Entomology

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Entomology is an event in which competitors must be able to identify insects from 30 orders and 100 families. On most tests, questions about behavior, structure, human impact, and any characteristics of certain insects may be asked. This event is similar to the old Division B event, Don't Bug Me.

The 2015 Official Insect List is located on soinc.org. For information about the insects on the official list, see Entomology/Entomology Insect List.

What is an insect?

An insect is an invertebrate with several distinguishing characteristics. These characteristics, which are also outlined in the table below, include: segmented bodies with paired, many jointed legs; 3 major body sections; 6 legs; and 2 antennae.

Insect Taxonomy

All insects are classified as members of the following taxonomic groups:

  • Kingdom: Animalia
    • Phylum: Arthropoda
      • Subphylum: Mandibulata
        • Superclass: Hexapoda
          • Class: Insecta

This table outlines major characteristics members of each group are required to possess.

Insect Taxonomy
Level Name of Rank Characteristics Required
Kingdom Animalia Heterotrophic; Eukaryotic; Multicellular; No cell wall, no chloroplasts; Motile (able to move, opposite of sessile); Sense Organs.
Phylum Arthropoda Chitinous exoskeleton that must be shed during growth (molting); Jointed paired appendages (legs and antennae); Segmented bodies that are arranged into regions, called tagmata (e.g., head, thorax, abdomen); Bilateral symmetry; Ventral nervous system; Open, dorsal circulatory system;
Subphylum Mandibulata Have modified appendages (mandibles) flanking the mouth and used as jaws;
Superclass Hexapoda 3 pairs of legs (6 total) that are located on the thorax
Class Insecta Head, thorax, abdomen; 3 pairs of legs (one on each thoracic segment); One pair of antennae on head; 1-2 pairs of wings in most; Pair of compound eyes in most, along with 1-3 simple eyes;

General Tips for ID'ing Insects

A very important part of this event is learning how to quickly identify the order and family of a given insect. The following is a list of tips for discerning the order/family of an insect.

  • Color is generally not a good way to ID and differentiate insects.
  • For orders such as Hymenoptera, Diptera, and Lepidoptera, wing venation is very important in ID'ing to the family
  • Know each major order's defining traits.
    • Diptera: Only one pair of functional wings, second pair of wings modified into halteres
    • Hymenoptera: Forewings usually lager than hind wings, hooked together by hamuli
    • Coleoptera: Forewings modified into elytra, which serve as protective covers for hind wings
    • Lepidoptera: Two large pairs of wings; Hooked together by a frenulum

Insect Development

  • Morphogenesis: All changes that involve growth, molting, and maturation

Molting

  • Triggered by hormones released when an insect's growth reaches the physical limits of its exoskeleton
  • Marks the end of one instar or growth stage, and the start of another
  • When it becomes sexually mature, an inset is known as an imago or adult. At this point, molting stops and energy for growth is channeled into production of eggs or sperm.
  • An insect cannot survive without the protection and support of its exoskeleton, so a new, larger one must be constructed inside the old one

Here is a summary of the processes involved in insect molting:

  • Step 1: Apolysis -- separation of old exoskeleton from epidermis
  • Step 2: Secretion of inactive molting fluid by epidermis
  • Step 3: Production of cuticulin layer for new exoskeleton
  • Step 4: Activation of molting fluid
  • Step 5: Digestion and absorption of old endocuticle
  • Step 6: Epidermis secretes new procuticle
  • Step 7: Ecdysis -- shedding the old exo- and epicuticle
  • Step 8: Expansion of new integument
  • Step 9: Tanning -- sclerotization of new exocuticle

Types of Metamorphosis

Not all insects develop in the same way. Types of metamorphosis are grouped based on the number of stages required to reach sexual maturity. The table below explains the different types of metamorphosis and gives example groups.

Types of Metamorphosis
Metamorphosis Type (alternate name) Description Wing Type Example Orders
Ametabola (no metamorphosis) Young resembles the adult, but is smaller. Development involves increasing the insect's size by going through successive molts. Apterogyte (adults like immature without wings) Protura, Diplura, Thysanura, and Collembola
Hemimetabola (incomplete metamorphosis) Developmental stages include egg, nymph, adult Exopterygote (wings develop externally on the nymph body) Emphemeroptera, Odonata, Blattodea, Mantodea, Isoptera, Grylloblattodea, Dermaptera, Plecoptera, Orthoptera, Phasmatodea, Psocoptera, Mallophaga, Anoplura, Thysanoptera, Hemiptera, Homoptera
Holometabola(complete metamorphosis) Developmental stages include egg, larva, pupa, adult Endopterygote (wings develop inside of body in immature insects and not visible until adult emerges from pupa) Megaloptera, Neuroptera, Coleoptera, Strepsiptera, Mecoptera, Siphonaptera, Diptera, Trichoptera, Lepidoptera, Hymenoptera

Larvae Appearance

Most larvae can be divided into five basic groups based on their appearance.

Larvae Types
Larval Type (common name) Picture Description Examples
Eruciform (caterpillar) Caterpillar.gif Body cylindrical with short thoracic legs and 2-10 pairs of fleshy abdominal prolegs Moths & Butterflies
Campodeiform (crawler) Crawler.gif Elongated, flattened body with prominent antennae and/or cerci. Thoracic legs adapted for running Lady beetle, Lacewing
Scarabaeiform (white grub) Grub.gif Body robust and "C"-shaped with no abdominal prolegs and short thoracic legs Scarabaeidae
Elateriform (wireworm) Wireworm.gif Body long, smooth, and cylindrical with hard exoskeleton and very short thoracic legs Elateridae
Vermiform (maggot) Maggot.gif Body fleshy, worm-like. No head capsule or walking legs House fly, flesh fly

Pupa Appearance

Pupae can be grouped into one of three categories based on physical appearance.

