Aquatic Insects: Ephemeroptera, Plecoptera & Trichoptera

Aquatic insects

spend most of life cycle associated with aquatic habitats

• Some have aquatic immature stage with terrestrial adult stage

• Exploit resources their terrestrial counterparts cannot occupy

• Insects inhabit nearly all aquatic systems except the ocean

Habitats

• Inhabit freshwater environments: streams, lakes, rivers

• Ponds and lakes have lots of plants but have low oxygen content

• Streams and rivers have moving waters with higher oxygen content

Adaptation: Breathing

• Adaptations for gas exchange are essential for survival

• Gills: organ allows dissolved oxygen to pass by diffusion under water

• Usually, outgrowths of the tracheal system covered by a thin layer of cuticle permeable to gases

Dragonfly Larvae Gill

• Internal gills in abdomen of larvae dragonfly

• Caudal end of alimentary tract is a rectal gill

• Water pumped into rectum provides oxygen to closed tracheae

• Doubles as jet propulsion system: contraction of abdomen expels water and thrusts insect forward

Plastron

• Structures visible as thin, silvery films of air covering parts of body surface

• Involve scales or microscopic ridges projecting from cuticle

• Mechanism allows aquatic insects with plastrons to remain constantly submerged

• Those that remain submerged or lack ability to reach surface are likely to have plastrons

Air Bubbles

• Diving insects carry trapped air bubbles and deplete oxygen more quickly: need replenishment

• Bubble cover spiracles so “breathing” air while submerged

• Plants can also trap air which acts as a resource for insects as a source of air stores (trapped bubbles)

Hemoglobin

• (respiratory pigment that facilitates binding of oxygen)

• Insects can remain submerged for long periods with high concentrations of hemoglobin in hemolymph

• In the larvae of midges, bloodworms. Live in muddy ponds/ streams where dissolved oxygen is low

Siphons (Siphoning Tubes)

• Air from surface through breathing tubes’

• Aquatic plants maintain buoyancy by storing oxygen (waste product) in vacuoles

• Insert siphons into air stores to obtain oxygen without swimming to the surface

Mosquito Siphoning

• Mosquito larvae siphon tube is spiracle extension

• Opening at end of siphon guarded by closely spaced hairs with waterproof coating

• At air-water interface, hairs break surface tension and maintain an open airway

• Insect dives, water pressure pushes hairs close together to seal opening and keep water out

Adaptation: Swimming

• Natatory legs: adapted for swimming

• Dragonfly uses abdomen

Water Striders

• Characterized by having hydrofuge hair piles and elongated legs and body

• Able to walk on water due high surface tension of water and their long,

hydrophobic legs

Adaptation: Temporary Habitats

• Occupy temporary habitats such as seasonal streams footprints and rain collection sites

• Mosquito species occupy this source

• Strategies for occupying temporary water

• Fast development

• Larval dormancy

• Immediate egg-laying to newly filled site

Adaptation: Avoiding Predators

• Trichoptera (caddisflies) have protective shell

• Create nets to filter food

Biological Indicators

• Organisms such as plants, animals, microbes that can determine ecosystem quality

• Can be utilized to screen health of ecosystem, assess environmental health and

determine changes taking place

• • Insect abundance can give idea of the

  overall biodiversity of plants and animals

  • Insects can re-colonize as environment

  changes or improves

  • Insects represent many levels in food web

  
  

Water Quality

• Biomonitoring in water quality become regular practice for determining pollution

• Insects are biomarkers for assessing water quality and indicate water pollution

Aquatic Insects of Interest

• Orders such as Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) are very sensitive to pollutants in aquatic environment

• Determine water quality through EPT richness index:

Ephemeroptera: Mayflies

• Immatures are aquatic: Naiads

• Prefer non-polluted, well oxygenated water

• While short lived as adults, live for years in water

• Detritivores & herbivores: nutrient recycling

• Naiads important source of food for aquatic animals, synchronous emergence provides excellent food source for birds

• Unique among insects by having subimago stage: winged non-reproductive form

• Adult (imago) mayflies are non-feeding, only mate

• Adult mayflies emerge in great numbers to maximize chance of finding a mate in short time

• Large numbers of dead mayflies can slick roads, create low visibility

Plecoptera: Stoneflies

• Naiads live in benthic zone of well-oxygenated lakes and streams

• Acquire oxygen through exoskeleton diffusion, require well-oxygenated water

• All species intolerant of pollution, presence usually indicator of excellent water quality

• Naiads feed on algae, mosses, and immature aquatic invertebrates

• Usually found in mountains and fast flowing streams

• Most stoneflies will emerge during spring or summer, but ‘winter’ stoneflies reproduce during

fall and winter

Trichoptera: Caddisflies

• Resemble moths, but wings covered in hair rather than scales

• Wings held over abdomen at rest with long, threadlike antennae

• Most diverse order of exclusively aquatic insects

• Larvae accumulate materials from environment to build protective cases

• Case held together by silk secretions produced from salivary glands

• Prolegs on terminal abdominal segments holds the case in place