Insects for Olfactory Insight

Insects are such an important part of olfactory science because they smell with their antennae, which are outside their bodies, making it easier to study. Also, their brains are pretty simple, which makes it easier to study how the most complicated and least understood sense works.

Another reason insects are so important to olfactory science isn't really about olfaction, it's about malaria, and Zika, and West Nile, you name it. Mosquitoes are one of the main drivers of infectious disease around the world. And if we could only figure out how they use their sense of smell to find us, we could stop them from finding us and infecting us.

The first article shows you just how important this effort is --

Researchers build mosquito testing arena to discover how they find us over long distances

May 2023, phys.org

https://phys.org/news/2023-05-mosquito-arena-distances.html

"This is the largest system to assess olfactory preference for any mosquito in the world."

Using an ice-rink-sized (1,000 m3) outdoor testing arena in Choma District Zambia, researchers found that human body odor is critical for mosquito host-seeking behavior over long distances. They had six people sleep in single-person tents surrounding the arena over six consecutive nights, and they used repurposed air conditioner ducting to pipe air from each tent—containing the aromas of its sleeping occupant.

The testing arena contained a ring of evenly spaced landing pads that were heated to human skin temperature (35ºC). Each night, the researchers released 200 hungry mosquitoes into the testing arena and monitored their activity using infrared motion cameras.

• mosquitoes were not attracted to heated landing pads unless they were baited with CO2 
• human body odor was a more attractive bait than CO2 alone
• some people were more attractive to mosquitoes than others
• one volunteer with a strikingly different odor composition from the others consistently attracted very few mosquitoes
• people who were more attractive to mosquitoes consistently emitted more carboxylic acids probably produced by skin microbes
• the person who was least attractive to mosquitoes emitted less carboxylic acids but triple the amount of eucalyptol, which may be related to the person's diet
• the team identified 40 chemicals that were emitted by all of the humans, though at different rates.
• "It's probably a ratio-specific blend that they're following" 

via Johns Hopkins Bloomberg School of Public Health, Johns Hopkins Malaria Research Institute, and Macha Research Trust: Conor J. McMeniman, Human scent guides mosquito thermotaxis and host selection under naturalistic conditions, Current Biology (2023). DOI: 10.1016/j.cub.2023.04.050.

https://dx.doi.org/10.1016/j.cub.2023.04.050

Washing with different soaps could make you more or less attractive to mosquitoes

May 2023, phys.org

https://phys.org/news/2023-05-soaps-mosquitoes.html

"It's remarkable that the same individual that is extremely attractive to mosquitoes when they are unwashed can be turned even more attractive to mosquitoes with one soap, and then become repellent or repulsive to mosquitoes with another soap," says senior author and neuroethologist Clément Vinauger.

"What really matters to the mosquito is not the most abundant chemical, but rather the specific associations and combinations of chemicals, not only from the soap, but also from our personal body odors," says Vinauger.

via Virginia Tech: Clement Vinauger, Soap application alters mosquito-host interactions, iScience (2023). DOI: 10.1016/j.isci.2023.106667.

https://dx.doi.org/10.1016/j.isci.2023.106667

Perfume component helps lure male moth pests

Apr 2023, phys.org

https://phys.org/news/2023-04-perfume-component-lure-male-moth.html

Smells are so complicated: "Nonenal is a universal attractant that, by itself, doesn't have much of an effect, but when a certain percentage is added to the multi-chemical attractant mixture discovered nearly 40 years ago, it has a highly stimulatory effect."

(The researchers started examining ways to attract and then trap armyworm moths as part of a "mating disruption" strategy.)

via North Carolina State University: Ahmed M. Saveer et al, Nonanal, a new fall armyworm sex pheromone component, significantly increases the efficacy of pheromone lures, Pest Management Science (2023). DOI: 10.1002/ps.7460

https://dx.doi.org/10.1002/ps.7460

Good smells, bad smells: It's all in the insect brain

Aug 2023, phys.org

https://phys.org/news/2023-08-good-bad-insect-brain.html

I don't think I've ever heard the sense of smell referred to in this way: "While it is more of an aesthetic sense in humans, for insects, including locusts, the olfactory system is used to find food and mates and to sense predators."

It certainly is different, because in insects, their "palp" mouth triggers automatically to eat food just from the presence of some specific odors. I think we would usually see this difference in the context of the pheromone-receptor parts of our olfactory system, which don't actually work anymore in humans. Lots of animals, insects too, and beyond of course, have their behavior very strongly (could you call it irresistibly?) controlled by smells. 

Back to the study:

Interestingly, some of the locusts showed no response to any of the odors presented. They found that locusts only associated appealing scents with a food reward. Delaying the reward, they found that locusts could be trained to delay their behavioral response.

"All information received by our sensory apparatus, and their relevance to us, has to be represented by electrical activity in the brain. It appears that sorting information in between positive and negative happens as soon as the sensory signals enter the brain."

via McKelvey School of Engineering at Washington University in St. Louis: Rishabh Chandak et al, Neural manifolds for odor-driven innate and acquired appetitive preferences, Nature Communications (2023). DOI: 10.1038/s41467-023-40443-2

https://dx.doi.org/10.1038/s41467-023-40443-2

A non-invasive way to turn a cockroach into a cyborg

Sep 2023, phys.org

https://techxplore.com/news/2023-09-non-invasive-cockroach-cyborg.html

First, we made remote control roaches by smashing an electric circuit through their head. But now, it's as simple as slipping over their antennae a sleeve made of gold and plastic, and fixed in place by a blast of ultraviolet light, like plastic shrink-wrap.

