L10 and 11 Ulrike Bauer - Plant/Insect Interactions

Question 1

What impact do plant insect interactions have on economy?

Answer 1

insects account for 13%of pre harvest losses, more than weeds and pathogens do
Pollinators provide 10% of global food production.

Question 2

What 3 types of influence factors do plant insect interactions have on indirect economic impact?

Answer 2

Chemical
Physical
Ecological

Question 3

What chemical influences do plants and insects have on each other?

Answer 3

Plants release Volatiles to attract/repel insects, and general communication between plants.
Allelochemicals released as defensive subatances.
Insect secretions can influence plants

Question 4

What physical influences do plants and insects have on each other?

Answer 4

colour
sticky secretions
touch
material properties
Tissue damage
surface properties

Question 5

What ecological influences do plants and insects have on each other?

Answer 5

Abundance
Apparency
Lifecycle
Community effects

Question 6

Describe generalist and specialist herbivores

Answer 6

1. specialists - rule of nature, 80%., it is the dominant habit. Feed on only 1 or very similar species (monophagous/oligophagous). V common in phsillids, aphids, leaf miners, leaf hoppers.
2. Generalists - exception of nature, only 10%,>3 species of plant. Most common in Orthoptera and Lepidoptera.

Question 7

Describe 2 types of mouthparts and how they affect herbivory.

Answer 7

1. Biting/Chewing- ancestral, mandibulate. Causes substantial damage to the plant, less selective, hard to avoid toxins. Often larger body size, Orthoptera
2. Piercing and sucking - polyphyletic origin, derived, ‘haustellate’ mandibles and maxilla fused to form stylet. Less damaging to plant. Often directly into xylem/phloem/cells. more easy to transmit disease. Selective of nutrients ingested so fewer toxins.

Question 8

6 apsects of resistance

Answer 8

Direct - negative effect on herbivore
Indirect - Positive effect on parasitoids/predators.
Constitutive - permanent, energetically expensive
Induced - Occurs in response to herbivory, energetically cheaper but slow response
Mechanical - Often constitutive, reduces vulnerability.
Chemical

Question 9

4 features of mechanical resistance

Answer 9

1. thorns on outside of leaf, Ilex aquiform - edge of leaf is yellow reinforced tissue which is unattractive to herbivores.
2. Cell walls reinforced with cellulose, lignin, callose, suberin.
3. SiO2 crystals on leaf are abrasive and wear down mandibles
4. Sclerenchyma cells - dead cells with heavily thickened walls containing lignin. occur as Fibres or Sclerids

Question 10

How can leaf toughness be measured?

Answer 10

Using a penetrometer, increase load on a leaf until it breaks. Unsophisticated method, can use relative measures for the same study but not inbetween studies.

There is usually a new correlation between leaf toughness and herbivore larvae establishment.

Question 11

4 types of leaf surface

Answer 11

Glabrous - smooth
Glaucous- epicuticular wax crystals
Pubescent - hairy
Glandular - trichomes- glandular hairs

Question 12

What effect do wax crystals have?

Answer 12

Make surfaces slippery to insects
Decreases herbivores directly, but also can decrease parasitoids/predators of herbivores which results in increasing herbivores.
Eg physillid species have low freq on young glaucous leaves, med freq on young de waxed leaves and high freq on old gla brows leaves.

Question 13

What are two modes of action of chemical resistance?

Answer 13

1. Quantitative- dose dependent effect, eg digestible try reducing, tannins, lignin, cellulose. 5-40% of plant dry weight.
2. Qualitative - toxic, dose independent effect. <2% of plant dry weight. Eg Alkaloids, terpenoids, toxic aa.

Question 14

Describe how leaf surface can add to mechanical resistance?

Answer 14

1 Plants can adjust the leaf surface to make it more or less easy for predators to keep hold of.
2. Can be glabrous - smooth
Glaucous - waxy
Pubescent - hairy
Glandular - With trichome hairs which secrete substances.

Question 15

What effect do epicuticular wax crystals have on the plant?

How does one species respond?

Answer 15

Epicuticular wax crystals can make surfaces slippery to insects. Can decrease amount of pests directly, but also indirectly increases them by reducing number of predators/parasitoids on them, or making it harder for them to move and catch herbivores.
Morphology of crystals varies across species and different species respond differently to different waxes.
eg Phsyllid species have poor survival on young glaucous leaves, mid on young de-waxed leaves, and high on old glabrous leaves.

Question 16

what are 4 plant compounds commonly used by humans?

Answer 16

Caffeine
Salicyclic acid
Taxol - new cancer nedicine
Artemisinin - malaria, cancer and schistosomiasis treatment

Question 17

What is the difference between quantitative and qualitative chamical resistance?

Answer 17

quantitative - dose dependent effect. eg digestibility reducing. Tannins, Lignin, cellulose. 5-40% of plant’s dry weight.
Qualitative - toxic, dose independent effect. <2% of plant’s dry weight. eg alkaloids, terpenoids, toxic amino acids.

Question 18

Describe a study of quantitative chemical defence.

Answer 18

Feeny 1970
Winter moth larvae, Operphtera brumata.
Larvae fed on old leaves had lower mean weight than those fed on new leaves.
Tannin content increases with leaf age and lower protein:tannin ratio so less nutritional value.
Additionally, fed larvae on either pure casein protein, or tannin with casein. Significantly less healthy with tannin.

Question 19

2 examples of qualitative chemical resistance

Answer 19

4-8 Ricinus communis seeds is a lethal dose.

Poison hemlock, Conium maculatum, lethal dose is 0.1g.

Question 20

Example of how specialists have evolved to utilise toxins

Answer 20

Monarch butterfly can sequester cardiac glycosides from milkweeds to use as protection from predatory birds.

