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*"Sensing the World: Insect Sensory Systems"*
- 2. Agricultural Entomology (Sixth Deans’ Committee Recommended Syllabus) Course No: ENTO: 121 Course Title: Fundamentals of Entomology By, Mr. Arshad K. Shaikh Assistant Professor Institute: Sharadchandraji Pawar Institute of Agricultural Sciences, Kharavate- Dahiwali, Tal. Chiplun, Dist. Ratnagiri. Dr. Balasaheb Sawant Konkan Krishi Vidyapeeth, Dapoli [email protected]
- 3. The sense organs in an insect body are distributed on different parts and respond to a given stimulus such as light, sound, touch, chemicals etc. The sense organs may be classified as; 1. Photoreceptors(or) Visual organs- To detect light energy. 2. Auditory receptors (or) organs of hearing- To detect sound waves. 3. Chemoreceptor’s which respond to chemicals- To detect smell and taste. 4. Mechanoreceptor/Tactile receptors which respond to touch- To detect mechanical force. 5. Thermoreceptor – To detect heat.
- 4. 1.Visual organs or photoreceptors: These are two types, Compound eyes and Simple eyes. I. Compound eyes: These organs possess the ability to perceive light energy and able to produce a nerve impulse. The compound eyes may be completely absent in insects like Protura or they may remain reduced in endoparasitic Hymenoptera. The compound eyes are present on either side of the head capsule of an adult insect and also in the nymphs of Exopterygota. These are a pair and consist of number of individual units (or) facets called ommatidia. Function is to gather light.
- 5. Classification of Compound eyes based on image formation; Apposition eyes: These are active during day time (diurnal insects);e.g.: butterflies. Superposition eyes: These are active during evening and night time (Nocturnal insects); e.g.: moths. Apposition eyes Superposition eyes
- 6. II. Simple eyes (or) ocelli: These are of two types Dorsal ocelli: Seen in nymphs and adults of Hemimetabolous insects and adults of Holometabola. Dorsal ocelli are represented by fenestrae in cockroach. It perceive light to maintain diurnal rhythm. Lateral ocelli: Also known as stemmata. These are present on the lateral sides of the head of Endopterygote larva. It helps to detect form, colour and movement.
- 7. 2. Auditory organs (or) organs of hearing: Insects are provided with structures (or) organs that are able to perceive the sound waves (or) the aquatic water currents. Among the organs of hearing, the auditory hairs, tympanal organ and Jhonston’s organ are important. 1. Auditory hairs : These are present on the body of insects such as larvae of Lepidoptera which are developed from the modified epidermal cells. These respond to the sounds of air (or) water currents mediated by the hair sensillae (or) trichoid.
- 8. 2. Tympanal organ : Tympanum is present one on either side of the 1st abdominal segment of short horned grasshoppers, on the base of foretibia in long horned grasshoppers and crickets, and on thorax or abdomen in Lepidoptera. 3. Jhonston’s organ: It is present on the pedicel of antennae and functions as an auditory organ responding to air (or) water currents. They are absent in Collembola. 4. Pilifer of hawk moths (Sphingid moths): A unique auditory organ, sensitive to ultrasonic frequencies is found in the head of several species of
- 10. 3. Mechanoreceptor: (Detect mechanical force) Trichoid sensilla: Hair like sense organ. Sense cell associated with spur and seta. These cells are sensitive to touch and are located in antenna and mouthparts. Campaniform / Dome sensilla: These cells are sensitive to pressure and located in legs joints and wing bases. Chordotonal organ: The specialized sensory organs that receive vibration are subcuticular mechanoreceptors called chordotonal organ.
- 13. 3. Chemoreceptors: (detect smell and taste): It contains sensilla with one pore (uniporous) or more pores (multiporous). ♣ Uniporous chemoreceptors mostly detect chemicals of solid and liquid form by contact called gustatory receptors and located in antennae. ♣ Multiporous chemoreceptor’s detect chemicals in vapour form at distant by smell called olfactory receptors and located in mouth and tarsi. 5.Thermoreceptor – (detect heat) Present in poikilothermic insects and sensitive to temperature changes. E.g. Bed bugs.
- 14. Sound and light producing organs They are generally well developed in male insects and are meant for attracting the opposite sex, warning about danger, stimulating female and expressing sexual rivalry. The sound is produced by different methods by, 1. Rubbing two body parts, e,g. a series of pegs on femur rubbed against a hard vein of forewing. 2. Wing vibration, producing buzzing or humming sound e.g. house fly vibrates wings at 330 strokes/ second and honey bee 440 strokes/ second. 3. Striking body parts against an object e.g. soldier termites strike the head against the floor to produce warning sound. 4. Vibration membrane at the base e.g. cicada bug producing shrills.
- 17. Light producing organs Such are popularly known as fire flies, glow worms, or blinkers. They may be self luminous due to photogenic organs or may contain photogenic bacteria or the food consumed by them may be luminous. The light produced may be continuous, intermittent or pulsating. It helps in attracting the sexes for mating. The light is emitted when luciferin is oxydised by free oxygen in presence of water and an enzyme luciferace producing oxyluciferin.