المحاضرة الثانية Insect-Plant Interactions [email protected].

الثانية الثانية المحاضرة المحاضرة

Insect-Plant InteractionsInsect-Plant Interactions

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Numbers of herbivorous species in Numbers of herbivorous species in different ordersdifferent orders

Insect Insect orderorder

Total no. Total no. of speciesof species

Herbivorous speciesHerbivorous species

NoNo..%%

ColeopteraColeoptera3490003490001220001220003535LepidopteraLepidoptera119000119000119000119000100100DipteraDiptera11900011900035700357003030HymenopteraHymenoptera950009500010500105001111HemipteraHemiptera590005900053000530009090OrthopteraOrthoptera20000200001990019900100100TysanopteraTysanoptera50005000450045009090PhasmidaPhasmida2000200020002000100100 HM

Specialization vs Specialization vs Generalization Generalization MonophagousMonophagous

Insects feed on one or a few closely Insects feed on one or a few closely related species. Many lep. Larvae, related species. Many lep. Larvae, hemi. and coleopt. hemi. and coleopt.

Oligophagous feed on a number of Oligophagous feed on a number of plant species belonging to the same plant species belonging to the same plant family example plant family example Pieris brassicae Pieris brassicae feeds on plant of Brassicaceaefeeds on plant of Brassicaceae

Specialization vs Specialization vs GeneralizationGeneralization

PolyphagousPolyphagous

Insects feed on many plant Insects feed on many plant species belonging to different species belonging to different plant families.plant families.

Myzus persicaeMyzus persicae


Limitations!Limitations!

LimitationsLimitationsMonophagous and OilgophagousMonophagous and Oilgophagous Individuals of the same insect species may Individuals of the same insect species may

show different host-plant preferences in show different host-plant preferences in different area of its distribution, and even different area of its distribution, and even individuals belonging to same population individuals belonging to same population may be much more restricted in their choice.may be much more restricted in their choice.

It is more convenient to distinguish only It is more convenient to distinguish only specialistspecialist (Monophagous and Oilgophagous ) (Monophagous and Oilgophagous ) and and generalistgeneralist (Polyphagous) (Polyphagous)


Host-plant specialization is the rule Host-plant specialization is the rule rather than the exception. rather than the exception.

An inventory (list) of about 5000 An inventory (list) of about 5000 British herbivorous insects species British herbivorous insects species show that 80% of them should be show that 80% of them should be regards as specialists.regards as specialists.

76% of all British aphids are 76% of all British aphids are mnophagous, 18% are oligophagous, mnophagous, 18% are oligophagous, and only 6% are polyphagous.and only 6% are polyphagous.

Specialization vs Specialization vs GeneralizationGeneralizationGeneralists seem to be privileged Generalists seem to be privileged

compared with specialists because compared with specialists because they have access to a much broader they have access to a much broader food range!food range!

BUT, specialists need to make decisions BUT, specialists need to make decisions based on a smaller number of options based on a smaller number of options than generalists, thereby increasing than generalists, thereby increasing the efficiency of decision-making the efficiency of decision-making process in the former group.process in the former group.


Polyphahous insect species prefer Polyphahous insect species prefer certain plant species. So they are certain plant species. So they are discriminate in what they choose discriminate in what they choose from their acceptable host plant from their acceptable host plant range.range.

Oilgophagous species are Oilgophagous species are indscriminateindscriminate……. .


The gypsy moth exhibits more The gypsy moth exhibits more discrimination prefers full-grown discrimination prefers full-grown leaves, leaves grown on sunny leaves, leaves grown on sunny side, in southern side of treeside, in southern side of tree

Age of the leavesAge of the leaves

Exposed to sunlightExposed to sunlight

Direction Direction

Specialization vs Specialization vs GeneralizationGeneralizationIt has been argued that some polyphagous It has been argued that some polyphagous

insects should be considered as insects should be considered as monophagous when their host plant monophagous when their host plant selection based on a selection based on a specific type of specific type of plant chemicalplant chemical..

