Ent
4015 Ornamentals and Turf Entomology
Insect
Morphology
All arthropods possess
:
- Exoskeleton - a hard protective covering around the outside of the body
(divided by sutures into plates called sclerites)
- Segmented body
- Jointed limbs and jointed mouthparts - that allow extensive
specialization
- Bilateral symmetry - whereby a central line can divide the body into two
identical halves, left and right
- Ventral nerve cord - as opposed to a vertebrate nerve cord which is
dorsal
- Dorsal blood pump
Adapted from
University of Sydney
Five important extant classes of Arthropods are arachnids, chilopods,
diplopods, crustaceans and hexapods.
Class Arachnida
(arachnids): spiders, scorpions, ticks,
mites, etc.
Arachnids possess:
- 2 body segments - cephalothorax and abdomen
- 8 legs
- 1 pair of chelicerae
- no antennae
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University of Sydney |
Class Chilopoda (centipedes)
Chilipods possess:
- many body segments
- 1 pair of legs per body segment
- 1 pair of antennae
- 1st pair of legs modified into venomous “fangs”
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University of Sydney |
Class Diplopoda
(millipedes)
Diplopods possess:
- Many body segments
- 2 pair of legs per body segment
- 1 pair of antennae
|
University of Sydney |
Class Crustacea
(crustaceans): crabs, shrimp, barnacles, sowbugs, etc.
Crustaceans possess:
- Several body segments - head, thorax and
abdomen
- Segments may be fused
- Varied number of legs
- 2 pairs of antennae
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University of Sydney |
Class Insecta (Insects); beetles, bugs, wasps, moths, flies, etc.
Insects possess:
- 3 body segments
- 6 legs
- 1 pair of antennae
- Diverse modifications to appendages
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University of Sydney |
Basic Insect Morphology:
Head,
thorax,
abdomen
HEAD
The head of an insect is composed of
mainly rigid sclerites or
sclerotized segments.
The insect head is a capsule that contains the compound eyes,
simple eyes (ocelli),
mouthparts, and
antennae.
Compound eyes and ocelli
In most insects there is one pair of large,
prominent compound eyes composed of units called ommatidia. There may be up to
30,000 ommatidia in a compound eye. This type of eye gives less resolution than
the vertebrate eye, but it gives acute perception of movement. When present,
ocelli (either 2 or 3), detect low light or small changes in light intensity.
Mouthparts
The 4 main mouthparts are the
labrum,
mandibles,
maxillae (plural maxilla)
and
labium. The labrum is a simple fused sclerite, often called the upper lip, and moves
longitudinally. It is hinged to the
clypeus.
The mandibles, or jaws, are highly sclerotized paired structures that move at
right angles to the body. They are used for biting, chewing and severing food.
The maxillae are paired structures that can move at right angles to the body and
possess segmented palps.
The labium (often called the lower lip), is a fused structure that moves
longitudinally and possesses a pair of segmented palps.
Mouthparts very greatly among insects of different orders but there are two main
functional groups: mandibulate and haustellate.
Shown above and below are mandibulate (chewing) mouthparts. Haustellate mouthparts can be
further classified as
piercing-sucking, sponging, and siphoning.
University of Florida
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Mandibulate (chewing) mouthparts are
used for biting and grinding solid foods (see diagram above).
Examples:
Dragonflies
and damselflies (order Odonata),
termites (order Isoptera), adult lacewings (order Neuroptera), beetles (order Coleoptera), ants
(order Hymenoptera), cockroaches (order Blattaria), grasshoppers, crickets and katydids (order Orthoptera),
caterpillars (order Lepidoptera). Adult Lepidoptera have siphoning
mouthparts.
