Entomology Lecture Notes PDF

**LECTURE 1** **INTRODUCTION TO PHYLUM ARTHROPODA** **Entomology** is the study of insects and their relationship to humans, the environment, and other organisms. **Entomologists** make great contributions to such diverse fields as agriculture, chemistry, biology, human/animal health, molecular sc...

**LECTURE 1** **INTRODUCTION TO PHYLUM ARTHROPODA** **Entomology** is the study of insects and their relationship to humans, the environment, and other organisms. **Entomologists** make great contributions to such diverse fields as agriculture, chemistry, biology, human/animal health, molecular science, criminology, and forensics. **Hierarchy of Classification** - - - - - **Insect Classification** Kingdom Phylum Class Order Family Genus Species ***Example:*** **Kingdom** Animalia **Phylum** Arthropoda **Class** Insecta **Order** Coleoptera **Family** Scolytidae **Genus** Dendroctonus **Species** brevicomis **Insect Relatives** Class Diplopoda Class Chilopoda Class Hexapoda **Most Abundant and Diverse Animal Class** - - - **Distribution of Insects** - - - - - - - - **Reasons for insect success** - - - - - - **Characteristics of Insects** - - - - - - - - - - - **Beneficial Contribution of Insects** 1. Pollinators 2. Produce products a. Honey b. Beeswax c. Silk d. Lacquer 3. Biological Control a. Control insect pests b. Control noxious weeds 4. Clean up and recycle nutrients 5. Solves crime 6. Treatment of wounds 7. Education, demonstration, models, scientific deduction 8. Aesthetic values 9. Serves as food for humans and wildlife 10. Research work **LECTURE 3** **EXTERNAL MORPHOLOGY OF INSECT** **Insect morphology** is the study and description of the [physical form](https://en.wikipedia.org/wiki/Morphology_(biology)) of [insects](https://en.wikipedia.org/wiki/Insect). Three physical features separate insects from other arthropods: they have a body divided into three regions (head, thorax, and abdomen), have three pairs of legs, and mouthparts located *outside* of the [head capsule](https://en.wikipedia.org/wiki/Insect_morphology#Head). **External Structure of a Generalized Insect** 15-2 - The exoskeleton of a grasshopper is made of chitin with ***softer regions*** called **sutures** that allow body ***movement***. **Head** The head consists of the following regions - The ***vertex*** -- top - The ***frons*** -- front - The ***genae*** -- sides - The ***clypeus*** -- a plate below the frons - 2 compound eyes - 3 simple ocelli - 2 antennae - Mouthparts - 1 labrum - 2 mandibles - 2 maxilla - 1 labium **Thorax** **The thorax is divided into 3 regions. These are** - ***Prothorax*** bears the 1^st^ pair of legs - ***Mesothorax*** bears the ^2nd^ pair of legs, 1^st^ pair of wings**,** - ***Metathorax*** bears the 3^rd^ pair of legs, 2^nd^ pair of wings **Insect legs** Each leg is made up of the following parts: - Coxa - Trochanter - Femur - Tibia - Tarsus **Types of Insect Legs** **1.  Cursorial legs.** These are the types of legs most people likely think of if they've ever pondered insect legs before.  Cursorial is a fancy word for running, so these are the kinds of legs you see on swiftly moving insects such as roaches and tiger beetles.    Cursorial legs tend to be long and narrow and are designed so that the insect can move very quickly.  Things with this type of leg are often hard to catch -- or hard to step on if you're dealing with roaches.  **Cursorial leg - cockroach** **2. Saltatorial legs.** Saltatorial legs are jumping legs.    Grasshoppers are the poster insects for saltatorial legs, but other jumping insects like fleas have them as well.  Saltatorial legs work well for jumping because they are enlarged legs filled with bulky, strong muscles.  All those muscles allow insects with this type of leg to jump, propelling themselves forward very long distances very quickly.  Saltatorial legs are usually hind legs. saltatorial Saltatorial leg (grasshopper hind leg) **3. Raptorial legs. **You are likely familiar with this sort of leg too.  Raptorial legs are hunting legs, the kinds of legs you see on predatory insects such as mantids and giant water bugs.  Like the saltatorial legs, these are enlarged legs full of strong, powerful muscles.  However, these legs are usually at the front of the insect and are used to grab and hold prey while they eat.  Many insects with raptorial legs hold them out in front of their bodies, positioned so that they can strike at prey at any time.  Raptorial leg (giant water bug foreleg) **4. Natatorial legs.** Natatorial is another word for swimming, so insects with natatorial legs are aquatic insects that require modified legs to move easily through water.  Natatorial legs are often flattened, broad, and fringed with dense hairs, as in the image of the predaceous diving beetle hind leg pictured at right.  These adaptations have the same sort of effect as a human wearing flippers as they swim -- they increase the surface area of the legs as they kick, allowing the insect to move more easily through water.  Many aquatic insects exhibit natatorial legs, especially in the hind and middle pairs of legs, but not all of them do.  They are especially common in aquatic beetles and bugs. natatorial leg Natatorial leg (predaceous diving beetle hind leg) **5. Fossorial legs.** Insects with fossorial legs live underground and use their highly modified legs, usually the forelegs, to dig burrows.  The mole cricket, the forelegs of which are pictured at left, are a prime example.  Fossorial legs tend to be very broad, very flat, and very dense.  They often have big, strong claws.  Fossorial legs work somewhat like shovels to rip soils apart quickly and easily and allow the insect to bury itself in the ground surprisingly quickly. This type of leg is much less common than the others, but it's a thrill to find an insect that has them!  They're really impressive.  