Transcript insects

INSECTS
Insect ???
• Any member of the class Insecta, the largest class of the
phylum Arthropoda is called an insect.
• In a popular sense, “insect” usually means the familiar
pests or disease carriers, from bedbugs, houseflies, and
clothes moths to Japanese beetles and aphids; the
annoyers, such as mosquitoes, fleas, horseflies, and
hornets; and the conspicuous butterflies and moths.
• Many insects are beneficial from a human viewpoint;
they pollinate plants, produce useful substances, act as
scavengers, and serve as food for other animals
ORIGIN
• The most primitive
insects known are found
as fossils in rocks and
lived about 350,000,000
years ago.
• Those insects originated
with the terrestrial branch
of the phylum Arthropoda.
The Arthropoda, whose
origin is thus far
unknown, probably arose
in Precambrian times,
perhaps as much as
1,000,000,000 years ago.
INSECT: IT’S PARTS
• The insect is covered by
the cuticle, a layer of inert
material laid down by a
single sheet of epidermal
cells.
• In present-day insects,
the primitive segments
are grouped into three
regions known as head,
thorax, and abdomen.
HEAD
• The first six segments have fused to form the
head. The appendages of these segments have
become modified into antennae that bear
numerous sense organs and mouthparts that
convey food to the mouth. Eyes also are
prominent on the head.
• Insect mouthparts have been modified strikingly
and reflect particular methods of feeding.
THORAX
• The insect thorax
consists of three
segments (called the
prothorax, mesothorax,
and metathorax), which
may be fused but are
usually recognizable.
• Each segment bears a
pair of legs, and, in the
mature insect, the
mesothorax and
metathorax typically carry
a pair of wings.
ABDOMEN
• The abdomen consists of
a maximum of 11
segments, although this
number commonly is
reduced by fusion.
• In some insects, notably
crickets and cockroaches,
two feelers, or cerci, at
the hind end of the
abdomen bear sense
organs.
Jerusalem Cricket
Sensory perception and
reception
• Insects have an elaborate system of sense organs.
Tactile hairs, concentrated on the antennae, palps, legs,
and tarsi, cover the entire body surface.
• Exceedingly sensitive organs called sensilla are
concentrated in organs of hearing
• Although the insect eye provides very poor form
perception, insects by using a process of scanning
probably can form adequate visual impressions of their
surrounding
• Insects have chemoreceptors, which help in reception of
smell and taste.
INSECT COMMUNITIES
• Social insects, however,
have developed a
division of labour in which
the members must do the
work required at the
proper time.
• If the society is to
succeed, its needs must
be communicated to the
individual, and the
individual must act.
• E.g.: Bees, wasps
Engine wasp
EFFECTS
• Many insects are
plant feeders; they
damage crops
• Direct injury to man
by insect stings and
bites is of relatively
minor importance,
• Swarms of biting flies
and mosquitoes often
make life almost
intolerable.
Damage to growing crops
• Insects are responsible for two major kinds of
damage to growing crops.
• First is direct injury done to the plant by the
feeding insect, which eats leaves or burrows in
stems, fruit, or roots.
• The second type is indirect damage, in which the
insect itself does little or no harm but transmits
bacterial or, more frequently, viral infection into a
crop
Commercial significance
• Insects provide sources of
commercially important
products—for example,
honey, silk, wax, dyes,
pigments—therefore, insects
can be of direct benefit to
man.
• The most important
domesticated insects are the
silkworm (Lepidoptera) and
the honeybee (Hymenoptera).
ROLE IN NATURE
• Insects and flowers have
evolved together. Many
plants depend on insects
for pollination. Some
insects are predators of
others.
• Insects aid bacteria,
fungi, and other
organisms in the
decomposition of organic
matter and in soil
formation.
pollination