Pupa Types
Pupal Type (common name) Picture Description Examples
Obtect (chrysalis) Obtect.gif Developing appendages (antennae, wings, legs, etc.) held tightly against the body by a shell-like casing. Often found enclosed within a silken cocoon Butterflies and moths
Exarate Exarate.gif All developing appendages free and visible externally Beetles, Lacewings
Coarctate (puparium) Coarctate.gif Body encased within the hard exoskeleton of the next-to-last larval instar Flies

Insect Behavior

In this event, it is important to understand the basics of insect behavior. While this is not a major portion of the event, a basic knowledge is necessary. For example, you should know about social interactions between insects, and have a rudimentary understanding of the ways in which insects communicate with one another.

Social Insects

Some groups of insects, such as termites and bees, live together in a common nest or colony. Social behavior can vary greatly from group to group. Different classifications of social behavior are outlined below.

Social Insects
Classification Name Common Nest Site Cooperative Brood Care Reproductive Castes Generation Overlap
Solitary No No No No
Communal or Subsocial Yes No No No
Quasisocial Yes Yes No No
Semisocial Yes Yes Yes No
Eusocial Yes Yes Yes Yes

Definitions for each classification outlined in the table are below:

  • Solitary: Not sharing a nest or providing care for offspring
  • Communal: Members of the same generation use the same composite nest site without cooperating in brood care
  • Subsocial: Adults provide some kind of parental care for their offspring
  • Quasisocial: Members of the same generation use the same composite nest site and also cooperate in brood care
  • Semisocial: Cooperative brood care within a composite nest is provided by a worker caste that is more or less sterile
  • Eusocial: Cooperative brood care within a composite nest is provided by a worker caste that is more or less sterile and lives long enough to assist the parents. In order to be considered eusocial, an insect group must possess all four of the following characteristics:
    • Share a common nest site
    • Individuals of the same species cooperate in caring for the young
    • Reproductive division of labor - sterile (or less fecund) individuals work for the benefit of a few reproductive individuals
    • Overlap of generations - offspring contribute to colony labor while their parents are still alive

Advantages and Disadvantages of Living in Groups

Advantages:

  • Can accomplish feats that are impossible for solo insects
  • Construction of huge nest sites
  • Widespread foraging for food
  • Constant vigilance against predation or parasitism

Disadvantages:

  • Large colonies are especially vulnerable to the spread of contagious pathogens
  • Nest sites may be exploited by "social parasites" who steal food or attack the brood
  • Individuals must compete with each other for space and resources (such as food)

Links for Information About Specific Social Insects

Insect Communication

  • Communication: An action or condition on the part of one organism that alters the behavior of another organism in an adaptive way.
  • Insects communicate with one another for a variety of reasons, including:
    • Recognition of kin or nestmates
    • Locating or identifying a member of the opposite sex
    • Facilitation of courtship and mating flasher
    • Giving directions for location of food or other resources
    • Regulating spatial distribution of individuals -- aggregation or dispersal
    • Establishing and maintaining a territory
    • Warning of danger; setting off an alarm
    • Advertising one's presence or location
    • Expressing threat or submission (agonistic behaviors)
    • Deception / mimicry
  • Types of communication include:
    • Tactile
    • Visual
    • Acoustic
    • Chemical

Tactile Communication

Many insects with poor vision and sound perception use physical contact as an important means of communication. Examples of insects that use tactile communication are listed below.

  • Meloidae: courtship begins with a series of antennal taps by the male on each side of the female's body. She signals her receptivity by lifting her wing covers (elytra) and allowing him to climb on her back. But to complete his quest, the male must continue tapping, alternating from side to side at just the right frequency until the female is stimulated to extend her genitalia and begin mating.
  • Formicidae and Isoptera: Antennal Tapping- It is unclear what type of information is exchanged during antennal tapping, but it certainly involves nestmate recognition and leads to exchange of food through trophallaxis.
    • Tandem Running: A "follow-the-leader" behavior in which the tapping informs the leader that she has not lost her disciple. If tapping stops, the leader instinctively turns around and searches in ever-widening circles until she re-establishes contact with the follower.
  • Honeybees: "Dance Language" For more information about the dance language of honeybees, please see this page
  • Gyrinidae: Tactile cues generated by ripples on the water surface allow the beetles to constantly monitor the location of dozens of other nearby whirligigs. Thanks to this tactile communication system, the whirligigs can swim rapidly in circles, avoid bumping into other members of their own species, and still detect the presence of nearby predators or prey.
  • Membracidae (certain species): Produce vibrations in the tissue of their host plant that can be felt by all other treehoppers on the same plant. The signals apparently work as an alarm system, and in some species, they may be used by nymphs to elicit protective maternal behavior. Substrate vibrations can be a particularly effective system of communication for small insects who cannot generate an acoustic signal loud enough to be heard more than few inches away.

Some benefits to tactile communication include:

  • Instantaneous Feedback
  • Localized Area
  • Individual Recipient
  • Effective in the dark (e. g. caves, wood galleries)

Some limiting factors to tactile communication include:

  • Not effective over distance
  • Insects must stay in direct contact
  • Message must be repeated to each recipient
  • Vibration signals can be intercepted by predators

Chemical Communication

Insects seem to rely more on chemical signals more than any other form of communication. They use their senses of taste and smell to detect the presence of chemical compounds in the air. Chemoreceptorscan be found anywhere on the body, but are most commonly found on the feet, antennae, palps, and ovipositor. These signals are divided into two main groups: semiochemicals and infochemicals.

Semiochemicals can be divided into two groups based on who "sends" a message and who "receives" it:

  • Pheromones are chemical signals that carry information from one individual to another member of the same species. These include sex attractants, trail marking compounds, alarm substances, and many other intraspecific messages.
  • Allelochemicals are signals that travel from one animal to some member of a different species. These include defensive signals such as repellents, compounds used to locate suitable host plants, and a vast array of other substances that regulate interspecific behaviors.
  • Allelochemicals can be further subdivided into three groups based on who "benefits" from the message:
    • Allomones benefit the sender such as a repellent, or defensive compound (e. g. cyanide) that deters predation.
    • Kairomones benefit the receiver- such as an odor that a parasite uses to find its host.
    • Synomones benefit both sender and receiver. Examples include plant volatiles that attract insect pollinators.

