Entomology PDF - Insects and Their Anatomy

What is entomology? Entomology is the study of insects and their relationship to humans, the environment, and other organisms. Insects are part of the group of animals known as arthropods. What is an insect?  Insects are the most common and successful animals on our planet. More than 1.3...

What is entomology? Entomology is the study of insects and their relationship to humans, the environment, and other organisms. Insects are part of the group of animals known as arthropods. What is an insect?  Insects are the most common and successful animals on our planet. More than 1.3 million species of insects have been named. This is three times the number of all other animals combined. Many are not discovered yet. Insects are everywhere.  The size, shape, color, biology, and life history are so different and make the study of insects interesting. Why do we need to study insects? The scientific study of insects is important for understanding insects, their roles in ecosystems, preserving human health, global economies, and sustainable food etc… Although less than 5% of pests consume 20% of the world's crops and insects have killed more people than conflicts throughout history. Fortunately, many insect species are beneficial, contributing in pest control, nutrient recycling, and crop pollination. They are found in practically every ecosystem and serve an important role in agriculture, biodiversity, evolution, and ecology. Insects and their relatives  Insects are a class of arthropods. Like other arthropods, they have exoskeletons made from the carbohydrate chitin, segmented bodies, and jointed appendages. Insects are distinguished by having three major body segments (head, thorax, and abdomen), with three pairs of legs attached to the thorax. Most adult insects have wings.  Many people call spiders, centipedes, ticks, scorpions by insects. Yet, this is not correct. Though they are close relatives of the insects and classified in one phylum with them (Arthropoda).  Another name of the insect class Hexapoda (six-legged) explains why the listed above animals cannot be included in this class: insects have six legs, ticks, and spiders 8 legs, scorpions and centipedes even more.  There are two main subclasses of insects: 1. Apterygota — primitive and wingless. 2. Pterygota — more advanced and winged. Silver fish (primitive insect) Some advanced insects  The first subclass includes the most primitive insects. Usually they are unseen by people; most of them feed on decaying remains of other organisms. They are small insects widely found in soil.  More advanced adult insects have wings (independent of whether these wings are used for flying or not). Some species of this subclass lost their wings because they adapted themselves to a specific way of life. For example, bedbugs, lice, and fleas.  Insects are divided up into 32 orders, or groups of insects.  Insects have an amazing number of differences in size, shape, and behavior, but they all have 4 characteristics in common. All insects must have: * Three body parts: head, thorax, and abdomen * Six jointed legs  * Two antennae to sense the world around them * An exoskeleton (outside skeleton)  If all four of these things are not true, then the animal cannot be called an insect! EXTERNAL ANATOMY An insect body has a hard exoskeleton protecting a soft interior, it is divided into three main parts (the head, thorax, and abdomen) each of which is in turn composed of several smaller segments. The Head The head capsule houses the brain, a mouth opening, mouthparts, and major sense organs (including antennae, compound eyes, and ocelli). Insect Antennae  Insect head bears a pair of antennae.  All insect antennae have three basic parts: The scape is the first segment and is attached to the head. The next segment is the pedicel. The rest of the antenna is called the flagellum and is made up of many segments.  Antennae may be short as in flies (only 3 segments) or longer than the body and consist of a large number of segments (e.g. cockroaches).  Antennae have different forms and shapes.  Insects use antennae for detecting odors! So, insects can smell and find food or partners for mating from a large distance (may be more than 11 Km like moths).  Antennae can listen to sounds or detect the movement of air or wind (e.g. males of mosquito).  Antennae are used also as tactile organs for measuring the temperature and humidity. The Eyes  Insects have two compound eyes.  Each compound eye is composed of several individual units (between hundreds and thousands).  Most insects have also a few numbers of simple eyes (ocelli).  There are insects with very small eyes or with no eyes at all, for example worker termites living underground. Completely blind insects are found also in caves. Mouth parts  There are various kinds of mouthparts found in insects depending on the type of food: chewing (cockroaches), siphoning, piercing-sucking, sponging.  The Insect mouth consists of several parts. The basic chewing mouthparts found in cockroaches and locusts have become highly modified in other insects. Siphoning in butterflies and moths, sponging in the houseflies, piercing sucking in Blood and sap sucking insects such as female mosquitoes. Some adult insects such as mayflies do not eat at all. Therefore, they do not need mouth. 2- The thorax The second (middle) part of an insect's body is called the thorax. It is composed of three segments and is mainly adapted for locomotion. It carries three pairs of walking legs and, in many adult insects, one or two pairs of wings. Insect Legs  Each leg contains five segments (coxa, trochanter, femur, tibia and tarsus).  There are many types of inset legs according to their function: Walking as in cockroaches, jumping as in locusts, swimming as in water beetles, digging as in Gryllotalpa, or seizing as in mantis). Walking Collecting Jumping Swimming Digging Seizing The wings  Most insects have two pairs of wings.  Wings of insects have different shapes and structures. The wings may be membranous as in bees, sclerotized as in beetles, or covered with scales as in butterflies and moths.  In most cases, a characteristic network of veins runs throughout the wing. Membranous wing Elytra wing Scaly wing 3- The abdomen  The abdomen is the third region of insect’s body, and it consists of several segments.  Abdominal segments often "telescope" inside each other, allowing the abdomen to expand and contract.  In many adult insects, there is a spiracle (opening to the respiratory system) on each side of most abdominal segments.  At the end of the abdomen there are the anus and genital opening.  In some insects there are structures for feeling egg laying (ovipositor) or stinging (stinger) like bees and wasps. Ovipositor Stinger