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Augmentation, with synergists, of the effect of natural plant activators against pest aphids - PS2124

Crop plants are constantly under threat from a variety of pest insects, particularly aphids. Insecticides are usually very effective, but potentially can damage the environment via toxic residues and effects on non-target species. This, along with the development of insecticide resistant strains of pest species, has led to increased pressure to find alternative approaches to pest control that are more environmentally friendly. Integrated pest management (IPM) is a sustainable approach to managing pests by combining biological, cultural, physical and chemical tools in a way that minimizes economic, health, and environmental risks. It rationalises the use of insecticides by use of monitoring systems and conserves parasites and predators of pests as a means of natural biological control. However, IPM still relies to some extent on the use of conventional insecticides, and there is a need for additional tools in the IPM armoury.

One approach that may contribute to IPM is the development of methods to enhance plants’ natural defence. Plants have evolved sophisticated mechanisms with which to defend themselves against pests and pathogens when attacked. In addition, plants detect chemical signals from damaged neighbours and can thereby activate defence metabolism in anticipation of attack. A number of chemicals are able to 'switch on' plant defence pathways, maximising the production and release of chemicals within the plant that act against insect infestation. One such plant produced signal or plant activator, cis-jasmone (CJ), identified and investigated at Rothamsted in Defra-funded projects (PI0339, PS2101, PS2105) has been shown to have intricate effects on plant/pest/natural enemy (tritrophic) interactions. For example, exposure of crop plants to CJ has resulted in reduced aphid population development and caused plants to release distress signals that deter pest colonisation and attract aphid parasitoids in the same way as aphid-infested plants. Practical use of CJ has focussed on its application to a crop so as to trigger induction of plant defence, prior to aphid arrival, and a consistent reduction in numbers of cereal aphids has been achieved in replicated field trials, demonstrating its potential as a suitable component of IPM or other pest control strategies.

Plants treated with activators such as CJ produce defensive xenobiotics, which deleteriously affect pest insect development and fecundity and in some cases survival. However, exposure to toxins generally may enhance metabolic enzyme systems within insects, particularly non-specific esterases and microsomal oxidases, thereby reducing the effectiveness of natural plant defences. Enzyme-inhibiting synergists can prevent detoxification of synthetic insecticides and thus increase their potency. It is important that sufficient time is allowed for the enzymes to be detoxified, leaving the insect in a hypersensitive state before the toxin is delivered, an aspect known as temporal synergism. This approach also has the potential to enhance the potency of plant activators. Work in Defra-funded project PS2110 is already testing a synthetic plant activator DL-beta-aminobutyric acid (BABA) and the synergist piperonyl butoxide (PBO). Unlike CJ, BABA is rarely found naturally in plants and is more widely associated with priming of enhanced resistance to both biotic and abiotic stresses, particularly plant pathogens.Preliminary studies have demonstrated that the combination of enzyme inhibitor synergists with CJ results in a much greater reduction in population development of the aphid Myzus persicae on sweet pepper than either treatment alone. In this project we propose to exploit the potential of this approach by extending the study to include two plant activators in combination with two synergists against aphid pests of a major UK arable crop, wheat.

The aim of the project will be to optimise the natural plant defence chemistry by applying a plant activator, whilst at the same time maximising the inhibition of the insects’ defensive enzymes by the use of a synergist. A straight mixture of these two components may give the required effect, but it may be that the components will need to be applied separately, at different times, to achieve the optimum effect (temporal synergism). The different combinations of activator and synergist treatments will be tested, initially under laboratory conditions, against the grain aphid, Sitobion avenae, and the bird cherry-oat aphid, Rhopalosiphum padi on wheat. The study will then be extended to a field trial, where the most effective treatments will be tested against natural cereal aphid populations under field conditions, to demonstrate their potential for further investigation.
1.Investigate the effects of formulations of plant activators and synergists, including temporal parameters, alone and in combination in developmental bioassays against the pest aphid species Sitobion avenae on wheat. (Milestone 1)
2. Investigate the effects of formulations of plant activators and synergists, including temporal parameters, alone and in combination in developmental bioassays against the pest aphid species Rhopalosiphum padi on wheat. (Milestone 2)
3. Determine the effects of the best formulations of plant activators and synergists, identified in 1 & 2, on the volatile profile of wheat for potential effects on aphid and aphid parasitoid behaviour. (Milestone 3)
4. Determine the efficacy of the best formulations from 1 and 2 against natural populations of the target aphid species in a replicated plot field trial (Milestone 4)
Project Documents
• Final Report : Augmentation, with synergists, of the effects of natural plant activators against pest aphids   (588k)
Time-Scale and Cost
From: 2008

To: 2009

Cost: £143,027
Contractor / Funded Organisations
Rothamsted Research (BBSRC)
Biological Control              
Crop Pests              
Insecticide use              
Pest and Weed Control              
Pesticide use              
Plants and Animals              
Fields of Study
Pesticide Safety