fig. 7.2 gullen & cranston, 2005 a current hypothesis for the cladistic phylogeny of the insects...

Fig. 7.2Gullen & Cranston, 2005

A current hypothesis for the cladistic phylogeny of the insects and primitive hexapods

“basal orders” (= “Apterygota”)

NEW ORDER! ca. 2000

“primitive hexapods”?

??

true INSECTS

ARCHAEOGNATHA (= MICROCORYPHIA)

jumping bristletails

THYSANURA (= ZYGENTOMA)

silverfish, firebrats

The Basal or Apterygote (wingless) Orders

ARCHAEOGNATHA

Shrimp-like profile; tail filaments relatively parallel, bristly. Primitive, spider-like, single-articulated jaws. Deocmposers. No economic significance.

“Jumping bristletails”

X-sec

Thermobia, a firebrat. Giant neurons in tail filaments studied at UW.

THYSANURA (ZYGENTOMA)“silverfish & firebrats”

Flattened profile, don’t jump, tail filaments held close to 90 deg. apart. A few are economic pests, damaging cellulose & fabric.

“Aquatic” Insects

A polyphyletic, ecological assemblage of taxa.

The aquatic lifestyle has arisen many times in insect evolution; only in a few orders is it the rule.

In most, the immature stages are truly aquatic while the adult is a winged terrestrial form.

Holometabolous, Endopterygote

Hemimetabolous, Exopterygote

Paleoptera

AQUATIC INSECTS, an ecological (polyphyletic) group

otherorderswithaquaticspecies

TRICHOPTERA

PLECOPTERA

ODONATAEPHEMEROPTERA

Importance of Aquatic InsectsMost references to nymphs/larvae; some taxa beyond this lecture

Natural World Nutrient cycle: decomposers

Water quality: filter feeders

Food Webs: prey & predators, e.g. salmon fry eat bugs

Anthropophilic World

Aquatic environmental quality indicators

Medical/Disease vectors, especially mosquitoes, other flies

Human Food (coryxid eggs; water bug wing muscle; fly pupae)

Sport Fishing (Fly Tying)

Life History & Physiological Aspects ofAquatic vs. Terrestrial Insects

Development Terrestrial: variable rateAquatic: Generally slower (colder temperature under water)

Water/Ion Balance Terrestrial: conserve water from dehydration Aquatic: conserve ions from dilution

Respiration Terrestrial: open system (siphon, physical gill, etc.)Aquatic: closed tracheal system (gills, cutaneous) with exceptions

Nitrogen Waste Removal Terrestrial: uric acid (conserves water) Aquatic: ammonia (conserves energy)

EPHEMEROPTERA, mayflies

aquatic immature

terrestrial (winged) adult

Fish-eye view through the mind of the fisherman (superpredator). Fish as entomologists!

Adult

gills

wing pads

3 “tail filaments” = cerci

Larva (nymph, naiad)

gill covers

Mayflies are predaceous or detritovores as nymphs. Adults do not feed.

forlegs

Mayfly adult antennae are small; hindwing may be small or vestigal.

hindwing

larval molt, subimago molt, & adult

ODONATA, dragon- & damselflies

damselflies

dragonflies

labial mask

All odonates are predators as both nymphs and adults.

1. lunge

2. grab

dragonfly larva labial mask hydraulic feeding mechanism

Some large dragonfly nymphs may take vertebrate prey!

adult eclosion

tracheal tubes

A tropical dragonfly. The wings are always held out at rest.

• Dragon flies have acute and fast vision.

• Up to 10,000 eye facets (high resolution!)

• Adaptations: small prey capture at high speed while flying & mate/mate competitor detection.

Well-known “loop” configuration of mating odonates; male grasps female with tail claspers; transfers sperm from secondary sex organs on 2nd abdominal segment.

A damselfly. Some are spider predators.

Males of some dragonfly species are territorial, with traditional perches.

Some ancient dragonfly relatives (“Griffinflies”) measured over two feet in wingspan. How could flying insects live at this scale?

PLECOPTERA, stoneflies

• Orthopteroids i.e., cricket- or roach-like.

• Nymphs fully aquatic, prefer highly oxygenated water.

• Thoracic gills.

• Two long cerci in nymphs & adults.

Stoneflies are predators or detritovores as numphs; adults do not feed.

thoracic gills

Some insects can be active at near-freezing temperatures. A “winter” stonefly nymph, one species among various snow-active insects.

wing pads

Stonefly exuviae.

TRICHOPTERA, caddisflies

hairy (vs. scaly) wingslong, thread-like antennae

reduced mouthparts

Features distinguishing adult caddisflies from adult moths.

wings membranous (~transparent)

• Sister order to the Lepidoptera.• Moth-like.

A true moth.

scales

diverse larval cases (including none!)

Caddisfly nymphs are predaceous or detritovores; adults do not feed.

TRICHOPTERA

caddis fly larval cases

typical caddisfly larva without case

from Gullen & Cranston 2000

Life stages of an aquatic snout moth (Pyralidae).Parallel evolution of the caddisfly-like natural history.

Marine Insects

all from Cheng 1976

Halobates, an open water predaceous bug.

Egg phoresy: eggs laid on tail of seabird.

Hydrophobic hairs on tarsi of Trochopus, a related genus.

Clunio californiensis, an open water marine midge (DIPTERA: Chironomidae)

male skating

mating behavior

male

female

all from Cheng 1976

• Sea skaters, genus Halobates, are the only insect known to live in the open ocean. More than 40 species have been described, but only five (H. micans, H. sericeus, H. sobrinus, H. germanus and H. splendens) are oceanic (Andersen & Cheng 2004).

–

Their overall range lies between 40°N and 40°S, but within that expanse each species has a different specific range (Cheng 1989). In the eastern tropical Pacific Ocean (ETP), four of five oceanic species can be found; H. germanus occurs in the Indian and western Pacific oceans (Andersen & Cheng 2004). Sea skaters have been reported thus far in the diet of more than a dozen surface-feeding seabirds.

END