INTRODUCTION TO THE STUDY OF ARTHROPODS CPT 201 INTRODUCTION TO THE STUDY OF ARTHROPODS

Module One INSECTS AND THEIR ALLIES Content ENTOMOLOGY (INSECT SCIENCE) PHYLUM ARTHROPODA

Entomology is a basic and applied science that is dedicated to the study of insects and other related arthropods. The study of insects helps us better understand How to protect our crops, livestock and properties from harmful insects How to protect and conserve insects that are beneficial to man Other animals including man

STRUCTURAL ENTOMOLOGY CAREER OPPORTUNITIES IN ENTOMOLOGY AGRICULTURAL ENTOMOLOGY MEDICAL ENTOMOLOGY TAXONOMIC ENTOMOLOGY STRUCTURAL ENTOMOLOGY MILITARY ENTOMOLOGY VETERINARY ENTOMOLOGY FORENSIC ENTOMOLOGY

were more closely related Among the mandibulates, insects have traditionally been set apart from the crustaceans, and grouped instead with the myriapods (centipedes and millipedes) In recent years, a mass of accumulating morphological and molecular data have shown that insects were more closely related to crustaceans than to any other arthropod group.

Subphylum Trilobitomorpha Subphylum Chelicerata Subphylum Atelocerata PHYLUM ARTHROPODA Subphylum Trilobitomorpha Subphylum Chelicerata Subphylum Crustacea Subphylum Atelocerata

Myriapods Subphylum Atelocerata (Mandibulata) Class Chilopoda Class Diplopoda Class Hexapoda or Insecta Myriapods

Super Order Apterygota e.g. silverfish Class Insecta Subclass Ectognatha Super Order Apterygota e.g. silverfish Super Order Pterygota Subclass Entognatha e.g. springtail

Super Order Pterygota Exopterygota Endopterygota

Stick insect Preying Mantid May fly Grasshopper Dragon fly EXOPTERYGOTA Order Ephemeroptera Order Odonata Order Orthoptera Order Phasmida Order Mantodea Stick insect Preying Mantid May fly Grasshopper Dragon fly

Stink bug Termite Louse Ear wig Stone fly Cockroach EXOPTERYGOTA Order Blattaria Order Isoptera Order Dermaptera Order Plecoptera Order Phthiraptera Order Hemiptera Stink bug Termite Louse Ear wig Stone fly Cockroach

Endoptery-gota Lacewing Scorpion fly Housefly Honey Bee Butterfly Order Hymenoptera Order Neuroptera  Order Coleoptera Order Mecoptera Order Siphonaptera Order Diptera Order Lepidoptera Lacewing Scorpion fly Housefly Honey Bee Butterfly Beetle Flea

Success of Insects as a Group Efficient water conservation methods Ability to consume different kinds and qualities of food. High adaptive capacity Possession of an Exoskeleton Dispersability by air current Exhibition of metamorphosis Smallness of size Capacity of flight

EXTERNAL STRUCTURE OF AN INSECT MODULE TWO EXTERNAL STRUCTURE OF AN INSECT Content THE INSECT’S CUTICLE BODY SEGMENTATION BODY REGIONS

THE INSECT’S CUTICLE Unlike vertebrates, insects have no backbones. Instead, they have a tough outer support framework or exoskeleton called cuticle. The cuticle of each segment is formed into several hardened plates called sclerites, separated by infolds (sutures), which give it flexibility. The sclerite covering each segment is divisible into 4 main parts, namely, a dorsal region or tergum, a ventral region or sternum and on either side, a lateral region or pleuron. The uppermost layer of the insect cuticle is waxy in nature; it controls water permeability and prevents desiccation.

THE INSECT’S SEGMENT

BODY SEGMENTATION The insect’s body is divided externally into a series of segments separated by inter-segmental membranes. The insect body comprises twenty (20) primitive segments, all of which may be apparent in the embryo. These segments are grouped into well defined regions – the head, thorax and abdomen. The grouping of body segments into distinct regions is known as tagmosis or tagmatization. Each body region is referred to as a tagma (Plural: tagmata).

The head is made up of 6 segments and an anterior non-segmental acron that have all fused together into a hard case or head-capsule. The thorax consists of 3 segments, each of which carries a pair of legs. The 2nd and 3rd segments each carry a pair of wings. The thorax is connected with the head by the cervix or neck. The abdomen comprises 11 segments and a terminal non-segmental telson.

