Insect vision ENTO-501

INSECT MORPHOLOGY

Name –Bhumika Kapoor Regd.no.- j-16-m-451

Division Of Entomology

ContentsCompound EyesImage FormationColor Vision Detection Of Polarized LightMagnetic SensitivityField View In InsectsDorsal OcelliStemmataOther Visual Receptors

INTRODUCTIONLight 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.

Compound eyesPresents 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) HolopticEach 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

Image formationa) 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.

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.

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.

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.

Field visionField 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; mantids2) Motion parallax; grasshopper

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.

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

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

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