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Hexapods. Chapter 21. Subphylum Hexapoda . Members of the subphylum Hexapoda are named for the presence of six legs. All legs are uniramous . Hexapods have 3 tagmata: Head Thorax Abdomen Appendages attach to head and thorax. Subphylum Hexapoda. Two classes within Hexapoda:
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Hexapods Chapter 21
Subphylum Hexapoda • Members of the subphylum Hexapoda are named for the presence of six legs. • All legs are uniramous. • Hexapods have 3 tagmata: • Head • Thorax • Abdomen • Appendages attach to head and thorax.
Subphylum Hexapoda • Two classes within Hexapoda: • Entognatha • Insecta
Subphylum Hexapoda • Entognathans are a small group characterized by having the bases of mouthparts enclosed within the head capsule. • 3 orders: Protura, Diplura, and Collembola. • Protura and Diplura - tiny, eyeless, and inhabit soils or dark, damp places. • Collembola are commonly called springtails because of ability to leap. • Animal 4 mm long may leap 20 times its body length. • Members live in soil, decaying plant matter, on freshwater pond surfaces, and along seashore. • Can be very abundant, reaching millions per hectare.
Class Insecta • Insecta is an enormous class whose members have ectognathous mouthparts – bases of mouthparts lie outside the head capsule.
Class Insecta • Insects are the most diverse and abundant of all arthropods. • 26 orders • Most are terrestrial or inhabit freshwater. • Few are marine.
Class Insecta - Distribution • Found in nearly all habitats except the sea. • Common in freshwater, brackish water, and salt marshes. • Abundant in soils, forest canopies, and can be found in deserts and wastelands. • Most animals and plants have insects as parasites externally and internally.
Class Insecta - Adaptive Traits • Flight and small size makes insects widely distributed. • Well-protected eggs withstand rigorous conditions and are readily dispersed. • Wide variety of structural and behavioral adaptations gains them access to every possible niche.
Class Insecta • Insects have: • 3 Tagmata: head, thorax, abdomen. • 3 pairs of legs and usually 2 pairs of wings on their thorax.
Class Insecta • Insects show a diverse array of morphological variation. • They consistently have 3 tagmata. • Head – compound eyes, one pair antennae, 3 ocelli, mouthparts (including mandibles & maxillae) • Thorax – 3 segments each with a pair of legs, the last 2 segments usually have wings as well. • Abdomen – 9-11 segments
Class Insecta • Antennae can act as tactile organs, olfactory organs, and sometimes auditory organs.
Class Insecta • Legs have also become highly specialized for walking, grasping, skating over water, and specialized jobs like gathering pollen.
Class Insecta • Insects also have highly variable body forms. • Land beetles are thick and shielded. • Aquatic beetles are streamlined. • Cockroaches are flat and live in crevices.
Class Insecta • Flight is one key to the great success of insects. • An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl.
Class Insecta • Insects are the only invertebrates that can fly. • Insect wings not homologous with bird and flying mammal wings. • Insect wings are outgrowths of cuticle from the mesothoracic and metathoracic segments.
Class Insecta - Power of Flight • Most have two pairs of wings. • Some are ancestrally wingless – silverfish. • Some are secondarily wingless – fleas. • Recent fossil evidence suggests insects may have evolved fully functional wings over 400 million years ago.
Class Insecta - Modifications of Wings • Wings for flight are thin and membranous. • The thick and horny front wings of beetles are protective. • Butterflies have wings covered with scales. • Caddisflies have wings covered with hairs.
Class Insecta - Wing Thrust • Direct flight muscles alter the angle of wings to twist leading edge to provide thrust. • Figure-8 movement moves insect forward. • Fast flight requires long, narrow wings and a strong tilt, as in dragonflies and horse flies.
Class Insecta • The internal anatomy of an insect includes several complex organ systems.
Insects - Nutrition • Most insects are herbivorous, feeding on plant juices and/or tissues. • Some are specialized, others will eat almost any plant.
Insects - Nutrition • Some insects are predaceous, catching & eating other animals.
Insects - Nutrition • Other insects are scavengers or parasites.
Insects - Nutrition • Some insect parasites are parasitized by other insects – hyperparasitism. • Parasitoids are a lethal type of parasite. • A tiny wasp lays eggs on the tomato hornworm. The wasp larvae will consume the hornworm.
Insects - Nutrition • Insects have mouthparts specialized for the many different foods they eat. • Sucking mouthparts (mosquitoes) – form a tube, can pierce animal or plant tissues.
Insects - Nutrition • Sponging mouthparts (house flies) – liquid food is lapped up, food may be liquefied first.
