3. INTRODUCTION
Light is perceived by insects through a
Number Of Different Receptors.
Most adult insects and larval
hemimetabolous insects have a pair of
compound eyes and often three single-
lens eyes, called Ocelli.
Larval holometabolus insects have one
or more single-lens eyes, known as
Stemmata, on sides of the head.
Some in sects are also known to
possess Epidermal Light Receptors,
and, in some cases, light is known to
have Direct Effect On Cells In The
Brain.
4. Compound eyes
Presents in most adults Pterygote Insects
And The Larvae of Hemimetabolus Insects.
Absents or Reduced in wingless parasitic
groups like fleas, female mealy bugs,etc.
Compound eyes may be :
a) Dicoptic
b) Holoptic
Each eye is made up of several thousands
of Ommatidia Or Facets.
Ommitidia consists of : Optic Part , Sensory
Part.
Four types of Facets-a) Eucone, b)Acone, c)
Pseudocone, d) Exocone
Fig: Ommitidium
5. Image formation
a) Superposition Eyes/ Scotopic Eyes: In this type of eye the pigment cells
only ensheath the top part of the ommatidium, around the facet and cone.
Overlapping of images( dim image). Found in nocturnal and crepuscular insects.
b) Apposition Eyes/ Photopic Eyes: In this type, the final image is made up
of discrete points, each point formed by a single ommatidium, placed side-by-
side to form an image which is a mosaic of points. Found in diurnal insects.
6. Resolution: The degree of fineness with which an
eye forms an image of the object.
oPresence of the interommatidial angle.
oIn appostion eyes, the fineness of image will be greater
the smaller the ommatidial angle.
oThe degree of resolution is decreased when the eye
becomes dark adapted and light from a greater area is
admitted to each unit. Fig: Day eyes and Night eyes.
Transduction: The conversion of electrical energy involves the visual
pigment. This is chromoprotein belonging to a group of chromoproteins known as
Rhodopsins.
Adaptation: The natural change from darkness
to full light involves change in light intensity.it may be
of two types in eyes:
a) the amount of light reaching photoreceptors is
regulated. Eg; in ant Camponotus shown in figure.
b) The receptor sensitivity can be changed.
7. Color vision
•Not all insects see colors. But maximum adsorption is in the green range of
spectrum(490-540nm).
•Most insects shows maximum sensitivity to wavelength in ultraviolet and
another with maximum absorption in the blue range. But for majority
insects, red color does not stimulates the eye.
•Honey bees can differentiate yellow, blue-green, violet, ultraviolet, purple
but not red. Figure showing Rove Bettle.
8. Polarization sensitivity
• Light said to be polarized when all
vibrations are in one plane the light
is plane-polarized.
• Certain insects used it for navigation
• Example in the homing of social
Hymenoptera, and is best known in
Apis and the Ant, Cataglyphis.
Magnetic sensitivity
•A number of insects species have been
shown to respond to changes in
magnetic field .
•Certain insects used this for
navigations because of presence of
particle of magnetitc, an iron oxide.
•Example the Male Drosophila show
different orientation in a magnetic field
w.r.t. Wave length.
9. Field vision
Field View:
•Insect with well-developed compound
eyes have an extensive field view.
•Example in Periplaneta has vision through
3600, has binocular vision in front and
behind the head.
Distance Perception:
•Insects are able to judge distance with
cosiderable accuracy, as in case of
grasshopper and mantids.
•It can be done with 2 mechanism:
1) Stereoscopic mechanism; mantids
2) Motion parallax; grasshopper
10. Visual tracking:
•An animal’s ability to keep a moving target
within specific area of the retina, often when
the animal itself is moving.
•For examples, when a predator such as a
mantisor dragonfly catches its prey, or when
a male fly pursues a female.
Form perception:
•The eye’s ability to detect the form of an
object depends on its resolving power.
•Bees provide a good model for
understanding form perception because they
can be trained to discriminate between
different shapes.
11. Dorsal ocelli:
• Found in adult insects and the
larvae of hemimetabolous insects.
• Three ocelli forming are inverted
triangle antero-dorsally on the
head.
• The ocelli are lost or absent in
wingless form.
• Ocelli are adapted for the
concentration of light and
perception of changes in intensity,
a pathway for rapid conduction.
Stemmata( lateral ocelli):
• Visual organs of larval holometabolous
insects.
• It is laterally on the head and vary in
number from one in sawfly larvae to six
on each side in lepidopteran larva.
• Stemmata are of two types:
a. Those with single rhabdom: eg:
mecoptera, neuroptera, etc.
b. Those with multiple rhabdom: eg: grubs
of adephaga, sawfly larva,etc.
12. Other Visual Receptors
•Dermal Light Sense:
•A number of insects, such as tenebrio larvae, still
respond to light when all the known visual
receptors are occluded.
•The epidermal cells are apparently sensitive to
light.
•Sensitivity Of The Brain:
•In several insects species, light affects neural
activity directly by acting on the brain, not via the
compound eyes or ocelli.
•In some species, daylength, regulating diapause, is
registered directly by the brain
13. References
•R.F.Chapman, The insect: structure and function, fourth
edition, cambridge university press, U.K., Page no. 587
•Cronodon.com>biotech>insect_vision
• ecoevodevo.com>pdffiles>outreachE
•Google search
