It has long been known that insects smell odors through the use of their antennae. It is also well established that detection occurs via tiny sensillae on these antennae. Beyond this, our understanding of insect olfaction is limited and research results are conflicting. The current paradigm is that odorants pass through tiny holes in the insect sensillae and diffuse through the sensillar lymph to eventually bind with a protein receptor on the dendrite. The current paradigm touts diffusion as the proposed mechanism. Although seemingly plausible, scientific investigation reveals that this is not possible. Diffusion alone is not fast enough since insect electrophysiologists report that odorant detection can occur in less than one millisecond. Further to this, no receptor-ligand binding has ever been shown and so the putative protein receptor remains elusive.
An alternative theory is that the insect sensillae act as dielectric waveguides picking up the energy or vibrational energies of the odorants. This theory bypasses the problem with diffusion, but does not have a clear mechanism. Energy coupling via the antennae is easy enough to understand using antenna theory, but the message is somehow eventually detected by the dendrites thus initiating a standard nervous impulse. This can be partially understood utilizing our current knowledge of protein semiconductors and rhodopsin.
Bacteriorhodopsin has been well-studied as a phototransducing protein with an extremely fast response time. The protein responds to electromagnetic energy in 1.61 picoseconds and possesses a recovery time of 10 milliseconds. In fact, 98% of the bacteriorhodopsin molecules reset within 20 milliseconds. In relation to insect olfaction, this recovery period is well within the recovery times reported in the scientific literature (several hundred milliseconds). Therefore, based on the temporal evidence, it is plausible that a similar mechanism might be at work in regards to insects.
The proteins most likely involved in insect olfaction include odorant receptor proteins and sensory neuron membrane proteins. The odorant receptor proteins are seven transmembrane proteins, similar to bacteriorhodopsin. However, sensory neuron membrane proteins are reported to be in higher concentrations than odorant receptors on the dendrite. Either of these proteins, or alternatively both proteins acting in concert, can be implicated as in vivo protein semiconductors. This new theory would help to explain how insects can detect odorants on the established temporal scale.
Tom Dykstra is Secretary of the SSE and is President of Dykstra Laboratories, Inc which is a laboratory devoted to electromagnetics and life. Tom’s background is in entomology with an emphasis on neurobiology. He is married to Karen, a Chicago native, and they have 3 children.
Recorded at the 27th annual SSE Conference in 2008 in Boulder, Colorado, USA.
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Published on November 13, 2018
