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Insect Defensive System

Insect Defensive System. Lecture 20. Insects face constant danger from enemies. Predators (vertebrate, invertebrate) Parasites and parasitoids Pathogens. Various insect defense mechanisms. Against predators Crypsis Thanatosis Startle display Modified body parts Autotomy

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Insect Defensive System

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  1. Insect Defensive System Lecture 20

  2. Insects face constant danger from enemies • Predators (vertebrate, invertebrate) • Parasites and parasitoids • Pathogens

  3. Various insect defense mechanisms • Against predators • Crypsis • Thanatosis • Startle display • Modified body parts • Autotomy • Chemical defense • Mimicry • Weapons • Against parasitoids and pathogens • Phagocytosis • Encapsulation • Nodule formation • Behavioral fever

  4. Crypsis: against visual predators • Camouflage: blending to the background Peppered moth (Bistonbetularia)

  5. Crypsis: against visual predators • Mimesis: resembling an object that is a specific feature of its environment

  6. Secondary defense • Predator may develop a “search image” • Thanatosis: feigning death by falling to the ground (many weevils) • Flash color and disappear (many band-winged grasshoppers)

  7. Secondary defense • Startle display • Eye spots • Mimicking vertebrate predators http://creationrevolution.com/2010/10/the-hindsight-of-mimicry/

  8. Modified body parts • Spines • Cases • Carcasses • Feces • Waxes

  9. Autotomy • Shedding of limbs • Many insects can shed a limb when faced with danger • Phasmatodea (Heteronemiidae) is the only insect order that can regenerate limbs after shedding

  10. Chemical defense • Class I chemicals: toxic, noxious, potent • Both immediate-acting and delayed effects • Specific against vertebrate predators • Often accompanied with aposematism • Class II chemicals: innocuous, antifeedant chemicals • Volatile • Specifically against invertebrate predators that rely on chemical communication

  11. Mimicry • Batesian mimicry: an aposematic inedible model and an edible mimic • Müllerian mimicry: the model and the mimic both distasteful and aposematic and benefit from coexistence Monarch (Danausplexippus) Queen (Danausgilippus) Viceroy (Limenitisarchippus) Used to be thought of as a classic example of Batesian mimicry

  12. Mimicry • Batesian mimicry: an aposematic inedible model and an edible mimic • Müllerian mimicry: the model and the mimic both distasteful and aposematic and benefit from coexistence Monarch (Danausplexippus) Queen (Danausgilippus) Viceroy (Limenitisarchippus) Now the system is interpreted as Müllerian mimicry

  13. Weapons • Stingers with venoms (Hymenoptera) • Venoms include many polypeptides, biogenic amines, enzymes

  14. Schmidt Sting Pain Index 1.0 Sweat bee Light, ephemeral, almost fruity. A tiny spark has singed a single hair on your arm. 1.2 Fire ant Sharp, sudden, mildly alarming. Like walking across a shag carpet and reaching for the light switch. 1.8 Bullhorn acacia ant A rare, piercing, elevated sort of pain. Someone has fired a staple into your cheek. 2.0Yellowjacket Hot and smoky, almost irreverent. Imagine W. C. Fields extinguishing a cigar on your tongue. 2.x Honey bee Like a matchhead that flips off and burns on your skin. 2.0 Bald-faced hornet Rich, hearty, slightly crunchy. Similar to getting your hand mashed in a revolving door. 3.0 Paper wasp Caustic and burning. Distinctly bitter aftertaste. Like spilling a beaker of hydrochloric acid on a paper cut. 3.0 Red harvester ant Bold and unrelenting. Somebody is using a drill to excavate your ingrown toenail. 4.0 Tarantula hawk Blinding, fierce, shockingly electric. A running hair drier has been dropped into your bubble bath. 4.0+ Bullet ant Pure, intense, brilliant pain. Like fire-walking over flaming charcoal with a 3-inch rusty nail in your heel.

  15. Bullet ant (Paraponeraclavata)

  16. Phagocytosis • Small numbers of bacteria, fungal spores or protozoans are phagocytosed by plasmatocytes • Changes hematocytes level after infection

  17. Encapsulation • Larger invaders (parasitoid larvae or nematodes) encapsulated by large numbers of hemocytes

  18. Nodule formation • Large numbers of bacteria or fungal spores are attacked by the formation of nodules • Coagulum produced by numbers of granulocytes • Little phagocytosis

  19. Behavioral fever • Insects can elevate internal body temperature to suppress pathogen activities Desert locust behavioral fever against fungal pathogens

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