Plant-insect interactions: an evolutionary arms race between two distinct defense mechanisms Marcia O. Mello and Marcio C. Silva-Filho M I N I R E V I

PlantPlant--insect interactionsinsect interactions: : an an evolutionary arms race between two evolutionary arms race between two

distinct defense mechanismsdistinct defense mechanisms

Marcia OMarcia O. . Mello and Marcio CMello and Marcio C. . SilvaSilva--FilhoFilho

M I N I R E V I E W

Braz. Plant Physiol. vol.14 (2), 2002

A CROSS-TALK BETWEEN A CROSS-TALK BETWEEN PLANTS AND INSECTSPLANTS AND INSECTS

PlantPlant--insect interactionsinsect interactions::an evolutionary an evolutionary arms race between two distinct defense arms race between two distinct defense mechanismsmechanisms

The coThe co--evolution theory proposed by evolution theory proposed by Ehrlich and Raven in 1964Ehrlich and Raven in 1964..

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A CROSS-TALK BETWEEN PLANTS AND INSECTSA CROSS-TALK BETWEEN PLANTS AND INSECTS

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Arm raceArm race

Co-evolution of plantsCo-evolution of plants

““an evolution change in a trait of the an evolution change in a trait of the individuals in one population in response individuals in one population in response to a trait of the individuals of a second to a trait of the individuals of a second population, followed by an evolution population, followed by an evolution response by the second population to the response by the second population to the changed to the first” Daniel Janzenchanged to the first” Daniel Janzen

Paul Feeny described this aspect of plant-Paul Feeny described this aspect of plant-insect relationships as an evolutionary insect relationships as an evolutionary arms racearms race

Copyright ©2008 American Society of Plant Biologists

Frost, C. J., et al. Plant Physiol. 2008;146:818-824

A conceptual model of defense priming in plant-herbivore interactions

EFN = Extrafloral nectar

A conceptual model of defenseA conceptual model of defense priming priming in in plantplant--herbivore interactionsherbivore interactions.. Where a Where a relaxed leaf is induced by herbivore feedingrelaxed leaf is induced by herbivore feeding. . Induced defenses include (1) a suite of Induced defenses include (1) a suite of chemical changes that are plant and chemical changes that are plant and situation specific and may include direct situation specific and may include direct defenses by synthesizing chemicals that are defenses by synthesizing chemicals that are toxic or unpalatable to the herbivoretoxic or unpalatable to the herbivore. . Induced defenses may also include(2) Induced defenses may also include(2) indirect defenses such as the production of indirect defenses such as the production of volatile compounds or EFN, both of which volatile compounds or EFN, both of which can attract natural enemies of the can attract natural enemies of the herbivoresherbivores.. ..

Primed StatePrimed StateSome of the chemical changes to the wounded leaf may act Some of the chemical changes to the wounded leaf may act as wound signals to undamaged regions within the plant or as wound signals to undamaged regions within the plant or to adjacent plantsto adjacent plants. . The wound signals include internal signals such as JA or The wound signals include internal signals such as JA or external signals such as volatilesexternal signals such as volatiles. . The recognition of these signals may initiate priming, which The recognition of these signals may initiate priming, which evidently comprises changes at the molecular level and evidently comprises changes at the molecular level and leads to a soleads to a so--called called primed stateprimed state in undamaged leaves in undamaged leaves. . Leaves in a Leaves in a primed stateprimed state are then able, by mechanisms are then able, by mechanisms that are poorly understood, to that are poorly understood, to respond more quicklyrespond more quickly or or vigorously to herbivore attack should such an attack occurvigorously to herbivore attack should such an attack occur. . But, primed leaves theoretically pay fewer costs relative to But, primed leaves theoretically pay fewer costs relative to a fully induced defense in the event that they do not a fully induced defense in the event that they do not actually experience herbivoryactually experience herbivory. . TFs, Transcription factorsTFs, Transcription factors. .

