Lagos State University, Faculty of ScienceDepartment of Zoology and Environmental Biology

ZOO 305: BASIC ENTOMOLOGY (3 UNITS)2016/2017 SESSION

EXTERNAL FEATURES OF INSECTSThe Team:

Abiodun A. Denloye, Ph. D ; Oyindamola Alafia, Ph. D; Oluwakemi Ajelara, M. Sc.

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DEFINITION AND CONTENT

• Entomology is the science that studies the biology (structure & function), Ecology and importance of insects.– Structure and function (morphology, physiology,

genetics & ecology). – Ecology (the study of the interrelationships

between insects and themselves as well as other organisms relative to their environment).

– Economic importance

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Content:Diagnostic features of insects. Evolution and taxonomy of insects. Insect orders. Insect ecology and distribution; population dynamics, sampling

methods and equipment. Economic importance of insects.

• Distribution• Diagnostic features of insects. Evolution and taxonomy of

insects – Denloye (1st – 3rd wk)

• Insect orders - Alafia (4th – 6th wk)

• Insect ecology and distribution; population dynamics, sampling methods and equipment – Denloye (7th – 9th wk)

• Economic importance of insects – Ajelara. (10th – 11th wk)

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Diagnostic features of insects• There many species (800, 0000 of insects but one basic body

plan. The Model: The American Cockroach (Periplaneta americana)• Why?• 1. It is a large insect – Large size enables good view of various

external structures and internal organs• 2. It is a common insect – Commonness makes it available for

studies• 3. It is important in public hygiene – It would highlight the

role of insects in human societies

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Plate 1: Dorsal view of adult American Cockroach ( Periplaneta americana)

It is such a common insect in Nigeria that it can be found in every house in Nigeria

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• Invertebrates with hard chitinous exoskeleton • Body divided into three tagmata

– Head – Thorax– Abdomen

• Three pairs of jointed legs– Pro-thoracic legs– Meso-thoracic legs– Meta-thoracic legs

• Two pairs of wings (in Pterygote insects)– Fore-wings– Hind wings

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Plate 2: Diagrammatic ventral view of adult female P. americanaNotice the external features of insects in the diagram

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Three tagmata – The head• It is anterior and the first tagma in the insect body• It is made of a fusion of the prostomium with 6 – 7 post oral segments• The fused segments bear appendages which are modified into the

mouthparts and serve as organ of food ingestion.• The head is therefore important to the insect itself and to Man. Why?

• Basic Composition– Cranium a.k.a head capsule (this is a hardened structure)– Antennae (a pair) – sensory – Eyes (simple and compound) - Sensory– Mouthparts – Oral Attachment to the ThoraxThe head is attached to the thorax by means of a membranous region

called the cervix (the neck)

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The head

The head is a fusion of the prostomium with 6 – 7 segmentsIt is normally a capsule with a sclerotized upper portion protecting the brain and a membranous floor in which is situated the oral opening or mouth.

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Plate 4: Frontal section of insect head

The head bears:1.Simple eyes (Ocelli)

Compound eyes 2.Antennae (One pair)3.Mouth parts Parts and funtions The Frons: The upper-mid portion of an insects face. It is that area of the face below the top two 'ocelli‘. it supports the 'pharyngeal dilator' muscles.The 'clypeus' is the area of the face immediately below the frons . It supports the 'cibarial dilator' musclesThe 'labrum' is equivalent to the insect's upper lip ,The vertex: This is the remaining part of the insect face.

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Plate 5: Side view of insect headThe head bears:1.Simple eyes (Ocelli)

Compound eyes 2.Antennae (One pair)3. Mouth parts

Parts and functionsGena: This is the side of the insect head.

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Plate 7: Compound Eyes (Drosophila melanogaster)Compound eyes are commonly found in arthropods A compound eye consists of hundreds or thousands of tiny lens-capped optical units called ommatidia. Each ommatidium has its own1.Cornea, 2.Lens3.photoreceptor cells for distinguishing brightness and color. Each ommatidium guide light through a lens and cone into a channel, known as a rhabdom, which contains light-sensitive cells. These are connected to optical nerve cells to produce the image.

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Plate 8: Compound eye of mosquito

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Two types of compound eyes

A. Apposition Compound Eye• Each ommatidium focuses

only rays that are almost parallel to its long axis, so that each forms an image of only a very small part of the visual field.

• The image of the whole results from a combination of these part images.

• Possessed by diurnal insects

B. Superposition Compound Eye• The sensory cells of an

ommatidium picks up light from a large part of the visual field so that the image received overlaps those received by as many as 30 neighbouring ommatidia.

• Image gains in brightness but loses in sharpness compared with the apposition image

• Possessed by nocturnal insects

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More facts to note on compound eyes

• Compound eyes generally allow only a short range of vision. eg, flies and mosquitoes can see only a few millimeters in front of them with any degree of resolution, although within this short range they can see detail that we could see only with a microscope.