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University of Florida
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Order Coleoptera:
Stag beetle, Jim Occi, BugPics,
www.insectimages.org |
Order Hymenoptera:
Carpenter ant, Camponotus sp., Jim Kalisch,
Department of Entomology, University of Nebraska-Lincoln |
Order Blattaria: Newly molted American cockroach, Periplaneta americana, Daniel R. Suiter, University of
Georgia, www.insectimages.org |
Order Neuroptera:
Green lacewing adult, Chrysopa oculata,
John Davidson,
The Insects of Cedar Creek Photo Album |
Order Coleoptera:
Scarab beetle grub, Ronald F. Billings, Texas Forest Service,
www.insectimages.org |
Order Odonata:
Damselfly eating mosquito, Richard Seaman,
Nature Wallpaper |
Order Lepidoptera:
Saturniid caterpillar, Hyalophora
columbia,
Connecticut Agricultural Experiment Station,
www.insectimages.org |
Order Orthoptera:
Katydid, Edward L. Manigault, Clemson University Donated
Collection, www.insectimages.org |
Order Isoptera:
Termite,
Coptotermes formosanus, Gerald J. Lenhard, Louisiana State University,
www.insectimages.org |
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Haustellate mouthparts are primarily used for
sucking liquids and
can be broken down into two subgroups: those that possess stylets and those that
do not.
Stylets
are needle-like projections used to penetrate plant and animal tissue.
The modified mandibles, maxilla, and hypopharynx form the stylets and the feeding
tube. After piercing solid tissue, insects use the modified mouthparts to suck liquids from the host.
To the left is a diagram of cicada mouthparts.
Some haustellate mouthparts lack stylets. Unable
to pierce tissues, these insects must rely on easily accessible food sources
such as nectar at the base of a flower. One example of nonstylate mouthparts
are the long siphoning proboscis of butterflies and moths (Lepidoptera).
Although the method of liquid transport differs from that of the a
Lepidopteran proboscis, the rasping-sucking rostrum of some flies are also
considered to be haustellate without stylets.
Piercing-sucking mouthparts are used to penetrate solid tissue and
then suck up liquid food. Examples: Cicadas (see diagram), aphids, and
other bugs (order Hemiptera),
sucking lice (order
Phthiraptera), stable flies and mosquitoes (order
Diptera). |
University of Florida |
Order Hemiptera:
Wheel bug, Arilus cristatus, Edward L. Manigault,
Clemson University Donated Collection,
www.insectimages.org |
Order Hemiptera:
Green peach aphid, Myzus persicae,
Scott Bauer, USDA ARS,
www.insectimages.org |
Order Diptera:
Stable fly, Stomoxys calcitrans,
North Dakota State University |
Order Hemiptera:
Spined soldier bug, Podisus maculiventris, attacking
caterpillar, Russ Ottens, University of Georgia,
www.insectimages.org |
Order Diptera:
Mosquito feeding on human, Jim Occi, BugPics,
www.insectimages.org |
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Siphoning mouthparts lack stylets and are used to suck liquids. Examples:
Butterflies,
moths and skippers
(order Lepidoptera),
bees (order
Hymenoptera). Larval Lepidoptera have chewing mouthparts.
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University of Florida |
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Sponging mouthparts are used to sponge and suck liquids.
Examples: House flies and blow flies (order Diptera).
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University of Sydney |
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Antennae
Antennae
function almost exclusively in sensory perception. Some of the information that
can be detected by insect antennae includes: motion and orientation, odor,
sound, humidity, and a variety of chemical cues. Antennae
vary greatly among insects, but all follow a basic plan: segments 1 and 2 are
termed the scape and pedicel, respectively. The remaining antennal segments (flagellomeres)
are jointly called the flagellum.
University of Florida
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Aristate antennae
are pouch-like with a lateral bristle.
Examples: House and
shore flies (order
Diptera).
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University of Sydney |
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Capitate antennae
are abruptly clubbed at the end.
Examples:
Butterflies (order
Lepidoptera).
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University of Sydney |
Order Lepidoptera:
Painted beauty butterfly,
Vanessa virginiensis, Jerry A. Payne, USDA ARS,
www.insectimages.org
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Order Lepidoptera:
Red-banded hairstreak, Calycopis cecrops, Jerry A. Payne, USDA ARS,
www.insectimages.org |
Order Lepidoptera:
Speckled wood butterfly, Pararge aegeria, Peter Wirtz, Personal Web Site,
www.insectimages.org |
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Clavate antennae
are gradually clubbed at the end.
