Wild plants call to carnivores to get rid of pests—could crops do the same?

October 4, 2015, Cell Press
This diagram shows how nectar can enhance the survival and efficiency of predators and thus allow the establishment of more stable populations of these biocontrol organisms. Credit: Stenberg et al./Trends in Plant Science 2015

Rose gardeners have a lot to say about aphids. Some may advise insecticides as a way to manage an infestation, but others will swear by live ladybugs (natural predators of aphids). The latter is more environmental friendly, and once the ladybugs run out of food to eat, they move on.

While this strategy may work in someone's backyard, it's not an option on a large farm. In an October 4 Trends in Plant Science Opinion paper, agricultural researchers in Sweden and Mexico argue that one way around the scalability problem is to bring back the odors and nectars found in that attract pest-eating predators. This could be done either through breeding programs or by using artificial devices.

"Wild plants commonly emit natural odors when they are damaged that attract natural enemies of pest insects—even as humans we smell it when our neighbour is mowing the lawn - odors can carry very precise information," says co-author Martin Heil of CINVESTAV-Irapuato in Mexico. "Agriculture has bred such defenses out of crops, and since these odors have no negative effects on human consumers, we want to replace what the plant would already be doing."

It's also not unusual for wild plants to produce nectar on their leaves to feed carnivores. While leaf-eating caterpillars or beetles are munching away on plant matter, predatory ants or wasps have a sugary substance to drink and a well-stocked spot to lay their eggs.

Heil and others theorize that the reason these rather helpful traits no longer exist in crops is because plant breeders and decision makers couldn't tell the difference between helpful insects and pests. Only in the past 30 years has it been recognized that plants use odors to communicate to one another and to other species. Such defenses involve multiple genes, however, and it won't be easy to simply bring them back.

This photo shows the effects of volatiles and intercropping. The plant on the left was cultivated in an intercropping scheme in which it was planted with volatile-emitting plants, the plant in the middle was treated with an artificial resistance enhancer, and the plant on the right was not treated. All plants were the same age and were grown outside in the field. Credit: Martin Heil.

One faster alternative would be to plant crops alongside other species that both attract carnivores and repel pests. The downside is that intercropping requires more work during harvesting and its success rate isn't 100%. Another option is to create mechanical dispensers that could release carnivore-calling odors and fungicidal nectar, which is something Heil and his team are now developing and testing.

"New regulations and changing consumer demands are gradually improving the prospects for more sustainable agriculture," Heil says. "This provides a ready market if we can give crops back their own immune system, either by breeding, genetic engineering, or replacing the traits artificially."

Explore further: Plant neighbors 's(c)ent' to protect

More information: Trends in Plant Science, Stenberg et al.: "Optimizing Crops for Biocontrol of Pests and Disease" dx.doi.org/10.1016/j.tplants.2015.08.007

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MR166
3 / 5 (2) Oct 05, 2015
The idea of placing scent dispensers to attract predators is a poor one. Yes your crop might be protected but if there is not enough food available to feed the bugs that you attract the predators will die causing more future losses.
Grallen
5 / 5 (1) Oct 05, 2015
Also insects evolve rapidly. If farmers attempt to attract them constantly(which they would do, just like the use antibiotics), the ones that don't respond to the trickery will survive to breed... We would likely be crippling, permanently, a symbiosis between insect carnivores and plants.
gkam
1 / 5 (2) Oct 05, 2015
"the ones that don't respond to the trickery will survive to breed"
-----------------------------

How will they find mates, if they cannot detect the odors? By feeding those who react positively, we are keeping them viable as a system. It will be those who cannot respond to the signals who will find survival troublesome.

And we want to encourage these insects, as we are showing them where to get food (the unwanted pests or diseases), not trying to kill them.

If it causes no problems with other biota, it is a good plan, in my opinion.
MR166
1 / 5 (1) Oct 05, 2015
Gkam the problem is that people/farmers will use these scents even when there are no pests to control as a prophylactic measure. The predators will come, find that there is no food and die.
gkam
1 / 5 (2) Oct 05, 2015
166, they will have to test carefully, as they should with all measures. But it sounds rational to me.
TheGhostofOtto1923
3 / 5 (2) Oct 05, 2015
166, they will have to test carefully, as they should with all measures. But it sounds rational to me.
-And yours is the learned opinion of someone who thinks that
Mosquitoes are sensitive to a particular wavelength of ultraviolet which kills them, which is not far from the frequency used to attract them
-when we know from a little research that mosquitoes arent attracted to UV.

So what can we surmise about georges similar uninformed rational hearings?

Oh and he mistakes poor otto for a gnat.

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