Plant responses to insect attackPlant responses to insect attack

Plants produce chemicals for defense Plants produce chemicals for defense purposes in two different ways; first, as purposes in two different ways; first, as constitutiveconstitutive substances to repel herbivores substances to repel herbivores through direct toxicity or by reducing the through direct toxicity or by reducing the digestibility of plant tissues and second, as digestibility of plant tissues and second, as inducible inducible substances synthesized in substances synthesized in response to tissue damage by herbivoresresponse to tissue damage by herbivores. . These strategies are able to prevent most These strategies are able to prevent most of the herbivores although there are a of the herbivores although there are a reduced number of insects that are able to reduced number of insects that are able to adapt to specific plant speciesadapt to specific plant species..

Induce mechanismsInduce mechanismsPlantPlant--insect interaction is a dynamic system, insect interaction is a dynamic system, subjected to continual variation and changesubjected to continual variation and change. . In order to reduce insect attack, plants In order to reduce insect attack, plants developed different defense mechanisms developed different defense mechanisms including chemical and physical barriers including chemical and physical barriers such as the induction of such as the induction of defensive proteinsdefensive proteins ((Haruta et alHaruta et al.., 2001, 2001)), , volatiles thatvolatiles that attract attract predatorspredators of the insect herbivores of the insect herbivores ((Birkett et Birkett et alal.., 2000, 2000)), , secondary metabolitessecondary metabolites ((Baldwin, Baldwin, 2001 and references herein; Kliebenstein et 2001 and references herein; Kliebenstein et alal.., 2001, 2001) ) and and trichome densitytrichome density ((Fordyce Fordyce and Agrawal, 2001and Agrawal, 2001) )

Insects overcomeInsects overcome

Insects developed strategies to Insects developed strategies to overcome plant barriers such as overcome plant barriers such as detoxification detoxification of toxic compounds of toxic compounds ((Scott and Wen, 2001Scott and Wen, 2001)), , avoidanceavoidance mechanisms mechanisms ((Zangerl, 1990Zangerl, 1990)), , sequestrationsequestration of poison of poison ((Nishida, Nishida, 2002 and references herein2002 and references herein) ) and and alteration of gene expressionalteration of gene expression pattern pattern ((Silva et alSilva et al.., 2001, 2001))

Secondary metabolites Secondary metabolites functions in the plantsfunctions in the plants

Secondary metabolites perform useful Secondary metabolites perform useful functions for the plant acting either in an functions for the plant acting either in an inducible or constitutive mannerinducible or constitutive manner. . Some Some compounds are (1) compounds are (1) plant growthplant growth regulators regulators while others (2) act as while others (2) act as chemical signalschemical signals in in the ecosystem, (3) the ecosystem, (3) antibiosis agentsantibiosis agents, (4) , (4) transport and storagetransport and storage of carbon and of carbon and nitrogen molecules which are directly nitrogen molecules which are directly involved in the plant primary metabolism involved in the plant primary metabolism

Secondary metabolites Secondary metabolites functions against insectsfunctions against insects

Secondary plant compounds are Secondary plant compounds are involved in plant defense against involved in plant defense against insect herbivores acting as insect insect herbivores acting as insect repellents, feeding inhibitors andrepellents, feeding inhibitors and//or or toxinstoxins. . In this paper, we have In this paper, we have classified these toxic compounds into classified these toxic compounds into chemicalchemical--derived substances and derived substances and proteinprotein--derived moleculesderived molecules


The emission of volatile compounds is The emission of volatile compounds is another important mechanism another important mechanism affecting the behavior of insects affecting the behavior of insects searching for foodsearching for food. . Odors from plants Odors from plants are one of the primary cues that are one of the primary cues that insects use to find the host plantinsects use to find the host plant..

