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Unformatted text preview: Insect Growth and Life Cycles
Web sites: http://www.earthlife.net/insects/lifecycles.html http://bioweb.biology.kent.edu/facultypages/lorch/mormon.html Key questions: 1. What are major advantages of complete metamorphosis? 2. What are advantages and disadvantages of laying a large number of eggs at one time? 3. Why are insects such important model systems in the study of development? 4. Why are organisms with complete metamorphosis more numerous than those with incomplete or no metamorphosis? 5. Why is it important to understand insect life cycles? I. Egg stage A. "Big bang" reproducers - lay large numbers of eggs 1. adult female life span is usually short if lots of eggs are laid (oviposition) in a short time 2. many insects that over-winter in the egg stage lay large mass of over-wintering eggs B. Abundant insect species where females lay few eggs in lifetime usually have rapid development 1. example: aphids give live birth, develop in about a week II. Development A. Insect eggs must go from an undifferentiated single cell to a larvae with organ systems, etc. 1. HOX (or homeotic) genes are how the insect does this. Patterns are laid down in the developing embryo that designate front, back, top and bottom. These are elaborated on until smaller areas of the egg are designated as head, thorax, gut, abdomen. 2. Homeotic genes are important because they also determine major structures in humans and other animals. Insect are important model systems in the study of development. III. Growth A. Instars (3-many,~7) = A stage between molts. B. Molting = Process of producing new cuticle and shedding the old. 1. Grow inside cuticle 2. Make new cuticle (soft) 3. Digest part of old cuticle 4. Split skin 5. Emerge and expand 6. Sclerotize cuticle (hard/dry) IV. Metamorphosis (= developmental change of form) A. None - rare; each stage looks about same, simply grows larger B. Incomplete metamorphosis = gradual change in each stage 1. Immatures are called nymphs; some species have a prepupal pupal stage 2. external wing pads visible in later stages (instars) 3. stages = egg, larva (plural = larvae) or nymph; (few have nonfeeding pupae); adult [examples include: Ephemeroptera = mayflies; Orthoptera = grasshoppers, katydids, and crickets; Hemiptera = true bugs] C. Complete metamorphosis = morphology of immature stages differ radically from adult 1. immatures (larvae) usually do not compete with adults for food ( except social insects) 2. greatest numbers of insect species have complete metamorphosis: egg, larva, pupa, adult 3. pupal stage often overwinters or passes adverse season [Examples include: Coleoptera = beetles; Lepidoptera = moths and butterflies; Diptera = flies; Hymenoptera = bees, ants and wasp] ...
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This note was uploaded on 09/18/2010 for the course ESPM 28981 taught by Professor O'grady during the Fall '10 term at University of California, Berkeley.
- Fall '10