THE HEAD AND ITS APPENDAGES The head tagma is highly sclerotized to from a hard capsule or cranium. The head articulates with the thorax through the neck or cervix. The insect head consists of several sclerites and sutures The appendages of the head are called Cephalic appendages Functions of the insect head include – food ingestion, sensory perception, coordination of body activities and protection of the coordinating centres.

SCLERITES AND SUTURES ON A MANDIBULATE’S HEAD

TYPES OF INSECT HEAD PROGNATHOUS HYPOGNATHOUS OPISTHOGNATHOUS

SOME CEPHALIC APPENDAGES INSECT ANTENNAE

SOME MODIFICATIONS OF THE INSECT’S ANTENNAE They are primarily used as organs of smell, but in some insects they may serve additional functions

CEPHALIC APPENDAGES B. INSECT MOUTHPART The insect mouthpart consists of the labrum, mandibles, maxilla and labium. Functionally speaking, the insect’s mouthparts are of two main types namely – Mandibulate (chewing): grasshopper, cockroach Haustellate (sucking): This could be a. Piercing-sucking mouthparts: aphids, mosquitoes b. Siphoning mouthparts: butterfly, bee c. Sponging mouthparts: housefly

MOUTHPART OF A TYPICAL MANDIBULATE

THE THORAX AND ITS APPENDAGES The prothorax does not bear wings. The thorax is made up of three consecutive segments namely the prothorax, mesothorax and metathorax. Each of these segments bears a pair of legs. When the mesothorax and metathorax each bear a pair of wings The prothorax does not bear wings. The segment of the thorax is made up of four body plates (sclerites)namely a dorsal body plate (Tergum or Notum), a ventral body plate (Sternum) and 2 lateral plates (Pleura). Function of the insect thorax is LOCOMOTION

INSECT LEGS AND THEIR MODIFICATIONS THORACIC APPENDAGES INSECT LEGS AND THEIR MODIFICATIONS Insects characteristically have three pairs of jointed legs on thoracic segments. Each leg has six major components: coxa , trochanter, femur , tibia , tarsus , and pretarsus (from proximal to distal). The femur and tibia may be modified with spines. The tarsus appears to be divided into one to five "pseudo-segments" called tarsomeres.

Divisions of a typical insect leg

Like the mouthparts and antennae, insect legs are highly modified for different functions, depending on the environment and habit of the insect. Ambulatory legs: are used for walking. Examples: Bugs Cursorial legs: They are modified for running. Examples: Cockroaches, ground beetles. Saltatorial legs: are hind legs adapted for jumping. Examples: Grasshoppers, crickets. Raptorial legs: are fore legs modified for grasping preys. Examples: Mantids, ambush bugs Fossorial legs: are fore legs modified for digging. Examples: Mole crickets and cicada nymphs. Natatorial legs: are modified for swimming. Examples: Aquatic beetles and bugs. Foragial legs: Legs of honeybee are adapted for various functions

FOSSORIAL FORAGIAL RAPTORIAL SALTATORIAL CURSORIAL NATATORIAL

INSECT WINGS AND THEIR MODIFICATIONS THORACIC APPENDAGES INSECT WINGS AND THEIR MODIFICATIONS Insects are the only flying invertebrates. Wings are present only in adult stage. Number of wings varies from two pairs to none. There is only one pair of wings in the true flies. Normally two pairs of wings are present in insects and they are borne on pterothoracic segments viz., mesothorax and metathorax. Venation (the arrangement of veins in the wings) is different for each group of insects and is used as a means of identification.

The wings of insects may have the following modifications – Elytra Halteres Scales Hemelytra Frenulum Hamuli Tegmina

THE ABDOMEN AND ITS APPENDAGES The abdomen is a highly flexible tagma formed by the fusion 9-11 segments . Each abdominal segment is made up of only two sclerite namely dorsal body plate (tergum) and ventral body plate (sternum). The first eight abdominal segments each bear a pair of spiracles. Abdominal appendages are genital organs and a pair of cerci at the tip of the abdomen. They cerci may be short, long or curved. The abdomen is concerned with the function of reproduction and metabolism.

ADDITIONAL READING Raven, P., Singer, S., Mason, K., Losos, J. and Johnson, G. (2013). Biology. 10th ed., McGraw-Hill Education, 1408 p. Johnson, N. F. and Borror, D. J. (2005). Borror and DeLong's Introduction to the Study of Insects. 7th ed., Thompson Brooks/Cole, 864p. Chapman, R.F. (2013). Insect, structure and function. Simpson, S.J and Douglas, A.E Eds., Cambridge University Press, New York,