Insects and Human Society Lecture 3: Insect Anatomy External Morphology Insects are heterotrophic invertebrates w/ an articulated exoskeleton and 6-legged adults Living organisms Kingdom: Animalia Phylum: Arthropoda Class: Insecta 1
External Anatomy Study of external anatomy is called Morphology Morphology is coined by Goethe in 1822 from the Greek world Morphē (= Form) and the German world Logie (= study) Morphology is the branch of biology that deals with form and structure of animals and plants External anatomy is important to 1) understand the functions of the various insect designs and to 2) allow identification of insects and their relatives Objectives of Lecture Describe and discuss the functions of different body parts of insects: Cuticle Body segmentation Structure of head, thorax, abdomen and their appendages 2
The cuticle Provides the strong exoskeleton of body (that serve to give rigid structure & protect internal organs) and the apodemes (internal support and attachment point for muscles) Cuticle may range from rigid and armor-like (adult beetles) to thin and flexible (many larvae) Prevention of water loss (desiccation) is a critical function of the cuticle Key contributor of the success of insect The cuticle Cuticle is a thin layer but a complex structure Epidermis: Single layer that lies beneath and secretes the cuticle Cuticle is composed of the thicker procuticle overlaid with thin epicuticle Epidermis and cuticle together form an integument (or body wall) which is the outer covering of living tissues of an insect In between sclerites the body wall is softer allows for growth, expansion and movement 3
The Body Wall The body wall or integument is composed of a layer of cells called the epidermis, with the basement membrane on the inside and the cuticle on the outside Procuticle The body wall-cuticle The epicuticle (top layer) prevents water loss, repels excessive water, deters predation, provides patterns for mimicry, reflect solar The exocuticle gives the cuticle its strength and resilience and is formed from chitin (also base for wood, hair, horns) 4
The body wall-pigments Brown and black pigments called melanin are present in cuticle to give insect color other colors may be possible by other pigments with clear cuticle or diffraction patterns in cuticle to give iridescence Some basic terminology Rear Front Top Bottom 5
Segmentation and Tagmosis Arthropod body is composed of several segments Primitive insects were worm-like with many segments (generally 20) In today s insects, segments are grouped into function units or regions or tagmata -- this process is called Tagmosis The 20 original segments composing insects are grouped into 3 regions: Head (6 segments) Thorax (3 segments) Abdomen (11 segments) Insect: Derived from the Latin word insecticum meaning cut into Insect body is cut into three parts: Head (H), Thorax (T) & Abdomen (A) A T H 6
Head Primary Functions of Tagmata Sensory perception Neural integration Food gathering and manipulation Thorax Locomotion Abdomen Houses visceral organs (Digestion, Reproduction, etc ) Structure Insect Head Head is entirely encased in rigid exoskeleton No sign of segmentation Anterior t i part of fthe head dis the frons Orientation Based on the inclination of the long axis of the head compared to the entire body, there are 3 basic types of orientation Prognathus: long axis of head horizontal and in line w/ long axis of insect body Hypognathus: long axis of head is at right angle (vertical) to the long axis of insect body Opisthognathus: long axis of head horizontal, but the tip end is directed backward and arises between the anterior legs 7
Insect Head Composed of the cranum, insect head bears eyes (compound eyes and ocelli), antennae and mouthparts Antennae Eyes Frons Mouthparts Insect Head -- Eyes (Insect Vision) Compound Eyes Compound eyes are large and well developed w/ many small individual facets or ommatidia (ommatidium in singular); has crystalline lens and light concentrating cells Form a picture of what insects see (light sensitive) Present in most adult insects but absent from larvae Ocelli (Ocellus) Simple eyes lack crystalline lens 3 light-sensitive eyes, typically arranged in a triangle are located in the dark surface on the face of the insect Stemmata (only present on some species) Simple eyes with crystalline lens located laterally on certain larvae (holometabolous) 8
