structure and type of sensila and their distribution in insect
- 1. STRUCTRE OF MAJOR TYPES OF SENSILAAND THEIR DISTRIBUTION IN INSECT BODY SUSHMITA SHARMA Department of entomology Agriculture and Forestry University Rampur chitwan
- 2. INTRODUCTION • Sensilla are the sensory organ of insects arising from cuticle of exoskeleton or lying beneath or within it • Sensila are in the form of hair or pegs modified for sensation of different stimuli • Each sensilum consists of two to three secondary neurons (Alexander, 2007) • Sensila are abundant in antenna, palps and cerci though small quantity is found all over the body.
- 3. TYPES OF SENSILA • MECHANORECEPTOR • CHEMORECEPTOR • AUDITORY RECEPTOR • THERMOHYGRORECEPTOR • PHOTORECEPTOR
- 4. MECHANORECEPTOR • They are the sensory cells that detect the mechanical pressure due to movement of objects in the environment • They are functionally divided into exteroreceptors ( mechanical forces) and proprioceptors ( position and orientation of body) (John C Tuthil, 2017) • Exteroreceptors include Trichoform sensila, Campaniform sensila and stretch receptors • Proprioreceptor contains crodotonal organ.
- 5. Tricoform sensila • These cells are located in antennae and mouth parts • These are hair like sense organ associated with spur and seta • It consists of trichogen cell, tormogen cell, thecogen cell, glial cell as accessory supporting cell
- 6. Campaniform sensila • These are dome shaped depression at the center of cuticle • These are cap like structure made up of highly ductile material (Krishnan, 2015) • They are found in wing base, halters, cerci, palp, base of trochanter, femur, tibia and tarsus
- 7. Stretch receptor • Ephemeroptera, Plecopteran, Dictyopteran, Coleoptera and Dermaptera have a pair of stretch receptors on dorsal side of abdominal region • Each receptor is connected with sensory neuron and one member of each pair has longitudinal and another has vertical orientation (M P, 1962) • Multipolar stretch receptors are found near the joints of legs of cockroach which respond to low frequency stimulus (Guthrie, 1967)
- 8. Crodotonal organ • Complex type of mechano receptor which consists of Johnston’s organ and subgenual organ • Johnstons organ contains scolopidia arranged in bowl shaped structure • Subgenual organ are located in proximal tibia of each leg • Johnstons organ is located in antennae
- 9. AUDITORYRECEPTOR • Auditory receptors consists of delicate tactile hair and tympanal ear. • Tactile hair are found in plumose antennae of mosquito. • Tympanal ear consists of tympanum, tracheal expansion and auditory crodotonal organ.
- 11. CHEMORECEPTOR • These are the senses in insects which detect and response towards chemical substances in environment • Chemoreceptor are divided into gustatory receptor and olfactory receptor • Olfactory receptors for detection of chemicals in air through smell • gustatory receptors for detection of dissolved chemicals through taste • In aquatic insects chemoreceptors are restricted to gustatory receptor only
- 12. Olfactory receptor • Mainly antennae and maxillary palp are used to detect sensation of odor • Majority of olfactory receptive neurons are found in antennae • Few of neurons are found in tarsus
- 13. Gustatory receptor • Gustatory receptors stimulate the feeding behavior of insect • Gustatory hairs and gustatory pegs of proboscis control opening of lobes and sucking food respectively (Thoma, 2017) • Taste sensilla are present on legs, wings, labellum and female genitalia
- 14. THERMOHYGRORECEPTOR • Thermo receptor is temperature sensor and hygro receptor are moisture sensor • These are non-porous and arise in different forms may be hair like structure or cap like structure • In bugs thermohygroreceptor is used to select the host by detecting the temperature of host • These receptors are found in antennae and wings
- 15. PHOTORECEPTOR Photoreceptor includes compound eye, dorsal ocelli and lateral ocelli
- 16. Compound eye • Compound eye is major visual organ of insect which contains thousands of ommatidia • Found in almost all adults and immature stages of ametabolous and hemimetabolous insects • Ommatidia are functional unit of vision and their number varies from species to species • Ommatidia are contain cornea, lens and photoreceptor cell
- 17. Dorsal ocelli • They are simple eye often called only ocelli found in all adults and larva of non-holometabolous insects • They are never found in the insect lacking compound eyes • They appear vas 3-4 convex swelling at dorsal part of head • They have single corneal lens covering several rhabdom
- 18. Lateral ocelli • They are also called stemmata which are solely visual organ of holometabolous larvae • Number of stemmata varies from one to six and lies laterally on the head • They help to detect form, color and movement of object
- 19. CONCLUSION • Insects detect and response to various stimuli occurring in the environment • Mechanoreceptor, chemoreceptor, photoreceptor, and thermohygroreceptor are major types of sense organ found in insect body • Different organs of insects are responsible for detecting stimuli • Insects have variety of receptors which when stimulated pass information through nerve signals to central nerve system