INSECTS!

1. Insects belong to –Kingdom Animalia–Phylum Arthropoda–Subphylum Uniramia–Class Insecta

•2. Insect bodies are divided into 3 main parts; head, thorax, abdomen.

•3. Insects have mandibles and one pair of antennae, three pairs of legs, and usually two pairs of wings.

The abdomen is composed of 9 – 11 segments.

4. The study of insects is called entomology. Insects are classified into 30 orders based on characteristics such as mouthparts, number of wings, and type of development.

5. Some entomologist believe there may be as many as 10 million species of insects. Why are they so successful? –They can fly to catch prey or escape from other animals.

–They have a light but strong exoskeleton.–They are small so several are able to live in different local environments without competing for resources and food.

–They have short life spans and produce large number of eggs so natural selection occurs more quickly.

6. A look at the grasshopper!

•External Structure–The body is divided into 3 tagmata (body parts). The head contains the mouthparts, a pair of unbranched antennaem, simple and compound eyes.

•The thorax is divided into 3 parts. The first is the prothorax. It attaches to the head and has the first pair of legs.

•Next is the mesothorax. It has the forewings and the second pair of legs.

•The last is the metathorax. It attaches to the abdomen and has the hindwings and large jumping legs. These have spines and hooks used for attachment.

•They have a pair of leathery forewings which cover the membranous hindwings when it is not flying. The hindwings are powered by muscles that are attached to the inside of the exoskeleton.

•The segments in the last tagmata (the abdomen) are composed of upper and lower plates joined together by a flexible sheet of exoskeleton.

•Feeding and Digestion•They are herbivores with mouthparts modified for cutting and chewing leaves and grass. The upper lip is called the labrum, the lower lip is called the labium.

•They hold the food while the mandibles tear off pieces. Behind the mandibles are the maxillae which also help hold and cut the food.

•Insect mouthparts are adapted to each ones food source. Mosquitoes have thin, long mouthparts made into a tube. Fly mouthparts are like sponges to soak up liquids.

•Food enters the mouth and is moistened by the salivary glands. It then passes through the esophagus into the crop where it is stored temporarily.

•From the crop it passes into the gizzard where it is shredded. The shredded food then enters the midgut where it is soaked with enzymes secreted from the gastic ceca.

•Nutrients are absorbed through the walls of the intestine into the body while the wastes are moved through hindgut and out the anus.

•Circulation, Respiration, and Excretion!–Insects have an open circulatory system. Their blood is called hemolymph and is moved around by a heart in the thorax and abdomen.

•They use a system of trachea that exchange oxygen and carbon dioxide.

•They use Malpighian tubules to collect water and cellular wastes from the hemolymph. For insects that live in dry environments this helps conserve water.

•Nervous System•The nervous system consists of a brain and a ventral nerve cord with ganglia located in each body segment. Nerves extend from the brain to the antennae, eyes, and other sensory organs.

•They have simple eyes that can detect changes in light intensity and compound eyes that can form images and detect movement.

•They have a sound sensing organ called a tympanum. It is a large oval membrane that covers an air-filled cavity on each side of the abdomen. Sound wave cause it to vibrate. These vibrations are detected by nerve cells inside the cavity.

•They also have sensory hairs located over the body. At the base of each hair is a nerve that can detect movement made by wind, vibration, etc.

•Reproduction!•All insects have separate sexes. During mating the male deposits the sperm into the females seminal recepticle where they are stored until the eggs are released from the ovaries.

•After the eggs are released they are fertilized internally.

•The last segment of the females abdomen has an organ called an ovipositor. She uses this to dig a hole in the soil where she lays her fertilized eggs.

7. Insect Development•Almost all insects undergo some type of body change within their lifetime. This developmental change in form is called metamorphosis.

There are two main types of metamorphosis; complete and incomplete.

•In incomplete metamorphosis a nymph hatches from an egg and gradually develops into an adult.

•A nymph is an immature form of an insect that looks somewhat like an adult but is smaller and has un-developed wings and reproductive organs. The nymph molts several times until adult form is reached.

•Examples of insects that undergo incomplete metamorphosis are grasshoppers, mayflies, dragonflies, and termites.

•In complete metamorphosis an insect undergoes two stages of development between the egg and adult. In both stages it looks nothing like the adult form.

•Ex. Butterflies.•A wormlike larva (caterpillar) hatches from an egg. Caterpillars have three pair of jointed legs on the thorax and lots of unsegmented legs on the abdomen. These are vegetarians and can cause major damage.

•The larva molts several times as it grows. In the last larval stage it finds a spot on a branch and hangs upside down. The exoskeleton splits and falls off revealing the pupa stage.

•A pupa is a stage of development in which an insect changes from a larva to an adult. The pupa of butterflies are encased in a chrysalis, moths are in a cocoon, and flies are in a puparium.

•Inside the pupa the larval tissue breaks down and transformation into adult form begins. When metamorphosis is complete a fully developed adult emerges.

