Shredders and Gougers• Consume CPOM (> 1 mm mesh) - leaves, etc., and thus depend heavily on

seasonal inputs of leaves to the stream• Mouthparts usually “chewing” (e.g., many Trichoptera)• Leaves entering the stream are first “conditioned” by bacteria and fungi,

reducing their toughness and creating more digestible proteins and carbohydrates for the invertebrates

• Most shredders can’t digest cellulose, but Tipula harbors endosymbiotic bacteria capable of cellulose digestion

• Gougers consume wood, and are often found inside submersed snags (e.g., the chironomid Brillia); these are unusually slow growing taxa

• Their feces form an important constituent of FPOM

Fam. Taeniopterygidae; O. Plecoptera Fam. Tipulidae; O. Diptera

Filter Feeders

• Consume suspended particles (FPOM), including phytoplankton, bacteria and seston (temporarily suspended particles)

• Frequently found below lakes and reservoirs• Includes many Trichoptera, e.g., Hydropsychidae• Blackfly (Simuliidae) larvae have cephalic fans which are held

at the edge of the boundary layer and trap particles, which are removed by labral bristles and transferred to the mouth

• Flocculation of DOM by bacteria converts it to a form consumable by filter feeders

Filterers

Fam. Simuliidae; O. DipteraFam. Unionidae

Fam. Philopotamidae; O. Trichoptera

Fam. Hydropsychidae; O. Trichoptera

Deposit Feeders• Also feed on FPOM, but by gathering it from the

sediments; the FPOM includes bacteria, algae, detrital particles, of widely varying food quality

• Typically brushlike mouthparts• Includes many mayflies, midges, crustaceans

Fam. Chironomidae; O. Diptera (many are deposit feeders)

Scrapers/Grazers

• Specialists on periphyton on solid surfaces• Mouthparts designed to shear attached algae

from the substratum (e.g., scythe-like mandibles of the caddisfly Glossosoma; the radula of snails)

Fam. Heptageniidae; O. Ephemeroptera Fam. Psephenidae; O. Coleoptera

Scavengers

Many macrocrustacea (amphipods, isopods, crayfish) opportunistically consume animal, algal and plant material

O. Amphipoda O. Isopoda

Invertebrate Predators

• This group is highly diverse, both in microhabitat and food specialization– many surface-feeding Hemiptera– sit-and-wait benthic predators (e.g., dragonflies)– fluid specialists (e.g., leeches), etc. etc.

• Some taxa are predaceous for only part of the life cycle (e.g., later instar Tanypodine chironomids, larval hydrophilid beetles)

Predators

fam. Nepidae; O. Hemiptera

fam. Gerridae; O. Hemiptera

Fam Perlidae; O. Plecoptera)

fam. Tabanidae; O. Diptera

Fam. Hydrophilidae; O. Coleoptera

Predator Behavior• Hunting Behavior– 1. stalking/active pursuit (e.g., perlid stoneflies)– 2. ambush (e.g., hemipteran family Nepidae)

• Prey detection Mechanisms– 1. tactile (e.g., the stream damselfly Calopteryx)– 2. Visual (e.g., most other damselflies)– 3. Chemical (perlid stoneflies search in an upstream,

following prey chemical trails)

Calopteryx visual damselfly

Prey Defenses• Primary (operate regardless of predator’s proximity)

– a. refuges (e.g., many Trichoptera, chironomids)– b. crypsis

• Secondary (behavioral responses)– a. Thanatosis (feigning death) (e.g., some Coenagrionid damselflies)– b. Secondary Compounds (e.g., many Coleoptera and Hemiptera)– c. Group Defense (e.g., Gyrinids may confuse predators)– d. Active (e.g., strigulating in the beetle Tropisternus; use of the

scorpion posture in ephemerellid mayflies)

Ephemerellid mayflies produce “scorpion posture” when threatened by stonefly predators

Macrophyte Consumers

• Leaf and stem feeders• Many Lepidoptera, some chironomids, some

beetles, some Trichoptera

Fam. Chrysomelidae; O. Coleoptera Fam. Pyralidae; O. Lepidoptera

Fish predation

• Evolutionary effects on invertebrate behavior/morphology – (e.g., Trichopteran cases provide protection against fishpredators)

• Effects of fish on stream inverts much harder to detect than in lakes, owing to the effects of drift

• The Trophic Cascade – The basic idea is that the food web can be simplified to a food chain in some streams. An

increase in size in a top trophic level may then reduce the size of the level below, increase the size of the level below that, etc.