Insects - Nutrition • Chewing mouthparts (grasshoppers) – strong plates can tear food.
Insects – Circulation & Gas Exchange • Insects have an open circulatory system. • Gas exchange is accomplished with a tracheal system – an extensive network of thin-walled tubes that branch into every part of the body. • Tracheal trunks open to the outside by spiracles.
Insects – Circulation & Gas Exchange • Insects & spiders have independently evolved an excretory system of Malpighian tubules – blind tubules opening into the hindgut. • Potassium is secreted into the tubules and water diffuses in after it. Other solutes and wastes are secreted or diffuse into the tubules as well.
Insects – Circulation & Gas Exchange • Insects that feed on dry grains must conserve water and excrete salts. • Leaf-feeders ingest & excrete lots of fluid. • Aphids pass fluid as honeydew that is consumed by other insects.
Insects – Nervous System • The nervous system resembles that of larger crustaceans, with fusion of ganglia. • A stomadeal system corresponds to the autonomic system of vertebrates. • Neurosecretory cells in brain function to control molting and metamorphosis.
Insects – Sensory Organs • Mechanoreception – Mechanical stimuli are received by sensilla (simple or complex) distributed over the antennae, legs, and body.
Insects – Sensory Organs • Auditory Reception – Very sensitive setae or tympanal organs detect vibrations that come through the substrate or the air. • Some moths detect ultrasonic pulses emitted by bats. They drop toward the ground in response to avoid the bats.
Insects – Sensory Organs • Chemoreception – Chemoreceptors for taste and smell are located in sensory pits on the mouthparts, antennae or sometimes the legs.
Insects – Sensory Organs • Visual Reception – Simple eyes (ocelli) are used to monitor light intensity, they do not form images. • Compound eyes in insects, similar to those of crustaceans, consist of thousands of ommatidia, each having its own pigment cells and lens.
Insects – Sensory Organs • Different insects have different capability to see color. • Bees can distinguish most colors (they don’t see red) beginning in the ultraviolet range. • To us a flower may look uniformly colored, but to the bee there are lines that appear in the UV range that act as nectar guides. • Other insects, like butterflies, can see red.
Insects - Reproduction • Sexes are separate, some are parthenogenetic. • Fertilization is internal. • In some, like butterflies, nutrients are passed to the female as well as sperm.
Insects - Reproduction • Insects have a variety of methods for attracting mates. • Pheremones play an important role in many species. • Fireflies communicate using light flashes. • Crickets communicate using sound.
Insects - Reproduction • Female insects deposit eggs on a specific habitat that will provide food for larvae. • Monarch butterflies lay eggs on milkweed plants. • Parasitoid wasp species lay eggs on tomato hornworms. • Mosquitoes lay eggs in standing water where the larvae will live as filter feeders.
Insects - Metamorphosis • Many insects undergo metamorphosis during their development. • Each stage between molts is called an instar.
Insects - Metamorphosis • Insects with complete metamorphosis have larval stages specialized for eating and growing that are known by such names as maggot, grub, or caterpillar. • The larval stage looks entirely different from the adult stage.
Insects - Metamorphosis • Female butterflies lay eggs on the plant that the caterpillars will feed on. • After the eggs hatch, the larvae (caterpillars) eat and grow, molting many times. • When it reaches a certain size, the larva will molt one more time, becoming a pupa (chrysalis in butterflies).
Insects - Metamorphosis • Metamorphosis from the larval stage to the adult stage occurs during a pupal stage.
Insects - Metamorphosis • In incomplete metamorphosis, the young, called nymphs resemble adults but are smaller and go through a series of molts until they reach full size.
Insects - Metamorphosis • Direct Development • Silverfish and springtails have young similar to adults except in size and sexual maturation. • Stages are egg-juveniles-adult. • Wingless insects.
Diapause • Insects are able to undergo dormancy during harsh conditions. • Hibernation – winter dormancy • Estivation – summer dormancy • Diapause – arrested growth that occurs regardless of conditions.
Defense • Aposematic coloration – many insects utilize bright colors as a warning that they are toxic.
Defense • Batesian mimicry – when a palatable species mimics the bright colors of an unpalatable species. • Müllerian mimicry – when two unpalatable species have come to resemble each other.
Defense • Cryptic coloration – often insects are colored and patterned very much like the plants they are found on, making them very difficult to see.
Defense • Other defensive features include the exoskeleton, offensive odor (as with the stink bug), bites and stings.
Insect Behavior • Insects exhibit a wide range of behaviors involving innate behaviors, pheromones, and learning.