Fossorial leg (mole cricket foreleg) **Wings** The ***1^st^ pair*** of wings are called the ***mesothoracic wings*** - these are the ***forewing***s - are ***narrow*** and ***leathery*** - these are the ***hindwings*** - are ***beneath*** the mesothoracic wings, are ***folded***, and ***thin*** **Types of wings** **Wing adaptations** ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ***Characteristic*** ***Appearance*** ***Order(s)*** ----------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------- ------------------------ **Elytra** \-- hard, sclerotized front wings that serve as protective covers for membranous hind wings elytra Coleoptera\ and\ Dermaptera **Hemelytra** \-- front wings that are leathery or parchment-like at the base and membranous near the tip  Hemiptera: Heteroptera **Tegmina** \-- front wings that are completely leathery or parchment-like in texture tegmen Orthoptera,\ Blattodea,\ and Mantodea **Halteres** \-- small, club-like hind wings that serve as gyroscopic stabilizers during flight  Diptera **Fringed wings** \-- slender front and hind wings with long fringes of hair fringed Thysanoptera **Hairy wings** \-- front and hind wings clothed with setae  Trichoptera **Scaly wings** \-- front and hind wings covered with flattened setae (scales) scaly Lepidoptera **Hamuli** \-- tiny hooks on hind wing that hold front and hind wings together  Hymenoptera **Frenulum** \-- Bristle near base of hind wing that holds front and hind wings together frenulum Lepidoptera ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Abdomen** - elongated and consists of ***11 segments*** at the ***posterior*** end the ***last segment*** is ***modified*** to form the ***ovipositor in females*** used to lay eggs. - there are ***8 pairs of spiracles*** -- used for breathing - there is ***1 pair*** of oval ***tympanic membranes*** used for hearing.  **Types of Insect Antennae (describe the function of insect antennae)** A macro photograph of the antennae of a solitary bee. The large filiform antennae of a [[solitary bee]](https://www.amentsoc.org/insects/fact-files/orders/hymenoptera-apoidea.html). The **antennae** are often called \'feelers\' because the insect waves them around. This is a wrong name because they are not only used for touch. The antennae are actually the insects \'nose\' - they are used for the sense of smell. The paired antennae are made up of a number of individual joints. This means they can be very mobile. The basic form of antenna is filiform. In this type there are many segments that are more or less equal in size. Filiform antennae are seen in a wide variety of groups, such as [Dragonflies](https://www.amentsoc.org/insects/fact-files/orders/odonata.html), [Grasshoppers and Crickets](https://www.amentsoc.org/insects/fact-files/orders/orthoptera.html), [Book Lice](https://www.amentsoc.org/insects/fact-files/orders/psocoptera.html), [Biting Lice](https://www.amentsoc.org/insects/fact-files/orders/phthiraptera.html), [Scorpion Flies](https://www.amentsoc.org/insects/fact-files/orders/mecoptera.html) and [Beetles](https://www.amentsoc.org/insects/fact-files/orders/coleoptera.html). The length and number of joints varies much between them. Filiform antennae This is the most basic form of insect antennae.  Illustration of filiform antennae. This basic structure is modified in a wide variety of ways. This means that a number of different types may be recognized. The main ones are as follows: a. b. c. d. e. f. g. h. **\ ** **LECTURE 4** **FEEDING ADAPTATIONS AND MOUTHPARTS** [Insects](https://en.wikipedia.org/wiki/Insects) have a range of [**mouthparts**](https://en.wikipedia.org/wiki/Arthropod_mouthparts), adapted to particular modes of feeding. Like most external features of arthropods, the mouthparts of hexapoda are highly derived. Insect mouthparts show a multitude of different functional mechanisms across the wide diversity of species considered insects. **1. Biting and Chewing:** - This type of mouth parts are supposed to be the most primitive type as the other types are believed to be evolved from biting and chewing type of mouth parts. - These consist of the labrum forming upper lip, mandibles, first maxillae, second maxillae forming lower lip, hypo pharynx and the epipharynx. - The labrum is median, somewhat rectangular flap-like. - The mandibles are paired and bear toothed edges at their inner surfaces; they work transversely by two sets of muscles to masticate the food. - The first maxillae are paired and lie one on either side of the head capsule behind the mandibles. Each possesses a five-jointed maxillary palp which is a tactile organ. - The first maxillae help in holding the food. - The second maxillae are paired but fused to form the lower lip. Its function is to push the masticated food into the mouth. - The hypo pharynx is single median tongue-like process at whose base the common salivary duct opens. - The epipharynx is a single small membranous piece lying under the labrum and bears taste buds. - This type of mouth parts are found in orthopteran insects like cockroaches, grasshoppers, crickets, etc. - These are also found in silver fish, termites, earwigs, beetles, some hymenopterans and in caterpillars of Lepidoptera. **2. Chewing and Lapping:** - This type of mouth parts are modified for collecting the nectar and pollen from flowers and also for moulding the wax, as is found in honeybees, wasps, etc. - They consist of the labrum, epipharynx, mandibles, first pair of maxillae and second pair of maxillae. - The labrum lies below the clypeus, below the labrum is a fleshy epipharynx which is an organ of taste. - Mandibles are short, smooth and spatulated, situated one on either side of the labrum; used in moulding wax and making the honeycomb. - The labium (second pair of maxillae) has reduced paraglossae, the glossae are united and elongated to form the so called retractile tongue, at its tip is a small labellum or honey spoon. The labial palps are elongated. - The glossa is used for gathering honey and it is an organ of touch and taste. - The first pair of maxillae are placed at the sides of labium, they bear small maxillary palps, lacinia is very much reduced but galea are elongated and blade-like. - The galea and labial palps form a tube enclosing the glossae which moves up and down to collect nectar from flower nectaries. - The nectar is sucked up through the tube, so formed, by the pumping action of the pharynx. - The labrum and mandibles help in chewing the food. Mouth parts of insects **3. Piercing and Sucking:** - This type of mouth parts are adapted for piercing the tissues of animals and plants to suck blood and plant juice, and found in dipteran insects like mosquitoes and hemipteran insects like bugs, aphids, etc. - They usually consist of labium, labrum and epipharynx, mandibles, maxillae (1st pair) and hypo pharynx. **This type of mouth parts can be discussed in the following two headings:** **(i) Piercing and sucking mouth parts of mosquitoes:** - The labium is modified to form a long, straight, fleshy tube, called proboscis. - It has a deep labial groove on its upper side. - The labial palps are modified to form two conical lobes at the tip of the proboscis, called labella which bear tactile bristles. - The labrum is long needle-like. The epipharynx is fused with the labrum. The labrum-epipharynx, thus, covers the labial groove dorsally from inside. - These structures appear C- shaped in transverse section having a groove, called food channel. - Mandibles, maxillae and hypo pharynx are modified to form needle-like stylets which are placed in the labial groove. - **In male mosquitoes, the mandibles are absent**. The mandibles are finer than the maxillae, but both have saw-like edges on their tips. The hypo pharynx possesses salivary duct which opens at its tip. **(ii) Piercing and sucking mouth parts of bugs:** - In bedbug, the labium constitutes a three- jointed proboscis. - The mandibles and maxillae are modified to form stylets; the mandibular stylets possess blade-like tips, while maxillary stylets possess saw-like tips. - The labrum is flap like and covers the labial groove at the base only. - Of the four stylets, mandibles are placed externally in the labial groove, while both the maxillae are placed internally in the labial groove. - The maxillae are grooved and placed in such a way that they form an upper food channel and lower salivary canal. The epipharynx and hypo pharynx are absent. **4. Sponging:** - This type of mouth parts are adapted for sucking up liquid or semiliquid food and found in houseflies and some other flies. - They consist of labrum- epipharynx, maxillae, labium and hypo pharynx; mandibles are entirely absent. - In fact, in this type of mouth parts, the labium, i.e., lower lip is well developed and modified to form a long, fleshy and retractile proboscis. **The proboscis is divisible into three distinct parts:** \(i) Rostrum or basiproboscis; it is broad, elongated and cone-shaped basal part of proboscis articulated proximally with the head and bears a pair of un-jointed maxillary palps representing the maxillae, \(ii) Haustellum or mediproboscis; it is the middle part of proboscis bearing a mid-dorsal oral groove and a ventral weakly chitinised plate-like theca or mentum. A double- edged blade-like hypo pharynx is located deep inside the oral groove; it bears salivary duct and closes the groove of labrum-epipharynx from below. The labrum-epipharynx is a long, somewhat flattened and grooved structure covering the oral groove. The food canal or channel is, thus, formed by labium-epipharynx and the hypo pharynx. \(iii) Labella or distiproboscis; it is the distal part of proboscis and consists of two broad, flattened and oval spongy pads having a series of channels called pseudo tracheae. These open externally by a double row of tiny holes through which liquid food is taken in. The pseudo tracheae converge into the mouth lying between the two lobes of labella which lead into the food canal. **5. Siphoning:** - This type of mouth parts are adapted wonderfully for sucking flower nectar and fruit juice, found in butterflies and moths belonging to the order Lepidoptera of class Insecta. - They consist of small labrum, coiled proboscis, reduced mandibles and labium. The hypo pharynx and epipharynx are not found. - The labrum is a triangular sclerite attached with the front clypeus of the head. - The proboscis is formed by well-developed, greatly elongated and modified galeae of maxillae. - It is grooved internally to form the food channel or canal through which food is drawn up to mouth. - At rest, when proboscis is not in use, it is tightly coiled beneath the head but it becomes extended in response to food stimulus. - The extension of proboscis is achieved by exerting a fluid pressure by the blood. - Mandibles are either absent or greatly reduced, situated on the lateral sides of the labrum. The labium is triangular plate-like bearing labial palps. **LECTURE 5** **INTERNAL STRUCTURE OF A GENERALIZED INSECT**  Nervous system ============== - The central [nervous system](https://www.britannica.com/science/nervous-system) consists of a series of [ganglia](https://www.britannica.com/science/ganglion) that supply nerves to successive segments of the body. - The three main ganglia in the [head](https://www.britannica.com/science/head-anatomy) (**protocerebrum, deutocerebrum, and tritocerebrum**) commonly are fused to form the [**brain**](https://www.britannica.com/science/brain), or supraesophageal ganglion. - The rest of the ganglionic chain lies below the [alimentary canal](https://www.britannica.com/science/gastrointestinal-tract) against the ventral body surface. - The brain is joined by paired connectives to the subesophageal ganglion, which is linked in turn by paired connectives to the three thoracic and eight abdominal ganglia (numbered according to segment). - In most insects the number of separate ganglia has been reduced by [fusion](https://www.britannica.com/science/fertilization-reproduction). - The last abdominal ganglion always serves several segments. - In homopterans and heteropterans all the abdominal ganglia usually fuse with mesothoracic and metathoracic ganglia; and in the [larvae](https://www.britannica.com/science/larva) of higher flies (Cyclorrhapha), the ganglia of the brain, [thorax](https://www.britannica.com/science/thorax), and [abdomen](https://www.britannica.com/science/abdomen) form one mass. - Each ganglion is made up of [nerve-cell](https://www.britannica.com/science/neuron) bodies that lie on the [periphery](https://www.merriam-webster.com/dictionary/periphery) and a mass of nerve fibers, the neuropile, that occupies the center. - There are two types of nerve cells, [**motor