ENT1Lect2_2008%20_Compatibility%20Mode_ - “If we do not...

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Unformatted text preview: “If we do not expect the unexpected, we will never find it.” Heraclitus “Imagination is more important than knowledge. Albert Einstein WHAT DO YOU OBSERVE? WHAT AM I? HOW AND WHY DO I LOOK LIKE THIS? Lecture 2 The Art of Insect Form and Development 1 Lecture Goals • Introduction to the insect body plan. • What is the insect exoskeleton and why is it important? • Introduction to insect development. Insects have an exoskeleton rather than an internal skeleton Insects must molt to grow. This katydid immature is completing the molting process. Nothing goes to waste! Katydid eating its molted exoskeleton. Cicada immature molts its exoskeleton. *Katydid photos from Alien Empire by Christopher O’Toole The exoskeleton is layered and is made of chitin Advantages: 1. Strong and rigid 2. Waterproof 3. Light weight 4. Versatile Disadvantages: 1. Limited insect size 2. Must be shed for growth to occur 3. Requires time to harden, leaving insect vulnerable 2 The Importance of Segmentation Segmentation is not unique to arthropods, but segmentation is more obvious than in other animals Larva of the net-veined beetle net- Adult male stag beetle Gary Larson cartoon Insects have done more with their segments than virtually any other group of animals! *Photos from Alien Empire by Christopher O’Toole Segmentation How can insects move their segments if the exoskeleton is rigid? Chitinous Exoskeleton Chitinous Exoskeleton Versatility and Adaptation: How the Exoskeleton Contributes to Insect Success •Foregut (equivalent to our esophagus) •Hindgut (equivalent to our rectum) •Spiracles, trachea and tracheoles (respiratory system or breathing apparatus) •Phragma (foundation for muscle attachment) 3 Versatility and Adaptation: How the Exoskeleton Contribute to Insect Success •Tools for feeding (mouthparts) •Tools for locomotion (legs, wings) •Extensions that are integral to the physical appearance of the insect (e.g. decoys, mimicry) •Spines for defense Mouthparts Are Appendages Modified for Feeding Mouthparts may be: •Chewing (________________) •Piercing-sucking (_______________) Piercing•Siphoning (__________________) •Sponging (__________________) •Chewing-Lapping Chewing(__________________) Chewing Mouthparts Four basic pieces: infinite variation 4 Siphoning Piercing-Sucking Sponging Chewing-Lapping Tools for Locomotion Legs are Extensions of the Exoskeleton Tiger beetle: Leg design = long, hollow, jointed. Movement = Very efficient. Possibly the fastest animal on earth, up to 1 meter/second (faster than a cheetah!) Wings Are Extensions of the Exoskeleton That Set the Insects Apart •All but one order of insects have wings. •Evolution of wings is considered one of the most important adaptations governing the success of insects. •Origin of wings = unknown and controversial. Diversity in wing structure, weight and size further demonstrates the versatility of the exoskeleton. 5 Types of Wings •Fixed wings Dragonflies Types of Wings •Flexed wings •Flies •Beetles •True Bugs Types of Wings Beetles have an outer pair of hardened wings (ELYTRA) that cover a membranous pair when at rest. The membranous pair do the work during flight. Beetles are largely ground dwellers. This adaptation affords the insect protection when on the ground. The first pair of wings do most of the work during flight in flies and mosquitoes. The second pair of wings (HALTERES) are tremendously reduced and used much like a gyroscope in flight. 6 Extensions of the Exoskeleton: Decoys, Mimicry and Defense Peanut Fulgorid, hollow extension of the exoskeleton on the head is a decoy for defense against predation by birds. Caterpillar with many stinging hairs that serve a defensive function. The Exoskeleton and the Body Cavity •The exokeleton encases and forms the body cavity (contains all the insect’s organs and blood). •Creates an open circulatory system. •Allows for a simple, passive respiratory system. The Exoskeleton and Growth: Two Ways of Growing Up •Incomplete Metamorphosis •Complete Metamorphosis 7 Incomplete Metamorphosis •The egg hatches into a larva resembling the adult (except no wings and sex glands are not developed). •Development is in several stages, requiring molting of the cuticle. •Immature stages usually have a diet & live in habitats similar to the adult Crickets, grasshoppers and cockroaches undergo incomplete metamorphosis. Complete Metamorphosis Adults mate and lay eggs. Eggs hatch into larvae that do NOT resemble the adult and differ from it in diet and habitat. Larvae undergo a series of molts as they grow and then they become pupae. Development and Molting •How does the insect know when to molt? How does the insect know when to change life stage? 8 ...
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This note was uploaded on 10/03/2009 for the course ENT 1 taught by Professor Ullman during the Fall '08 term at UC Davis.

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