PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
HEAD
SEGMENTATION
ANTENNAE
Movement
Smelling
Feeling
Tasting
Hearing
SINGLE HARD HEAD CAPSULE
Although originally formed of 6 segments, the head is compacted into a
single hard head capsule.
There is usually a narrow ‘neck’ region behind the head which allows the
head to move.
ONE PAIR OF ANTENNAE
The antennae arise from the front of the head, usually situated between or in
front of the compound eyes. Antennae are:
Used for smelling, feeling and occasionally for tasting and hearing.
Mobile and can move in all directions.
Made up of few or many segments.
Variable in size and shape.
Butterfly
antenna
Moth
antennae
Weevil
antenna
(clubbed) (variable) (elbowed)
EYES
MOST INSECTS HAVE BOTH COMPOUND AND SIMPLE EYES
However, only one or other may be present.
COMPOUND EYES
Most insects have 1 pair.
They are usually conspicuous
shiny objects on the side of the
head, eg in flies, and are round,
convex or kidney-shaped.
1 pair large compound eyes
Compound eyes are composed of minute hexagonal panes fitted closely
together. Each pane admits a point of light, a bit of the total scene that the
insect sees. Nerves carry the information to the brain and all the bits of the
picture are then pieced together to form the whole picture (like a television
picture). The more panes an insect has the sharper the picture, eg flies have
4,000 and dragonflies more than 20,000 panes.
Insects cannot move their eyes but they can move their heads.
They have no eyelids, their eyes are always open.
They can see a sharp image up to 1 meter, further is a blur.
They can quickly see movement.
They can discriminate colors, see colors we cannot see, eg ultraviolet and
infrared.
3 tiny simple eyes
arranged in a triangle
between 1 pair of
large compound eyes
‘ Eyespot’ on grapevine
hawk moth caterpillar
SIMPLE EYES (ocelli)
Each adult insect has up to 3 simple eyes, each with only 1 lens, usually
arranged in a triangle on the top of the head. It is doubtful if any of them
see a clear image but they are able to distinguish light from darkness and
may discern faint images. The simple eyes found in larvae are called
‘stemmata’.
Larvae of insects with a complete metamorphosis do not have compound
eyes, they have 6 simple eyes on the side of their head.
‘EYESPOTS’
Eyespots on caterpillars and insect wings are not real eyes, they are for
decoration to frighten predators.
Insects and allied pests - Biology 13