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Plate 9: DragonflyDragonflies have one of the most elaborate eyes of any insect, capable of pinpointing the motion of a small prey insect several meters away, even his while the dragonfly is traveling fast. Each compound eye of dragonflies has 30,000 ommatidia.

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Plate 10: A Monarch butterflyButterflies have color vision that is more enhanced than our own, enabling them to locate food from flowers.

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Plate 11: American cockroach

Each compound eye of the cockroach has 2000 ommatidia.

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Plate 11: A typical antennae

They are a pair of movable segmented appendages usually situated between the eyes The function is largely to perceive chemical stimuli.

They are extremely varied in shape and numbers of segments and are important diagnostic features.

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Plate 12: Modifications of insect antennae1. Filiform e.g Cockraoches and

grashoppers2. Moniliform e.g wrinkeled bark

beetle3. Clavate e.g Carrion beetle4. Serrate e.g Click beetle5. Pectinate e.g fire colored beetle6. Flaballate e.g Cedar beetle7. Geniculate e.g Honey bee8. Plumose e.g male mosquito9. Aristate eg. Flesh fly

10. Stylate e.g Horse fly

For more follow this link: http://bugs.bio.usyd.edu.au/learning/resources/Entomology/externalMorphology/antennaTypes.html

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Plate 12: Insect MouthpartsThe typical mouthpart of the insect is the chewing type as shown in the plate 12 on the rightIt consists of: 1.Clypeus2.Labrum3.Labium4.Mandible5.Maxillae6.Hypopharynx

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Plate 13: Illustrations of typical mouthparts of insects

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Modification of mouthparts• Piercing-sucking type. The mouthparts of aphids, cicadas, leaf-hoppers,

scale insects and others are modified to pierce their plant host and suck juices from it. Predaceous insects like assassin bugs, and bloodsucking insects such as mosquitoes are similarly modified.

• Siphoning tube type. Adult moths and butterflies feed on nectar and other liquids sucked up through a long proboscis.

• Cutting-sponging type. The mouthparts of many flies are modified to cut an opening into tissue and sponge up the fluid.

• Chewing-lapping type. Bees and wasps have mouthparts which permit chewing and tearing of tissue; the fluid material is "lapped up".

• Lapping and Sponging: Houseflies liquify their food and then lap it up.

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Plate 14: Mouthparts of Honey Bee

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Hypognathous: Mouthparts hang ventrally from the head capsule . This is the commonest orientation among plant feeders with chewing mouthparts .

Prognathous: Mouthparts positioned anteriorly to the head capsule. This is commonest among predatory insects.

Opisthognathous: Mouthparts positioned ventroposteriorly (rearwards) relative to the head capsule. (a) hinged, so that they can be swung forwards; commonest among predators with piercing-sucking mouthparts, and (b) fixed, commonest among plant feeders with piercing-sucking mouthparts.

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The thorax

• The insect thorax consists of three segments– Prothorax– Mesothorax– Metathorax

• Each thoracic segment has four sclerites (Plates).Each segment bears one pair of wingsIn mature pterygote insects each of the mesothorax

and metathorax bear a pair of wingsThe mesothorax and metathorax bear one pair of

spiracles each.

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Plate 15: Transverse Section of Insect thorax

The insect thorax is a box-like structure. It is made up of four sclerites (i.e cuticular plates) namely

1.Notum/tergum (Dorsal plate)2.Sternum (Ventral plate)3.Pleuron (2 nos) (Lateral)

The sclerites play important roles in the locomotion of the insect.

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The Leg of InsectsPlate 16 : A typical Insect LegMainly of six sections viz:1.Coxa - the most basal section of the insect leg ; articulates with the 'sternites'. 2.Trochanter - joint between the 'coxa' and the 'femur‘3.Femur - long and stouter than the other segments and contains the main muscles used in running, jumping and digging4.Tibia - generally long; increases the length of the leg; adds an extra joint and thus extra flexibility & the underside of the tarsal segments may possess pads. 5.Tarsus - consists of 1 – 5 segments. Serves as the foot of the insect leg.6.Claws - at the end of the 'tarsus' and assist the insect in holding onto the substrate or to its prey. May possess “arolium”

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Plate 17: Clockwise from Top left - Variegated Grasshopper, Zonocerus variegatus, Paper wasp, Polistes fuscatus; Common Housefly , Musca domestica; and Rhinocerus beetle, Oryctes rhinoceros . Centre – American Cockroach, Periplaneta americana.

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Plate 18:

Cursorial (Running) – e.g Coleoptera: Cicindelidae such as the tiger beetle, a voracious predator. It chases down its prey, much like the tiger after which it is named. The long reach of the leg allows it to move so quickly and results from the long femur and tibia. Even the tarsal segments have lengthened.

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Plate 19: Raptorial legs of a giant water bug (Top) and a Praying Mantis (Bottom) Raptorial: This is for grasping prey.Egs1. Hemiptera: Belostomatidae The giant water bug (Lethocerus americanus) is a ferocious predator . It traps its prey using the large raptorial prothoracic legs. The femur and tibia form a pincer-like grip. Once the prey is immobilized it sucks out the fluids of the haemocoel of the prey . 2. Mantodea: Mantoidea The classic example of raptorial legs is the prothoracic leg of the preying mantid. (Mantis religiosa) . The reach of the pincer-like tibia and femur is extended by elongation of the coxa.

