Hello, everyone! Jess here. Lots of exciting things have happened in the last two weeks. First, I have begun to raise a group of silkworms into moths (#mothmom). This involves feeding them Mulberry leaves from my backyard each day, keeping everything extremely clean and crossing my fingers in hopes that I know what I’m doing. If first grade classrooms can keep them alive, so can I, right? In addition to raising silkworms myself, I have been getting shipments of cocoons to ensure I have plenty of moths to work with this summer.
As I mentioned in my last post, I have been working with cockroaches to refine methods until the moths are ready. Rather than looking at pheromones, I have been investigating olfaction with natural attractants and repellents. Unlike silkmoths, cockroaches have multiple pheromones and they cannot be easily ordered. So, I chose something we all know cockroaches love and are able to locate through olfaction: food. Additionally, it is well known that getting rid of cockroaches without the help of a exterminator can be extremely difficult, so why not investigate a variety of repellents I found on a garden blog and see what happens?
The first (and most important) step was to design an experiment to observe the natural cockroach response to these odorants. After going through multiple iterations of a behavioral chamber that involved a lot of laser cutting (and a lot of recutting because measuring a box without parallel sides is hard), I’ve found a design that works well. It’s extremely simple: a large tupperware with a clear top, dixie cups, tape, filter paper and the odorants of your choice.
Initially, I had the idea of setting up a classic choice paradigm. Cockroaches would enter the arena and choose whichever chamber contained the odorant of their preference. I quickly ran into issues because they hate being out in the light, and had no interest in my contrived scent experiment. So, I used their hate for the light to my advantage. I placed shelters (dixie cups) around the arena with different odor filter papers taped inside. This way, they were making a choice of which shelter they preferred. So far this design has been working well, and I will continue to optimize it and run trails throughout the summer.
The second portion of my cockroach experiment has been focused on electrophysiology. I wanted to design a simple, DIY method for recording from cockroach antennas, also known as an electroantennogram (EAG). The type of electrical activity I am looking for is a low frequency summed potential sent from the end of the antenna towards the base. This electrical potential is then transmitted to higher order areas of the cockroach brain where the scent is perceived and a response is initiated.
To do this, I’ve made pad electrodes with sewing pins and solder to lay the antenna across. I then cut off the antenna, put it on the electrodes and apply plenty of electrode gel to prevent it from drying out. Using syringes and aquarium tubing, I blow odorants tested in the behavioral experiment on the antenna and examine the electrical response.
Here is a snippet of my data below compared with results previously seen in literature:
The signal is similar to what has been published in literature, suggesting this DIY method works (yay!). Further, there are differential signals when ethanol is introduced and when the control is introduced. This suggests the cockroach is capable of sensing ethanol, and the response is not due to the puff of air itself. How this sensation may affect behavior will then be determined in the preference experiment I described earlier.
Now that I have some moths to work with, the cockroach portion of my project will be put on the backburner for a little bit. The silk moths only live for 5-10 days, so I’ve got to work with them while I can. Looking forward to sharing my moth data with you all next post!
For any questions or comments- feel free to contact me at firstname.lastname@example.org. In the mean time, here’s a timelapse video I took of my silkworms spinning a cocoon: