As mentioned in an earlier post, the beetle ecology/physiology project has split into two separate sets of experiments. For the ecology project, I am hoping to get some good data regarding beetle abundance, seasonality and predation, but that will be the subject of other posts.

To get a more mechanistic understanding of heat stress in the beetles, I plan to do two sets of experiments once the beetles are available later in the summer. One will be a relatively straightforward measure of the range of temperature tolerance for the stink beetles (Amphidorini) and their non-stinky mimics (Asidini).

The other experiment will measure activity in the nervous systems of the beetles when they are under heat stress. There is considerable evidence that there is a blast of neural activity, sometimes referred to as a “spreading depolarization” when insects enter a state of paralysis known as heat coma. I would like the measure the temperature that is required for the spreading depolarization in the Amphidorini, which are relatively heat sensitive, and the Asidini, which are more resistant. The hypothesis is that it will take a higher temperature to induce spreading depolarization in the Asidini.

To get those data, I will need an amplifier to record neural activity in the beetles. Although I could spend a few thousand dollars on a new, ready made amplifier, there are some nice DIY designs in the literature. The circuit I chose (from Land et al., 2001, J. Neurosci Meth. 106:47) should do everything I need. It can amplify signals between 100X and 1000X, it has filters to stabilize the signal and reduce noise, and is relatively inexpensive to build.

The circuit diagram from the original paper is shown above. It uses two op-amps for amplification and filtering, and was designed to be powered by two 9V batteries. I will use the same circuit, but plan to use a 9V DC power supply for simplicity.

Most of the components arrived from Mouser Electronics today, and I can get started once a few more things (like the circuit boards) arrive. I plan to build one single channel amplifier to work out the process (little box on top), then assemble a four channel unit to record multiple beetles at once (bottom box).

The middle box will house the analog-to-digital converter (ADC), which will allow me to record the data on a computer.

I will post more details about the setup and procedures as things progress.

Special thanks to Dr. Hans Ruppel, whose support is making this project possible.