Insect Sensory Systems

Question 1

What are mechanical stimuli?

Answer 1

Stimuli associated with distortion caused by mechanical movement resulting from external (environmental) and internal (e.g. muscles) forces.

Question 2

What does tactile mechanoreception involve?

Answer 2

• Insect bodies are clothed with cuticular projections of different lengths and sensitivities
• The sensory organ itself is called sensilla
• The projections can be called hairs, bristles or setae

Question 3

What is position mechanoreception?

Answer 3

• Insects require continuous knowledge of the relative position of their body parts, or how their body relates to gravity.
• This information is obtained via proprioceptors (“self-perception receptors”)

Question 4

What does sound reception involve?

Answer 4

• Sound is a pressure fluctuation transmitted in a wave form via movement of the air or substrate
• Common sound reception organ is the tympanum, a membrane that responds to sound at distance
• Tympani are located on the thorax (ventrally, between legs, metathorax, wing base, prosternum, cervical membranes in some beetles, on the legs) or on the 1st abdominal segment.

Question 5

What does this kind of sound reception help insects do?

Answer 5

• Tympanal sound reception is well developed in Orthopterans
• Can identify the point source of the sound > highly specific
• Mate location, predator avoidance

Question 6

How do insects produce sound?

Answer 6

• Most common method is stridulation > a “scraper” is rubbed against a “file”
• Common in Orthopterans (crickets - acoustic and visual communication) also in Hymenopterans (some ants)
• Tymbals are another method of sound production (crickets, some plant hoppers, cicadas)
• Individual clicks from a specialised elastic cuticle, vibrates like a drum skin.

Question 7

How do insects respond to thermal stimuli?

Answer 7

• Thermoreception is often in antennae or legs

Question 8

How do insects thermoregulate? And what does temperature impact?

Answer 8

• Insects are ectothermic: the regulation of body temperature depends on external sources (small size > lose heat fast)
• Can thermoregulate by behavioural or physiological mechanisms: hair for insulation, anti-freeze compounds in heamolymph
• Development is temperature-dependent
• Activity patterns may be temperature-dependent

Question 9

How do insects respond to chemical stimuli?

Answer 9

• Chemical senses may be divided into taste (gustatory receptors) and smell (olfactory receptors)
• Chemical stimuli are assessed by chemosensors, which may be located on the antennae, feet, oviposter, mouth etc.
• Chemosensors are sensilla with one or more pores

Question 10

What are semiochemicals and what are their role?

Answer 10

• To be as efficient as possible, insects usually have many sensilla (e.g. some antennae of moths have 17,000 sensilla for finding mates)
• Many insects rely heavily on chemical odours (semiochemicals - chemicals that convey information from one individual to another)
• Pheromones: mediate communication within species
• Allelochemicals: communication chemicals between species

Question 11

How do male and female insects communicate?

Answer 11

• Male and female conspecifics often communicate with sex pheromones
• Male moths use both their antennae to accurately detect which direction the female moth is releasing pheromones from

Question 12

What are some other pheromones and their roles?

Answer 12

• Aggregation pheromones (insects clump together)
• Nestmate recognition pheromones
• Orientation pheromones (e.g. bee releases to indicate to other bees where a certain resource is)
• Trail-marking pheromones (e.g. ant use to stay on the same path)
• Alarm pheromones

Question 13

What are allelochemicals and how are they grouped?

Answer 13

• Communication chemicals between species
• Kairomones: disadvantage the producer, benefit the receiver
• Allomones: benefit the producer, neutral effects on the receiver
• Synomones: benefit the producer and the receiver

Question 14

What structures are used in detecting visual stimuli?

Answer 14

• Ocelli: dorsal light sensing organs, typically in a triangle on top of the head
• Compound eyes: bunches of individual ommatidia

Question 15

What is the compound eye comprised of and what are their function(s)?

Answer 15

• Composed of many individual units called ommatidia
• Each ommatidia has a field view of 2-5 degrees
• Sensitive to image motion; but not generally good for 3D and high resolution
• Within one ommatidia, there are sveral cells that respond to different wavelengths
• Insects can see colour, ultraviolet light, polarised light