Examples: Carrion
beetles (order
Coleoptera). Adult carrion beetles feed on decaying
animal matter or maggots. |
University of Sydney |
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Filiform antennae
have a thread-like shape.
Examples: Ground and
longhorned beetles
(order Coleoptera), cockroaches (order
Blattaria).
|
University of Sydney |
Order Coleoptera: Ground beetle,
John A. Weidhass, Virginia Tech,
www.insectimages.org |
Order Coleoptera: Asian longhorned beetle,
Anoplophora
glabripennis, Donald Duerr, USDA Forest Service,
www.insectimages.org |
Order Blattaria:
American cockroach, Periplaneta americana, Clemson
University - USDA Cooperative Extension Slide Series,
www.insectimages.org
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Geniculate antennae
are hinged or bent like an elbow.
Examples: Bees and
ants (order
Hymenoptera).
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University of Sydney |
Order Hymenoptera:
Bumble bee, Bombus sp., Russ Ottens, University of
Georgia,
www.insectimages.org |
Order Hymenoptera:
Blueberry bee, Habropoda laboriosa, Jerry A. Payne,
USDA ARS,
www.insectimages.org |
Order Hymenoptera:
Carpenter ant, Camponotus sp., Jim Kalisch,
Department of Entomology, University of Nebraska-Lincoln |
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Lamellate or
clubbed antennae end in nested plates.
Examples: Scarab beetles (order
Coleoptera). |
NC State University |
Order Coleoptera:
Japanese beetle, Popillia japonica, Clemson University
- USDA Cooperative Extension Slide Series,
www.insectimages.org
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Order Coleoptera:
Conifer scarab, Polyphylla occidentalis, Gerald J.
Lenhard, Louisiana State University,
www.insectimages.org |
Order Coleoptera:
Rose chafer, Macrodactylus subspinosus, Clemson University -
USDA Cooperative Extension Slide Series,
www.insectimages.org
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Moniliform
have a beadlike shape.
Examples: Termites (order
Isoptera). |
University of Sydney |
Order Isoptera:
Termite,
Coptotermes formosanus, Gerald J. Lenhard, Louisiana State University,
www.insectimages.org |
Order Isoptera:
Termite, Reticulitermes sp., USDA Forest Service - Wood
Products Insect Lab Archives,
www.insectimages.org |
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Pectinate antennae
have a comb-like shape.
Examples:
Fire-colored beetles and fireflies (order
Coleoptera).
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University of Sydney |
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Plumose
antennae have a feather-like shape.
Examples: Moths (order
Lepidoptera) and mosquitoes (order
Diptera). |
University of Sydney |
Order Lepidoptera:
Luna moth, Actius luna, Gerald J. Lenhard, Louisiana
State University,
www.insectimages.org |
Order Lepidoptera:
Cecropia moth male, Hyalophora cecropia, David Keith,
Department of Entomology, University of Nebraska-Lincoln |
Order Diptera:
Mosquito male, Culex sp.,
Nikon Digital Eclipse Image Gallery |
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Serrate antennae
have a saw-toothed shape.
Examples: Click
beetles (order
Coleoptera).
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University of Sydney |
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Setaceous antennae
have a bristle-like shape.
Examples:
Dragonflies and damselflies (order
Odonata).
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University of Sydney |
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THORAX
The insect
thorax is divided into three parts: the prothorax (pro=first), mesothorax (meso=middle),
and metathorax (meta=last). Each segment consists of hardened plates, or
sclerites. Dorsal sclerites are called nota (singular notum), lateral sclerites are
called pleura (singular pleuron), and ventral sclerites are called sterna (singular
sternum). The first segement of the prothorax is the pronotum.
Each of the
three thoracic segments contains one pair of legs. Wings are found only on the meso- and metathoracic segments.
University of Florida
Pronotum
The pronotum is the
dorsal sclerite of the prothorax, which can be highly modified in various orders such as the Hemiptera, Blattaria, and Coleoptera.
University of Florida
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Treehoppers (order Hemiptera) have some of the most
bizarre pronotums of all insects.