Plant responses to insect attackPlant responses to insect attack The presence of chemical volatile The presence of chemical volatile compounds in plants indicates a double compounds in plants indicates a double meaningmeaning. . First, they can repel a wide range First, they can repel a wide range of potential herbivores due to the nature of of potential herbivores due to the nature of toxic compounds released in the airtoxic compounds released in the air. . Second, Second, they have the property of attracting a small they have the property of attracting a small number of specialized pest species and also number of specialized pest species and also of acting as an indirect plant defense of acting as an indirect plant defense mechanism by attracting other insects that mechanism by attracting other insects that prey on or parasitize the herbivores prey on or parasitize the herbivores

Plant responses to insect attackPlant responses to insect attack According to Kessler and Baldwin According to Kessler and Baldwin ((20012001)), the , the volatilevolatile cocktail released by tobacco plants cocktail released by tobacco plants attracts predatoryattracts predatory bugs to tobacco hornworm bugs to tobacco hornworm eggs and eggs and feeding larvae dramatically increasingfeeding larvae dramatically increasing the predation ratesthe predation rates. . Furthermore, these released Furthermore, these released volatiles volatiles decrease oviposition ratesdecrease oviposition rates from adult from adult moths since adults moths since adults avoid plantsavoid plants on which on which predators are likely to be present, predators are likely to be present, decreasing decreasing herbivore loads by 90%herbivore loads by 90%. . Plant volatiles may also Plant volatiles may also act as act as signals between plantssignals between plants, where volatiles , where volatiles from a damaged tissue from a damaged tissue induce defenseinduce defense response response in neighboring in neighboring undamaged plantsundamaged plants


The induced resistance allows maximum The induced resistance allows maximum expression of the plant's potential to expression of the plant's potential to tolerate either herbivory or diseasetolerate either herbivory or disease. . This has This has been experimentally shown by the been experimentally shown by the observation that insect feeding induces the observation that insect feeding induces the production of production of phytoalexinsphytoalexins, which have , which have antimicrobial properties antimicrobial properties

((PhytoalexinsPhytoalexins are antibiotics produced by are antibiotics produced by plants that are under attack )plants that are under attack )


In addition, intact cells surrounding In addition, intact cells surrounding areas of damaged tissue form physical areas of damaged tissue form physical barriers to restrict pathogen invasion barriers to restrict pathogen invasion by by strengtheningstrengthening the cell wall, the cell wall, sealingsealing the wound site or the wound site or isolating isolating the cells the cells from their neighbors from their neighbors

HerbivoryHerbivory//wounding signaling pathwayswounding signaling pathways

The early events detected after wounding The early events detected after wounding include ion fluxes across the plasma include ion fluxes across the plasma membrane, changes in cytoplasmic membrane, changes in cytoplasmic calcium concentration, generation of calcium concentration, generation of active oxygen species and changes in active oxygen species and changes in protein phosphorylation patterns protein phosphorylation patterns ((de de Bruxelles and Roberts, 2001Bruxelles and Roberts, 2001))

These events lead to:- These events lead to:- 1.1. cell wall fortification at the wound site cell wall fortification at the wound site 2.2. alterations in metabolism and the alterations in metabolism and the

generation of signalsgeneration of signals, which regulate , which regulate defense gene expressiondefense gene expression..

HerbivoryHerbivory//wounding signaling wounding signaling pathwayspathways

The signals that travel from damaged tissue The signals that travel from damaged tissue throughout the plant include throughout the plant include pectic pectic fragmentsfragments derived from the plant cell wall, derived from the plant cell wall, jasmonic acid jasmonic acid ((JAJA)), , abscisic acid abscisic acid ((ABAABA)), , ethyleneethylene, , electrical potentialelectrical potential, intermediates , intermediates of the of the octadecanoidoctadecanoid pathway pathway ((HPOTre, 12-HPOTre, 12-oxooxo--PDAPDA)), , systeminsystemin ((an 18-amino acid an 18-amino acid polypeptide isolated from leaves of tomato polypeptide isolated from leaves of tomato plantsplants) ) and other plant polypeptide and other plant polypeptide molecules molecules ((Ryan and Pearce, 2001Ryan and Pearce, 2001).).