neurons**](https://www.britannica.com/science/motor-neuron) and **association neurons**. - **Motor neurons have main processes**, or [**axons**](https://www.britannica.com/science/axon), that extend from the ganglia to contractile muscles, and minor processes, or [dendrites](https://www.britannica.com/science/dendrite-neuron), that connect with the [neuropile](https://www.britannica.com/science/neuropil). - **Association neurons**, usually smaller than motor neurons, are linked with other parts of the nervous system by way of the neuropile. - **Cell bodies** of the sense organs, called [**sensory neurons**](https://www.britannica.com/science/sensory-neuron), lie at the periphery of the body just below the [cuticle](https://www.britannica.com/science/cuticle). - **Sensory neurons** occur as single cells or small clusters of cells; the **distal process, or dendrite**, of each cell extends to a cuticular sense organ ([sensillum](https://www.britannica.com/science/sensillum)). - The **sensilla** are usually small hairs modified for perception of specific stimuli (e.g., touch, smell, taste, heat, cold); each sensillum consists of one sense cell and one [nerve fib](https://www.britannica.com/science/axon)er. - Although these small sense organs occur all over the body, they are particularly abundant in [antennae](https://www.britannica.com/science/antenna-animal-appendage), palps, and cerci. - The sense cell of each sensillum gives off a proximal process, or sensory axon, which runs inward to the central nervous system, where it enters the neuropile and makes contact with the endings of association neurons. - Bundles of both sensory axons and motor axons, which are enclosed in protective membranous sheaths, [constitute](https://www.merriam-webster.com/dictionary/constitute) the nerves. - **[Tactile](https://www.merriam-webster.com/dictionary/Tactile) [hairs](https://www.britannica.com/science/hair-anatomy)** may be sensitive enough to perceive air vibrations and thus serve as organs for [sound reception](https://www.britannica.com/science/sound-reception). - Tympanal organs (eardrums) are present in certain butterflies and grasshoppers. - **Mechanical sensilla** (chordotonal organs) below the surface of the cuticle serve for perception of internal strains and body movements. **\ ** **Digestive System is divided into three regions:** a. **Foregut includes** - Mouth (including salivary gland) - Esophagus --short and tubular - Crop -- a thin walled storage organ - Gizzard -- used for grinding food b. **Midgut includes** - Stomach -- most of the foregut and hindgut is lined with chitin, most absorption occurs in stomach. - Gastric caeca -- organ that open into the stomach and secretes enzymes c. **Hindgut includes** - Ileum - Colon - Rectum - Anus - Genital Chambers https://bugwoodcloud.org/bugwoodwiki/thumb/Digestive\_system.jpg/400px-Digestive\_system.jpg Generalized insect digestive system illustrating the three main regions. Modified from Imms 1934. The internal anatomy of insects is amazingly complex. A good sized caterpillar has more muscles than a human. The internal anatomy of insects differs from vertebrates (including humans) in several major ways. **Digestive/excretory system:**  - Insects have a complete digestive system just like vertebrates (tube from the mouth to the anus) but it differs in a very important way. - The insect digestive system has three major regions, **foregut**, **midgut**, and **hindgut**.  - The foregut and the hindgut are lined with chitin, the same stuff that makes up much of the exoskeleton of the insect. - When an insect molts (sheds it\'s \"skin\", see below) it also sheds the internal lining of the fore- and hindguts. - Loss of the gut contents is a problem if the insect relies on gut microorganisms (gut fauna) to help with digestion. - The gut fauna often lives in the hind gut (termites, for example). Suddenly the gut fauna is lost and must be replenished with every molt. Insects do not have kidneys. Instead, metabolic wastes are removed with the Malpighian tubules. 1. The excretory system consists of ***Malpighian tubules*** which are ***joined*** to the anterior end of the ***hindgut***. 2. They ***remove wastes*** from the blood in the ***hemocoel*** and pass it into the ***hindgut***. 3. They ***rid*** the body of ***uric acid*** and solid ***nitrogenous wastes***. **\ ** **Respiratory (ventilation) system:**  - Insects don\'t have lungs. - They obtain oxygen and dispel carbon dioxide through a series of tubes called tracheae. - The tracheae are attached to openings on the body called spiracles. - The number and placement of spiracles varies and smaller insects may not have any. - Traditionally, the view has been held that respiration in insects is passive, but recent evidence has demonstrated that some insects actively expand and contract trachea to ventilate their bodies.  1. Respiration is taken care of by an ***extensive network*** of ***tubes*** called ***trachea*** that communicate with all parts of the body. 2. This network ***open***s to the ***outside*** through ***openings*** in the body wall called spiracles. **Circulatory system:**  - Insects do not have blood, or blood vessels that are part of a closed circulatory system. - Instead insects have an open circulatory system where a substance called **hemolymph** bathes the organs directly. - Some insects have a long heart-like organ along the dorsal side of the internal organs that helps circulate the hemolymph through the body. - It comprises a single sheath of tissue and a series of muscles, and in many insects includes a tubular portion that functions as a dorsal aorta. - Hemolymph also circulates through the legs, wings, and antennae via a series of simple one-way valves. 1. The circulatory system is much ***reduced*** when compared to other arthropods 2. As in other arthropods it is an ***open system***. There are ***no capillaries or veins***. 3. The elongated heart consists of a ***row of chambers***. 4. Blood enter the heart thru openings called ostia in the chambers. 