I've been trying to do olfactometer experiments with Callosobruchus spp. (Coleoptera: Bruchinae) for two months, but the results are unreliable. I have two arms for beans and the other two arms for pure air, but the results are that 50% of the insects go to the beans and 50% go to the pure air. In reality the insects should prefer odour of the beans over the pure air.
I think that the light source might induce bias as I work in a control environment room where is ideal for growing plants, so the light source in the room is fluorescent tubes. My olfactometer is on a shelve, and I illuminate the olfactometer from the tubes beneath the shelve (see attached picture). I have to record videos, so I can't open the light above the olfactometer as it creates reflection on the olfactometer. I think that the light beneath the shelve scatters not evenly in the room, so the insect behaviour is influenced by the light.
What type of lamp should I use in this situation while I also can record the video of the insect?
Hello Ussawit,
i have carried out these types types of experiments in the past, but not on Callosobruchus. There is no doubt that light, especially directional light, can mess up your results. We found that to do this sort of work using Anthrenus verbasci required darkness; any light completely messed it up. I have come to the conclusion that Sitophilus are stupid. When given a choice, similar to the ones your are providing your insects, I think they wander off at random, sample whatever they come across and then decide whether or not to stay. For the first few hours or even a day, they tend to distribute themselves at random across the design. I have two questions. That's a fancy piece of kit you have. I assume that when they have wandered into one chamber they can escape to another chamber. If not, and they are as stupid as Sitophilus, you will end up with a random distribution (so this assumes that they can't detect the bean odour). The second concerns the design. Why do you need to video the insects if you just need to record their choice? Why can't you leave them for a day or two to find out where they end up; this will reflect their choice. If this is what you are after, run the experiment in the dark, in a lab on the bench with the kit covered completely to make it dark, or in a small(?) room with no windows and no rectional light. Good luck.
Graham
Hello Ussawit: Mr Holloway has it right. On the other hand, you might try to null experiment to determine if the beetles' behavior is influenced by the light. Do it without beans. A random distribution is predicted. That's quicker than rearranging the whole apparatus. Best regards, Jim Des Lauriers
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