The woundThe wound--induced increase in JA induced increase in JA levels is amplified by herbivore feeding levels is amplified by herbivore feeding and by the application of larval oral and by the application of larval oral secretions or regurgitant to secretions or regurgitant to mechanical wounds, as well as the mechanical wounds, as well as the release of volatiles that attract release of volatiles that attract parasitoids in an indirect defense parasitoids in an indirect defense mechanism mechanism


Two known products that trigger the Two known products that trigger the synthesis and emission of volatile synthesis and emission of volatile chemical signals have been reported chemical signals have been reported so farso far: : a b-glucosidase from a b-glucosidase from Pieros Pieros brassicaebrassicae caterpillars (Mattiacci et caterpillars (Mattiacci et al., 1995) and a low-Mr fatty acid al., 1995) and a low-Mr fatty acid derivative, N-(17-hydroxylinolenoyl)-derivative, N-(17-hydroxylinolenoyl)-L-Gln (volicitin) from beet army-worm L-Gln (volicitin) from beet army-worm caterpillars (Alborn et al., 1997). caterpillars (Alborn et al., 1997).


After leaf damage and introduction of the After leaf damage and introduction of the elicitors. elicitors. SysteminSystemin is released into the vascular is released into the vascular system of damaged tissue activating the system of damaged tissue activating the octadecanoid signaling cascadeoctadecanoid signaling cascade. . Several Several reactions result in JA biosynthesis, up regulation reactions result in JA biosynthesis, up regulation of the synthesis of signal pathway genes of the synthesis of signal pathway genes ((early early genesgenes) ) in the vascular bundles, and H2O2, which in the vascular bundles, and H2O2, which is a second messenger, that activates putative is a second messenger, that activates putative defense genes (late genes) such as the defense genes (late genes) such as the antifeedant proteinase inhibitor genes in antifeedant proteinase inhibitor genes in mesophyll cells (de Bruxelles and Roberts, 2001; mesophyll cells (de Bruxelles and Roberts, 2001; Orozco-Cárdenas et al., 2001) Orozco-Cárdenas et al., 2001)


Even though JA is thought to be the Even though JA is thought to be the predominant defense signal against predominant defense signal against chewing insects, ethylene seems to chewing insects, ethylene seems to be an important defense modulator be an important defense modulator in different plant species, acting in different plant species, acting concomitantly or sequentially with JA concomitantly or sequentially with JA in receiver leaves in receiver leaves ((Arimura et alArimura et al.., , 2000; Stotz et al2000; Stotz et al.., 2000, 2000).).

HerbivoreHerbivore--induced plant gene expressioninduced plant gene expression

Induced responses to herbivory can(1) reduce the Induced responses to herbivory can(1) reduce the preference and performance of a variety of preference and performance of a variety of herbivores,(2) increase competitive ability against herbivores,(2) increase competitive ability against nonnon--induced neighboring plants, (3) increase induced neighboring plants, (3) increase tolerance to subsequent herbivory and, (4) tolerance to subsequent herbivory and, (4) ultimately, increase plant fitness in natural ultimately, increase plant fitness in natural environments environments ((Agrawal, 2000Agrawal, 2000). ). In addition, this In addition, this represents an adaptive plasticity since the represents an adaptive plasticity since the induced phenotype has greater fitness induced phenotype has greater fitness under strong herbivory while the nonunder strong herbivory while the non--induced phenotype shows the greatest induced phenotype shows the greatest fitness in an environment with low fitness in an environment with low herbivoryherbivory..