Question 21

What chain of events does herbivore attack usually start?

Answer 21

Herbivore attack, local wound response, Systemic hormone response, Biosynthesis of secondary metabolites

Question 22

What is an ecological effect of chemical resistance?

Answer 22

Associational effects - planting onions and carrots together can increase resistance as they both produce volatiles to keep both species herbivores away.

Question 23

What are 5 services provided by insects (mainly ants)?

Answer 23

• pollination
• Protection against herbivores
• seed dispersal
• Nutrient supply
• Protection against plant competitors

Question 24

How can volatile release help plants?

Answer 24

Perceived by insects ad other plants.
Can be leavesof same plant or another individual, within or between plant signalling.
Neighboring plants can receive signal of damaged plant and prepare own defences.

Question 25

volatile release on damaged and undamaged plants

Answer 25

Damaged leaf - strongest measure of volatile release
Undamaged leaf - Some volatile release
Undamaged plant with parasitoids of herbivore introduced - firstly no preference, later, more volatile release and preference of damaged leaves to herbivores.

Question 26

What are myrmecophilic plants?

Answer 26

‘ant loving’

Attract ants but dont host them, are not symbiotic.

Question 27

What are the advantages of attracting ants using EFN rather than using toxins as a defence?

Answer 27

• EFN release can be timed accurately according to need
• cheaper and easier to produce EFN than toxins, although it is rich in AA.
• More difficult for herbivores to evolve immunity to ants than to toxins.

Question 28

What is an important plant stress hormone?

Answer 28

Jasmonic acid

Question 29

Describe a study of Jasmonic acid and herbivore attack

Answer 29

Heil et al 2001
5 plants: 
1. Control
2. Spray control, water
3. Holes punched
4. Herbivory
5. Jasmonic acid applied
3,4, and 5 had higher EFN production
No defenders doubled with Jasmonic acid spray, and after 9 days increased to 4x.
Herbivores on JA induced plant had less than 1/2 the no. herbivores at the start and 9 days later <1, compared to control with >5.

Question 30

What is mymecochory?>

Answer 30

Seed dispersal by ants

1100 species use ants for dispersal.

Question 31

What adaptation may plants have to encourage myrmecochory?

Answer 31

Elaiosomes - lipid rich ant attracting seed appendages. Ants chew off lipids and feed to larvae.
Evolved many times independently.

Question 32

How does an ant garden form?

Answer 32

Complex mutualism involving >1 ant species, host tree (phorophyte) and >1 ant dispersed epiphytes.
Ants build a ‘carton nest’ on tree trunk and bring seeds in. Seeds germinate and grow as epiphytes. can see roots of epiphytes interwoven with carton nest. Epiphytes often produce EFN too - food source for ants.
Almost symbiosis.

Question 33

What are myrmecophytes?

What adaptations may they have?

Answer 33

Plants symbiotic with ants.
Ants live permenently on plants.
Domatia - small hollow nesting structures with external entrance holes, or thin walled part of domatia which ants can bite through.
EFN, homopterans, to provide food for ants
Food body = protein/lipid structures for feeding ants.

Question 34

What is a homopteran farm?

Answer 34

Plants allow a small amount of herbivory by aphids, forming a homopteran farm. Used to feed ants.

Question 35

Where may plants depend on ants for nutrition?

Answer 35

Where the soil had poor nutrient quality, eg Brunei where there is often v white soil.
Plants either cooperate with insects or prey on them.

Question 36

Where cn domatia be found?

Answer 36

Hollow leaves - Dischidia major, roots of epiphyte grow into hollow leaf, and ants fill it with nutrition.
Hollow internodes - Clerodendrum fistulosum
Chambered tubers - myrmecophytum arfakianum.
Hollow rhizomes - Lecanopteris spinosa

Question 37

4 types of food body

Answer 37

Beltian body - Acaicia, protein
Beccarian body - Macaranga, lipid
Mullerian body - Cercropia, lipid
Pearl body - Ochroma, glycogen

Question 38

When are food bodies produced and why?

Answer 38

v costly to plant, can only produce in a nutrient rich environment
Plant only produces food bodies when it can sense it is inhabited by ants.

Question 39

Describe a Protective mutualism

Answer 39

Macaranga and crematogaster
Has wax crystals to protect cramatogaster from competitor ants. Cr. can walk up wax crystals which others can’t, as it is much smaller and less competitve.
Wax crystals have fine thread like structure. crematogaster has sharp claw tips to hook onto wax and is light weight.
Without cr present herbivory levels hugely increased.

Question 40

why do ants prune plants

Answer 40

remove vines off epiphytes so they arent covered. prevents macaranga being crushed by weight of lianas. Also beneficial to ants as removes access of competing ants to plant. `

Question 41

Where are ant plants and carnivorous plants found?

Answer 41

Ant plants - exclusively tropical

Carnivorous - worldwide

Question 42

3 eg of active traps

Answer 42

Venus flytrap - Dionaea muscipula - trap closes and seals to form a digestive chamber
Bladderwort - Utricularia - Aquatic, insect sucked into bladder.
Sundew - Drosera - Tentacles bend and stick glue drops onto insects.

Question 43

How does Dionaea muscipula work?

Answer 43

3 trigger hairs per lobe, red colour and EFN for attraction.
Mechanosensory ion channels which open upon a touch stimulus, triggering Ca2+ influx.
Needs additive effect of stimuli to reach threshold.
If threshold reached, AP caused.
AP cause aquaporins to open, allowing water transport from inner - outer layer of cells, causing trap to bend.
(when trap is open, turgor pressure is higher on inner layer)
‘Snap-buckling’ completes movement.

Question 44

How do nepenthes attract insects

Answer 44

Nectaries
UV and contrasting colour
Sweet scent