Some benefits of chemical communication include:

  • Not limited by environmental barriers
  • Effective over distances and around corners
  • Effective either day or night
  • Longer lasting than visual or auditory signals
  • Metabolically "inexpensive" because only small quantities are needed

Some limiting factors of chemical communication include:

  • Low information content (presence/absence)
  • Not effective in an upwind direction

Acoustic Communication

Most insects detect sound with a tympanic membrane in the abdomen (e.g. grasshoppers and moths) or in the tibiae of the front legs (e.g. crickets and katydids). Mosquitoes have antennal hairs that resonate to certain frequencies of sound. But sound vibrations can also travel through solid objects, and some insects (e.g. some species of ants, bees, termites, and treehoppers) can sense substrate vibrations with mechanoreceptors (chordotonal organs) in their legs. Since these signals are "felt" rather than "heard", they are usually regarded as a form of tactile communication.

Some benefits of acoustic communication include:

  • Not limited by environmental barriers
  • Effective over distances and around corners
  • Highly variable, fast change- high information content
  • Some limiting factors of acoustic communication include:
  • May reveal location of sender to a potential predator
  • Less effective in "noisy" environments (e.g. seashore)
  • May be metabolically "expensive" to produce
  • Attenuation- intensity falls rapidly with distance from source (cube-root function)

Visual Communication

Many insects communicate with visual signals. These visual signals usually fall into one of two groups: active or passive signals.

Passive signals, such as eyespots and color patterns can serve as a form of "free advertising". The colorful wings of a butterfly, for example, are a "billboard" publicizing its species identity. Individual insects incur little or no metabolic cost for displaying these messages because they are an integral part of the integument. It may be prudent to hide these signals from a potential predator, so some insects have a way to conceal their message when necessary. The red admiral butterfly, for example, has bright, distinctive markings on the upper wing surface and drab, protective coloration on the underside.

Active signals, like body movements and light flashes, are more costly to produce, but they can be withheld from use at inappropriate times. They may also have a higher information content because signal frequency, duration, or periodicity may convey additional meaning. In fireflies, for example, pulses of light are used in a courtship dialogue between a male (usually flying) and a female (usually perched in the vegetation). Each species has a unique flash pattern and response time.

Some benefits of visual communication include:

  • Effective over long distances
  • Can be used while moving
  • Fast- speed of light
  • Effective in all directions (independent of wind)
  • Passive signals require no expenditure of energy

Some limiting factors of visual communication include:

  • Requires a clear line of sight
  • Visual signals may be intercepted by predators
  • Only effective in daylight (in fireflies, only at night)
  • Active signals may be metabolically "expensive" to produce

Insect Ecology

Relating to insect ecology in this event, you will most likely be asked if an insect is a herbivore/carnivore/decomposer and what it feeds on. It is also important to have a basic understanding of parasitism, as many insects are parasites.

Trophic Levels

  • All insects are consumers. They may be found in all levels of a food chain except the first.
  • For more information about tropic levels and basic ecology, please visit this page.

Herbivores

  • Phytophagy/phytophagous: Relating to plant feeding
  • Monophagous: An insect that restricts itself to a single host species
  • Oligophagous: An insect with a slightly broader host range
  • Polyphagous: Equipped with "broad-spectrum" detoxification enzymes that can overcome a wide range of plant defenses
  • Feeding Guild: Within a feeding guild, all species compete directly with each other for exactly the same resource. Between members of different guilds, competition is usually less direct and less severe.

Insects that eat plants generally use visual or olfactory cues to locate a host plant. Visual cues can include the vertical silhouette of a tree or certain shapes/colors that insects associate with "food". Odor cues are plant volatiles such as the saponins in alfalfa, the mustard oils in crucifers, or the terpenes in conifers.

Carnivores

  • Zoophagy: A term for all insects that: catch and kill other insects (or non-insect arthropods) as food, parasitize the bodies of other animals, and feed by sucking blood
  • Predators: zoophagous insects that kill and eat numerous prey individuals in the course of their growth and development. Usually much larger than their prey
Parasitism
  • Parasite: an organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense. Usually much smaller than their host, and may complete their development on the body of a single host individual.
  • A "true" parasite does not kill its host, but it may spread disease pathogens or cause other disability such as skin irritation, intestinal blockage, organ failure, or allergic reactions.
    • Endoparasites: Live inside the host's body
    • Ectoparasites: Live in the host's nest or on the surface of its body
  • Hematophagy: Blood feeding- a common practice among insects that parasitize vertebrate animals (Siphonaptera, Phthiraptera)
  • Parasitiod: An insect that lives in or on the body of a single host individual during their larval stage but become free-living as adults. These insects do not fit the classical definition of a "parasite" because they feed on the internal organs and tissues of the host individual and eventually kill it.
  • Hyperparasites: parasites (or parasitoids) of another parasitoid species.
  • Autoparasites: species in which the females feed on males to obtain a nutritional advantage.
  • Brood Parasites: insects that live in the nests of social insects and feed on the juveniles.
  • Social Parasites: insects that steal food or other resources from the nests of social insects.

Decomposers

  • Saprophages: Insects that eat the dead bodies of plants and animals. These insects are an important part of the biosphere because they help recycle dead organic matter
  • Within the ranks of saprophagous insects, entomologists recognize several major groups:
    • Those that feed on dead or dying plant tissues
      • Include a wide variety of soil- and wood-dwelling species that shred leaves or tunnel in woody tissues. They accelerate decay by increasing the surface area exposed to weathering and the action of other decomposers. They are largely responsible for creating a layer of humus that often covers the soil. This layer serves as an incubator for the fungi, bacteria, and other microorganisms that release carbon, nitrogen, and mineral elements for uptake by living plants.
    • Those that feed on dead animals (carrion)
      • Include numerous beetles, fly larvae (maggots), wasps, ants, mites, and others. Each species colonizes the dead body for only a limited period of time but, as a group, they rapidly consume and/or bury the decaying flesh. Blow flies, usually the first to arrive on a carcass, are also the first to complete development and depart. Other species follow over time in a relatively predictable sequence as the body decomposes.
    • Those that feed on the feces of other animals
      • Many species of manure flies and dung beetles are attracted to the odor of animal excrement. Adults lay their eggs on fresh feces and larvae feed on the organic matter in these waste products. Many dung-feeders exhibit distinct preferences for particular types of manure: the species associated with horse manure, for example, may be quite different from those found on the same farm in cattle manure.
  • In addition to their role as decomposers, some saprophagic insects also serve as pollinators for plants like skunk cabbage and wild ginger. These plants produce drab colored, foul smelling flowers that attract the attention of blow flies or carrion beetles. The insects crawl around in the flowers looking for food and unwittingly pick up pollen.

