Tag Archives: disease vectors

Building the olfactometer!

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After a long digital design and modelling process I was delighted to finally have all the component parts in hand and ready to assemble. In the interest of working uninterrupted, I chose to carry out the construction at home rather than in the lab. Hence the dining table, and occasional clutter you’ll see in these images.

Due to the late design changes after the computational fluid dynamic modelling of the previous iteration I had enough acrylic sheet to build 2 main flight chambers rather than  one. Since the build this has proven fortuitous as it means I can carry out twice as many behavioural assays at the same time. This is particularly important as my study mosquitoes require overnight assays which makes time a real limiting factor.

If you could buy a flat-pack dual choice olfactometer this is what it might look like

If you could buy a flat-pack dual choice olfactometer this is what it might look like. (N.B. the syringe is for applying the acrylic cement)

Acrylic is quite nice to work with as the “glue” is very watery and so provide you can get a tight bond between surfaces you can apply the glue in one place and allow capillary action to draw it in and fill the void.

Insulating tape was used to hold the pieces in place whilst the glue was applied and set. Because

Insulating tape is slightly elastic it is great for this as it can be pulled very tight and allowed to relax again; once relaxed the acrylic sheet is held securely but not deformed.

Insulating tape is slightly elastic it is great for this as it can be pulled very tight and allowed to relax again; once relaxed the acrylic sheet is held securely but not deformed.

Also, because the edges were very nearly square, after the laser cutting, forming the box was easier than I feared it might be.

Once the insulating tape was removed I was left with something remarkably similar to the design!

Once the insulating tape was removed I was left with something remarkably similar to the design!

The gallery below shows the stages of construction before moving the units back to the laboratory.

In the next blog post I’ll look back over the installation and first test assays using this dual choice olfactometer.

Flight chamber design is now finalised.

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Following a number of different design versions I am pleased to have settled on a final version that is going forward to prototyping.

The biggest, most obvious, change is the size of the flight chamber. This is significantly reduced in cross sectional area in response to the computational fluid dynamic work that has been carried-out. The reduced area leads to a reduction of required air volume needed to generate the flow rate and means that I can use the same unit for both static air testing and dynamic wind tunnel like tests.

In the static air tests the mosquitoes are loaded as normal, as are the variables ( or variable and control). However, no air supply will be attached. Testing with no air flow will allow me to test whether the odours from the variables is enough to cause the mosquitoes to investigate them without other ‘activators’. These tests will typically run overnight, and require a slight, removable, modification to the mosquito traps to prevent exit once a ‘decision’ has been made.

The dynamic, or wind tunnel, tests are typically much quicker, and can occur in a few seconds to minutes. There are different assumptions made of these types of tests than in the static air test, as a method it is equally applicable to my study. It is my plan to use both methods in conjunction to develop as complete a representation of behaviour as possible.

A round-up of early meetings

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To my mind, the difference between lecturing an audience about a project and true outreach is accepting feedback from the audience, and allowing that feedback to improve the final outcome. Having a conversation about the choices that are made in the project, and being able to objectively defend and explain them, can only make for stronger science leading to increased confidence in results.

One of the very first people that I reached out to is an oil and gas engineer, whose day to day work focusses on piping, filtration and transit of fluids. He is, therefore, something of an expert in many of the mechanical aspects of olfactometer, although he tends to work on a somewhat larger scale! Once we had arrived at a common language, him not blinding me with fluid dynamics and me not retaliating in Latin binomials, we were able to have a productive series of meetings which went a long way in shaping my initial thoughts on how this machine should operate.

These meetings were particularly useful when digesting some of the more technical papers on dual-choice olfactometer design.

special interest lecture screen grab

In March 2014 I introduced the project to, as then, first year undergraduate biological sciences students. This introduction was simply a 5 minute slot within a lecture that I was giving. I was very pleased that some students expressed an interest in taking part in the project workshops. Unfortunately, due to the time in the semester in terms of the student’s examinations and deadlines it was the wrong time to schedule these workshops. These workshops will now take place early in the autumn semester, reviewing the design and build process, and working on the testing and experimental design.

PG meeting screen grab

 

A landmark meeting took place at the start of May 2014, where I was able to get a group of my fellow PhD students to discuss the project direction. Following an initial introduction and outline of my early design there was well over an hour of discussion, diagramming and gesticulation. All helping to further refine and define the design. Perhaps more importantly, the meeting started a long running conversation, I can bring up this project with any or all of these postgrads and they know exactly what I am talking about and can get straight into the meat of the issue at hand.

 

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.