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Scarab beetles (order Coleoptera) and other beetles may also have unusual pronotums.
In addition,
the specimens shown here also have bizarre modifications of the head
capsule. Male insect use horns to fight with other males over females and
territory.
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Hercules beetle, Dynastes granti, Oldrich Jahn,
InsectNet |
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Cockroaches (order
Blattaria) have pronotums
that extend forward over the head.
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Orange-headed cockroach, Eublaberus prosticus, E.
Tenczar,
Lotsalegs Arthropods |
German cockroach, Blattella germanica, Clemson University -
USDA Cooperative Extension Slide Series,
www.insectimages.org
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Legs
The
fore-legs are located on the prothorax, the mid-legs on the
mesothorax, and the hind legs on the metathorax. Each leg has six major
components, listed here from proximal to distal: coxa (plural coxae),
trochanter, femur (plural femora), tibia (plural tibiae), tarsus
(plural tarsi), pretarsus.
The femur
and tibia may be modified with spines. The tarsus appears to be divided into
one to five "pseudosegments" called tarsomeres. Like the
mouthparts and antennae, insect legs are highly modified for different
functions, depending on the environment and lifestyle of an insect.
University of Florida
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Ambulatory
legs are used for walking. The structure is similar to cursorial (running)
legs.
Examples: Bugs (order Hemiptera), leaf beetles beetles
(Corder oleoptera). |
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Order Hemiptera:
Boxelder bug, Boisea trivittata, Clemson University - USDA Cooperative Extension
Slide Series,
www.insectimages.org |
Order Hemiptera:
Tarnished plant bug, Lygus lineolaris, Scott Bauer,
USDA ARS,
www.insectimages.org |
Order Coleoptera:
Cottonwood leaf beetle, Chrysomela scripta, Lacy L.
Hyche, Auburn University,
www.insectimages.org
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Cursorial
legs are modified for running. Note the long, thin leg segments.
Examples: Cockroaches (order
Blattaria), ground and
tiger beetles (order Coleoptera). |
University of Florida |
Order Blattaria:
Oriental cockroach,
Blatta orientalis, Clemson University - USDA
Cooperative Extension Slide Series,
www.insectimages.org
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Order Coleoptera:
Ground beetle,
John A. Weidhass, Virginia Tech,
www.insectimages.org |
Order Coleoptera:
Bronze tiger beetle, Richard Seaman,
Nature Wallpaper |
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Fossorial fore legs are modified for
digging.
Examples: Ground
dwelling insects; mole crickets (order
Orthoptera) and
cicada nymphs (order
Hemiptera).
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University of Florida |
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Natorial legs
are modified for swimming. These legs have long setae on the tarsi.
Examples: Aquatic beetes (order Coleoptera) and bugs (order Hemiptera). |
University of Florida |
Order Coleoptera:
Predaceous diving beetle, Rhantus sp., Dale Parker,
AquaTax Consulting,
Saskatchewan
Aquatic Insects |
Order Coleoptera:
Predaceous diving beetle and close up of leg, Acilius sulcatus, David
Jones,
mybitoftheplanet |
Order Hemiptera:
Backswimmer (aquatic bug), Dale Parker, AquaTax Consulting,
Saskatchewan
Aquatic Insects |
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Raptorial
fore legs modified for grasping (catching prey).
Examples: Mantids
(order Mantodea), ambush bugs, giant
water bugs and water scorpions (order
Hemiptera).
|
University of Florida |
Order Mantodea:
Carolina mantis, Stagomantis
carolina,
Wikipedia |
Order Hemiptera:
Ambush bug, Phymata pennsylvanica,
The Insects of Cedar Creek Photo Album |
Order Hemiptera:
Water scorpion,
Murray Darling Freshwater Research Centre, Wodonga |
Order Hemiptera:
Giant water bug, Lethocerus americanus, Edward L.
Manigault,
Clemson University Donated Collection,
www.insectimages.org |
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Saltatorial
hind legs adapted for jumping. These legs are characterized by an
elongated femur and tibia.
