INSECTS II What stages of life do insects go through? How do caterpillars relate to butterflies? Larvae, Nymphs & Adults Exoskeletons
Stages of Life • Incomplete metamorphosis: an egg becomes a nymph, which evolves gradually into an adult. • Complete metamorphosis: an insect progresses through several distinct stages: egg to larva to pupa to adult.
Incomplete metamorphosis Nymphs and adults eat the same food and live in the same surroundings.
Complete Metamorphosis Larvae and adults may eat different foods, thus avoiding competition for a single resource.
The Life Cycle of a Butterfly • The first stage is called the egg stage. The mother butterfly lays eggs on a leaf. • In the larva (2cd) stage, the egg hatches on the leaf and out comes a caterpillar. • In the pupa (3rd) stage the caterpillar grows and it pops out of its old skin, already wearing a new one. • The adult (4th) stage is also called the Imago. • The Imago (5th) stage begins when the chrysalis is broken and the butterfly breaks out.
The Larva Stage • The caterpillar grows and it pops out of its old skin, already wearing a new one four or five times, after which the caterpillar begins to produce silk. With this silk, it attaches its body to a leaf or twig. It then sheds its furry skin for the last time. Under the skin is a hard form called chrysalis. The caterpillar's body turns to a soft liquid, from which the wings, legs and other body parts of the butterfly will form.
Exoskeletons I An insect's exoskeleton serves as a: • protective covering over the body • a surface for muscle attachment • a water-tight barrier against desiccation • sensory interface with the environment
Exoskeletons II • Composed of overlapping, hardened plates, with membranous areas between the plates, for maximum strength with flexibility • Good at reducing water loss to the environment, which is critical for a small organism with a large surface area to volume ratio
Exoskeletons III • The exoskeleton is composed of chitin surrounded by a matrix of protein that varies in composition from insect to insect • Our fingernails are composed of chitin—the same material in an insects exoskeleton!
Molting II • The destruction of old cuticle, formation of new and larger cuticle, and shedding of remnants of old cuticle. • Old cuticle is partially used to make new one. • Newly molted insect appears whitish, since no color in cuticle. They are NOT albinos. • New cuticle tans (like a hide), hardens, and takes color in short time.
Controls of Molting • Controlled by endocrine system, and by brain. • Gut receptors, elsewhere indicate stretching. • Cells in brain secrete hormone that stimulates prothoracic gland. This gland produces a molting hormone called ecdysone. • Molting controlled by brain and prothoracic gland in prothorax.
Sources 1. Insects and Human Society http://www.ento.vt.edu/ihs/distance/lectures/abundance/abundance_slide04.shtml • O. Orkin Insect Zoo http://insectzoo.msstate.edu