Odour detection and blood feeding arthropods Flashcards
What senses affect mosquito behaviour?
Vision, auditory, mechanical, heat, moisture and chemicals/volatiles
Which sense is related to the olfactory system?
Chemicals/volatiles that attract the mosquito to blood hosts, nectar, mates, resting sites and oviposition sites.
What are the two types of semiochemicals?
Pheromones and allelochemicals
What are the types of pheromones and their roles?
Releasers - create immediate behaviour change.
Primers - create a physiological or developmental change.
What are the different types of allelochemicals and their roles?
Kairomones that are favourable to the receiver (CO2).
Allomones favourable to the emitter not receiver (natural repellants from humans)
Synomones that are favourable to both.
Name 3 main olfactory appendages
Maxillary palp, proboscis and antennae
What does the maxillary palp detect?
CO2 sensing organ and 1-octen-3-ol produced by humans and cattle.
What is the role of the proboscis in olfactory systems?
Chemosensilla express olfactory receptors at the labellum (tip) of the proboscis.
Short range detection of host compounds.
What is the role of the antennae?
Long range detection of volatiles, and the Johnson organ in the end segment detects sound.
What is the difference between placing of chemosensilla on the antennae of female and male mosquitoes?
Females have chemosensilla on all 13 segments of antennae, but males only have them on distal 2 segment, this is because odour is more important to females.
Why do the appendages have olfactory sensilla?
To increase the surface area.
What is the role of odourant binding proteins (OBPs)?
Volatiles/semiochemicals are hydrophobic so when the volatiles enter through pores and enter the lymph they have to bind to the OBP to move across the lymph to the olfactory receptor neuron (ORN)
What happens when the volatile reaches the olfactory receptor?
The volatiles reach the dendrite and bind, and the OR senses molecules outside the cell and activates signal transduction inside the cell. There is depolarisation of the ORN cell creating an action potential up to the antennal lobe in the brain.
What is the OR co-receptor (Orco) needed for?
It is needed for correct signalling.
Mutants had a reduced attraction to honey and no response to human odour in the absence of CO2. With CO2 they were attracted to humans and animals but loss preference for humans.
No longer repelled by DEET.
What is coincidence detection in relation to ORNs?
When there is co-location of 2 ORNs in 1 sensillum and there is simultaneous stimulation of both this allows the mosquito to recognise the human host, as humans produce both chemicals. If just one is stimulated/or stimulated at different times it will not recognise the human host.
What is the role of odour degrading enzymes?
Degrade the odour chemicals to halt stimulation of receptor and produce behavioural response.
Do mosquitoes prefer skin odour plume structures as homogenous, filamentous or turbulent?
Homogenous which gives them a constant smell.
When the mosquito was presented with just CO2, how do the preference for plume structure change and why?
They preferred filamentous plume structure as CO2 is constantly in the air so filamentous plumes allows the mosquito to distinguish between host and background CO2. And is representative of breathing.
How does age of the insect effect olfaction?
Older tsetse flies had a lower responsiveness to host compounds
How do blood meals effect olfaction?
After blood meals the female mosquito stops host seeking to find an oviposition site. The sensilla that respond to host cues become less sensitive.
How does infection status effect olfaction?
Infected mosquitoes are more attracted to host odour, they pick up different odours to enhance detection and change behaviour.
Same with plague fleas.