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Plate 20: Praying Mantis (Mantis religiosa)

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Plate 21: Natatorial legs of the giant water bug (Top), Whirlgig beetle (Middle) and Diving beetle (Bottom) Natatorial (Swimming) legsHemiptera: Belostomatidae In addition to its raptorial prothoracic legs, the mesothoracic and metathoracic legs of the giant water bug are modified for swimming. The inner and outer surfaces are lined with a fringe of setal hairs. Which fold out during the power stroke, and back during the during the recovery stroke Coleoptera: Gyrinidae These beetles get their name, whirligig beetles, from the way they swim, spinning around and then shooting off in one direction. Instead of using setal hairs, the mesothoracic and metathoracic legs have been modified as paddles that scull in the water to create the propulsive force. Coleoptera: Dytiscidae Diving beetles swim using hind legs that are fringed with setal hairs. They move their legs in a manner similar to rowing. During the power stroke the hairs increase the surface area and fold back on the recovery stroke .

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Plate 22: A mole cricket (Gryllotalpa gryllotalpa)and its prothoracic leg

Fossorial (Digging) Orthoptera: Gryllotalpidae

The prothoracic legs of the mole cricket are modified for burrowing (fossorial), the modification is when you compare them to the mesothoracic legs . Mole crickets dig and burrow in soft, moist soils.

Key to lower plate: ta = Tarsus, ti = Tibia, fe = Femur, tr = Trochanter, co = Coxa.

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Plate 23: Saltatorial legs of grasshoppers (Top) and Flea (Bottom)

Saltatorial (Jumping) Orthoptera: Acrididae Grasshoppers and crickets have the classic example of the sartorial jumping leg. When the muscles in the femur contract, the joint between the femur and tibia straightens, and the hopper is launched into the air.

Siphonaptera: Pulicidae Fleas are also excellent jumpers, and when at rest the coxa, femur, and tibia are all folded against each other. When they jump, the legs straighten, and the rapid increase in length lifts the flea up and off the ground

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Plate 24: Honey bee leg

Odds 'n ends Hymenoptera: Apidae The metathoracic leg of the honey bee is modified for gathering pollen. The first tarsal segment is very large, and students often confuse it with the tibia. The shape of the tibia and setal hair form a pollen basket. Pollen is packed into the basket by the spine of cuticle on the first tarsomere and is indicated by the pointer.

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The Wings

• Insects are the only invertebrates with wings.• Insect wings are adult outgrowths of the insect exoskeleton that enable them to

fly.• Wings are found on the

Mesothorax (Fore wings) (Protects the hind wings)Metathorax (Hind wings) (For flight)

Fully functional wings are present only in the adults.Only Pterygote insects possess wings but some lose the wings e.g lice and fleas. The wings may be present in only one sex (often the male) in some groups such as

velvet ants and strepsiptera, or selectively lost in "workers" of social insects such as termites and ants.

In some cases, wings are produced only at particular times in the life cycle, such as in the dispersal phase of aphids.

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Plate 25

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Plate 26: A typical Insect wing

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Plate 27: Insect Abdomen

It is the third functional tagma of the insect bodyEach segment of the abdomen consists of - a dorsal sclerite called the tergum -

a ventral sclerite, the sternum

Pleural membrane which joins the sclerites.

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Features of the abdomen• 1. Spiracles: Respiratory openings. On each of the first eight segmentS• 2. Anus: Rear opening of the digestive tract. Sandwiched between three

sclerites namely a dorsal epicropt and a pair of paraproct.

• 3. Genital openings: Found just below the anus. Surrounded by specialized sclerites that form the external genitalia (GO). In males, the GO is usually enclosed in a tube-like aedeagus which functions as the Penis.

• 4. Pincers -- In earwigs (Dermaptera), the cerci are heavily sclerotized and look like forceps. Used for defense, courtship and in folding the wings.

• 5. Median caudal filament -- a thread-like projection arising from the center of the last abdominal segment (between the cerci). Found only in "primitive" orders (e.g. Diplura, Thysanura, Ephemeroptera).

• 6. Sting -- a modified ovipositor, found only in the females of aculeate Hymenoptera (ants, bees, and predatory wasps).

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Plate 28: Insect Ovipositor

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More features of the abdomen7. Abdominal gills -- respiratory organs in the nymphs (naiads) of certain

aquatic insects.

8. Furcula -- the "springtail" jumping organ found in Collembola on the ventral side of the 5th segment. A clasp (the tenaculum) on the third abdominal segment holds the springtail in its "cocked" position.

9. Collophore – This is a fleshy, peg-like structure found in Collembola. It is located on the ventral side of the 1st segment. It maintains homeostasis by regulating absorption of water from the environment.

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Plate 28: Spring tail (Collembola). Notice features of the abdomen

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