Category Archives: Background Theory

Testing and commissioning the dual-choice olfactometer

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With the build completed I moved the olfactometer into the insectary for testing and commissioning. This was quite an exciting time as I was getting closer to the moment of truth. Would the equipment, that had thus far lived in my head and in computer software, be fit for purpose. Would the careful design, modelling and building pay off and furnish me with kit that would be central to my study of mosquito olfactory mediated behaviour, or would it leave me scratching my head on the way back to the drawing board.

Hurrying the development of the soon to be experimental candidate mosquitoes. Preconditioning for temperature and light cycle.

Hurrying the development of the soon to be experimental candidate mosquitoes. Preconditioning for temperature and light cycle.

Once all the connections has been made to the newly purchased air compressor, carbon filter, inline heater and humidifier it was time to check that it was capable of delivering steady air flow at the right temperature and humidity.

Air flow was a simple matter of setting the litres per minute to match the modeled input. The humidity and temperature required a little more finesse, as it required a balancing of the water volume and temperature in the humidifier; once set, however, it remained steady at 25 degrees centigrade and 75 % relative humidity.

Importantly, I was unable to find any airflow bias between the trap chambers and variable delivery chambers, meaning that I could move on to the next step – a live run with mosquitoes.

 

 

 

Meet Ochlerotatus punctor, the puddle dweller!

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Today’s blog post is not directly linked to the olfactometer design and build process but instead introduces a little detail around one of the UK’s native mosquitoes.

Both of these are Ochlerotatus punctor and were collected as larvae from the same temporary puddle in the middle of a path through a forest. They were then reared on to adult emergence in the university insectary. It is worth noting that the puddle only lasted about 10 days, yet it yielded many larvae; I do not know however whether the development cycle completed before the puddle dried up. I do know that I did not collect any 4th instars (the final larval stage of mosquitoes) or pupae from the puddle before it dried up.

The images below are included to help highlight some of the physical differences between male and female mosquitoes. The lighting is not great as the photos are taken through the eyepiece of the dissecting microscope in the insectary. These are quite small mosquitoes, about 2/3 the size of the Culiseta species which forms the title image of this blog site.

Ochlerotatus punctor are widely distributed in Britain dependent upon the availability of temporary woodland pools. They females feed on a range of mammals and will readily bite humans, particularly at dusk near aquatic sites (Snow, 1990).

Female Ochlerotatus punctor head with annotations showing pilose antennae and short maxillary palps.

Female Ochlerotatus punctor head with annotations showing pilose antennae and short maxillary palps.

Male Ochlerotatus punctor head with annotations showing plumose antennae and elongate maxillary palps.

Male Ochlerotatus punctor head with annotations showing plumose antennae and elongate maxillary palps.

 

References:

Snow, K.R. (1990). Mosquitoes. Slough: The Richmond Publishing Co. Ltd.

What is a Dual-Choice Olfactometer?

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In simplest terms a dual-choice olfactometer is a piece of experimental equipment which allows the testing of the apparent preference of one odour against another, as shown by the organism “choosing” which smell to approach. This choice is assessed by observation of the behaviour of the organism within a choice arena or chamber.

It therefore needs to be an enclosed space where organisms can be presented with a choice between two odours. These odours may be two different added odours (variables), or there may only be one odour added which is tested alongside a control where no odour variable is offered. By carefully designing a strategy of testing the variables against a control, and also against each other, it is possible to develop a data set which indicates which variables are most preferred by the organism.

Dual-choice olfactometers are designed to minimise the possibility of other factors influencing the observed behaviour. If behaviour is being influenced by other factors then little confidence can be placed in the experimental outcome. For example, if the organism can see the source of the odour it may prefer the sight of the source, so this would no longer be a test of olfactory driven behaviour. Similarly, if the air flow through the variable delivery system is unbalanced then the organism may prefer the higher or lower air flow and make its choice based upon this mechanism. Special attention is therefore needed to “design out” these potential confounding variables, and “dry-runs” where no variables are loaded will help to spot any bias in the system which can be remediated.

So far I have only referred to “the organism”. This is because we can, in principle, make this type of choice arena for any organism that has a sense of smell and can display a behavioural response which indicates preference, where one exists. Humans regularly take part in odour preference studies, particularly in areas such as perfume development, although we are able to communicate preference in more ‘intelligent’ ways than just pointing at or moving towards the favoured smell.

Adult female mosquito

Adult female mosquito

Obviously, for this project the organisms being studied will be adult mosquitoes, which have a history of being involved in olfactometer studies. In the next blog, I will look at some of the designs that have been used previously, and discuss the results of a design workshop that took place a few weeks ago.

Thanks for reading, and please ask questions or leave a comment below.

 

Olfactometer Design and Build Workshop Series Introduction

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Introduction

Thanks for visiting the blog for my olfactometer design and build project.

Below you can see the introductory video for the project, which gives a brief overview of what you can expect to see on this site and in the subsequent videos. It is my intention that this blog is readable by everyone with an enquiring mind, so please let me know if I am using too much subject specific jargon or terminology without properly explaining what I mean.

With that in mind, the next blog entry will focus on what a dual-choice olfactometer actually is and how they work.

Please leave comments, suggestions and questions using the interface below.