5. Blood is ***forced*** in an ***anterior direction*** through the ***aorta*** into the hemocoel where it I bathes the internal organs. **\ ** **LECTURE 6** **INSECT LIFE CYCLES, GROWTH & DEVELOPMENT** [Insects](https://www.thoughtco.com/insects-profile-130266) may undergo gradual metamorphosis, in which the transformation is subtle, or they can undergo a complete metamorphosis, in which each stage of the life cycle has a distinctly different appearance from the one before and the one after the current stage---or they can experience something in between. Entomologists classify insects into three groups based on the type of metamorphosis they undergo: ametabolous, hemimetabolous, and holometabolous. **Ametabolous: Little or No Metamorphosis** The most primitive insects, such as [springtails](https://www.thoughtco.com/what-are-these-tiny-black-bugs-that-jump-1968031), silverfish, and firebrats, undergo little or no true metamorphosis over the course of their life cycles. Entomologists refer to these insects as \"ametabolous,\" from the Greek for \"having no metamorphosis.\" When they emerge from the egg, immature ametabolous insects look like tiny versions of their adult counterparts. They continue molting and growing until they reach sexual maturity.  Ametabolous metamorphosis - BugGuide.Net **Hemimetabolous: Simple or Gradual Metamorphosis** Gradual metamorphosis is marked by three life stages: egg, nymph, and adult. Entomologists refer to insects that undergo gradual metamorphosis as \"hemimetabolous,\" from \"hemi,\" meaning \"part,\" and may classify this type of transformation as incomplete metamorphosis.   Growth for hemimetabolous insects occurs during the nymph stage. Nymphs resemble the adults in most ways, particularly in appearance, exhibit similar behaviors, and typically share the same habitat and food as the adults. In winged insects, nymphs develop external wings as they molt and grow. Functional, fully-formed wings mark their emergence into the adult stage of the life cycle. Some hemimetabolous insects include grasshoppers, mantids, cockroaches, termites, dragonflies, and all [true bugs](https://www.thoughtco.com/true-bugs-order-hemiptera-1968634). **Holometabolous: Complete Metamorphosis** - Most insects undergo complete metamorphosis** **over the course of a lifetime. - Each stage of the life cycle---egg, larva, pupa, and adult---is marked by a distinctly different appearance. - Entomologists call insects that undergo complete metamorphosis \"holometabolous,\" from \"holo,\" meaning \"total.\" The larvae of holometabolous insects bear no resemblance to their adult counterparts. - Their habitats and food sources may be entirely different from the adults as well. Holometabolous metamorphosis - BugGuide.Net - Larvae grow and molt, usually multiple times. Some insect orders have unique names for their larval forms: butterfly and moth larvae are caterpillars; fly larvae are maggots, and beetle larvae are grubs. When the larva molts for the final time, it transforms into a pupa. - The pupal stage is usually considered a resting phase, although many active changes are occurring internally, hidden from view. The larval tissues and organs break down entirely, then reorganize into the adult form. After the reorganization is complete, the pupa molts to reveal a mature adult with functional wings. Most of the world\'s insect species---including butterflies, moths, true flies, ants, bees, and beetles---are holometabolous. Growth progresses through successive stages. Females lay eggs, which hatch into an immature stage. After passing through a series of immature stages, the insect emerges as an adult. Adults mate and the cycle begins again. - Most insects start as eggs, which vary in size, shape and color. - They can be deposited singly or in compact masses but are usually protected in some way. - They may be laid in the ground or in or on plant tissue. - Eggs left exposed are often protected from the elements and natural enemies by a coating. Eggs may be round, oval, barrel shaped, disk shaped or suspended on long stalks. The tough outer surface protects the embryo and prevents water loss. The first immature stage of the insect hatches from the egg. **As the insect's rigid exoskeleton cannot expand much, it must be shed and replaced with a larger one as the insect grows**. This process is called **molting**. The life stage between each molt is called an instar. - Molting is governed by hormones. - Cuticle secretion and the molt cycle are controlled by ecdysone, a steroid hormone. - The hormone is secreted by a gland in the thorax, which is in turn controlled by a hormone from the brain. - Whenever the brain receives the appropriate stimulus, the insect will molt. - A new cuticle forms under the old one, then the old exoskeleton splits and the insect wriggles its way out. - Many insects eat their own discarded skin. - The new cuticle is soft at first. The insect may swallow air to expand its own volume and stretch the new exoskeleton before it hardens, usually within about an hour. **Metamorphosis** - Most insects change in form during their development, and the successive stages are not all alike. - This change in form is called **metamorphosis**. - It is controlled by a juvenile hormone secreted by glands in the insect's head. - The **juvenile hormone** is released during each molt, but the amount decreases each time. - As the concentration of juvenile hormone declines, more adult characters will appear until very little or no juvenile remains and the adult stage is produced. - If the juvenile hormone is introduced at the wrong time or in the wrong amount during the insect's life cycle, normal growth can be disrupted. - Insect growth regulators use this principle for pest control. - Some insects change very little in form, and the young and adults are similar except for size. - This type of development is known as **simple metamorphosis**. - The young, which are called **nymphs**, usually share the same habitat and feed on the same host as the adults. - **Nymphs lack wings and reproductive organs**. Aphids and leafhoppers are among the insects that go through simple metamorphosis, as do mites. - Some insects have young and adults that are quite different in appearance from each other and often live in different habitats. - This type of development is known as **complete metamorphosis**. - The young are called **larvae.