In the last months I found in literature several very intriguing papers about aphids and their biological control. A good example is the paper entitled “Effect of synthetic and plant-extracted aphid pheromones on the behaviour of Aphidius colemani” recently published by O. M. C. C. Ameixa and P. Kindlmann in the Journal of Applied Entomology.
According to this paper the aphid parasitoid Aphidius colemani (in the photo from the Viridaxis homepage) is sensitive to a mixture of odours including both synthetic and plant-extracted nepetalactone (a component of aphid sex pheromone) and (E)-b-farnesene (aphid alarm pheromone). The behavioural responses of A. colemani to three semiochemical groups with different concentrations were studied in a square arena by Ameixa and Kindlmann showing that parasitoid females were significantly attracted by the semiochemicals, when their concentrations were high, in which case the females spent more time in squares with semiochemicals. However, the majority of females preferred plant-extracted nepetalactone, when it was in high concentration, but they consistently did not respond to (E)-b-farnesene.
These results support previous data showing that a high concentration of (E)-b-farnesene became repellent to the egg parasitoid Chrysonotomyia ruforum and that parasitoid females were not attracted by different concentrations of (E)-b-farnesene, but when this component was offered against a background of a non-attractive natural blend of pine volatiles, the combination became attractive… suggesting as a whole that to be detected by the parasitoid, (E)-b-farnesene must be in a combination with other plant volatiles.
As a whole these results are extremely important considering that some trials with genetically modified plants producing (E)-b-farnesene are in progress (as reported here) using (E)-b-farnesene alone making these plants probably not really effective to fight aphids.
Ameixa, O., & Kindlmann, P. (2012). Effect of synthetic and plant-extracted aphid pheromones on the behaviour of Aphidius colemani. Journal of Applied Entomology, 136 (4), 292-301 DOI: 10.1111/j.1439-0418.2011.01638.x