HerbivoreHerbivore--induced plant gene induced plant gene expressionexpression

Several Several genesgenes are selectively activated by are selectively activated by volicitin, systemin or volatiles released from volicitin, systemin or volatiles released from attacked plants attacked plants The genes encoding indole-3-glycerol phosphate The genes encoding indole-3-glycerol phosphate lyase lyase ((IGLIGL)), that catalyses the formation of free , that catalyses the formation of free indol, an important step in the formation of indol, an important step in the formation of defense secondary metabolites defense secondary metabolites and allene synthase and allene synthase (AOS(AOS), that catalyzes the ), that catalyzes the first step in JA biosynthesisfirst step in JA biosynthesisInterestingly, another class of defense proteins, Interestingly, another class of defense proteins, the Hevein-like protein the Hevein-like protein (HEL(HEL), was only induced ), was only induced after insect feeding. after insect feeding.

Storage proteins and plant defenseStorage proteins and plant defense

The synthesis and accumulation of a The synthesis and accumulation of a variety of storage proteins have been variety of storage proteins have been shown to be closely related to plant shown to be closely related to plant defense since several of these proteins defense since several of these proteins present entomotoxic properties such as a-present entomotoxic properties such as a-amylase and proteinase inhibitors, lectins amylase and proteinase inhibitors, lectins and globulins. These proteins are usually and globulins. These proteins are usually present in present in seeds seeds and vegetative organs of and vegetative organs of leguminous plants (Negreiros et al., 1991; leguminous plants (Negreiros et al., 1991; Sales et al., 2000; Franco et al., 2002).Sales et al., 2000; Franco et al., 2002).


Proteinase inhibitor Proteinase inhibitor ((PIPI) ) levels in plant levels in plant leaves are normally low but they can be leaves are normally low but they can be actively induced to high levels when plants actively induced to high levels when plants are attacked by insects are attacked by insects

In addition to a local inducible synthesis of In addition to a local inducible synthesis of PIs, it was demonstrated that specific PIs, it was demonstrated that specific signals from the damaged tissue are signals from the damaged tissue are transported via phloem and stimulate the transported via phloem and stimulate the synthesis of PIs throughout the plant synthesis of PIs throughout the plant


ProteinaseProteinase inhibitors act by causing inhibitors act by causing an amino acid deficiency influencing an amino acid deficiency influencing the insect growth, development and the insect growth, development and eventually causing their death either eventually causing their death either by inhibition of gut proteinases or by inhibition of gut proteinases or due to a massive overproduction of due to a massive overproduction of the digestive enzymes, reducing the the digestive enzymes, reducing the availability of essential amino acids availability of essential amino acids for the production of other proteins for the production of other proteins Slowing herbivore growth.. Slowing herbivore growth.. predatorspredators


During evolution, plants and insects During evolution, plants and insects developed ecological, physiological developed ecological, physiological and biochemical mechanisms to and biochemical mechanisms to weaken the effect of insect weaken the effect of insect proteinases and plant proteinase proteinases and plant proteinase inhibitors, respectively inhibitors, respectively


LectinsLectins are carbohydrate are carbohydrate--binding binding proteins usually found in legume proteins usually found in legume plants, mainly in the storage organs plants, mainly in the storage organs and protective structures and protective structures The common bean The common bean ((Phaseolus Phaseolus vulgarisvulgaris) presents three classes of ) presents three classes of these insecticidal proteins, these insecticidal proteins, phytohemagglutinins, arcelins and a-phytohemagglutinins, arcelins and a-amylase amylase


VicilinsVicilins, which belong to the globulin , which belong to the globulin family, are another class of storage family, are another class of storage proteins found in leguminous seeds proteins found in leguminous seeds ((Oliveira et alOliveira et al.., 1999, 1999). ). They bind strongly They bind strongly to several chitinto several chitin--containing structures containing structures found in insect midguts and cell walls or found in insect midguts and cell walls or plasma membranes of filamentous fungi plasma membranes of filamentous fungi and yeast, interfering negatively in the and yeast, interfering negatively in the growth and development of the invader growth and development of the invader organism organism

Insect response mechanismsInsect response mechanisms

Insect herbivores present Insect herbivores present complementary adaptations as a complementary adaptations as a response to each defensive response to each defensive adaptation in host plants adaptation in host plants

Insect response mechanismsInsect response mechanismsInsects possess a powerful assemblage of Insects possess a powerful assemblage of enzymes that constitute their defense enzymes that constitute their defense against chemical toxicantsagainst chemical toxicants. .