Examples: Grasshoppers, crickets and katydids (order Orthoptera). |
University of Florida |
Order Orthoptera:
Redlegged grasshopper, Melanoplus femurrubrum, Clemson
University - USDA Cooperative Extension Slide Series,
www.insectimages.org |
Order Orthoptera:
House cricket, Acheta domestica, Joseph Berger,
www.insectimages.org |
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Wings
Insects have
evolved many variations of the wings, and an individual insect may posess more
than one type of wing. Wing venation is a commonly used taxonomic
character, especially at the family and species level.
In most
living insects (the Neoptera), there are three axillary sclerites that
articulate with various parts of the wing. In the Neoptera, a muscle on the
third axillary causes it to pivot about the posterior notal wing process and
thereby to fold the wing over the back of the insect. (In some groups of Neoptera, such as butterflies, the ability to fold the wings over the back has
been lost.) Two orders of winged insects, the Ephemeroptera and Odonata, have
not evolved this wing-flexing mechanism, and their axillary sclerites are
arranged in a pattern different from that of the Neoptera; these two orders
(together with a number of extinct orders) form the Paleoptera. (Univerisity
of Florida)
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Primitive insects of the Paleoptera are unable to fold
their wings. Instead, these insects carry their wings vertically or
horizontally to their bodies. |
Most modern insects of the
Neoptera are able to fold their wings over the body. This enables the
insects to fit into smaller spaces. |
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Mayfly, Hexagenia sp. (order
Ephemeroptera), Alex Wild,
www.myrmecos.net |
Leaf footed bug (order Hemiptera), Clemson University - USDA
Cooperative Extension Slide Series,
www.insectimages.org |
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Membranous
wings are thin and more or less transparent, but some are darkened.
Examples:
Dragonfiles and damselflies (order
Odonata), lacewings (order
Neuroptera), flies
(order
Diptera), bees and wasps (order
Hymenoptera), termites (order
Isoptera).
Note the paleopterous wing conditions of the
damselflies and dragonfly to the right and below and the neopterous wing conditions of the other insects.
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University of Florida |
Order Odonata:
Dragonfly, Sympetrum corruptum, Edward L.
Manigault, Clemson University Donated Collection,
www.insectimages.org |
Order Hymenoptera:
Bald-faced hornet, Dolichovespula maculata, Edward L.
Manigault, Clemson University Donated Collection,
www.insectimages.org
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Order Isoptera:
Termites, Reticulitermes virginicus, Gerald J. Lenhard,
Louisiana State University,
www.insectimages.org |
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Halteres are an extreme modification
among the order Diptera (true flies), in which the hind wings are reduced to
mere nubs used for balance and direction during flight.
Examples: All flies
(order
Diptera).
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University of Florida
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Elytra (singular elytron) are the hardened, heavily sclerotized forewings of beetles
and are modified to protect the hind wings when at rest.
Examples:
All beetles (order
Coleoptera).
Order Coleoptera: Flatheaded wood borer, Buprestis fasciata,
William M. Ciesla, Forest Health Management International,
www.insectimages.org
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University of Florida |
Order Coleoptera:
Colorado potato beetle, Leptinotarsa decemlineata,
Clemson University - USDA Cooperative Extension Slide Series,
www.insectimages.org |
Order Coleoptera:
Dung beetle, Heliocopris andersoni, in flying
position, A Davis, Dept. of
Zoology and Entomology, University of Pretoria,
Transvaal Museum |
Order Coleoptera:
Spotted june beetle, Pelidnota punctata, Jim Occi,
BugPics,
www.insectimages.org |
Order Coleoptera:
Margined blister beetle, Epicauta pestifera, Clemson
University - USDA Cooperative Extension Slide Series,
www.insectimages.org |
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A variation of the elytra is the
hemelytra. The forewings of Hemipterans are said to be hemelytrous
because they are hardened throughout the proximal two-thirds, while the
distal portion is membranous. Unlike elytra, hemelytra function primarily as
flight wings.
Examples: Bugs (order
Hemiptera).