Survival Strategies

Insects owe their success throughout geologic time to a variety of adaptations and survival strategies.

Relating to anatomy, insects have the following adaptations:

  • An Exoskeleton
  • Small Size
  • Flight
  • Reproductive Potential
  • Metamorphosis
  • Adaptability

Relating to behavior, insects have the following adaptations:

  • Migration
  • Diapause
  • Cold-Hardiness
  • Parthenogenesis
  • Polymorphism

Anatomical Defenses

The Exoskeleton

An insect's supporting skeleton is located on the outside of its body. This exoskeleton gives shape and support to the body's soft tissues, protects from attack or injury, minimizes the loss of bod fluids in both arid and freshwater environments, and gives a mechanical advantage for strength and agility in movement. As a "suit of armor", the exoskeleton can resist both physical and chemical attack. It is covered by an impervious layer of wax that prevents desiccation. Much of the exoskeleton is fabricated from chitin, a polysaccharide that binds with various protein molecules to form a body wall that may be as flexible and elastic as rubber or as hard and rigid as some metals. Freedom of movement is ensured by membranes and joints in the exoskeleton. Muscles that attach directly to the body wall combine maximum strength with near-optimum mechanical advantage (leverage). The result is an ant, for example, that can lift up to 50 times its own body weight.

Small Size

Many insects are between 2 and 20mm in length. For an animal with an exoskeleton, small size is a distinct advantage. If insects were as large as cows or elephants, their exoskeleton would have to be proportionately thicker to support the additional mass of body tissue. A thicker exoskeleton would also be heavier and more cumbersome. Even the simplest movements would require a larger muscle volume and consume more energy.

Small size also minimizes the amount of resources insects need for survival and reproduction. For example, a crumb can be a large meal, a dewdrop can be a large drink, and a pebble can provide shade. Many insects may live on a single plant or animal for its entire life and never exhaust its food supply.

Lastly, small size is an advantage to insects that must avoid predation. They can hide in the cracks of a rock, beneath the bark of a tree, behind the petal of a flower, or under a blade of grass. The exoskeleton is hard enough for them to burrow between individual grains of sand, yet flexible enough to let them squeeze through the tiniest of cracks. Small size, together with adaptations in body shape and coloration, gives many species the ability to blend so well with their environment that they become virtually undetectable.

Flight

Insects are the only invertebrates that can fly. Judging from the fossil record, they acquired this ability about 300 million years ago - nearly 100 million years before the advent of the first flying reptiles. Flight is a highly effect mode of transportation and escape from predators. It allowed insects populations to expand more quickly into new habitats.

Reproductive Potential
  • High Fecundity: Females produce large amounts of eggs
  • High Fertility: A majority of the eggs hatch

High fecundity, high fertility, and a short life cycle allow insects to produce large numbers of offspring. Since most insects die before they ever have an opportunity to reproduce, a high reproductive potential is the species' best chance for survival. Many adaptations help maximize this potential. Most females, for example, can store sperm for months or years within the spermatheca, a special region of the reproductive system. A single mating can supply a female with enough sperm to fertilize all the eggs she will produce in her lifetime. An unbalanced sex ratio, where females outnumber males, is another way to maximize reproductive potential. Since most insects are not monogamous, a few males can supply sperm for a large number of females. And finally, there are many species (e.g. aphids, scale insects, thrips, and midges) where males are entirely absent - all members of the population are female and contribute offspring through a process of asexual reproduction.

Metamorphosis
  • Metamorphosis: The significant developmental changes experienced by insects as they grown from immatures to adults. Can include physical, biochemical, and/or behavioral alterations that promote survival, dispersal, and reproduction of the species.

More primitive insects typically experience changes gradually as they mature. Since this transformation process is slow and does not include all body tissues (incomplete metamorphosis) the immatures and adults share many characteristics - they often live in similar habitats and feed on similar types of food.

Advanced insects, however, undergo complete metamorphosis. In these cases, a larva is adapted for feeding and growth. It assimilates energy reserves which, in some cases, will sustain the insect for the rest of its life. When fully grown, a larva molts into a transitional stage, called the pupa, and begins a period of massive internal and external reorganization. Body organs and tissues encoded by larval DNA are disassembled and rebuilt according to a second DNA blueprint that had been repressed during larval life. An adult insect (imago) eventually emerges from within the pupal exoskeleton bearing little or no resemblance to its larval form. Its primary function is dispersal and reproduction.

Metamorphosis gives the more advanced insects an advantage because through natural selection, larval form and function can be optimized for growth and feeding without compromising adaptations of the adult for dispersal and reproduction. Each stage of the life cycle is entirely free to adapt to its own ecological role. In some cases, this means that immatures and adults may consume different types of food, exploit different environmental resources, and even occupy different habitats.

Behavioral Strategies

Migration
  • Migration: A period of directional movement that carries an insect beyond the range of their local habitat. This survival strategy has at least six potential advantages:
    • Escape from natural enemies
    • Find more favorable growing conditions
    • Reduce competitions or relieve overcrowding
    • Locate new/unoccupied habitats
    • Disperse to alternate host plants
    • Reassort the gene pool to minimize inbreeding

More about insect migration

Although most insects migrate by flying, a few species (chinch bugs, Mormon crickets, and armyworms, for example) travel on the ground. Migration by flight is often aided by prevailing winds. Once airborne, small insects may be lifted by thermal convection and carried hundreds of miles on frontal air masses. Even wingless individuals may be carried aloft by "ballooning" on silk threads or blowing off tall vegetation. Larger insects, like dragonflies and monarch butterflies, may control the direction of their migratory flights, but most smaller insects are carried wherever the wind blows them.