** - Larvae generally have chewing mouthparts, even when the adults have sucking mouthparts. - The larva goes through a series of stages, finally transforming into a pupa before becoming an adult. The pupa does not feed and is usually inactive. Many insects pass the winter in the pupal stage before emerging as adults.  Insects that go through complete metamorphosis include moths (whose larvae are caterpillars), flies (whose larvae are worms or maggots) and beetles (whose larvae are grubs). The metamorphosis of some insects is somewhere between simple and complete. These include thrips and male scale insects. The length of a generation and how it is influenced by the seasons varies from insect to insect. Many insects have one generation each year. However, some beetles and moths need two or three years to complete one generation. Other insects have more than one generation each year. In some cases, the insect has a constant number of generations. In others, the number of generations may vary depending on the climate. A few insects, such as aphids, have many generations each year and keep reproducing as long as the weather is favorable. In most cases, the insect passes the winter in a state of dormancy. The overwintering stage can be the egg, nymph, larva, pupa or adult. Dormancy can last from days to years. It can be triggered either by environmental or genetic factors. Most insects go into dormancy when the weather becomes unfavorable and become active again when it turns favorable. Others will go into dormancy at a certain time of year before conditions become unfavorable. This is known as diapause. Diapause is often triggered by the shortening days as winter approaches. Many insects require a prolonged period of chilling before they will break diapause. **Reproduction in Insects and Mites** Reproduction in insects and mites can take a wide variety of forms, often very complex. Some can switch their type of reproduction during their life cycle based on environmental triggers. Others reproduce the same way throughout their life history. The basic theme, and some of the variations are described below. **Sexual reproduction** - The standard model for reproduction is where males and females occur throughout the life cycle, and each produces a germ cell (egg and sperm, respectively). - The male inseminates the female during mating. - The female often stores sperm in special pouches in her abdomen called **spermathecae** (singular, spermatheca). - The eggs are fertilized within the female's body, producing an **embryo.** - Eggs are deposited on a host. They hatch and develop into either male or female offspring. **Parthenogenesis** - This is asexual reproduction, where eggs grow and develop without fertilization. - There are several variations of parthenogenesis. - ***Arrhenotokous*** parthenogenesis is where unfertilized eggs produce only males. - In ***deuterotokous*** parthenogenesis, both males and females are produced from unfertilized eggs. - In ***thelyotokous*** reproduction, unfertilized eggs produce only females. - Spider mites, for example, undergo arrhenotokous parthenogenesis, where unfertilized eggs produce males and fertilized eggs produce females. **External insemination** - Insects may reproduce by sexual means, but insemination occurs without mating. - The males deposit spermatophores, which are packets of sperm, and the females extract the sperm from these packets by various means. Rust mites undergo external insemination. **Viviparity** - Most insects deposit eggs that hatch into nymphs or larvae, a process called oviparity, but some insects bear living young. - A common example are aphids, which are viviparous during part of their life cycle. - A variation is ovoviviparity, where eggs are held within the female's body, where they hatch, and the young are born live. **Polyembryony** - This is where two or more embryos develop from a single egg, as in the parasitic Hymenoptera, such as braconid, encyrtid, and dryinid wasps. - Typically, between two and several dozen embryos are produced, but some encyrtids can produce up to 1,500 embryos from a single egg. **\ ** **LECTURE 7** **INSECT ECOLOGY** The word ecology is derived from the Greek term "oikos" meaning "house" combined with "logy" meaning "the science of" or "the study". Thus, literally ecology is the study of earth's household comprising of the plants, animals, microorganisms and people that live together as independent components. The term ecology was coined by a German biologist Ernst Haekel (1869). **Terminologies:** **Habitat** is the place where the organism lives. **Population** denotes groups of individuals of any kind of organisms. Insect populations are group of individual set in a frame that is limited in time and space. **Community** in the ecological sense includes all the populations of a given area. Community can also be defined as interacting 'web' of populations where individuals in a population feed upon and in turn are fed upon by individuals of other populations. **Ecosystem or ecological system** is the functioning together of community and the nonliving environment where continuous exchange of matter and energy takes place. In other words ecosystem is the assemblage of elements, communities and physical environment. Ecosystem is the ultimate unit for study as they are composed of living organisms and the nonliving environment. *Example of natural ecosystems: Ponds, lakes and forests ecosystems* **Biosphere** is the term used for all the earth's ecosystems functioning together on the global scale. **Agroecosystem** is largely created and maintained to satisfy human wants or needs. It is not natural ecosystem but is man- made. Agroecosystem is the basic unit of pest management -- a branch of applied ecology. **A typical agroecosystem is composed of** a. more or less uniform crop-plant populations b. weed communities c. animal communities (including insects) d. microbiotic communities e. and the physical environment the react with. **Unique features of Agroecosystem** a. Dominated by plants selected by man b. No species diversity and no intraspecific diversity. Genetically uniform phenological events germination, flowering occur simultaneously c. Lack