Order Hemiptera: Big-eyed bug, Geocoris sp., Bradley Higbee, Paramount
Farming,
www.insectimages.org
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University of Florida
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Order Hemiptera:
Four-lined plant bug, Poecilocapsus lineatus, Steve
Mayer,
Purdue University |
Order Hemiptera:
Brown stink bug, Euschistus servus, Russ Ottens, University of Georgia,
www.insectimages.org |
Order Hemiptera:
Leaf footed pine seed bug, Leptoglossus corculus,
Larry R. Barber, USDA Forest Service,
www.insectimages.org |
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Tegmina (singular tegmen) are the leathery forewings of insects
in the orders Orthoptera, Blattaria, and Mantodea. Like the elytra on
beetles and the hemelytra on bugs, the tegmina help protect the delicate
hind wings.
Examples: Grasshoppers, crickets and katydids (order Orthoptera), Cockroaches (order
Blattaria),
Mantids (order Mantodea).
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Order Blattaria: Smokybrown cockroach, Periplaneta fuliginosa, Daniel
R. Suiter,
University of Georgia,
www.insectimages.org
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Order Orthoptera: Grasshopper, Tropidacris dux, Ronald F. Billings,
Texas Forest Service,
www.insectimages.org
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Order Blattaria: Orange-headed cockroach, Eublaberus prosticus, E.
Tenczar,
Lotsalegs Arthropods |
Order Mantodea: Madagascan marbled mantis, Polyspillota aeruginosa,
www.exotic-pets.co.uk |
Order Orthoptera:
Katydid, Pterophylla camellifolia, Herbert A. "Joe"
Pase III, Texas Forest Service,
www.insectimages.org |
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Some insect wings are covered with scales.
The scales make
the wings colorful.
Examples: Butterflies, moths and skippers
(order Lepidoptera), caddisflies (order
Trichoptera).
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Order Lepidoptera: Tiger swallowtail, Papilio turnus,
Edward L. Manigault, Clemson University Donated Collection,
www.insectimages.org
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Order Lepidoptera: Io moth, Automeris io, Ronald F. Billings, Texas
Forest Service,
www.insectimages.org |
Order Lepidoptera:
Hoary edge skipper, Achalarus lyciades, Jerry A. Payne,
USDA ARS,
www.insectimages.org |
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ABDOMEN
The abdomen contains the reproductive
organs and the majority of the organ systems. The dorsal
and ventral abdominal segments are termed terga (singular tergum) and sterna
(singular sternum), respectively. Spiracles usually can be found in the
conjunctive tissue between the terga and sterna of abdominal segments 1-8.
Reproductive structures are located on the 9th segment in males (including the aedeagus, or penis, and often a pair of claspers) and on the 8th and 9th
abdominal segments in females (female external genitalia copulatory openings and
ovipositor). (University of Florida)
University of Florida
Ovipositor
The
ovipositor is the egg-laying device found only in female insects. In some
insects, the ovipositor is highly modified and conspicuous. In
others, the apparatus may be needle or blade-like.
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Parasitic wasps (order
Hymenoptera) use their ovipositors to insert eggs or small larvae into or
onto a host. The stingers of bees and many wasps are modified ovipositors
that have lost the egg-laying ability.
Order Hymenoptera:
Braconid wasp, female, Spathius pallidus,
Gerald J. Lenhard, Louisiana State University,
www.insectimages.org
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Order Hymenoptera:
Torymid wasp, female, Monodontomerus dentipes,
Arnold T. Drooz, USDA Forest Service,
www.insectimages.org
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Order Hymenoptera:
Ichneumonid wasp, female, Megarhyssa macrurus,
Jim Occi, BugPics,
www.insectimages.org
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Crickets and katydids
(order
Orthoptera) have needle-like and blade-like ovipositors, respectively.