Migration is usually a distinct phase in the life cycle, almost always occurring before the onset of reproductive maturity. Migrants are innately programmed to move; they are not distracted by food or mates. Once the migratory urge is satisfied, the insect is generally in a physiological state to continue development or commence reproduction. Migration can be a very risky venture: in some species more than 90% of a population may die in transit. Despite such high mortality rates, the reproductive success of individuals who survive the trek apparently makes the gamble worthwhile for the species as a whole.

Diapause
  • Diapause: A period of hormone-induce "dormancy". Characterized by reduction in oxygen consumption, metabolic rate, and physical activity. Feeding and growth are generally interrupted while the individual subsists on stored food reserves. Diapause typically occurs during the egg stage in some species, during a nymphal or larval instar in other species, or during the pupal stage in still other species. Even adults may enter a "reproductive diapause" which causes a significant delay in the onset of sexual maturity.

In temperate climates, many species enter diapause in the fall as an overwintering adaptation. Other species, however, have a summer diapause that helps them survive the dryness and/or heat. In either case, the onset of diapause is triggered by an environmental cue that precedes the adverse weather conditions (short daylengths in fall, for example). Diapause continues, even under apparently favorable conditions, until it is "broken" (terminated) by other environmental cues, such as long day lengths or exposure to a substantial period of low temperature.

Diapause is not always correlated with adverse environmental conditions. It can also regulate development within a population to ensure optimal timing of emergence or temporal synchrony with environmental resources. Female rabbit fleas, for example, have an obligate adult diapause that is broken only by feeding on the blood of a pregnant host rabbit. By the time the baby rabbits are old enough to be weaned, the flea's offspring will be mature and ready to accompany the rabbits when they leave the nest. In this ecological relationship, diapause is an adaptation that keeps the flea population from exceeding the carrying capacity of its host.

Cold-Hardiness

Since insects are poikilotherms (cold-blooded animals), their body temperature is usually similar to that of the air (or water) around them. Species that live in cold mountain streams (like mayfly naiads) or on the surface of ice and snow (like grylloblattids) are adapted for activity at low temperatures. Most other insects, however, slow down as the temperature falls.

They reach a dormant state, called torpor or quiescence, when they get very cold. Physiologically, many insects prepare for winter weather by producing "antifreeze" compounds (such as glycerol, sorbitol, or trehalose) in their hemolymph and body tissues. High concentrations of these compounds can increase cold-tolerance by lowering the freezing point of body fluids and preventing the formation of ice crystals that would cause internal injury. In species that manage to survive in arctic and alpine environments, the overwintering stage may undergo extensive dehydration - any ice crystals that do form will be too small to cause cellular damage.

Unlike diapause , a period of quiescence lasts only as long as the weather is cold. When temperatures rise, quiescent insects resume normal activity - at least until the next cold front arrives.

Insect External Anatomy

In this event, questions about general anatomy can come in two basic forms: diagrams to label, or arrows pointing to a specific structure on an insect. For the latter, competitors are generally asked to identify the structure, and possibly name its function.

Head

The head is the anterior oval-shaped body region that that houses the brain, a mouth opening, mouthparts used for ingestion of food, and major sense organs (including antennae, compound eyes, and ocelli). The surface of the head is divided into regions (sclerites) by a pattern of shallow grooves (sutures).

  • Vertex: The uppermost sclerite (dorsal surface) of the head capsule
  • Coronal Suture: runs along the midline of the vertex and splits into two frontal sutures as it extends downward across the front of the head capsule
  • Frons: The triangular sclerite that lies between these frontal sutures
  • Epistomal Suture: A deep groove that separates the base of the frons from the clypeus
  • Clypeus: A rectangular sclerite on the lower front margin of the head capsule
  • Genae: Lateral sclerites that lie behind the frontal sutures on each side of the head

See [1] for more information and an interactive diagram of the head that includes all features listed above.

Eyes

Insects generally have two types of eyes, simple and compound eyes. For more information about insect eyes, please visit this website

Simple Eyes (Ocelli)

Most insects have three simple eyes, also known as ocelli, located on the upper front part of the head. Several insects lack ocelli or only have two. The term ocellus (the singular form of ocelli) is derived from the Latin oculus (eye), and literally means "little eye".

There are two distinct types of ocelli: dorsal ocelli (or simply "ocelli"), and lateral ocelli (or stemmata).

Dorsal ocelli are commonly found in adults and in the immature stages (nymphs) of many hemimetabolous species. They are not independent visual organs and never occur in species that lack compound eyes. Whenever present, dorsal ocelli appear as two or three small, convex swellings on the dorsal or facial regions of the head. They differ from compound eyes in having only a single corneal lens covering an array of several dozen rhabdom-like sensory rods. These simple eyes do not form an image or perceive objects in the environment, but they are sensitive to a wide range of wavelengths, react to the polarization of light, and respond quickly to changes in light intensity. No exact function has been clearly established, but many physiologists believe they act as an "iris mechanism" -- adjusting the sensitivity of the compound eyes to different levels of light intensity. Dorsal ocelli are generally larger and more prominent in flying insects, such as bees, dragonflies, wasps, and locusts. In these insects, they are typically found in groups of three. Two lateral ocelli are directed to the left and right of the head, while a central ocellus is directed frontally. Some insects, such as ants and cockroaches, only possess two ocelli. In these cases, the median ocellus is absent, and both lateral ocelli are present.

Stemmata are the sole visual organs possessed by the larvae of insects that experience complete metamorphism, and certain adult orders that exhibit various types of metamorphism (ex: Collembola, Thysanura, Siphonaptera, and Strepsiptera). Stemmata always occur laterally on the head, and vary in number from one to six on each side. Structurally, they are similar to dorsal ocelli but often have a crystalline cone under the cornea and fewer sensory rods. Larvae use these simple eyes to sense light intensity, detect outlines of nearby objects, and even track the movements of predators or prey.

Compound Eyes

Compound eyes are the most commonly found visual organ of insects. They are situated on the upper portion of an insect's head. As suggested by their name, they are composed of many similar facets, called ommatidia. The number of ommatidia varies considerably from species to species: some worker ants have fewer than six while some dragonflies may have more than 25,000. For more information about the composition of an individual ommatidia, please see the link specified earlier in this section.

