (Du etal., 1998). 

Turlings, T. C. J., Waeckers, E, Vet, L. E. M Lewis, W. J. and Tumlinson, J. H. (1993b). Learning of host-finding cues by hymenopterous parasitoids. In Insect Learning Ecological and Evolutionary Perspectives, eds. D. R. Papaj and A. Lewis, pp. 51-78. New York Chapman Hall. 

Variability in induced plant volatiles complicates the reliance of natural enemies on these cues. One way of dealing with variability is through associative learning, which may allow parasitoids to learn which cues are most likely to lead them to suitable hosts at a particular time in a particular area. Moreover, recent studies suggest that plant volatile blends alone carry specific information on the herbivores by which they are attacked. For example, predatory mites can distinguish between the blends of apple trees infested by two herbivores species (20). Du et al. (21) showed that different aphid species elicit different volatile blends in bean plants and that the aphid parasitoid, Aphidius ervi, can use these differences to distinguish plants infested by its host. Aphis pisum from those infested by a nonhost. Aphis fabae... 

Vinson, S. B., Barfield, C. S. and Henson, R. D. (1977) Ovipositional behavior of Bracon mellitor Say, a parasitoid of the boll weevil (Anthonomus grandis Boh.). II. Associative learning. Physiol. Ent., 2,157-64. 

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