Insect Head -- Eyes (Insect Vision) Compound Eyes Insects cannot move or focus their eyes; they have a sharp vision for only a short distance (less than 1 yard) they can see a broader range of light rays than people Insects have no eye lid, their eyes are always open Ocelli Simple eyes cannot form images can only tell differences between dark and light A fly has huge compound eyes that cover most of its head Insect Head -- Antennae One pair of antennae Most insects have 2 antennae between their eyes These antennae are jointed and mobile Used chiefly to smell and feel (touch) Some insects use antennae to taste and hear Antennae can detect humidity changes, vibrations, wind velocity and direction, chemical cues Most insects become distress when antennae damaged or removed and some are helpless 9
Insect Head -- Antennae Antennae vary greatly among insects but all follow a basic plan w/ 3 main divisions 1. basic segment called scape is generally larger than the other segments; it is inserted into the insect head 2. the second segment or pedicel follows the scape contains a sensory organ known as Johnston s organ that responds to movement of the distal part of the antenna 3. the remaining part is the flagellum is often filamentous w/ multiple segments Antennae are reduced or almost absent in some larval insects (e.g. Hymenoptera) Insect Head -- Antennae 10
Insect Head -- Antennae Numerous variations in the antennae of different insects Insect Head -- Antennae Numerous variations in the antennae of different insects Type Description Found on Filiform thread-like field cricket Setaceous bristle-like cockroach Capitate head-shaped nitudilid beetle Clavate tapering club-like butterfly Lamellate flat plate-like June beetle Moniliform string of beads termites Serrate saw toothed click beetle Geniculate elbowed chalcid Pectinate comb-like moth Plumose with plumes mosquito Aristate with an arista housefly Flabellate pile of thick plates cedar beetle 11
Mouthparts Insect Head -- Mouthparts Group of structures on the lower part of the head that are adapted to diet Formed from modified appendages of segments making the head As insects take many forms and have a wide range of food types, they also have various mouthparts that can be grouped into two main categories: Mandibulate (chewing) Haustellate (sucking) Insect Head -- Mouthparts 1. Mandibulate Mouthparts Most primitive mouthparts Adapted to solid diets, these mouthparts are generally biting and chewing Composed of five primary parts: clypeus the upper lip or labrum 2jaw-like structures or mandibles the maxillae (singular maxilla) the lower lip or labium Maxillae and labium are further divided into various substructures 12
Insect Head -- Mouthparts Insect Head -- Mouthparts Chewing mouthparts are present in grasshoppers, crickets, locusts, cockroaches, beetles, caterpillars (larvae of moths and butterflies) Grasshopper Cricket Ground Beetle Black swallowtail caterpillar 13
Insect Head -- Mouthparts 2. Haustellate Mouthparts Used primarily for sucking up liquids of fluids from plants and animals Haustellate mouthparts are divided into 2 groups based on: presence or absence of stylet stylety is a needle-like projection used to penetrate plant or animal tissues Insect Head -- Mouthparts Haustellate Mouthparts Insects w/ stylate MP have a stylet used to pierce and pump up fluids (piercingsucking) Insects with stylet include aphids, leafhopper, flies, fleas, mosquitoes 14
Insect Head -- Mouthparts Haustellate Mouthparts Some haustellate mouthparts lack stylet Unable to pierce tissue they must rely on easily accessible liquid food such as nectar at the base of flower Insects with nonstylate MP comprise butterflies, moths which have long siphoning proboscis Insect Head -- Mouthparts Haustellate Mouthparts Some insects w/haustellate mouthparts feed on liquid but also on solid and semisolid diet by external digestion Solid food is liquefied by digestive fluids before being sucked up. These insects have sponging MP E.g. Housefly 15
Insect Head -- Mouthparts Haustellate Mouthparts Some insects w/haustellate t mouthparts feed on liquids but also semisolid diet by lapping labium modified into a hairy tongue E.g. Honeybee Insect Head -- Mouthparts Most common five mouthparts 16