Periphyton

Grazers

Invertivores

Piscivores

Invertiv.

Inv. Inv. Grazers

Periphyton

The River Continuum Concept

As stream order increases:– a. the influence of the riparian

canopy diminishes as a light interceptor

– b. production by periphyton and macrophytes increases

– c. inputs of leaf litter decline– d. shredders are largely replaced

by FPOM feeders – e. P/R increases, but then may

decrease once more in very large rivers

– f. plankton communities become sustainable in river systems

Vannote et al. (1980)

Aquatic Insect Respiration• Tracheal system

– Usually consists of a spiracle leading to a trachea, then branching tracheoles

• Atmospheric oxygen obtained by – visiting the surface– Transporting a bubble underwater (“physical gill”). – e.g., most Hemiptera and Coleoptera

• Dissolved oxygen extracted from water – e.g., into gills or across the integument– e.g., mayflies, stoneflies, odonates, dipterans – Oxygen ultimately reaches “closed tracheal system” (no spiracles)

The Physical Gill

– The bubble is brought down from the surface

– As oxygen is drawn from the bubble through the spiracles into the insect, oxygen from the water diffuses into the bubble (greatly prolongs its use)

Hemipteran

Coleopteran

Oxygen from Plant Stems

The beetle Donacia and its relatives tap into the roots of water lilies and other submersed plants

Hemoglobin as an adaptation to low-oxygen environments

• Enhanced ability to take up oxygen from oxygen-poor environments

Midge (Chironomus) larva

Aquatic Insects

• Typically the immatures are found in water; the adults may either aquatic or terrestrial. The change from water to land during the life cycle may require considerable ontogenetic modification of body form. Two general and distinct types of life histories:

• Hemimetabolous: (Odonata, Ephemeroptera, Plecoptera, Hemiptera)egg larva or nymph adult

• Holometabolous: (Megaloptera, Neuroptera, Trichoptera, Coleoptera, Diptera, Lepidoptera)

egg larva pupa adult– The pupal stage may either be motile or non-motile, and is the principal

means for reorganizing the body structure

Life History Stages

A. Holometabolous

(e.g., Trichoptera)

B. Hemimetabolous

(e.g., Plecoptera)

Mayflies are hemimetabolous

• Hexagenia mayflies typically spend a year as larvae, emerge as a pre-reproductive adult (“dun”), then molt again to reproduce (“spinner”). There is no pupal stage.

Holometabolous Life Cycle

• Whirligig beetles (fam. Gyrinidae) have morphologically very distinct larval, pupal and adult stages.

Pupa

More primitive insect orders have more larval instars

Order Typical No. larval Instars

Ephemeroptera 15-25

Odonata 10-12

Plecoptera 12-22

Hemiptera 5

Megaloptera 10-11

Coleoptera 3

Trichoptera 5

Diptera 4-7

Time to complete the life cycle

• univoltine – Species which require one year to

complete the life cycle • bivoltine

– two generations per year• Multivoltine

– > 2 generations/yr

• Larger, or higher latitude, taxa may require more than one year to complete the life cycle, and two or more distinct size classes may thus co-occur in the same location.

Larval hellgrammites (O. Megaloptera) may require 5-7 years before emerging to become adults

Adult Megalopteran

Hemimetabolous or holometabolous?

Overview of the Orders of Aquatic Insects covered in lab

• Ephemeroptera: Mayflies• Plecoptera: Stoneflies• Odonata: Dragonflies and Damselflies• Trichoptera: Caddisflies• Hemiptera: True Bugs• Coleoptera: Beetles• Megaloptera: Alderflies and Dobsonflies• Diptera: True Flies

A few examples are shown in the slides that follow; the complete list of taxa, with slides, is provided in the “Macroinvertebrates for Practicum” file posted on Blackboard