of temporal continuity -- due to various agricultural operations carried out by man like ploughing, weeding, pesticide application, etc. d. Plants contain imported genetic material e. Nutrients are added f. Outbreak of pests, weeds and diseases occur frequently **Balance in Nature** Is defined as the natural tendency of plants and animal population resulting from natural regulative processes in an undisturbed ecosystem (environment) to neither decline in numbers to extinction nor increase to indefinite density. In unmanaged ecosystems, a state of balance exists or will be reached, that is species interact with each other and with their physical environment in such a way that on average, individuals are able to only replace themselves. Each species in the community achieves a certain status that becomes fixed for a period of time and is resistant to change which is termed as the balance of nature. When man begins to manage creating new ecosystems (agroecosystems) where natural ecosystems existed previously, the balance is altered. The exceptionally strong forces react in opposition to our imposed change toward a return to the original system (e.g. outbreak of a pest is one of the forces). So insect pests are not ecological aberrations. Their activities counter wants and needs of human populations. Factors that determine insect abundance 1. **Biotic potential** *Example of High Reproductive Rate* A single moth of *Earias vitelli* (Bhendi fruit borer) lays about 200 eggs per female. Life cycle is completed in 1 month After 1 month 200 adults 100 male + 100 male 100 x 200 = 20,000 eggs After 2^nd^ month 10,000 x 200 = 2,000 eggs After 1 year adults 2,000,000,000,000,000,000,000,000 (i.e., 2 followed by 24 zeroes) If a single moth can produce this much, they will cover 24.32 above earth surface in 1 year. But in reality only a fraction of progeny completes life cycle due to environmental resistance. **Environmental resistance** is the physical and biological restraints that prevent a species from realizing its Biotic potential. Environmental resistance may be of 2 types. 1. Biotic factors includes a. Competition (interspecific and intraspecific) b. Natural enemies (predators, parasites and pathogens) 2. Abiotic factors a. Temperature b. Light c. Moisture and water d. Substratum and medium **BIORESOURCES IN ECOSYSTEM** Ecosystem comprises of biological communities and non-living environment e.g. Agroecosystem, pond ecosystem, etc). **Bioresource** refers to the biodiversity of various organisms living in that ecosystem. e.g. The different pests of cotton, its natural enemies, hyperparasitoids, microbes, etc. are referred to the bioresources in cotton ecosystem. **The ecosystem should have more bioresources**. Such ecosystems will be more stable. Insecticides will deplete the bioresources in ecosystem and make it less stable and prone to pest outbreak. **Natural control will be high when bioresources** (e.g. parasitoids and predators) are more. **LECTURE 8** **INSECT BEHAVIOR** It is defined as the way that organisms respond to their environment and to internal signals. In addition to many basic behaviors that are shared by other invertebrates, such as mating, there are some insect [species](https://www.ck12.org/c/biology/species) that are capable of more advanced forms of interaction with each other and with their environments. There are two types of behavior that can be observed in organisms:  1. **Innate behavior**. 2. **Learned behavior.**  - Flight and mating habits are considered innate behaviors. - You have probably seen a clear example of innate insect behavior called the dorsal light reaction. - Flying insects will sense the direction of light coming from the [sun](https://www.ck12.org/c/earth-science/sun) and fly in a way that keeps the sun overhead, or on their dorsal side. - This is a means for the insect to maintain a flight plan that is parallel to the ground. - You may have witnessed that this innate behavior is not so helpful when a moth encounters an [artificial light](https://www.ck12.org/c/physics/artificial-light) source and flies in continuous circles around it to keep the light on its dorsal surface. - At times, the moth is not able to fly away from that light source and, in essence, becomes trapped. - Another insect behavior that you have probably experienced firsthand is sound production. Some insects produce sounds in order to communicate. - An example is the chirping of crickets that often lulls us to sleep on warm summer nights. - They are obtained through life experiences, and they can change or improve over time. - Learned behaviors require acute sensing of environmental signals and a fairly complicated network of nerve cell connections for transmitting those signals in order to process the information and modify or initiate a behavior. - Insects are capable of this level of behavior. In order to forage for food and return to the same food source repeatedly\\, they use a type of learning called **associative learning.**  - Associative learning is when separate ideas or environmental stimuli are connected to each other. - For example, the [location](https://www.ck12.org/c/earth-science/location) of a food source can be associated with a series of visual cues seen on the way to the source. - In this way, the organism learns that if it follows a path that includes all of those visual cues, it will again find the food source. - There are examples of this type of learning that can be tested experimentally. - For example, honeybees can be taught to obtain their food from a particular source based on [color](https://www.ck12.org/c/physics/color) cues, even when the location of that source changes. - They can learn that their food (sugar [water](https://www.ck12.org/c/biology/water)) is located on a yellow dish next to a blue dish containing only water. - If the dish positions are switched, the bees remember which color has the food, and they seek that dish. There are several groups of insects that have evolved complex social networks that involve elaborate patterns of [communication](https://www.ck12.org/c/biology/communication) between individuals within the community. These [species](https://www.ck12.org/c/biology/species) are