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.
how do you propose to control the PPM in the olfactometer with regards to the pollens/scent to give a representative cross section of what concentrations occur in nature.
This is not something that I will be controlling specifically in the early stages of this study, but will be a factor of the rate of emission of the scent by the plants being used, and the rate of air flow (volume / time).
Previous studies, which have focused on dose-response have shown that certain chemicals only elicit a response in mosquitoes when a concentration threshold is reached. This is why it is important that the airflow through the olfactometer can be adjusted, facilitating the testing of scents at different concentrations.
Later in the study, when I am using specific chemicals rather than whole flowers as variables, it may be desirable to calculate the optimum ppm (or ppb in some cases) by creating a dose-response curve. An example of this type of method can be seen here: http://chemse.oxfordjournals.org/content/24/6/647.short
Thanks for asking the first question on this blog!
Do you have any ideas as to the scale of the experiment? For instance, how many adult mosquitoes are you hoping will be in the olfactometer at a given time and will they be an equal proportion of male to female etc. Also, do you intend to have more than one of these choice experiments running at a given time?
Small groups of mosquitoes will be used for each test, in the region of 10-15 at a time. However, as mosquitoes appear to be able to learn, and so each group used needs to be new, and naive to the test chamber.
Males and females will be tested separately, as mixing them will add possible confusion to the interpretation of the results. For example, how confident could I be that the males were attracted to the variables being used, and not simply following the females within the chamber.
The overall scale of the experiment needs to be carefully controlled, particularly in terms of the number of scents that are being tested. For the most part I will be carrying these experiments out on my own, and so labour time is the main limiting factor (assuming I can breed sufficient mosquitoes). The number of test runs grows incredibly quickly as new scent variables are added. I will go into this in detail in a later blog post, but as a quick comparison: 4 variables requires 50 runs and 500-750 naive mosquitoes, 6 variables requires 105 runs and 1050-1575 naive mosquitoes. This is based on 5 repetitions, testing against a control and against each other, at 1 concentration. If I choose to compare 2 concentrations then I need to double it! I’ll definitely need to be very selective in my variable choice!
I’ll almost certainly only be running one choice experiment at any one time. Although if I need to I can always make another olfactometer.
Thanks for a great question.
What chemical extracts/plants are you planning on using initially, and what attributes do they possess which, from previous findings attract the mosquitoes to them? Or are you testing extracts/plants which have not yet been explored in this context?
Initially, the experiments will focus on plants that are found at the main ecological survey sites that are being used for other aspects of the PhD. The sites being studied do not have many obvious sugar sources for much of the year, and it will be interesting to see whether the mosquitoes are travelling to uncut grassland for a sugar meal, or opportunistically using whatever ephemeral sources are available to them within the wet woodland sites.
The co-incidence of mosquitoes and flowers, in conjunction with a literature review will help me to develop a short-list of candidate species.
I am particularly interested in the volatile organic chemicals (VOC’s) that are given off by the flowers, as these form the group of chemicals which will typically be available to the mosquito’s olfactory system in nature.