•Insects that undergo complete metamorphosis include butterflies, moths, beetles, mosquitoes, bees, flies, and most insects.

8. Importance of metamorphosis.

It helps reduce competition between the adult and larval stages for resources such as food and space.

•It also helps insects survive harsh weather conditions. Most butterflies and moth spend the winter encased in the protective chrysalis or cocoon.

•Defense•Insects have developed several passive and aggressive defenses to help them survive.

•One form of passive defense is camouflage which helps them hide. They may look like sticks or leaves.

•Some have venomous stingers like bees and wasps.

•Some use chemical warfare. The bombardier beetle defends itself by spraying a hot stream of noxious chemicals through an opening in its abdomen which it can aim at a target.

•Insects that defend themselves by being poisonous or by tasting bad often have bold, bight, color patterns that serve as warnings.

•This is called warning coloration. Ex. bees and wasps often use yellow and black.

•Mullerian mimicry is when one dangerous species mimics the warning coloration of another dangerous species. Ex bees and wasps.

•Batesian mimicry is when a harmless species looks like a dangerous one to encourage predators to avoid it.

•Insect behavior -Most insect behavior is innate. These are genetically programmed. They are known without any experience.

•Social insects live in colonies. Members of the colony have different responsibilities. This is highly evolved in bees, wasps, ants, and termites.

•Each kind of individual in a colony is called a caste. Usually 3 or 4 castes are present.

•Reproductive females are called queens.

• Workers may be sterile males or females. They support and defend the colony.

•Reproductive males are called drones.

•Soldiers are sterile males with large mandibles for defense and attack.

•Insects and Humans• Insect pollination of crops is worth 19 billion dollars in the U.S.

• They are used as biological control agents by feeding on or destroying harmful substances.

•In the soil they help in decomposition, aeration, and soil formation.

• Important part of the food web.

Many are parasites and spread diseases such as malaria, yellow fever, bubonic plague, encephalitis, and typhus.

•They can destroy crops and spread plant diseases such as Dutch elm disease and potato viruses. Crop damage due to insects in the U.S. is estimated to be 5 billion dollars annually.

•Order Archaeognatha•Bristletails are wingless insects that hide under bark, in litter, and in rock crevices. They feed on algae, lichens, and plant debris.

•Order Zygentoma - Silverfish and firebrats often live in people's houses, but are also found in habitats such as caves and nests of other animals, including ant colonies.

•Order Ephemeroptera - Mayflies are an ancient lineage of winged insects. Adult mayflies live only for a few hours, but nymphs live under water in ponds and streams for a long time.

•Order Odonata - •Dragonflies and damselflies are charismatic insects that have captured the imagination of naturalists and artists across cultures. Juveniles are voracious underwater predators, while the winged adults are fierce aerial hunters.

•Order Grylloblattodea - Rock crawlers are extremophilic insects that thrive in near-freezing temperatures.

•Order Dermaptera - Earwigs have a pair of forceps-like cerci at the tip of their abdomen. They are used to open the wings, to capture prey, and for defense.

•Order Embioptera - Webspinners use silk glands on their enlarged forelimbs to weave silk tunnels and chambers on rocks, the bark of trees, or in leaf litter.

Order Phasmida - Stick Insects are large, slow-moving insects that resemble sticks or leaves.

•Order Orthoptera -includes familiar insects like grasshoppers, locusts, crickets, and katydids. The members of this group are readily identified by their strong hind legs which are modified for jumping.

•Order Hemiptera - a diverse order of hemimetabolous insects. Members of this group are characterized by unique mouthparts modified to form an articulated beak (rostrum) for piercing and sucking liquid food.

Order Blattodea - Cockroaches are mostly nocturnal insect, with biting mouthparts and legs that are adapted for swift running. flattened, allowing the animals to hide in narrow spaces, for example under bark or in crevices of trees and rocks.

Order Mantodea - Mantids are ferocious predators. Insects form their primary prey, but large mantids have been known to capture and consume small scorpions, lizards, frogs, birds, snakes, fish, and even rodents.

Order Coleoptera - The most unusual property of beetles is not some aspect of their structure or natural history, but their sheer number. There are more known species of Coleoptera than any other group of organisms, with over 350,000 described species.

Order Siphonaptera - Fleas are ectoparasites of mammals and birds. Both males and females use piercing-sucking mouthparts to feed on the blood of their host. Some species are vectors of human disease including plague (Yersinia pestis).

Order Diptera - Flies are minute to small, soft-bodied insects with sucking mouthparts and only one pair of functional wings.

•Order Lepidoptera - The butterflies, moths, and skippers. For most species, the majority of the life cycle is spent in the larval (caterpillar) stage.

•Order Hymenoptera - include insects like wasps, bees, ants, bumblebees, and sawflies. Hymenoptera are of economic significance as pollinators, agents of biological control of other insects, and household and forest pests.