Antennae

The antennae are usually located on the front of the head below the simple eyes. They can be used to sense motion, orientation, odor, sound, humidity, chemicals in the air.

Antennae are divided into three basic parts: the scape: the basal segment that articulates with the head capsule; the pedicel: the second antennal segment; and the flagellum: all the remaining "segments" (individually called flagellomeres)

See [2] for pictures. The table found at this link is definitely something to include in a cheat sheet.

Antennal Forms
Name Examples
Setaceous: Bristle-like Dragonflies
Filiform: Thread-like Ground beetles and cockroaches
Moniliform: Bead-like Termites
Serrate: Sawtoothed Click Beetles
Clavate: Gradually clubbed Carrion Beetles
Capitate: Abruptly clubbed Butterflies
Pectinate: Comb-like Fire-colored beetles and Male glow-worms
Plumose: Brush-like Mosquitoes
Geniculate: Elbowed Weevils and Ants
Aristate: pouch-like with lateral bristle Houseflies
Flabellate/Flabeliform: Fan-like Some beetles, Hymenoptera, Lepidoptera
Lamellate: Nested Plates Scarab beetles
Stylate: Stylus-like Robber flies; Bee flies

Mouthparts

The mouth parts of an insect are located on the ventral or anterior part of the head. The mouth part structures typically present include:

  • Labrum: a cover which may be loosely referred to as the upper lip.
  • (Jaw-like) Mandibles: hard, powerful cutting jaws
  • (Jaw-like) Maxillae: 'pincers' which are less powerful than the mandibles. They are used to steady and manipulate the food. They have a five segmented palp which is sensory and often concerned with taste.
  • Labium: the lower cover, often referred to as the lower lip. It actually represents the fused pair of ancestral second maxillae. They have a three segmented palp which is also sensory.
  • Hypopharynx: a tongue-like structure in the floor of the mouth. The salivary glands discharge saliva through it.

Mouth parts are generally divided into groups, as explained below. Two major groups include chewing (or mandibulate) and sucking (or haustellate). Haustellate mouthparts can be further divided into piercing-sucking, sponging, and siphoning.

Chewing (Mandibulate)

These forms of mouthparts are among the most common in insects, which are used for biting and grinding solid foods. Examples of chewing insects include dragonflies, grasshoppers and beetles. Some insects do not have chewing mouthparts as adults but do as larvae, such as moths and butterflies.

Sucking (Haustellate)

Insects with sucking mouth parts have parts like a beak which is called the proboscis through which liquid is sucked.

Diagram of head: Insecthead.gif

Thorax

This is the middle section of the body and is divided into 3 segments called the prothorax, mesothorax, and metathorax. Each segment bears a pair of legs, and the mesothorax and metathorax usually bear a pair of wings if the insect is not wingless. Each of the thoracic segments bear 4 groups of sclerites, or platelike areas. These are the notum (dorsally), pleuron (there's one on each side), and sternum (ventrally). These segments are then divided into even smaller segments.

Wings

The wings are located dorsolaterally (they're near the top) on the mesothroax and/or the metathorax. The muscles that move wings are attached to the walls of the thorax most of the time. Insect wings vary in number, size, shape, texture, venation, and in position held at rest making them a great assist in identification. Most insect wings are membranous, though some are thickened or leathery. Some are covered in hair and others in scales. Most insects fold their wings over the abdomen at rest, but others hold them vertically over the body or hold them outstretched. Here's a picture of wing venation:

General Venation

Insectwing.gif See bottom of http://www.cals.ncsu.edu/course/ent425/tutorial/wings.html for more.

Legs

Most insects have three pairs of legs. Each leg contains five structural components (segments) that articulate with one another by means of hinge joints. These five components are known as the coxa, the trochanter, the femur, the tibia, and the tarsus.

InsectLegDiagram2.gif

Different insects' legs are modified for different tasks. This table outlines the major types of leg adaptations found in insects.

Insect Leg Adaptations
Leg Type and Purpose Picture Example Groups
Cursorial- Adapted for running Cursorial.gif Ground beetles and Cockroaches
Raptorial- Adapted for catching and holding prey Raptorial.gif Praying mantids
Natatorial- Adapted for swimming Natatorial.gif Diving bugs and water beetles
Fossorial- Adapted for digging in soil Fossorial.gif Mole crickets
Saltatorial- Adapted for jumping Saltatorial.gif Grasshoppers

Abdomen

The abdomen typically consists of 11 segments, but the last segment is usually represented by appendages only. Many insects have fewer abdominal segments because of fusing of some insects. Each abdominal segment generally contains 2 sclerites (or hardened body wall plate), a dorsal tergum and ventral sternum. The terga usually extend down the sides of most segments and overlap the sterna. Most insects lack appendages on the abdomen other than at the posterior end. This appendages may be lacking or drawn into the body and hidden. When these terminal appendages are present, they usually consist of a pair of cerci, a median dorsal epiproct (appendage above anus), a pair of paraprocts (pair of lobes located below and on each side of anus), and genitalia. The anal opening is on the posterior end of the abdomen, right under the epiproct. The sexes in many groups can be identified by the genitalia at the end of the abdomen.

Structures Found on Abdomen
Structure Name Function Description of Structure Example Taxons
Pincers Defense, courtship, folding wings Heavily sclerotized and forceps-like Dermaptera
Median Cadual Filament A thread-like projection arising from the center of the last abdominal segment (between the cerci) "Primitive" orders suchas Diplura, Thysanura, Ephemeroptera
Cornicles produce substances that repel predators or elicit care-giving behavior by symbiotic ants paired secretory structures located dorsally on the abdomen of aphids Aphididae
Abdominal Prolegs Locomotion Fleshy, found in larvae Mostly Lepidoptera, also in Mecoptera and some Hymenoptera
Sting Modified ovipositor Found only in females of aculeate Hymenoptera (ants, bees, and predatory wasps)
Abdominal Gills Respiration Ephemeroptera-paired gills are located along the sides of each abdominal segment; Odonata- the gills are attached to the end of the abdomen Found in aquatic nymphs (naiads) of Ephemeroptera and Odonata
Furcula "Jumping" The "springtail" jumping organ found in Collembola on the ventral side of the fifth abdominal segment. A clasp (the tenaculum) on the third abdominal segment holds the springtail in its "cocked" position. Collembola
Collophore Maintains homeostasis by regulating absorption of water from the environment Fleshy, peg-like structure found on ventral side of first abdominal segment Collembola

Insect Identification (Orders Only)

For more detailed information about each taxon (both orders and families), please visit the Entomology/Entomology Insect List page.