1- One of the strategies to overcome this 1- One of the strategies to overcome this problem is the detoxification of defense problem is the detoxification of defense chemicals by oxidation, reduction, chemicals by oxidation, reduction, hydrolysis or conjugation of molecules hydrolysis or conjugation of molecules

Insect response mechanismsInsect response mechanisms

2- Another manner for insects to avoid 2- Another manner for insects to avoid plant poisons is by sequestering and plant poisons is by sequestering and deploying the poisons for their own deploying the poisons for their own pheromone system and defensepheromone system and defense

3- Simply feeding on parts of the plant 3- Simply feeding on parts of the plant that lack these compounds that lack these compounds

Insect response mechanismsInsect response mechanismsExamplesExamples

1- Lepidoptera sequesters plant secondary metabolites such some terpenes, 1- Lepidoptera sequesters plant secondary metabolites such some terpenes, phenols and many nitrogenphenols and many nitrogen--containing compounds and uses them as toxic containing compounds and uses them as toxic or unpalatable to predators or unpalatable to predators

2- An example of this adaptation is illustrated by the tobacco hornworm2- An example of this adaptation is illustrated by the tobacco hornworm. . This This insect accumulates the nicotine synthesized by tobacco plants in its own insect accumulates the nicotine synthesized by tobacco plants in its own body which is toxic to most insects and uses it as a deterrent to parasitoids body which is toxic to most insects and uses it as a deterrent to parasitoids ((de Bruxelles and Roberts, 2001de Bruxelles and Roberts, 2001). ).

3- The presence of caffeine, the major alkaloid in coffee, is not effective 3- The presence of caffeine, the major alkaloid in coffee, is not effective against the against the PerileucopteraPerileucoptera coffeellacoffeella larvae. This suggests that insect larvae. This suggests that insect adaptation to this potentially toxic compound was probably due to a adaptation to this potentially toxic compound was probably due to a tolerance mechanismtolerance mechanism

3- An interesting mechanism of avoiding toxic substances was observed by 3- An interesting mechanism of avoiding toxic substances was observed by Musser et al. (2002). In their research, glucose oxidase, one of the principal Musser et al. (2002). In their research, glucose oxidase, one of the principal components of components of Helicoverpa zeaHelicoverpa zea saliva, was detected as responsible for saliva, was detected as responsible for suppressing induced resistance in tobacco plants. They infer that this suppressing induced resistance in tobacco plants. They infer that this enzyme may prevent the induction of nicotine by inhibition of the signaling enzyme may prevent the induction of nicotine by inhibition of the signaling pathway.pathway.

4- Symbiont microorganisms 4- Symbiont microorganisms

Insect response mechanismsInsect response mechanisms5-Protein inhibitors circumvented by herbivore insects 5-Protein inhibitors circumvented by herbivore insects

A- Patankar et alA- Patankar et al. (. (20012001) ) showed that showed that Helicoverpa armigeraHelicoverpa armigera larvae is able to overcome the effect of various host plant larvae is able to overcome the effect of various host plant PIs by altering its midgut composition after PIs ingestion, PIs by altering its midgut composition after PIs ingestion,

B-Patankar et alB-Patankar et al. (. (20012001) ) showed that showed that Helicoverpa armigeraHelicoverpa armigera larvae is able to overcome the effect of various host plant larvae is able to overcome the effect of various host plant PIs by altering its midgut composition after PIs ingestion, PIs by altering its midgut composition after PIs ingestion,

C- MazumdarC- Mazumdar--Leighton and Broadway Leighton and Broadway ((2001a2001a) ) showed that showed that lepidopteran insects have constitutive trypsins and trypsins lepidopteran insects have constitutive trypsins and trypsins induced after ingestion of PIs that are insensitive to the induced after ingestion of PIs that are insensitive to the inhibitorsinhibitors. . Similar results were also reported for Similar results were also reported for chymotrypsins chymotrypsins

Generalists x SpecialistsGeneralists x Specialists

Generalist insect herbivores rear on Generalist insect herbivores rear on a wide variety of plant species and a wide variety of plant species and their adaptive mechanisms are more their adaptive mechanisms are more complex since polyphagous insects complex since polyphagous insects tend to respond to a large array of tend to respond to a large array of different plant chemicals and different plant chemicals and proteinsproteins..


