The struggle against crop pests by means that are directly inspired by nature, while minimising the use of pesticides, sometimes leads to perplexing discoveries. For example, when we see that aphids and their natural predators (onion bulb flies and lady bugs), are in some respects much closer than was previously thought. How then, in the context of integrated pest control, is it possible to eliminate one of them without affecting the other?
Communication means survival. What seems obvious for mankind is even more so for insects which are located lower down on the food chain. Without an elaborate communication system, it is impossible for them to transmit information about the presence of food in their environment or the appearance of predators ready to swoop on them.
Why this interest in pheromones? Quite simply because these volatile molecules play a fundamental role in the communication between insects and because their biological system shows itself to be extremely sensitive and selective with regard to pheromones : often only one molecule is required to set off a very precise phsiological answer and behaviour. In the context of perfecting new methods of combat in the fight against aphids, work on the (E)- β-farnesene (EBF) involves opening the potentially enormous field of discoveries that can be used in integrated pest management of aphids. This field is being developed as a series of techniques which favours using natural methods and reducing the use of insecticides to the strict minimum, for example, by preventing the pests from communicating effectively between themselves in case of alert or when they are searching for a sexual partner, or by helping the predators to locate their prey.
Recognizing odors
In collaboration with the Chemical ecology and olfaction group of the University of California(Davis, USA), Sophie Vandermoten, Postdoctoral researcher (FNRS) at the Functional and Evolutionary Entomology Unitof Gembloux Agro-Bio Tech, focussed her interest more particularly on the EBF perception mechanism in the grain aphid, Sitobion avenae, known to be an important pest in cereal crops. In 2009, British researchers had highlighted the fact that in a related species (the pea aphid), the first step in EBF perception by the insect is done via recognition of this molecule by an Odorant Binding Protein (OBP) which is specific to it. What are these OBPs made up of ? Present in the lymph of antennae, these little globular proteins play a fundamental role in the olfaction of insects by linking itself to the odorous molecules, the pheromones, by carrying them to the sensorial receptors of the organism. "Up to now we thought that the OBPs were not specific to particular odours.
(1) The results have been obtained by means of different techniques commonly used in molecular biology. Firstly, thanks to the technique of Polymerase Chain Reaction (PCR), it has been possible to locate and amplify the gene coding for the OBP of interest in the three selected species of insects. Secondly, the gene of interest is used to produce the protein (in the present case: the OBP) that it encodes. Here this production was achieved by using bacteria (E. coli), a relatively simple and well-known system of production. The recombinant proteins were then purified and used in such a way as to evaluate their affinity for the different odorous molecules. These, which include the EBF, were chosen based on two criteria : on one hand, to bring about a behavioural response in the selected species and, on the other, to possess a chemical structure close to that of the EBF.
Citation: Vandermoten S, Francis F, Haubruge E, Leal WS (2011) Conserved Odorant-Binding Proteins from Aphids and Eavesdropping Predators. PLoS ONE 6(8):e23608. doi:10.1371Contacts and sources:
Lady bug and aphids
Communication between insects
At the Functional and Evolutionary Entomology Unitof Gembloux Agro-Bio Tech - University of Liège, a lot of attention is being paid to the aphid. This hemiptera is not only the dread of gardeners caring for their rose bushes. A great lover of vegetable sap and a carrier of viral diseases, it is also capable of causing great damage to market garden products, fruit, cereals as well as forests when in sufficient numbers. For several years, researchers at the unit have focussed their interest on a chemical compound, (E)-β-farnesene, which in many species of aphids, constitutes the alarm pheromone (See article entitled : The aphids betrayed by their odours). In addition, this same component has the particularity of attracting some of their natural enemies such as ladybugs and Marmalade hoverfly.
At the Functional and Evolutionary Entomology Unitof Gembloux Agro-Bio Tech - University of Liège, a lot of attention is being paid to the aphid. This hemiptera is not only the dread of gardeners caring for their rose bushes. A great lover of vegetable sap and a carrier of viral diseases, it is also capable of causing great damage to market garden products, fruit, cereals as well as forests when in sufficient numbers. For several years, researchers at the unit have focussed their interest on a chemical compound, (E)-β-farnesene, which in many species of aphids, constitutes the alarm pheromone (See article entitled : The aphids betrayed by their odours). In addition, this same component has the particularity of attracting some of their natural enemies such as ladybugs and Marmalade hoverfly.
Why this interest in pheromones? Quite simply because these volatile molecules play a fundamental role in the communication between insects and because their biological system shows itself to be extremely sensitive and selective with regard to pheromones : often only one molecule is required to set off a very precise phsiological answer and behaviour. In the context of perfecting new methods of combat in the fight against aphids, work on the (E)- β-farnesene (EBF) involves opening the potentially enormous field of discoveries that can be used in integrated pest management of aphids. This field is being developed as a series of techniques which favours using natural methods and reducing the use of insecticides to the strict minimum, for example, by preventing the pests from communicating effectively between themselves in case of alert or when they are searching for a sexual partner, or by helping the predators to locate their prey.