Insect Identification
Order Name (nickname) Metamorphosis Characteristics
Protura (Telsontails) Simple conical head, piercing mouthparts, lacks eyes and wingless, 12 segments in abdomen, .6-1.5mm
Collembola (Springtails) Simple wingless, long bodies, 4-6 abdominal segments, multicolored, tube protrudes from abdomen, microscopic
Diplura (Diplurans) Simple 1-segmented tarsi, chewing mouthparts, 2 cerci on head
Thysanura (Bristletails,Silverfish) Simple spindle shaped, flat bodies with 3 long, bristly tail like appendages
Ephemeroptera (Mayflies) Simple distinguished easily by their two large, triangular wings
Odanata (Dragonflies & damselflies) Simple two pairs of elongate membranous wings, compound eyes large, abdomen long and slender, antennae very short
Plecoptera (Stoneflies) Simple 4 membranous wings, elongate, flattened, cerci present, long antennae, mouthparts chewing
Orthoptera (Grasshoppers & crickets) Simple usually 2 pairs of wings, antennae many-segmented, cerci present, has ovipositor, FW is long, narrow, and many veined
Blattodea (Roaches) Simple flattened oval bodies, long laid back antennae, wings (almost never used)
Isoptera (Termites) Simple small, soft-bodies, usually pale-colored, antennae generally short and thread- or bead-like
Dermaptera (Earwigs) Simple slender flattened bodies, large pincers at end
Mallophaga (Chewing lice) Simple bristly body, toothed mandibles, small compound eyes, abdomen more wide or as wide as head
Anoplura (Sucking lice) Simple flattened and wingless, sucking mouthparts, abdomen thiner than head
Thysanoptera (Thrips) Simple slender bodies, short antennae, short legs, feathery wings
Hemiptera (True bugs) Simple FW (front wing) thickened at base and membranous at tip, HW (hind) shorter than FW, wings held flat on body, tips of FW overlap, mouthparts sucking, antennae of 5 or fewer segments (long and conspicuous or short and concealed)
Homoptera (cicadas and more) Simple beak short and rising at back of head (different from Hemiptera), wings held rooflike over body, tarsi 1- to 3-segmented, antennae sometimes short and bristlike or sometimes long and threadlike
Neuroptera (dobsonflies, lacewings, antlions) Complete (finally) FW and HW almost same size, four membranous wings, wings held rooflike over body at rest, wings with many veins, antennae long, cerci absent, mouthparts chewing
Coleoptera (beetles) Complete FW horny or leathery, FWs meet in straight line on back, HW membranous and are usually longer than FW, wings rarely absent or reduced, antennae usually with 11 segments (sometimes with 8-10), antennae variable in form
Mecoptera (Scorpionflies) Complete slender, soft bodies; long legs and elongated, snout like heads
Trichoptera (Caddisflies) Complete shaped or colored like certain moths, antennae long and threadlike, antennae usually long as body or longer, HW a little shorter than FW
Lepidoptera (Moths & Butterflies) Complete 4 membranous wings, usually have proboscis in form of coiled tupe, wings covererd in scales
Diptera (True flies) Complete one pair of membranous wings (you can identify them instantly from this), have knoblike projections called haltares
Siphonaptera (Fleas) Complete laterally flattened abdomens, tough skin, enlarged coxae, mouthparts with 3 piercing stylets for blood sucking
Hymonoptera (Bees, Ants, Wasps, and more) Complete wings are sometimes present, FW a little larger than HW, antennae usually fairly long

Dichotomous Keys

On the tests, you may be asked to create a simple dichotomous key for identification of various insects. To create, just remember some simple tips:

There should be one less number of steps than number of insects you're including in the key.

You want to start off by dividing the insects into groups. If they do not have the insects already identified for you, then quickly identify them. For example, if they give you a house fly, a mantid, a dragonfly, and a mosquito, you'll divide them like this:

1. Two pairs of wings...................................go to 2

1. One pair of wings.....................................go to 3

Keep them very basic at first, then eventually divide them into more specific groups.

For example, you could then divide the two groups into colors, or whatever is most convenient.

Keep dividing the groups until you end up with the final step(since there are four insects in this case, there will be three steps) leading to the final insect being identified.

Human Impact

A very important aspect of this event is learning about how insects impact humans, the environment, and the world. Usually tests will feature stations with questions regarding identification and human/environmental/economic impact. Some insects are very prominent pests, such as certain species of Coleoptera, while others are highly beneficial, such as butterflies or bees that pollinate.

Beneficial Insects

Insect populations can have a positive impact on humans in a variety of different ways. They can be sources of food, decompose organic matter, manufacture products such as silk and honey, recycle carbon/nitrogen/other essential nutrients, and control populations of harmful invertebrates including other insects. Some are also valuable organisms to study for scientific and technological advances. Others have medical and therapeutic value.

Harmful Insects

In= addition to having a positive effect on humans, insects can be very harmful. For example, some insects damage crops/trees and destroy products such as wood and paper. Many termites can destroy entire homes. Some can bite or sting, and many vector diseases. Others are household pests and parasites.

Disease Vectors

As stated above, many insects serve as vectors for diseases. Arbovirus is a term used to refer to a group of viruses that are transmitted by arthropod vectors. It is an acronym (ARthropod-BOrne virus). Haematophagous insects feed on blood at some stage of their life.

