Aquatic Insects

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					Aquatic Insects

   8 April 2009
Aquatic Insects
• Insecta (even
  Hexapoda) are
  plesiomorphically
  terrestrial.
• But there have been
  numerous colonizations
  of the freshwater
  aquatic environment.
• Far fewer colonizations
  of marine aquatic
  environment.
Hemimetabolous Aquatic Insects

• Some lineages have
  almost* exclusively
  aquatic naiads.
   – Ephemeroptera
   – Odonata*
   – Plecoptera (the only
     aquatic
     Polyneoptera)
• All of these have
  terrestrial adults.
Hemimetabolous Aquatic Insects
• There are multiple
  colonizations of
  aquatic
  environments by
  Heteroptera.
• Most of these are
  also aquatic as
  adults.
   Holometabolous Aquatic Insects

• Colonized aquatic
  environments much
  more recently.
• Numerous colonizations
  within numerous orders
• Only two have
  exclusively* aquatic
  larvae.
• Only some Coleoptera
  remain aquatic as
  adults.
   Holometabolous Aquatic Insects

• Neuroptera: One
  lineage (Sisyridae,
  spongillaflies).
• Coleoptera: Numerous
  colonizations
  throughout.
• Diptera: Numerous
  colonizations, especially
  in Nematocera.
• Lepidoptera: Numerous
  origins, but NOT
  common
   Habitats for aquatic insects

• Lotic: flowing water
   – Influenced strongly by
     velocity of flow
       • Particle size
       • Substrate type
   – Inputs from outside and
     local nutrient supplies
• Lentic: standing water
   – Often strong zonation
       • Limnetic zone- penetrated
         by light
       • Profundal zone- deeper
         zone w/o much light
               Unusual Habitats
• Marine environments
   – Intertidal habitats
       • Between high and low tide
       • biting flies, plant feeding
         insects, detritivores
   – Littoral habitats
       • Coastal regions with
         shallow water
       • Some midges and beetles
   – Open ocean: water striders
     feeding on food of terrestrial
     origin
• RARE! WHY???
Unusual Habitats
•   Temporal water bodies (e.g.
    vernal pools)
     – Common in areas with
       seasonal rainfalls
•   Numerous adaptations
     – Ability to find ephemeral pools
       (meteorological cues?)
     – Desiccation resistant diapause
         • Very common as eggs
         • Some with ability to undergo
           numerous dehydrate/rehydrate
           cycles: anhydrobiosis
•   Plant container habitats:
    Phytotelmata
           Oxygen Supplies
• Air: 200,000 ppm (20%)
• Lotic environments (15 ppm)
  – Depends on O2 production/consumption by plants
  – Affected by turbulence and water quality
• Lentic environments
  – Oxygen levels vary with temperature, salinity, and
    depth
  – Turbulence affects nutrient and oxygen distribution
• Anoxic
  – No oxygen present
 How do aquatic insects obtain oxygen?
• Atmospheric oxygen
  – Keep part of body out of
    water
  – Carry oxygen into water
• Aqueous oxygen
  – Use of open tracheal
    system
     • Adult insects
     • Immature forms
  – Use of closed tracheal
    system
     • Specialized structures
       for gas exchange in
       water
     • Often adults have open
       tracheal system
Tracheal System
       Closed Tracheal System

• Gills- lamellar
  extensions of tracheal
  system
• Found in many insect
  orders
• Gills may be in many
  places
   –   Base of legs
   –   Abdomen
   –   End of abdomen
   –   How is this analogous to
       insect ears?
 Open tracheal system in flies
• Respiratory siphons near abdomen or thorax
• Different location in mosquito pupa than larva
 Open tracheal system in diving beetles
• Bubble stored beneath elytra
• Gas exchange can occur in water

                                    Does the bubble
                                    increase linearly
                                    with oxygen
                                    consumption?

                                    What happens
                                    to the exhalation
                                    product?
        Other air bubble gills
• Water kept away from body through ‘hairs’ or ‘mesh’
• Oxygen diffuses from water to air against body
• Usually slow moving insects with low oxygen demand
                Lotic Adaptations
 • Flattened bodies
 • Attachment through suckers




Water pennies (Coleoptera: Psephenidae)
                                             Net-winged midges
                                          (Diptera: Blephariceridae
     More Lotic Adaptations
• Nets & Cases




     Trichoptera net

                       Trichoptera cases
         Lentic Adaptations
• Taking advantage of surface             Water Strider (Gerridae)
  tension of still water




                Whirligig Beetle (Gyrinidae)
Adaptations to nearly anoxic environments

• Hemoglobins
  –   Many larval chironomid midges (Diptera) = bloodworms
  –   Some notonectid bugs (Heteroptera) = backswimmers
  –   Very, very high affinity for oxygen (unlike us)
  –   Only downloads when oxygen concentrations in tissues
      decrease, not when tissues become acidic
Using insects to monitor aquatic environments
 • Usefulness
    – Diverse taxa to choose from, many common
    – Functionally important to ecological community
    – Ease of sampling many individuals without major
      ethical constraints
    – Ability to identify species
 • Responses
    – Increases of certain taxa in waters with sediment,
      low
    – Oxygen, increases in temperature
    – Loss of diversity with pollution and or
      eutrophication
            Ephemeroptera
• Naiads often with
  abdominal gills
  – Also maxillary and
    labial gills!
• Generally 3 styli on
  naiads and adults.
• As many as 45
  instars
• Anything else?
                 Odonata
• Dragonflies &
  Damselflies
• Rectal/anal internal
  gills.
• Caudal lamellae
  also serve as gills.
• Up to 20 instars.
• Predators as naiads
  and adults.
  Plecoptera
• Mostly temperate
  regions
• 10-33 instars
• Closed tracheal
  system with anal
  gills.
• Need high oxygen,
  good environmental
  indicators.
   Hemiptera:                    Notonectidae:
                                 Backswimmers
   True Bugs
• Diving or at surface
• Adults and naiads both         Corixidae:
  aquatic.                       Water Boatmen
• Highly modified legs.
• Generally wings still
  functional as adults, can
  disperse between
  waterways.                     Naucoridae:
                                 Creeping
                                 water bugs
                Gerridae:
                Water striders
                  Hemiptera




• Left: Nepidae (water scorpions) tails are breathing
  tubes
• Right: Belostomatidae (toe-biters) egg tending by
  males
                  Trichoptera




• Case & net makers.
• Abdominal tracheal gills.
 Coleoptera
• Aquatic larvae,
  aquatic adults
• Aquatic larvae,
  terrestrial adults
• Terrestrial larvae,
  aquatic adults
• Pretty much all
  pupate on land
                  Diptera

• Often with anal
  spiracles breathing
  at surface
• Very diverse
• Almost all disease
  vectoring Diptera
  have aquatic larvae
  (?)
Megaloptera & Neuroptera

				
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posted:3/12/2012
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