Recognizing odors
In collaboration with the Chemical ecology and olfaction group of the University of California(Davis, USA), Sophie Vandermoten, Postdoctoral researcher (FNRS) at the Functional and Evolutionary Entomology Unitof Gembloux Agro-Bio Tech, focussed her interest more particularly on the EBF perception mechanism in the grain aphid, Sitobion avenae, known to be an important pest in cereal crops. In 2009, British researchers had highlighted the fact that in a related species (the pea aphid), the first step in EBF perception by the insect is done via recognition of this molecule by an Odorant Binding Protein (OBP) which is specific to it. What are these OBPs made up of ? Present in the lymph of antennae, these little globular proteins play a fundamental role in the olfaction of insects by linking itself to the odorous molecules, the pheromones, by carrying them to the sensorial receptors of the organism. "Up to now we thought that the OBPs were not specific to particular odours.
In other words that they played a simple role of undifferentiated transportation towards the neurones of the insect. Yet here, while working on Sitobion avenae, I noticed that they played a role in the discrimination of odours. The OBPs are able to ‘filter’ them, to recognise them,’’explains Sophie Vandermoten. The results of this research were published in PLOs ONE. This specificity of EBFrecognition by a particular OBP is clearly of great importance to agriculture. It could be used in the perfection of a method for fighting the aphid pest exclusively without having an impact on the other species involved in the agricultural ecosystem concerned.
The drawback is that the same work (1) has yielded another result which complicates matters: the very important similarity between the OBP of the aphid studied and the OBP of its two main predators: the Marmalade hoverfly (Episyrphus balteatus) and the multicolored Asian lady beetle (Harmonia axyridis)."These OBPs are known to be protein chains composed of up to around 150 amino acids, By comparing the OBP sequences of the three insects selected for the research, I noticed that only two to six amino acids were different. This minimal difference was a great surprise because we thought up to the present that the OBPs varied strongly from one order of insects to another. Yet here, the molecule is almost identical in the three species belonging to different orders : The coleoptera (ladybugs), the diptera (syrphid) and the hemiptera (aphids).’’ Explains the young researcher.
The drawback is that the same work (1) has yielded another result which complicates matters: the very important similarity between the OBP of the aphid studied and the OBP of its two main predators: the Marmalade hoverfly (Episyrphus balteatus) and the multicolored Asian lady beetle (Harmonia axyridis)."These OBPs are known to be protein chains composed of up to around 150 amino acids, By comparing the OBP sequences of the three insects selected for the research, I noticed that only two to six amino acids were different. This minimal difference was a great surprise because we thought up to the present that the OBPs varied strongly from one order of insects to another. Yet here, the molecule is almost identical in the three species belonging to different orders : The coleoptera (ladybugs), the diptera (syrphid) and the hemiptera (aphids).’’ Explains the young researcher.
Fascinating ? Without a doubt yes in terms of fundamental research. But it is necessary to perfect a concrete weapon in the fight against the aphid. Yet, this result represents nothing other than a great challenge because by attacking the pest (by disturbing the protein which carries the message of alert to his fellow creatures : watch out there is a predator nearby !), we could, if we are not careful, contribute to an exactly opposite effect ; that is to say, frighten off the predators, those very ones that it is generally neccessary to attract to their prey, as integrated pest control usually does !
Are these results frustrating? "This kind of ambivalence is not exceptional in research of this nature. This demonstration makes the case that it is better not to rush headlong into concrete applications, but to take a step back whilst carefully assessing the balance between the benefits and the later impacts upon the species that are not being targeted. The development of new methods of combatting a given crop pest, targeting a biochemical mechanism as vital as olfaction can only be envisaged when we posess the fullest possible understanding of this mechanism.
Are these results frustrating? "This kind of ambivalence is not exceptional in research of this nature. This demonstration makes the case that it is better not to rush headlong into concrete applications, but to take a step back whilst carefully assessing the balance between the benefits and the later impacts upon the species that are not being targeted. The development of new methods of combatting a given crop pest, targeting a biochemical mechanism as vital as olfaction can only be envisaged when we posess the fullest possible understanding of this mechanism.
Sometimes, this can take more than ten years, or even an entire career", comments Sophie Vandermoten. It is for this purpose that a third laboratory, this time an Australian one, (Eskitis Institute for Cell & Molecular Therapies, Griffith University, Brisbane), has joined in the work. The objective is to crystallise this famous OBP and discover the key to its specificity for the EBF. It is only then that we will perhaps know how to direct the rest of the research in order to get rid of the grain aphid, and probably, dozens of other species of its fellow creatures.
Contacts and sources:
University of Liege(1) The results have been obtained by means of different techniques commonly used in molecular biology. Firstly, thanks to the technique of Polymerase Chain Reaction (PCR), it has been possible to locate and amplify the gene coding for the OBP of interest in the three selected species of insects. Secondly, the gene of interest is used to produce the protein (in the present case: the OBP) that it encodes. Here this production was achieved by using bacteria (E. coli), a relatively simple and well-known system of production. The recombinant proteins were then purified and used in such a way as to evaluate their affinity for the different odorous molecules. These, which include the EBF, were chosen based on two criteria : on one hand, to bring about a behavioural response in the selected species and, on the other, to possess a chemical structure close to that of the EBF.
Citation: Vandermoten S, Francis F, Haubruge E, Leal WS (2011) Conserved Odorant-Binding Proteins from Aphids and Eavesdropping Predators. PLoS ONE 6(8):e23608. doi:10.1371Contacts and sources:
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