Insect Disease Vectors
Name of Insect Disease
Siphonaptera (fleas) Plague
Culicidae (mosquitoes) Malaria, filarisis*, arboviral encephalitides, dengue fever, Rift Valley fever, West Nile encephalitis viral infection
Calliphoridae (blow flies) Dysentery rabbit haemorrhagic disease, flystrike, salmonellosis

*Only female mosquitoes of the genus Anopheles transmit malaria and filarisis

Binder Checklist

*NOTE* The 2013-2014 competition only allows for one double-sided, 8.5 x 11 inches page of information. However, previous years have allowed for a binder, so it may still be helpful to create one for studying purposes.

Here is a binder checklist that was useful in the past: Make sure you have the following information in your binder or known by memory: Definitely necessary:

  • Insect identification guide and sheets
  • Nymph identification sheets
  • Insect pictures (obviously)
  • Insect characteristics sheets
  • Human impact information
  • Basic insect information

Optional:

  • Entomology glossary (to be on the safe side)
  • Note Sheets (for quick finding if they have a section where you must answer questions about insects not already identified) for the following:
    • Vectors
    • Record-winning insects (largest, smallest, fastest fliers, most deadly, etc.)
    • Historical info. (safe side, horrible test making at state had at least five questions on this subject)
    • Invasive species

Cheat Sheet Suggestions

In this event, there are a variety of ways which one can use to structure their cheat sheet. Three basic methods are listed below. The bottom line is to find a method that works the best for you, and practice with it. You may want to add more information for certain groups (that are easier to identify, such as Mecoptera or Neuroptera families), and more pictures for others (that are hard to identify, such as Lepidoptera families).

Information you should definitely save space for on your cheat sheet that is not taxon specific includes:

  • A table with different types of leg adaptations (adaptation name and picture, can be found above)
  • A table with different types of antennae adaptations (adaptation name and picture, can be found above)
  • A table with different types of wing adaptations (adaptation name and picture, can be found above)
  • Insect taxonomy (see section of this page on Insect Taxonomy, you will want to include the characteristics required for each group)
  • Anatomy diagrams- usually works to find a good one for the head, mouthparts, leg, wing, and whole body.
  • Wing Venation- General info and a diagram

Method 1- Information and Pictures

This method involves having information about all of the families on one side of the sheet, and information about orders and other misc stuff on the other side. Information about all families and orders can be found on the Entomology/Entomology Insect List page. The identification tables at the end of each section are definitely a good idea for ID'ing, along with pictures.

Pros and Cons- Method 1
Aspect Pro Con
Location of Information During Test Can be very easy to located information if you know the location of everything well If you don't have a good idea of where everything is, it can be very hard to locate it in time
Amount of Information Will include lots of information Can sometimes be hard to fit everything, be careful about adding irrelevant information;
Identification Because it includes both pics and descriptions, you will be much more confident in your identification of a specimen Some pictures can be misleading, for insects that mimic each other. (Example: Sesiidae, resembles a Hymenoptera

Method 2- Pictures Only

This method involves putting only pictures to aid with identification on your cheat sheet. For example, you may choose to designate a small space on the back side of the sheet for a few pictures of each family, and on the front put a few pictures for each order (along with some anatomy diagrams, because there would be space left over). The main issue with this method is that you will have to look in your field guide for the answers to questions such as "What does this insect eat?" or "Where does this insect live?" (etc).

Pros and Cons- Method 2
Aspect Pro Con
Location of Information During Test You are allowed to annotate the field guide, so feel free to add as much information about each group that you have room for. You will need to use your field guide to locate information during the test. Tabbing for at least the orders is a good idea, and you can put page numbers on the sheet for the families.
Amount of Information Won't include any useless information- Identification is the most important aspect of this event Will include no information other than pictures of appearance
Identification A VERY good method for those who struggle with ID'ing insects, you will have more room to add more pictures for each group. Therefore, you will have more confidence in your identification of a specimen. If you're not organized about the location of your pictures, you could accidentally place one under the wrong group

Method 3- Information Only

This method involves only adding information about each taxon to your cheat sheet, without pictures. For example, under Corixidae you may put the information found here, in either format. (See top of page for more info). The main issue with this method is since it does not involve adding pictures, you will have to become very confident with ID'ing. Please note that the field guide is generally not a good way to ID insects if you are using the Audubon, because the pictures are arranged by appearance and not by taxonmic group. Flipping through the book to find the correct order or family will waste time during the test.

Pros and Cons- Method 3
Aspect Pro Con
Location of Information During Test Will be easy if you know the cheat sheet well and work out a color coding scheme. Might be somewhat harder since there aren't pictures to give you a guide, but isn't a huge issue if you become familiar with layout.
Amount of Information Will include tons of information Some information may be irrelevant, and it doesn't provide visual aids (pictures) for ID'ing
Identification The information found here gives a basic idea of anatomy (but pictures are often more helpful for this) You will have to learn identification very well in order for this to be an effective method for you.

Recommendations For Group Members

  • Both team members should have a strong background in Environmental Science (AP Level for C).
  • The team should be prepared for both types of events (visual: power point/pictures, and live specimens); a lack of practice in either area can result in false identifications.
  • The team should be able to use various types of microscopes.

Resources

The following guides are highly recommended:

  • Audubon Field Guide to Insects and Spiders: official field guide of the Entomology event, on which taxonomic scheme and questions are based on, has nice colored pictures and good bug descriptions, good for general insect knowledge; -note- this field guide groups bugs into groups based on their basic appearance rather than their correct phylogenetic groups (not good since the insects in here must be ID'd according to family and order), is also rather outdated regarding dates and population statistics, but contains the most reliable information simply because the test will be based on it.
  • National Wildlife Federation Field Guide to Insects and Spiders & Related Species of North America: contains close-up color photographs with informative description, very up-to-date; -note- has more than 2,000 photos of over 940 species, which may be confusing. However, if you highlight only the necessary insects with the necessary families, the guide becomes much more clear.
  • Peterson Field Guides: Insects - shows differences between different insects, has all insects on insect list; -note- contains a lot of information on how to collect and preserve an insect, which may not be useful when preparing for this event.
  • Smithsonian Handbooks: Insects - really nice pictures, great for nymphs and larva identification; -note- thin and is best utilized as a supplement (the first two/three field guides are better suited for use during the event)

Good Links

See Also

Entomology/Entomology Insect List

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