Tag Archives: insect olfaction

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.

 

 

 

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.

Reader contributed content. Animation of gate mechanisms

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The animations seen in this video were contributed by regular blog reader David, and I would like to thank you for your input. They show quite nicely how each release/trap gate rotates on its axis to open or close the chamber. They also indicate the fact that these chambers will be removable to allow easier handling of the mosquitoes at the start and end of each experimental iteration.

David I hope you don’t mind my adding the title and captions.

 

David was instrumental in helping develop the model in Autodesk Inventor 2015.

He has also convinced me to test the design using computational fluid dynamics, which is yielding interesting results and may result in some design changes to the main body of the olfactometer.

Thanks again David!

First drawings of the experimental chamber for my olfactometer

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I am delighted to be able to share some of the imagery showing the design of the olfactometer as it currently stands. Hopefully these pictures are worth a thousand words, as today’s blog post is intended to be quite short…

The material being used for the panels and tubing which make the parts illustrated is transparent, colourless, acrylic. The pin which for the hinge and handle for the rotating doors in the mosquito trap/release chambers is stainless steel, as is the mesh which covers the ends and surface of the gate.

3 dimensional drawing of the proposed olfactometer experimental chamber.

3 dimensional drawing of the proposed olfactometer experimental chamber.

With reference to the 3 dimensional diagram above, the air will be blown into the ports at the rear of the unit, where they will pass through the 2 variable chambers. Here the air will flow over the variable/s being tested (or the control), where it will become ‘loaded’ with chemicals which may or may not cause a behavioural change in the mosquitoes. The air will then flow through the main flight chamber before exiting through the mosquito release chamber at the front of the unit.

Plan view of the experimental chamber. 3 dimensional drawings of the proposed olfactometer mosquito release/traps chambers.

Plan view of the experimental chamber. 3 dimensional drawings of the proposed olfactometer mosquito release/traps chambers.

There are a few design points which are currently still under discussion; such as the design of the rotating gates in the mosquito trap/release chambers. Currently they are designed as an acrylic ring which has a stainless steel mesh across it, there is some suggestion that it may be easier to simply use an acrylic disk and drill this through with many small holes. This is the potential drawback that the drilled holes will not provide a visual barrier to the stimulus being offered, where the stainless steel mesh is opaque and will therefore help control against the mosquitoes being able to see rather that smell the stimuli.

Side view of the experimental chamber, showing plane for sectional diagram to the right.

Side view of the experimental chamber, showing plane for sectional diagram to the right.

The airflow inlets shown in sectional view in the 3rd drawing are slightly misrepresented in the drawing. The internal portion, that which is inside the chamber, is actually shorter than shown. This will be adjusted in the next round of design reviews.

As always comments and questions are greatly appreciated!

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.