Order Orthoptera: Field cricket, female, Gryllus pennsylvanicus, Joseph
Berger,
www.insectimages.org
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Order Orthoptera: Katydid, Paracyrtophyllus robustus, Herbert A. "Joe"
Pase III, Texas Forest Service,
www.insectimages.org
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Internal Anatomy and Metamorphosis
Diagrams and text from
University of Florida
Digestive & Excretory Systems
The digestive system
(sometimes referred to as the alimentary canal) is a long tube-like structure that runs from the
mouth to the anus and is centrally located within the body cavity,
or hemocoel. The anterior-most region is called the foregut (or
stomodeum) which includes the Buccal cavity, the esophagus, and the
crop. The primary function of the foregut is to begin the breakdown of food
particles and transport them to the next region, the midgut (or
mesenteron). The midgut is the major area of digestion and absorption. Undigested food particles then pass into the third region, the hindgut
(or proctodeum), which consists of the ileum, colon, rectum, and
(often) rectal pads. The hindgut functions in water and solute reabsorption and
waste excretion.
The three sections of the
digestive tract can be easily identified by structures found at the junction of
each region. Gastric caecae, for example, mark the end of the foregut
and beginning of the midgut. It is believed that the purpose of these
structures is to increase surface area for greater nutrient absorption. The
constriction at the gastric caecae also marks the spot of the cardiac valve
(or sphincter).
Near the junction of the
midgut and hindgut are long, thin structures called Malpighian tubules.
These range in number from a few to hundreds, but only aphids are currently known to have none. Malpighian tubules are creamy to yellow in
color and work in conjunction with the ileum to provide the primary site for
osmoregulation and excretion.
Circulatory System
Unlike the closed
circulatory system of humans, insect circulatory systems are said to be open,
meaning that they lack a complex network of veins and arteries to help transport
blood throughout the body. Instead, insect blood (called hemolymph)
flows relatively freely throughout the hemocoel.
Only one vessel is present in
the insect circulatory system: the dorsal vessel. Posteriorly (in the
abdominal region), the dorsal vessel acts as the heart, pumping hemolymph
forward into the anterior region (in the head and thorax), where it acts as the
aorta and dumps the hemolymph into the head. It flows posteriorly and is
returned to the heart via ostia, which are small slits in the heart
region of the dorsal vessel designed for hemolymph uptake.
Nervous System
The ventral nerve
cord, resembles a
railroad track running from the head posteriorly to the abdominal region (above,
lower diagram). The
ventral nerve cord is made up of two nerve cords (connectives) that run
longitudinally with a series of node-like ganglia.
The anterior most region of
the ventral nerve cord is called the subesophageal ganglion. Just dorsal
to that structure is the insect brain (or supraesophageal ganglion).
Respiratory System
The insect respiratory system
is made up of a series of tubes that originate from spiracles (openings
of the exoskeleton that allow for gas exchange) and extend throughout the body. Internally, the tubes, or tracheae, appear as thin white lines throughout
the hemocoel and are particularly noticeable surrounding internal organs. Trachea deliver oxygen to internal organs and tissues.
Reproductive System
The female reproductive system
is shown on the left. The male is on the right.
Variation among insect
reproductive systems is great. Closely related species are often isolated from
one another via small variations in the morphology of reproductive organs that
prohibit interspecies mating. However, a generalized system can be constructed
that closely represents all sexually reproducing insects. Be familiar with
differences in male and female genitalia and be able to identify structures when
given a diagram.
Insect Growth and Development (Metamorphosis)
Information and diagrams are adapted from:
Hoffmann, M.P. and Frodsham, A.C. (1993) Natural Enemies of Vegetable Insect
Pests. Cooperative Extension, Cornell University, Ithaca, NY. 63 pp.
Insects go through several separate life stages: egg, larva or nymph, pupa
(complete metamorphosis only),
and adult. Eggs are laid one at a time or in masses, in or on plants, or even
inside another insect! Eventually a larva or nymph emerges from the egg. There
are usually several larval or nymphal stages, called instars. During each stage
the nymph grows larger and molts, or sheds its outer skin before the next stage.
They grow the most during the last one or two instars, or stages. All the
growing happens during the larval or nymphal stages. The eggs, pupae, and adults
don't grow in size.
The
two types of metamorphosis typical of insects are:
incomplete metamorphosis (egg --> nymph
--> adult) and complete metamorphosis (egg --> larva --> pupa --> adult).
| Order Hemiptera: flower bug, incomplete
metamorphosis |
 |
| Order Coleoptera: lady beetle, complete
metamorphosis |
 |
