Science Interviews

Interview

Sun, 16th Oct 2011

Insect Recruitment to keep Pests at Bay

Professor John Pickett, Rothamsted Research

Listen Now    Download as mp3 from the show Plant Pests and Plant Pathology

Sarah -   Insects can be a real problem to plants but they can also surprisingly be their salvation.  Some plants actually recruit insects in order to keep other pests away.  We are joined now by Professor John Pickett from Rothamsted Research.  Thank you so much for joining us.

John -   Hello

Sarah -   So, how do plants do this and why on earth would they want to attract insects to them?

John -   Well, all insects are attacked by other insects and so if you’re a plant being attacked by one set then it’s a neat trick to bring in insects that will attack your attacker.  And that’s just what the plants do.  So, when the herbivorous insect starts to bite into the plant, chemical signals are produced which bring in predators but more particularly parasitic wasps which we call parasitoids because they actually kill their host.  And they can do a really spectacular job normally, but they do it rather late and so if it’s a crop you’re wanting to protect, you've got to bring them in earlier.

Sarah -   Are the plants able to be very specific to bring in just the right kind of parasitoid wasp or it just kind of sending out a distress signal and it calls all sort of things there?

John -   Yes, at the moment a lot of plants attract specific parasitic<img src='uploads/RTEmagicC_Parasitic_wasp_01.jpg.jpg' style='width: 300px; height: 225px; float: right;' title='Parasitic wasp from http://www.ars.usda.gov/is/graphics/photos/index.html

 

Image Number K7867-1

A quarter-inch-long parasitic wasp, Peristenus digoneutis, prepares to lay an egg in a tarnished plant bug nymph. Photo by Scott Bauer.

(c) Ellmist @ Wikipedia

' alt='parasitic wasp' > wasps.  So the pea plant attracts in a particular wasp adapted entirely to feeding on that particular pea aphid.  And in fact, the wasp can find the plant that is being fed on by just this host using particular chemicals associating with that interaction.  Unfortunately, your horse-chestnut leaf miner is actually attracting quite a range of wasps.  There’s nothing really specific yet.  We hope we’ll get a very specific wasp for it eventually.

Sarah -   And is it just insects that the plants look to for help?  Do they recruit anything else like bacteria or fungi?

John -   Yes, it’s a more sophisticated process and less understood at the moment but we think it’s probably true of other antagonistic organisms.  These are multitrophic interactions and can get very complicated but I think we should stress that the parasitic wasps, they can do a spectacular job.  They do it naturally but as I said, they do it rather late in the day and that’s where some science and technology comes in to try and improve the way that they find their pests – our pests and their food.

Sarah -   So, what sort of time scale are look at here?  Are we looking at hours? Days?

John -   Yes, as soon as the plant is fed upon by the herbivore the plants starts to go into various defensive modes.  And it can in fact herbivore itself but if those processes start to take place as soon as the insect has bitten or has punctured, the cell sap system, as soon as that process starts to operate then these signals start to come out.  And these could be picked up by the parasitic wasps on their own antenna in fact.  And then they can start to forage for the host.

Sarah -   And how do – does it affect just plant that’s being munched on or does it affect the other plants around it?

John -   Well very recently we, and various labs around the world, have found out that not only is the plant signalling to this sort of higher trophic level for help but it’s also signalling to other plants particularly of the same species.  And so it can switch on defence in adjacent plants prior to them being attacked.

Sarah -   And you mentioned that science comes in to this to sort of bring down the time of response, how can we take advantage of this response in plants?

John -   Well, we can try and breed it in.  In fact, very recently we’ve Maizepublished a paper showing that the open-pollinating varieties of maize, the land raises of maze can do this kind of job really very well.  They can even do it when the eggs are laid on their leaves by stem borer moths.  And the eggs caused the plant to send out signals that attract in not just egg parasite but larval parasites.  They’re really smart these plants are.  Now, we can breed that in but we need to know a little bit more about the chemistry, which we are working on at the moment, so we can give a very simple protocol for African maize breeders to use in choosing this trait.  We also hope it will be useful back in hybrid maize which seems to lost this ability all together to make better hybrid maize varieties.

Sarah -   So, is this something that we’re already seeing going into production?  Are we seeing trials of this sort of modified?

John -   Well, we’ve already used plants that can do it but we haven’t done any improvement of this using breeding.  What we’re doing at the moment in our own agricultural research programs is to try and use GM to give the parasites a better cue for coming in and looking for aphids in this case.  So next year, we’ve just received field trial clearance to do some trials, after a very, very successful laboratory results on modifying wheat plant to produce the aphid alarm pheromone the thermo. 

Now, this is a pheromone which is a signal from members of the same species which causes the aphids to disperse when they’re attacked but it also attracts in these parasitic wasps. And so, we will actually have experimental plots with full GM containment next year,  wheat that can produce not only a frightening signal for aphids but one which will attract in later birds as predators but more particularly parasitic wasps to attack the aphids as they try to build up their population and damage the crop.

Sarah -   Well, it sounds like it could be really potentially good news for agriculture in the future.  Thanks John.  That’s Professor John Pickett from Rothamsted Research

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