ENTOMOLOGY 10

Mantis feeding on butterfly

What insects do for a living: scavengers, predators, parasitoids, and parasites

  1. Herbivores (separate lecture)
  2. Scavengers
    1. Definition - animal that feeds on "nonliving" organic material (animal or plant); succession of insect species.
    2. Types of insect scavengers
      1. Saprophagous (Gr. sapros, rotten; phagein, to eat) - feed on dead organic material
      2. Coprophagous (Gr. kopros, dung) - feeding on fecal material
      3. Necrophagous (Gr. nekros, corpse) - feeding on carrion (Forensic entomology)
      4. Xylophagous (Gr. xylon, wood) - feeding on dead wood
      5. Most saprophages - fungal or bacterial feeders
    3. Role of scavengers
      1. Decomposition of organic matter
      2. Dung beetles (native home Africa) - Australia - reduce bush fly problem.
      3. Potential food source for poultry. House fly degrade manure, feed house fly to poultry
      4. Blue bottle flies and blow flies used during Civil War to clean wounds.
        Eat bacteria, produce antibiotics, prevent gangrene.
    4. Scavengers as pests
      1. Fur and hair feeders - household pests (clothes moth, dermestids)
      2. Cockroaches - adapted to houses; scavengers in homes
      3. Flies - scavengers as maggots, pests as flies. Need protein for ovarian development; some blood-suckers like horse flies, deer flies.
      4. Stored products and processed food - beetles and caterpillars
  3. Predators
    1. Definition - capture and consume a succession of prey (living individuals)
    2. Invertebrate predators
      1. Insects: praying mantids, lady beetles, lacewings, dragonflies, assassin bugs, robber flies
      2. Special case: wasps (yellowjackets, hornets) - feed prey to offspring.
      3. Other arthropods: centipedes, spiders, scorpions
    3. Vertebrate predators (many insectivorous)
    4. Adaptation of insect predators
      1. Prey/host location (continuum)
        1. Sit-and-wait strategists (praying mantids; dragonfly nymphs)
        2. Active foraging strategists (dragonfly adults)
      2. Modification of structures
        1. Mantids - modified of front legs for capturing prey ("praying position")
        2. Dragonflies and mantids - large compound eyes
    5. Adaptation of prey
      1. Morphological defenses - exoskeleton with armor, spines
      2. Chemical defenses
      3. Camouflage - cryptic coloration, resemble sticks, thorns, leaves, bird droppings
      4. Aposematic (warning coloration) - distasteful, poisonous, insects display their colors ; Ex. Monarch butterfly eat milkweed and are distasteful to predators (birds) and wasps with stingers and venom.
      5. Batesian mimicry - palatable species resemble unpalatable ones
      6. Mullerian mimicry - all distasteful species or with effective defenses resemble each other
      7. "Playing possum" - feigning death
  4. Parasitoids
    1. Definition - Lives in a close association with a single host. It is the immature (egg and larva) stages which develop, usually inside the host, and cause the death of the host as it reaches maturity. Adults are free-living.
    2. Parasitoids attack other insects, spiders, and snails, but not vertebrates
    3. Because parasitoids live in or on their hosts, they are always smaller than their hosts
    4. Parasitoids - highly specialized group. Effect on population like a predator.
      1. Flies (tachinids) - resemble housefly
      2. Wasps (major parasitoid groups - braconids, ichneumonids)
        1. Show high degree of specificity for host and stage
        2. Many parasitoids used for pest suppression. (Separate lecture later in course)
    5. Adaptation of hosts against parasitoids
      1. Morphological - long hairs, thick cuticle
      2. Behavioral - jerk violently, regurgitate saliva and gut contents
      3. Encapsulation by blood cells.
  5. Parasites (Medical Entomology)
    1. Definition - Live in close association with an animal host at its expense without causing its death. Live in or on its host for much of their lives. Generally have a single host or a few hosts.
    2. Insect-parasite relationships
      1. Parasites of vertebrates including humans blood suckers - mosquitoes, lice, bed bugs. Myiasis (Gr. myia, fly) - bot flies in humans and cattle; screwworms of cattle.
      2. Vectors of animal diseases
    3. Adaptations of insect parasites
      1. Smaller than host; inconspicuous; does not kill host.
      2. Restricted diet. Blood not very nutritious, many blood suckers have relationship with microorganisms (called symbionts) that provide additional nutrition.
      3. Hemimetabolous vs. holometabolous
    4. Examples of insect parasites on vertebrates
      1. Living in or on hosts
        1. Ectoparasites (external to host) - adult fleas, sucking lice, biting lice
        2. Endoparasites (internal to host) - bot flies, screwworms
      2. "Intermittent parasites" (hematophagus and non hematophagus insects) -- approach a vertebrate host for a meal and leave.
        1. Feed for short period of time on host
        2. Mobile, feed on a number of hosts
        3. Examples: Bed bugs and kissing bugs (hemimetabolus insects).
          Female mosquitoes, deer flies, horse flies, black flies, sand flies (holometabolus insects).
          Face flies (holometabolous insect)- feed on lachrymal secretions
    5. Adaptations to reduce parasitism
      1. Grooming, preening, dusting, swatting
      2. Dense fur, feathers, thick hides
      3. Migrate to areas with less bloodsuckers

Gullan, P.J. and Cranston, P. S. (1994): Pp. 200-208 (scavengers), pp. 390, 392 (forensic entomology), pp. 324-329 (predators and parasitoids), pp. 376 (parasites)

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