The Senses of Insects PDF

THE SENSES OF INSECTS CPROT4205MDSLABE:DCPCAgCLSU1STSEM20242025 For insects to exist, they MUST SENSE the realities of the environment and govern their activities accordingly. They must locate food, find mates, avoid enemies, make nests and perform internal functions. They accomplish th...

THE SENSES OF INSECTS CPROT4205MDSLABE:DCPCAgCLSU1STSEM20242025 For insects to exist, they MUST SENSE the realities of the environment and govern their activities accordingly. They must locate food, find mates, avoid enemies, make nests and perform internal functions. They accomplish these tasks only by perceiving conditions and integrating this information to perform the appropriate behavior. Perception is achieved by a number of different sense organs, and behavior results from integration of information and stimulation by the nervous system. THE SENSES OF INSECTS  GROUPS OF  ORGANS/RECEPTORS BASIC SENSES (ECTODERMAL IN 1. SIGHT ORIGIN) 2. SMELL 1. PHOTORECEPTORS (OLFACTION) 2. CHEMORECEPTORS 3. TASTE 3. MECHANORECEPTORS (GUSTATION) 4. AUDITORY ORGANS 4. TOUCH 5. TEMPERATURE AND 5. HEARING HUMIDITY RECEPTORS PHOTORECEPTORS  Detect presence and quality of incident light; when images are produced it is called sight.  e.g. eyes as the most complex photoreceptor involved in forming images  COMPOUND EYES (CE)  perceive images, color, movement  not found in primitively wingless insects (have evolved along with flight); Lacking in immature of most advanced insects; Most insects with CE also have simple eyes  Principal visual organ, characterized externally by the cornea being divided into hexagonal facets. Each facet is part of the individual sensory units called ommatidium. PHOTORECEPTORS NOTE: … THE NUMBER OF FACETS TO A CE VARIES  20,000 in dragonflies  12,000 or more in Lepidoptera  4,000 in Musca (house flies)  Fewer than a dozen in workers of certain ants PHOTORECEPTORS STRUCTURE OF THE CE/HOW THE CE WORKS Light is gathered in ommatidium by lens or cornea The lens focuses light thru a crystalline cone (CC) to a light-receptor apparatus (LRA). [The LRA comprises 6 – 8 retinula cells (RC) which combine to produce a central light sensor (rhabdom). The CC and LRA are surrounded by pigment cells that isolate to various degrees, 1 ommatidium from another] PHOTORECEPTORS RC turn light into electrical energy which is carried to nerve fibers by the brain. Images produced by ommatidia are believed to result in an overall mosaic object, each ommatidium supplying only a piece of vision. PHOTORECEPTORS  SIMPLE EYES/OCELLI  Present in many immatures of Endopterygota  Also believed to perceive images although probably produce a less complete mosaic; some appreciation of color; perceive movement of objects in their vicinity; responsible for orientation to light  Some insects with only simple eyes scan environment by moving head back and forth  Structure varies among insects  Some similar to individual ommatidia (caterpillars)  Some with a single cornea overlying PHOTORECEPTORS  SIMPLE EYES  distinct from the CE thru the presence of a single corneal lens  2 classes:  Dorasl ocelli of imagines and nymphs  3 arranged in a triangle on frontal region of head or on the vertex  Lateral ocelli of most endopterygote larvae  No general uniformity of structure  May occur singly (e.g.sawfly larvae) or in groups on either side of the head (e.g. Lepidoptera larvae) NOTE: SOME INSECTS HAVE NO EYES, THUS THEY DETECT LIGHT THRU THE CUTICLE CHEMORECEPTORS  Detect the presence of chemical substances in the air thru the sense of smell (OLFACTION) OR on substrates thru the sense of taste (GUSTATION)  Based on the detection of certain molecules by receptor organs that subsequently produce a nerve impulse FORMS OF CHEMORECEPTORS - short pegs or hairs on various body parts (antennae,palps) CHEMORECEPTORS  TASTE RECEPTORS  Contactchemoreceptors prevalent on surfaces of mparts, antennae (some Hymenoptera) and tarsi (Lep, Dip, honeybees); sensilla usually hairs or cones with 4 neurons  Sense molecules from liquids  Have fine nerve endings exposed to the environment at hair tips TASTE RECEPTORS  In general, wide differences in taste thresholds of different substances with a given species and for different species with the same substance happen sugar solution ] preferred to distilled H2O dilute acid/salt soln] more conc acid,salts soln ]  rejected esters, alcohols,amino acids ] Individual sense cells of a single gustatory sensillum respond specifically to particular CHEMORECEPTORS  SMELL RECEPTORS  Perceived by olfactory sensilla characterized by the presence of numerous pores  Peglike; have greater number of nerve endings at the surface  Most numerous on insect’s antennae, also abundant on palpi of mparts  More numerous on males: e.g last 8 antennal segments in male Apis about 30,000 sensilla compared to workers = 6,000 & queens = 2,000 SMELL RECEPTORS  Play an important role in the life of insects since many behavioral and developmental changes are caused by pheromones pheromones – highly specific, volatile substances perceived thru the olfactory sensilla after being secreted by other members of the same species e.g. Scents produced by virgin females of some moth attract the males MECHANORECEPTOR S  Detectmovements, vibrations, other mechanical disturbances TOUCH – monitored by hair sensilla, innervated by a single neuron HEARING - perception of aerial vibrations by long, slender, trichoid sensilla MECHANORECEPTOR S  FOR THE TYMPANUM to vibrate = perceived by chordotonal organs made up of scolopidia Where is the tympanum? In grasshoppers, on 1st abdominal segment In crickets, on tibiae In moths, abdomen and metathorax  Johnston’s organ in the pedicel of adult insects responds to movements of antennae; maybe SENSILLA _ COELONICA, CAMPANIFORMIA SENSILLA _ CHAETICA SENSILLA _ TRICHOIDEA SENSILLA - BASICONICA