1.1. Larvae of cabbage white butterfly feed on Larvae of cabbage white butterfly feed on plants of different families but they contain plants of different families but they contain glucosinolate. One can say that cabbage glucosinolate. One can say that cabbage white butterfly is monophagous on white butterfly is monophagous on glucosinolate-containing plants. glucosinolate-containing plants. (Limitations!) (Limitations!)


2- Similar, larvae of the brown tail, 2- Similar, larvae of the brown tail, Euproctis chrysorrhoea,Euproctis chrysorrhoea, attack trees with tannins in their leaves.

(Limitations!)(Limitations!)

Specialization on plant Specialization on plant partsparts

Food-plant range and host-plant rangeFood-plant range and host-plant range

Food-plant range and host-Food-plant range and host-plant rangeplant range

Oviposition female selects the plant Oviposition female selects the plant on which its offspring will feed on which its offspring will feed

The diet breath of the larvae is The diet breath of the larvae is often wider than the range of often wider than the range of plants acceptable as oviposition plants acceptable as oviposition substrate to the adult female 2.6substrate to the adult female 2.6


The oviposition female is governed The oviposition female is governed by different part of genome than by different part of genome than those coding to for food selection those coding to for food selection behaviour in the larvae.behaviour in the larvae.

There is a positive correlation There is a positive correlation betweenbetween……....


Different females of same population of the Different females of same population of the butterfly butterfly Euphydryas edithaEuphydryas editha showed host showed host different plant preference for oviposition. different plant preference for oviposition. Larval performance correlated positively with Larval performance correlated positively with it. 2it. 2

Tipworm Tipworm Crovidosema plebbejanaCrovidosema plebbejana on different on different plant stages of cotton and Malva showed plant stages of cotton and Malva showed that there is a strong correlation between that there is a strong correlation between the acceptable level of a plant as an the acceptable level of a plant as an oviposition substrate and larval oviposition substrate and larval performance. 2.7performance. 2.7


Thus, larvae grew best on the Thus, larvae grew best on the plants that their mothers had plants that their mothers had selected.selected.

Specialization on plant Specialization on plant partspartsIn addition to host plant specialization, also show In addition to host plant specialization, also show

specialization with regard to the feeding sites specialization with regard to the feeding sites they occupy on their host.they occupy on their host.

different leaf parts taste different and possess different leaf parts taste different and possess different physical properties.different physical properties.

Grass hopper many lepidoptera and Coleoptera larvae are leaf Grass hopper many lepidoptera and Coleoptera larvae are leaf foragers (folivores), ingesting large chunk of leaf material. foragers (folivores), ingesting large chunk of leaf material.

Plant bugs penetrate epidermal cellPlant bugs penetrate epidermal cellAphids suck from the sap flow in phloemAphids suck from the sap flow in phloemLeaf-hoppers tap (hit) the xylemLeaf-hoppers tap (hit) the xylem Leaf miners HMLeaf miners HM

Specialization on plant Specialization on plant partspartsCompound leavesCompound leavesLarvae of Larvae of CatacalaCatacala spp. Can spp. Can

discriminate between the basal, discriminate between the basal, alteral and terminal leaflets of alteral and terminal leaflets of their compound leaved food their compound leaved food plant, and they showed a dislike plant, and they showed a dislike the basal leaflets. the basal leaflets. 2.10 2.10

Specialization on plant partsSpecialization on plant partsStem borersStem borers

Fig 2.11Fig 2.11

Specialization on plant Specialization on plant partsparts

ConclusionConclusion

These examples show how all parts These examples show how all parts of plant are shared out and can of plant are shared out and can support some insect or others.support some insect or others.

Below-ground Below-ground herbivoryherbivory

The total biomass of the life The total biomass of the life beneath our feet is mach more beneath our feet is mach more than above the ground.than above the ground.

The subterranean life of forest The subterranean life of forest consists of 100 000 to 500 000 consists of 100 000 to 500 000 insects and other arthropods per insects and other arthropods per square metersquare meter


The interactions of insect and plant The interactions of insect and plant below ground surface are likely to below ground surface are likely to mirror the above-ground interactions.mirror the above-ground interactions.

