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Pleasant Smell
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Unpleasant Smell
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Pramod Kumar K.
2010-11-150
Dept. of Agricultural Entomology
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Can insects be repelled by bad odour ?-
Mechanism of olfaction in insects
Contents
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Definition
Distribution of olfactory receptors
Structure of olfactory receptors
Cuticular components
Cellular components
Mechanism of olfaction
Semiochemicals
Insect attractants
Insect Repellants
Examples for insects repellence
Conclusion
Olfaction
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The sense of smell
Distribution of Olfactory Receptors
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Maxillary palps
(Mosquitoes)8
Olfactory sensilla are present on
Antennae
(Praying mantis)
Labial palps
(Butterfly)
Structure of Olfactory Receptors
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Cuticular components Cellular components
Cuticular Components
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Multiporous
Pores accommodate
olfactory receptors
helps in perception of
smell
Different Types of Sensillum
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Trichoid sensilla
Basiconic sensilla
Coeloconic sensilla
Placoid sensilla
(Chapman, 2006)
Trichoid Sensilla
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Hair like structures (thin walled or thick walled)
eg. Antennae of Bombyx mori
Basiconic Sensilla
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Peg or cone like organs
eg. Maxillary palps of female culicidae
Coeloconic Sensilla
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Cuticular peg is sunk below the general surface of the cuticle.
Opening at surface of
cuticle
Cavity
Peg
Dendrite
Cuticle
Dendrite sheath
Placodea Sensilla
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Flat or raised in to a slight dome
eg. Antennae of honey bee
Pore
Dendrite
Neuron
Cellular Components
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Cells of olfactory sensilla are derived from the epidermis
Trichogen cell
Cellular Components contd…
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Number of sensory neurons in olfactory sensilla
varies from 2 to 20
Male moths Grasshopper
Mechanism of Olfactory Reception
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Insect Olfactory Sense
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Odorants (smells/volatile chemicals) have to travel
through pores in the cuticle
Distinctive smell from environments like
semiochemicals
Semiochemicals
Pheromones Allelochemicals
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Sex pheromone
Aggregation pheromone
Alarm pheromone
Trail pheromone
Allomones
Kairomones
Synamones
Apneumones
(Ragumoorthui et al., 2007)
Pheromone
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Intraspecific chemical substances that mediate
communication between insects
Ectohormones
1959: Karlson and Butenandt
Silkworm moths
Sex Pheromone
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Pheromone released by one sex only and trigger
behaviour patterns in the other sex that facilitate in
mating
Female insect produce pheromone
eg. Pink bollworm – gossyplure
Helicoverpa armigera - helilure
Female Sex Pheromone
Bactrocera dorsalis
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Methyl eugenol
Female Sex Pheromone contd…
Bactrocera cucurbitae
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Cuelure
Aggregation Pheromone
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Pheromones which induce aggregation or
congregation of insects for protection,
reproduction and feeding
Coleoptera and Dictyoptera
Cockroach – periplanone Phloem beetle - ipsenol
Aggregation Pheromone contd…
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Red palm weevil – Rhynchophorus ferrugenius
Ferrolure
Alarm Pheromone
Chemical substance released by insects to warn
members of same species about the presence or
attack by an enemy
eg. Aphids
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Trail Pheromone
Pheromones laid in form of intermittent or
continuous lines on a soil substrate which trail
followers perceive to reach their destination which
could be a mate or food source
eg. Ants
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Allelochemicals
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Interspecific chemicals mediate the communication
between two different species of insects
They are classified in to four categories
Allomones
Chemical released by one insect that induce a
response in another insect
Helpful to emitter
eg. Sting glands in bees
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Kairomones
Chemical released by one insect that induce a
response in another insect
Helpful to recipient
eg. Heptanoic acid releases by potato tuber moth
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Synamone
Chemical released by one insect that induce a
response in another insect
Helpful to emitter and receiver
eg. Termites and protozoan's
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Apneumones
A chemical substance emitted by non living material
that evoke the behavioural or physiological reaction
adaptively for receiving organism
eg. Oat meal oil
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Insect Attractants
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Chemicals that cause insect to make oriented
movements towards their source
Types of attractants are
Pheromone
Natural food lures
Natural Food Lures
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Chemicals present in plant and animal hosts that
attract insect for feeding
Floral scents nectar feeding insect
Decomposing products
Fish Meal Trap
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Sorghum shoot fly is attracted to rotten fish meal
Coconut shell trap
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Insect Repellants
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An oriented movement of insects away from
their source of food
Insect Olfactory Sense contd...
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Smell travels through air
Then they diffuse and are
carried by an odorant
binding protein (OBP)
Many odorants are received
by insect olfactory
sensillum and perceived by
the olfactory receptor
neurons (ORNs)
(Galizia and Rossler, 2010)
Neuron
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Antennae
Sensilla
Na+ , K+ channel
Glomeruli
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Projection neuronProtocerebrum
Motor neuron
Response
Insect Olfactory Sense contd...
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OBP
Insect Olfactory Sense contd...
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Receptor neurons project an axon through the
olfactory nerve into the primary olfactory centers –
olfactory bulb
Insect Olfactory Sense contd...
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Deutocerebrum
Have the olfactory lobe
Receives signal from
glomeruli
Projection neurons will
send the signal to
protocerebrum
Insect Olfactory Sense contd...
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Projection neurons, connecting olfactory lobes to
mushroom bodies and other parts of protocerebrum.
Insect Olfactory Sense contd...
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The physiological characteristics of the projection
neurons vary
They respond only when the antennal receptors are
simulated by a specific odour like a pheromone,
attractant or repellent components
Others are simply ignored or not recognized
Olfactometer
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Specific reaction to olfactory stimuli to be verified by olfactometer responses
Examples for insect repellence by
bad odour
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(Mandavgane et al., 2005)50
Repelling mosquitoes by burning neem leaves
along with cow dung
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To repel honey robber, some stingless social beeserect walls of sticky resin in front of or around thenest entrance, while other species smear arepugnant liquid there
(Lett and Kraus, 1994)52
Eucalyptus oil – pleasant smell in human, repellent
effect on insects like mosquitoes and fleas
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Cocoa leaves, eucalyptus oil, garlic extract, olive
oil mixture of these ingredients will repell the ants,
cockroach, mosquitoes and spiders
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Osmeterium, an orange, Y-shaped structure on the
neck of caterpillar gives off a strong, unpleasant
odour when it is threatened
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Conclusion
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Odour perception is like visiting a library. Thousands of
books are present in the library. Similarly there are a
number of odorants present in the environment. All
groups of insects have specific odours which they
receive through specific glomeruli.
Only odour stimuli in the case of insects. They
receive only those known to them
There is nothing like good or bad odour
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