VL 3 Flashcards
Types of plant defense
Resistance:
prevent herbivore to come, drive it away
Tolerance:
herbivore can be on plant, plant can tolerate the insect to some extent
Types of resistance
physical, chemical
direct & indirect
constitute & induced
What is the difference between direct and indirect resistance?
Direct:
directly resist herbivory through traits that deter herbivores from attacking plant and/or negatively affect the performance and survival of herbivores
effective against generalist herbivorous insects but generally does not affect specialist herbivores
Indirect:
Plant can indirectly resist herbivory by employing bodyguards
Acacia-Ant symbiosis
acacia plants provides food and accommodation in the form of food bodies and nectar as well as hollow thorns which can be used as nests
the ants resturn this favour by protecting the plants against herbivores
Indirect resistance: employing bodyguards
association with aggressive protectors (for example acacia-ant symbiosis)
Herbivore-induced plant volatiles (HIPV) that attract natural enemies of the herbivores
Constitutive and induced resistance
Constitutive:
Always present
Costly to continuously maintain
Good against generalists
Induced:
Activated by herbivore feeding
Temporarily costly, but only activated when needed
Specific to insect/type of attack - targeted and more effective
Tolerance
Insect herbivores can induce important physiological responses that allow plants to tolerate the damage caused by their feeding
Plants can respond to herbivore attack by regrowing vegetative tissues, altering the allocation of resources, enhancing speed of resproduction and by increasing selfing rates
Mechanisms of host plant resistance against insects
Antixenosis:
plant properties evoking negative (non-preference) responses or total avoidance by insects
Antibiosis:
plant properties adversely affect the physiology of a herbivore
Tolerance:
polygenic trait that helps a plant to tolerate or recover from an insect infestation
Evolutionary arms race
Selection and adaptation
Insect adaptibility
Resistance stability: durability of resistance
Why do polycultures lead to fewer pests?
Discuptive-crop hyptohesis
Enemies hypothesis
Trap-cropping and crop-weed systems
Disruptive-crop hypothesis
Resource concentration:
herbivores are more likely to find and remain on host individuals grown in monoculture than host plants grown in spatially diluted systems
Olfactory masking:
Volatile organic compounds (VOCs) emitted by non-host intercrops may mask teh odour of the host plant, thereby disrupting host-finding behaviour of the pest insect
Increased tendency to leave their host
Enemies hypothesis
Polyculture fields provide additional food sources, more shelter refuges, more alternative preys
Trap-cropping and crop-weed systems
Trap crops are plant stands in the vicinity or in certain parts of a field where the trap plant is grown that attract pest insects so that the target crop escapes pest infestation
