primitive hexapods basal orders Apterygota true INSECTS NEW

“primitive hexapods” ? ? ? “basal orders” (= “Apterygota”) true INSECTS NEW ORDER! ca. 2000 A current hypothesis for the cladistic phylogeny of the insects and primitive hexapods Fig. 7. 2 Gullen & Cranston, 2005

The Basal or Apterygote (wingless) Orders ARCHAEOGNATHA (= MICROCORYPHIA) jumping bristletails THYSANURA (= ZYGENTOMA) silverfish, firebrats

ARCHAEOGNATHA “Jumping bristletails” X-sec Shrimp-like profile; tail filaments relatively parallel, bristly. Primitive, spider-like, single-articulated jaws. Deocmposers. No economic significance.

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

“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.

other orders with aquatic species TRICHOPTERA PLECOPTERA ODONATA EPHEMEROPTERA Holometabolous, Endopterygote Hemimetabolous, Exopterygote Paleoptera AQUATIC INSECTS, an ecological (polyphyletic) group

Importance of Aquatic Insects Most 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 of Aquatic vs. Terrestrial Insects Development Terrestrial: variable rate Aquatic: Generally slower (colder temperature under water) Respiration Terrestrial: open system (siphon, physical gill, etc. ) Aquatic: closed tracheal system (gills, cutaneous) with exceptions Water/Ion Balance Terrestrial: conserve water from dehydration Aquatic: conserve ions from dilution Nitrogen Waste Removal Terrestrial: uric acid (conserves water) Aquatic: ammonia (conserves energy)

aquatic immature terrestrial (winged) adult EPHEMEROPTERA, mayflies Fish-eye view through the mind of the fisherman (superpredator). Fish as entomologists!

wing pads Mayflies are predaceous or detritovores as nymphs. Adults do not feed. gill covers gills 3 “tail filaments” = cerci Adult Larva (nymph, naiad)

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

larval molt, subimago molt, & adult

ODONATA, dragon- & damselflies

damselflies dragonflies

labial mask All odonates are predators as both nymphs and adults.

2. grab 1. lunge dragonfly larva labial mask hydraulic feeding mechanism

Some large dragonfly nymphs may take vertebrate prey!

tracheal tubes adult eclosion

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 2 nd 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?

• Orthopteroids i. e. , cricket- or roach-like. • Nymphs fully aquatic, prefer highly oxygenated water. • Thoracic gills. • Two long cerci in nymphs & adults. PLECOPTERA, stoneflies

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

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

Stonefly exuviae.

TRICHOPTERA, caddisflies • Sister order to the Lepidoptera. • Moth-like. long, thread-like antennae hairy (vs. scaly) wings membranous (~transparent) reduced mouthparts Features distinguishing adult caddisflies from adult moths.

scales A true moth.

Caddisfly nymphs are predaceous or detritovores; adults do not feed. diverse larval cases (including none!)

caddis fly larval cases TRICHOPTERA

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.

Halobates, an open water predaceous bug. Marine Insects Hydrophobic hairs on tarsi of Trochopus, a related genus. Egg phoresy: eggs laid on tail of seabird. all from Cheng 1976

male skating male female Clunio californiensis, an open water marine midge (DIPTERA: Chironomidae) mating behavior 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.

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