Light Perception in Insects
INTRODUCTION
Light
is
perceived
by
insects
through
a
n
umber
of different
receptors
.
Most
adult insects and larval
hemimetabolous
insects
have
a
pair
of
compound
eyes
and
often
three
single- lens
eyes, called
Ocelli
on the dorsal side of the
head
.
Larval
holometabolus
insects
have
one or
more
single-lens
eyes,
known as
Stemmata
,
on
lateral
sides
of the
head.
Some insects
are
also
known
to
possess
Epidermal
Light
Receptors
,
and, in some
cases,
light
is
known
to
have
Direct
Effect
On Cells In
The
Brain
.
The light-sensitive receptors of
insects, the compound eyes, ocelli,
and stemmata, responds to light
from about 350nm(UV)-
700nm(RED)
Compound
eyes
Compound eyes are so called because they are constructed
of
several
thousands
of similar units
called ommatidia.
Most adult insects have a pair of 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
nd in some
species that live in very dark places.
Compound
eyes may
be
:
a)
Dicoptic
:
viewing a separate and independent field by each eye. In dichoptic
presentation, stimulus A is presented to the left eye and a different stimulus B is
presented to the right eye.
b)
Holoptic
: :
holoptic eyes meet along the
median dorsal
line of the head, in many
species nearly covering the exterior of the head.
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
Ommatidium
.
Ommatidia are basic unit of
compound eyes. It contains a
cluster of photoreceptor cells
surrounded by support cells
and pigment cells. The outer
part of the ommatidium is
overlaid with a transparent
cornea.
They vary in size and number
The sizes of ommatidia vary
from about 5 to 40 microns in
diameter.
Components: a) Optical part,
optical eye consists of Corneal
lens,crystalline cone.
b) Sensory part
consits
ofRhabdome cell, Retinula
cells. A nerve axon projects
from each retinula cell.Each
ommatidium has its own an
optic nerve.
Ommatidium
Surface view of facets of a
compound
Types of image
Two types of images are formed: Diurnal insects forms the apposition image and
they are active during the day. Nocturnal insects forms the superposition eye and they are
mainly active in night.
a)
Apposition
Eyes/
Photopic
Eyes:
Apposition eyes are the most common form of eyes
and are presumably the ancestral form of compound eyes. Apposition eyes work by
gathering a number of images, one from each ommatidium, and combining them in the
brain, with each eye typically contributing a single point of information. The typical
apposition eye has a lens focusing light from one direction on the rhabdom, while light
from other directions is absorbed by the dark wall of the
ommatidium
.
b)
Superposition
Eyes/
Scotopic
Eyes:
S
uperposition
eye has a gap between the lens and
the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it
to the same angle on the other side. The result is an image at half the radius of the eye,
which is where the tips of the rhabdoms are. This type of compound eye, for which a
minimal size exists below which effective superposition cannot occur, is normally found
in nocturnal insects, because it can create images up to 1000 times brighter than
equivalent apposition eyes, though at the cost of reduced resolution.
[
Resolution
:
The degree of fineness with
which
an
eye
forms
an
image of
the
object.
o
Presence
of the
interommatidial
angle.
o
In
appostion
eyes,
the
fineness of image will be
greater
the
smaller
the
ommatidial
angle.
o
The 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.
Significance of Compound Eyes
Flicker effect
The compound eye is excellent at detecting motion.As an object moves
ommatidia are turned on and off.
Distance Perception
Most insects must be able to judge distance.As in prey catching insects, in
grasshopper’s jumping, and when they are landing.Simultaneous stimulation of
ommatidia.
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.
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.
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.
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
Insects perceive light through various receptors such as compound eyes, ocelli, and stemmata. Compound eyes, made up of ommatidia, play a key role in capturing light stimuli ranging from UV to red wavelengths. Different types of compound eyes, like dioptric and holoptic, form images differently for diurnal and nocturnal insects. This comprehensive overview delves into the intricate mechanisms of how insects sense and process light information.
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Presentation Transcript
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 on the dorsal side of the head. Larval holometabolus insects have one or more single-lens eyes, known as Stemmata, on lateral sides of the head. Some insects are also known to possess Epidermal Light Receptors, and, in some cases, light is known to have Direct Effect On Cells In The Brain. The light-sensitive receptors of insects, the compound eyes, ocelli, and stemmata, responds to light from about 350nm(UV)- 700nm(RED)
Compound eyes Compound eyes are so called because they are constructed of several thousands of similar units called ommatidia. Most adult insects have a pair of 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 nd in some species that live in very dark places. Compound eyes may be: a) Dicoptic: viewing a separate and independent field by each eye. In dichoptic presentation, stimulus A is presented to the left eye and a different stimulus B is presented to the right eye. b) Holoptic: : holoptic eyes meet along the median dorsal line of the head, in many species nearly covering the exterior of the head. Each eye is made up of severalthousands of Ommatidia Or Facets. Ommitidia consists of : Optic Part , Sensory Part. Four types of Facets-a) Eucone, b)Acone, c ) Pseudocone, d) Exocone
Ommatidium .Ommatidia are basic unit of compound eyes. It contains a cluster of photoreceptor cells surrounded by support cells and pigment cells. The outer part of the ommatidium is overlaid with a transparent cornea. They vary in size and number The sizes of ommatidia vary from about 5 to 40 microns in diameter. Components: a) Optical part, optical eye consists of Corneal lens,crystalline cone. b) Sensory part consits ofRhabdome cell, Retinula cells. A nerve axon projects from each retinula cell.Each ommatidium has its own an optic nerve. Surface view of facets of a compound Ommatidium
Types of image Two types of images are formed: Diurnal insects forms the apposition image and they are active during the day. Nocturnal insects forms the superposition eye and they are mainly active in night. a) Apposition Eyes/ Photopic Eyes: Apposition eyes are the most common form of eyes and are presumably the ancestral form of compound eyes. Apposition eyes work by gathering a number of images, one from each ommatidium, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium. b) Superposition Eyes/ Scotopic Eyes: Superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur, is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution.[
Resolution: The degree of fineness with whichan 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 infigure. b) The receptor sensitivity can be changed.
Significance of Compound Eyes Flicker effect The compound eye is excellent at detecting motion.As an object moves ommatidia are turned on and off. Distance Perception Most insects must be able to judge distance.As in prey catching insects, in grasshopper s jumping, and when they are landing.Simultaneous stimulation of ommatidia. 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.
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.
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 inintensity, 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.
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 orocelli. In some species, daylength, regulating diapause, is registered directly by the brain