called social insects, and we will examine their behavior in the next section. #### **Social Insects and Communication** Insects and other organisms that live together in well-organized and tightly integrated colonies are called **eusocial** [animals](https://www.ck12.org/c/biology/animals). Eusocial insects include [species](https://www.ck12.org/c/biology/species) of ants, termites, bees, and wasps. Some colonies can include millions of individual animals. These are two of the major features of eusocial m I nsects: - Division of reproductive labor. - Cooperative care of the young members of the colony. Social ants are a good example of the division of reproductive labor. The individual ants within a colony divide up into three major groups: - Fertile females (queens). - Infertile (sterile) females (workers). - Fertile males (drones). Fertile males and queens carry out the reproductive activities of the colony, while workers focus on obtaining food as well as building and maintaining the nest or hive. In some social insect colonies there are other specialized individuals; nurses, for example, feed and care for young larvae. Often times, some individuals in a colony will form a defensive army with the main purpose of defending the nest. https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3A04c887bb2b05663afbb202c3a737aee01fb29016782a49e49d9b3902%2BIMAGE\_THUMB\_POSTCARD\_TINY%2BIMAGE\_THUMB\_POSTCARD\_TINY.1 **Communication between members of a colony can take several different forms.** - Ants generally communicate using **pheromones.**  - Pheromones are hormones that are released by one individual to be sensed and responded to by another individual. - You may have noticed how a group of ants making their way to a crumb on the ground will generally travel lined up one in front of the other. - This is because they are sensing and following a trail of pheromones that was laid down by an earlier ant that discovered the crumb. - On its way back to the nest, this little pioneer (called a forager) left a trail of pheromone for other colony members to follow. - Honeybees have evolved a fascinating form of [communication](https://www.ck12.org/c/biology/communication) using body movement. - These insects perform an elaborate dance called the "waggle dance" to tell other colony members where to find a source of food. The angle of the dance indicates the particular direction of the food source relative to the [sun](https://www.ck12.org/c/earth-science/sun), and the length of the dance correlates with how far away the food is, as shown in **Figure** [below](https://www.ck12.org/biology/insect-behavior/lesson/Insect-Behavior-Advanced-BIO-ADV/#x-ck12-QmlvSUktMjkwMy0xNg..)**.**  - This is considered a form of abstract symbol [communication](https://www.ck12.org/c/biology/communication), meaning that they use a behavior to represent information (in this case a [location](https://www.ck12.org/c/earth-science/location)) about something in [the environment](https://www.ck12.org/c/chemistry/the-environment).  https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3A4e30cdad5b9b02d55eafde610cdba658bf1d1cd5831a5ad5f77c6c49%2BIMAGE\_THUMB\_POSTCARD\_TINY%2BIMAGE\_THUMB\_POSTCARD\_TINY.1 In addition to the ability to learn, some species of social insects have also been shown to teach behaviors to other individuals. An example of this is seen in one ant species where the forager ant (the one who ventures out to find food) will actually take the time to lead a nest-mate to a new food source, in a way teaching the nest-mate how to forage. **Altruism** is another feature of many social insects. - Altruism is the act of self-sacrifice for the benefit of others. - A worker bee, for example, forfeits her own potential for [reproduction](https://www.ck12.org/c/biology/reproduction) in order to obtain food and provide shelter for the benefit of the queen bee. - This allows the queen bee to focus on the reproduction of her genetic material at the cost of the worker bee reproducing her own genetic material. - This complex phenomenon is a favorite topic of study among philosophers and sociologists, and there are a number of different [theories](https://www.ck12.org/c/earth-science/theories) on the evolutionary advantage of altruism that you can read about in the *Animal Behavior: Evolution (Advanced)* concept. ***Ladybugs: A Population of Millions*** - Ladybugs, also known as ladybird beetles, have a [life cycle](https://www.ck12.org/c/biology/life-cycle) of four to six weeks. In one year, as many as six generations of ladybird beetles may hatch. - In the spring, each adult female lays up to 300 eggs in small clusters on plants where aphids are present. After a week the wingless larvae hatch. - Both the ladybird beetle larvae and adults are active predators, eating only aphids, scales, mites, and other plant-eating insects. - The ladybugs live on the vegetation where their prey is found, which includes roses, oleander, milkweed, and broccoli. - Adult ladybugs don't taste very good. A bird careless enough to try to eat one will not swallow it. - By late May to early June, when the larvae have depleted their food supply, the adults migrate to the mountains. - There, they eat mainly pollen. - The ladybugs gain fat from eating the pollen, and this [tides](https://www.ck12.org/c/earth-science/tides) them over during their nine-month hibernation. - Thousands of adults hibernate overwinter in tight clusters, called aggregates, under fallen leaves and ground litter near streams. - In the clear, warmer days of early spring, the ladybugs break up the aggregates and begin several days of mating.  **Remember:** - There are two types of behavior that can be observed in organisms: **innate and learned**. - Insects are capable of [learned behavior](https://www.ck12.org/c/biology/learned-behavior). - Two of the major features of eusocial insects are division of reproductive labor and cooperative care of the young members of the colony. - Communication between members of a colony can take several different forms such as \"dances\" or pheromones. - In addition to the ability to learn, some species of social insects have also been shown to teach each other various behaviors.