A recent post on Scientific American reported that in UK some field trials are in progress studying the effects of a genetically modified (GM) wheat that should strike fear into aphids and attracts deadly predators to devour them.
The genetically modified wheat emits a pheromone which aphids generally release when they are under attack to create panic and prompt the insects to flee (alarm pheromone). As frequenly occurs in nature, some predators may use the prey chemical communication to locate preys. Similarly, this wheat also attracts some parasitoid wasps to provide a second line of defence for crops since these wasps lay eggs in the aphids killing them.
As you can see in the following video by Christine Woodcock, aphids become agitated and move away after perceiving the alarm pheromone:
According to this assumption on GM wheat, aphids should move toward other plants… BUT… according to a paper published some years ago in Ecology Letters (here a summary), aphids were shown to react mainly to the frequency of pheromone release and not the actual quantity present, possibly to avoid manipulation by plants. Thus, to reduce damage caused by aphids, the major insect pests in Europe, it may prove effective to apply pulses of alarm pheromone to infested fields in place of a continuous production. At the same time, a recent paper published in BMC Ecology by Grit Kunert, Carolina Reinhold and Jonathan Gershenzon provided no support for the hypothesis that plant emission of the aphid alarm pheromone has a direct defense effect against aphids and they suggested that if plants continuously produce EBF aphids may become habituated. In particular Kunert et al concluded that “the results of this investigation demonstrate that EBF produced continuously by transgenic A. thaliana does not act as a direct defense against aphids. The same conclusion might well be applicable to the continuous emission of EBF from other plants though more studies are necessary. (…) This may be due to the fact these transgenic plants release EBF constantly as opposed to the pulsed release caused by natural enemy attacks on individual aphids. ”
This does not imply that this trial is not interesting at all, since there is scattered evidence in the literature suggesting that alarm pheromone emission might serve as an indirect defense by attracting aphid predators and it will be very interesting to see what will happen to aphid predation. Aphids are ancient pest crop insects and I fear (or as aphidologist I’m sure) that we are at present not near to their debacle.
Kunert G, Reinhold C, Gershenzon J (2010). Constitutive emission of the aphid alarm pheromone, (E)-β-farnesene, from plants does not serve as a direct defense against aphids BMC Ecology (10)