ExamplesExamples

Grubs eat rootletsGrubs eat rootlets

Larvae of onion flies, carrot flies, and Larvae of onion flies, carrot flies, and cabbage root flies are root borers.cabbage root flies are root borers.

Sap feeders like aphidsSap feeders like aphids


Root-infesting insect may affect Root-infesting insect may affect their above-ground counterparts their above-ground counterparts (and vice versa) via changes in (and vice versa) via changes in their host's chemistry and their host's chemistry and physiology.physiology.

The rice water weevils that feed on The rice water weevils that feed on rice` roots reduced the growth rice` roots reduced the growth rate of the fall armyworms. rate of the fall armyworms.


Herbivore damage to roots may Herbivore damage to roots may also affect indirect plant defence.also affect indirect plant defence.

ExampleExample

Cotton plants exposed to root-Cotton plants exposed to root-feeding wirworms (feeding wirworms (AgriotesAgriotes sp.) sp.) increased their extrafloral nectar increased their extrafloral nectar production 10-fold. extrafloral production 10-fold. extrafloral nectar recruits predatorsnectar recruits predators

Number of insect species per Number of insect species per plant speciesplant species

No. plant species vs herbivorous insect speciesNo. plant species vs herbivorous insect species

An insect species occur on more one plant species.An insect species occur on more one plant species.

Number of insects species attacking a single plant Number of insects species attacking a single plant species Not necessary competitionspecies Not necessary competition

Spatial separationSpatial separation Temporally separated because of differences in Temporally separated because of differences in

phenology between insectsphenology between insects Behavioral separationsBehavioral separations

ExampleExample

Plant of Plant of Urtica dioicaUrtica dioica is the host plant of eight is the host plant of eight species. 2.12species. 2.12


143 different insect species were 143 different insect species were found upon Tansy Plant, found upon Tansy Plant, Tanacetum vulgareTanacetum vulgare, ,

Host Plant is more than food Host Plant is more than food plantsplants

Fed onFed on

Lived onLived on

Housing facilities provided by host Housing facilities provided by host plant: biotic and abiotic factors plant: biotic and abiotic factors other than foodsother than foods


Larvae of Larvae of platyprepia virginalisplatyprepia virginalis were parasitized by a tachinid fly were parasitized by a tachinid fly in 83% and in 50% on hemlock in 83% and in 50% on hemlock and lupin plants in the same and lupin plants in the same habitat, respectively.habitat, respectively.

The avoidance reaction The avoidance reaction

hemlock plant lupin plant (legume) hemlock plant lupin plant (legume) Apiaceae or Umbelliferae



Nutritionally optimal hostNutritionally optimal host

Nutritionally suboptimal hostNutritionally suboptimal host

survival ratessurvival rates


Nutritionally optimal hostNutritionally optimal host

Nutritionally suboptimal hostNutritionally suboptimal host

Insect may prefer the suboptimal Insect may prefer the suboptimal host that not visited by some of host that not visited by some of their natural enemies. Such plant their natural enemies. Such plant provide better overall survival provide better overall survival rates rates


Microclimate around plantsMicroclimate around plants

The upper leaf surface may be The upper leaf surface may be warmer or cooler than ambient warmer or cooler than ambient level, depending on the rate of level, depending on the rate of transpiration.transpiration.

The lower surface of a leaf is The lower surface of a leaf is usually cooler and more humid usually cooler and more humid than the upper surface than the upper surface



The temperature of the leaf surface The temperature of the leaf surface may be up to 10 c, and even may be up to 10 c, and even more, above or below the air more, above or below the air temperature.temperature.

Fig 2.15; Table Fig 2.15; Table 2.62.6



The microclimates may also be The microclimates may also be studied at level of whole plants or studied at level of whole plants or within natural vegetations Fig. within natural vegetations Fig. 2.16 2.17 2.16 2.17

المحاضرة الثانية Insect-Plant Interactions [email protected].

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