Insect Head -- Mouthparts Recognition of the types of mouthparts Insect Name Mouthpart Plant injury type? Chewing Hole in leaves Aphid? Removal of juices Honey bee Lapping? Insect Thorax Thorax is the locomotor tagma The thorax of insect consists of 3 segments prothorax p (pro = first) mesothorax (meso = middle) metathorax (meta = last) Each segment consists of hardened plates or sclerites Dorsal sclerite is notum (plural nota), lateral sclerite is pleuron (plural pleura) and ventral one is sternum (plural sterna) Each of the 3 thoracic segment contains one pair of legs Wings are found only on the meso- and meta-thorax. No wings on the prothorax 17
Insect Thorax Legs 3 pairs of legs (6 total) Insect Thorax Fore-legs (2) on the prothorax mid-legs (2) on the mesothorax hind-legs (2) on the metathorax Each leg has 6 major components coxa (plur. Coxae) t h t trochanter femur (plur. femora) tibia (plur. tibiae) tarsus (plur. tarsi) pretarsus (plur. pretarsi) 18
Insect Thorax Legs Femur and Tibia are generally the longest segments Insect Thorax Leg modification: Insect legs are modified for adaptation to various functions walking (gressorial or ambulatorial) like in field cricket running i (cursorial) like in roaches grasping (raptorial) like in praying mantis digging (fossorial) like in Gryllotalpa (ground-dwelling insects) clinging (scansorial) like in fleas hearing (tympanum) like in prothoracic leg of grasshopper swimming (natatorial) like in scavenger beetle jumping (saltarorial) like in hind legs of grasshopper clasping legs in some males to hold females, e.g. Dytiscus male making sound (stridulatory organ) like in tettigoniid collecting food like pollen, e.g. metathoracic leg of bees 19
Insect Thorax -- Common types of legs Wings Insect Thorax When present, wings arise from the meso- and metathorax, but many insects are wingless (without wings or apterygota) Typically, there are 2 pairs of wings, but in few groups wings are reduced to one pair (true flies or Diptera) Wings are mostly membranous but in beetles the forewings (elytra) y are hard cases and do not take part of flight Membranous wings are supported by thickened ribs called veins Pattern of arrangement of these veins used in insect classification 20
Insect Thorax Wing regions Insect Thorax -- Wing Variation - Elytra for protection - Halteres: hind wings completely reduced to mere nubs used for balance and direction during flight (e.g. true flies) - In some male insects, sound producing mechanisms (file and scraper) are present on the underside of forewings and forelegs-- sound used mating calls (e.g. male grasshopper). 21
Insect Abdomen Insect abdomen has 11 segments although segment 1 may be reduced or incorporated into the thorax (e.g. Hymenoptera) and the last 2 segments are variously modified or diminished hard dorsal part of abdomen is tergum (terga) and ventral part is sternum (sterna) Dorsal and ventral plates are joined together by a soft intersegmental membranes There are small dark openings (spiracles) set into the soft membranous area, each along side the abdomen-- one pair on each segment 2 pairs of spiracles are also present on the thorax a pair of cerci of the 11th abdominal segment; cerci permit sensory pickup from the back Insect Abdomen 22
Insect Abdomen Abdomen hosts major viscera, heart, and reproductive organs Reproductive organs are located on the 9th segment for males (aedegus or penis and often a pair of claspers) and on the 8th and 9th abdominal segments for females (external genitalia or copulatory openings and ovipositor for egg laying) In higher Hymenoptera, the ovipositor is modified to form a poison injecting apparatus, the sting (wasps, bees) used for defense Summary of Insect Body 23
Study questions How many segments can be found on a primitive insect? What are the main tagmata of an insect? Are there spiracle on a) head?, b) thorax? How many ocelli are present on an insect? y p What is the function of antennae? Why are they modifications of insect legs? What are the two major groups of insect mouthparts? What are the major functions of an insect head and how do these compare with those of other animal heads? Name the major appendages associated with the insect head? What is the major function of insect thorax? How many segments make up the thoracic region, 20, 11, 9 or 3? Are wings found on all stages and all insects? What is an ovipositor? 24