mechano and chemoreceptors

Question 1

define mechanoreception

Answer 1

the ability for an insect to detect and respond to certain kind of stimuli; notably touch, sound and changes in pressure or posture in its environment

= tactile or proprioceptive cues

Question 2

what are the 3 broad categories of mechanoreceptors in insects

Answer 2

1) cuticular (bipolar neurons) = 2 classes
2) sub-cuticular (bipolar neurons)= chordontonal organs
3) internal stretch/tension receptors (multi-polar neurons)

Question 3

what are the two classes of cuticular mechanoreceptors

Answer 3

1) hair sensilla = projections from the cuticle with a basal socket

2) campaniform (dome like) sensilla

Question 4

outline the structure of hair sensilla which act as cuticular mechanoreceptors

Answer 4

= taper from base-tip –> trichoid sensilla

= shorter, peg-like –> basiconic

Question 5

outline the structure of campaniform sensilla which are a class of cuticular mechanoreceptors

Answer 5

• structure vary according to position
• occur on mouthparts, tibial spines, basal segments of antennae, veins close to wing base, ovipositor and haltere

Question 6

what are the function of hair sensilla and list the ways this is performed

Answer 6

EXTEROCEPTION = detecting information from the outside environment

PROPRIORRECEPTION = perception or awareness of the position and movement of the body

Question 7

how do hair sensilla allow exteroception

Answer 7

1. Tactile hairs – all over body
2. Air movement detectors – stimulated by flow of air over body
   and head during flight
   * Maintain wingbeat, control yaw
   * On cerci – respond to sound
3. Gravitational orientation – also involves proprioreceptors
   * Modified hair sensilla contribute (some Orthoptera)
4. Pressure receivers – depth perception in aquatic insects
   * Detect changes in volume of plastron
   * Responds to increasing pressure (depth)

Question 8

how do insects allow proprioreception

Answer 8

1) hair sensilla = groups/rows of small hairs
- joints between leg segments, basal antennal segemnts, cervical sclerites, wing base
- movement of one parts which causes the other hairs to bend

2) campaniform sensilla - detect shearing stress
- produce change in shape from stimulation
- load sensors which show direction and force
- ones on wing veins control flight stability
- ones halteres control wing stroke
- on antennae control sterring and maitence

Question 9

what is shearing stress

Answer 9

a type of stress which acts a s coplanar with cross section of material

Question 10

what are subcuticular mechanoreceptors

Answer 10

found within the cuticle throughout the body consisting of single or groups of sclopidia and whos function is to convert vibration into nerve impulses

Question 11

what are some of the other functions of sub-cuticular mechanoreceptors

Answer 11

joint proprioception
substrate vibration detection
hearing
wind and gravity sensation in the antennae

Question 12

outline how sub-cuticular mechanoreceptors function for joint proprioception

Answer 12

1) the femoral chordtonal organ in the femur of the insect leg detects position, speed, acceleration and vibrayion of of the tibia relative to the femur

2) the johnstons organ is located in the pedicel of the antennae detects position and movement of flagellum relative to the pedicel

3) hymenoptera have a janets organ which detects flexsion at antennal joints

Question 13

what organ detects substrate vibration

Answer 13

subgenual organ
= proximal part of the tibia
= detects high frequencey acoustic vibrations transmitted through substrate
= found in all insects but diptera and coleoptera

Question 14

what is the tympanal organ

Answer 14

a membrane (the tympanum) which is stretched across a frame of rigid cuticle and backed by air sacs allowing it to vibrate

Question 15

outline how hearing occurs in insects

Answer 15

the tympanal organ vibrates and the vibrations are detected by the chorodontal organ attached to the inside of the tymanum

= this organ can be found in many parts of insects but subgeneal organs can also detect some air borne vibrations

Question 16

in summary the functions of the sub-cuticular mechanoreceptors are a) joint proprioception b) substrate vibration detection c) hearing and d) wind and gravity sensation
name the organs involved in each of these functions

Answer 16

a) femoral chordotonal organ
b) subgenual organ
c) tympanal organ, crista acoustica and subgeneal organ
d) Johnstons/Janet organ

Question 17

outline stretch and tension receptors

Answer 17

• Different in having multi-polar neurons
• May be integral part of muscle fibre or connective tissue or have no
  specific orientation or associated structures
• Monitor abdominal distension during feeding
• Respond to movement and position of tibia wrt femur
• Monitor movement of food along gut
• Control oviposition rate
• Play key role in controlling wing movements

Question 18

outline the transmission of mechanical signals

Answer 18

• insects produce communication signals in many different ways
• neuromuscular activity leads to mechanical vibration of some exoskeletal structure
• the transduction of vibrations as cycle of compression and rarefaction to the surrounding medium
  = mechanisms producting this vibration may also generate airborne sounds which can be detected

Question 19

outline the significance of mechanical signals

Answer 19

1) intraspecific communication
2) reproductive isolation
3) attraction from a distance
4) courtship
5) signalling physiological or genetic quality
6) territorial behaviour and compeititon
7) communication in social insects
8) interspecific communication

Question 20

what are the different mechanisms to producing sounds and vibrations

Answer 20

1) percussion = impact of part of the body on substrate or another part of the body e.g. death watch beetle

2) stridulation = production of vibration by moving cuticular ridge over tooth ridge e.g. orthoptera

3) tymbal mechanisms = vibrations produced when timbal buckles

4) oscillation of flight muscles = produce throacic and wing vibrations e.g. waggle dance in honey bees

5) air expulsion = expel air through the mouth or enlarged abdominal spiracle

Question 21

outline chemoreception in insects

Answer 21

• Stimulation by chemicals involves senses of
  olfaction and gustation by gustatory receptors
• Possess ‘taste’ receptors on many parts of body
• Some used for purposes unrelated to feeding
• Detect chemicals on dry surfaces (= contact
  chemoreception)
• Range of olfactory receptors (remote
  chemoreception) sensitive to odours
• Mechanism of detection allows overlap between
  olfaction and contact chemoreception (taste)
• Processes in CNS different for each mode

Question 22

outline some examples of chemoreception mediated sense organs

Answer 22

1) Sensilla tichodea = hair like structures on the distal region of the proboscis of moths

2) sensilla basiconica - peg like and can be found on the antennae of mosquitos

3) sensilla coeloconica = peg sunken pits e.g. apical antennae of leaf cutter ants

Question 23

outline chemosensory sensilla in insects

Answer 23

olfactory sensilla clustered on the antennae, maxillar and labial palps and the genitalia of some insects

• contact of these distributed across the entire body but cluster in specific regions and can be grouped on mouthparts
  = none on the manibles
  = high density on legs and some antennae

Question 24

what is the difference between a pheromone and an allelochemical

Answer 24

P= mediates interaction between conspecifics

A= involoved in interactions between different spp

Question 25

what are the different functions of pheromones

Answer 25

1) aggregation
2) sex
3) alarm calling
4) marking
5) trails
6) social

Question 26

what is the different types of allelochemicals and what is the difference between them

Answer 26

1) Allomones = benefit only to the emitter e.g. deterrents or repellents

2) Kairomones = benefit only to the receiver e.g. pollinator spp

3) Synomones = benefit to both the emitter and reciever e.g. flower and pollinator