Specialist insect herbivores hosting Specialist insect herbivores hosting only on a few related plant species only on a few related plant species might be expected to have a more might be expected to have a more efficient form of adaptation, either efficient form of adaptation, either involving the production of large involving the production of large quantities of an enzyme to detoxify quantities of an enzyme to detoxify their food, or evolve storage their food, or evolve storage mechanisms mechanisms


The majority of insect herbivores are The majority of insect herbivores are relative specialists, using a restricted relative specialists, using a restricted number of hosts with similar number of hosts with similar phytochemicals and taking phytochemicals and taking advantage to colonize an open niche advantage to colonize an open niche

Generalists x SpecialistsGeneralists x Specialistsspecialist herbivores adapted to plant chemical specialist herbivores adapted to plant chemical defenses developing mechanisms that use these defenses developing mechanisms that use these chemicals as attractantschemicals as attractants. . These insects frequently These insects frequently detoxify or sequester plant defense compounds detoxify or sequester plant defense compounds and, sometimes, they result in protection against and, sometimes, they result in protection against parasitoids and predators being used as toxic or parasitoids and predators being used as toxic or unpalatable at defenseunpalatable at defense. . Sequestering specialists Sequestering specialists have developed the ability to incorporate these have developed the ability to incorporate these compounds with relative impunity, ingesting, compounds with relative impunity, ingesting, transporting and depositing the substances to be transporting and depositing the substances to be sequestered in particular sites of the larvae, adult sequestered in particular sites of the larvae, adult body and even in the eggs body and even in the eggs

Generalists x SpecialistsGeneralists x SpecialistsFurther, these compounds are of great Further, these compounds are of great importance since they provide insects with importance since they provide insects with signals for identification of the host, turning the signals for identification of the host, turning the process of host finding at feeding and oviposition process of host finding at feeding and oviposition rapid and efficient rapid and efficient secondary metabolites of a nonsecondary metabolites of a non--host plant have host plant have the potential to deter specialists that show an the potential to deter specialists that show an equal sensitivity to these phytochemicalsequal sensitivity to these phytochemicals. . The The ability to choose superior hosts is shown to be ability to choose superior hosts is shown to be greater in specialists than in relative generalists greater in specialists than in relative generalists in the presence of a choice of mixedin the presence of a choice of mixed--quality hosts quality hosts

ConclusionsConclusionsThe coThe co--evolution of plants and insects is evolution of plants and insects is very intriguingvery intriguing. . Plants have developed Plants have developed efficient mechanisms to protect them efficient mechanisms to protect them against herbivory while insects have found against herbivory while insects have found diverse ways of avoiding negative effects diverse ways of avoiding negative effects of their host plants defense mechanismsof their host plants defense mechanisms. . Even though many workers have Even though many workers have attempted to study plantattempted to study plant--insect insect interaction, our knowledge is still limited interaction, our knowledge is still limited

ConclusionsConclusions

The better understanding of this The better understanding of this process will allow us to achieve more process will allow us to achieve more effective methods for the biological effective methods for the biological control of insect pests with natural control of insect pests with natural products by the development of new products by the development of new plant varieties with enhanced plant varieties with enhanced chemical defenses chemical defenses

Documents

Plant-insect interactions: an evolutionary arms race between two distinct defense mechanisms Marcia O. Mello and Marcio C. Silva-Filho M I N I R E V I