Note to self -- insects don't get "injured," they get "damaged" -- "damaging cockroaches during attempts to control them results in a very short life expectancy, which then results in very little payoff for a lot of work".

via Nanyang Technological University in Singapore: Qifeng Lin et al, Resilient conductive membrane synthesized by in-situ polymerisation for wearable non-invasive electronics on moving appendages of cyborg insect, npj Flexible Electronics (2023). DOI: 10.1038/s41528-023-00274-z

https://dx.doi.org/10.1038/s41528-023-00274-z

Post Script: For a cockroach, and for all insects, their antenna is their nose, and so this is how we'll do it for humans too. (Except laser pulses through the retina are a likely candidate as well. Why not both?)

Image credit: AI Art - Old Man Standing next to Giant Hairy Ant Monster - 2023

Path Dependence and Phylogenetic Incongruity

Giuseppe Penone – The Hidden Life Within

As a thing develops, be it an organism or a building, its path follows a similar pattern wherein the available options diminish with time until it reaches a locked-in phase. At this point, path dependence becomes most evident.

Humans are complex and have many parts, many of them developed at different times in the organism’s phylogeny, or evolutionary history.*

This issue of phylogenetic incongruence arises when one feature, such as olfaction, reaches its locked-in phase before another feature, like language.

And so, it is this way with our sense of smell. Olfaction is the earliest sense to develop. Vertebrates are the first creatures to have an olfactory system. But this is confusing because we can say that plants smell too. Olfaction at its base is chemoreception, requiring only a chemical and a receptor for recognizing that chemical. To think of it, some early, old, simple organism could sense light levels and acoustic/mechanical vibrations, but we would not say they could see or hear. Vision in humans is much more than mere photoreception (isn’t it?). But olfaction is not so much.

All this is to say that the ‘network architecture’ of our olfactory system is so old, so far back to the beginning, that although humans have evolved other parts of themselves as to deprioritize its use, its structure persists. This necessitates the kludge, the chimerical retrofit that is our olfactory-language system. To talk about smells, to generate an empirical, consensual recognition of olfactory experience – which requires language – is like trying to eat an electron. Sure you can say that’s what you’re doing, but is it really?

*The sequence of these developments are reflected in the ontological development, that is the development of an individual from gestation through maturity, and are so vividly illustrated in this chart by the master Ernst Haeckel.

Post-Script:

Electron Buffet – bacteria that eat pure energy

Here is a good example of how the sequence of system-design impacts development:

Before nature selects, gene networks steer a course for evolution

Post Post-Script:

Bose-Einstein condensates, the Matthew effect, and other laws metaphysical

Non Traditional Computing, Complex Problems, and Approximation

Illustration for Death of a Salesman by Brian Stauffer for the Soulpepper Theater Company, Toronto

It may seem like a stretch to write about combinatorial optimization problems (aka the traveling salesman problem) on a blog about the ‘language of smell,’ but Limbic Signal isn’t just about smells, or language, but the connections between olfaction and computation. Our olfactory system is a champion at dealing with very large, very complex datasets.

Olfaction uses our brain in ways the other senses don’t. Some of the ways olfaction diverges from the other senses are akin to novel solutions to very complex problems in computation, such as big-data-sifting, pattern recognition, or the aforementioned traveling salesman problem.

 Also note that, in addition to the magnet network described below, another unconventional solution to the traveling salesman problem is to use mold. In fact, slime mold was used to design Spain's motorways and the Tokyo rail system.

So this article below does a good job of explaining the traveling salesman problem; I straight copied it from the writers at phys.org. And in the second section is an explanation of an interesting solution to the problem.

Researchers create a new type of computer that can solve problems that are a challenge for traditional computers

Oct 2016, phys.org

The traveling salesman problem

There is a special type of problem - called a combinatorial optimization problem - that traditional computers find difficult to solve, even approximately. An example is what's known as the "traveling salesman" problem, wherein a salesman has to visit a specific set of cities, each only once, and return to the first city, and the salesman wants to take the most efficient route possible. This problem may seem simple but the number of possible routes increases extremely rapidly as cities are added, and this underlies why the problem is difficult to solve.

...

It may be tempting to simply give up on the traveling salesman, but solving such hard optimization problems could have enormous impact in a wide range of areas. Examples include finding the optimal path for delivery trucks, minimizing interference in wireless networks, and determining how proteins fold. Even small improvements in some of these areas could result in massive monetary savings, which is why some scientists have spent their careers creating algorithms that produce very good approximate solutions to this type of problem.

An Ising machine

The Stanford team has built what's called an Ising machine, named for a mathematical model of magnetism. The machine acts like a reprogrammable network of artificial magnets where each magnet only points up or down and, like a real magnetic system, it is expected to tend toward operating at low energy.

The theory is that, if the connections among a network of magnets can be programmed to represent the problem at hand, once they settle on the optimal, low-energy directions they should face, the solution can be derived from their final state. In the case of the traveling salesman, each artificial magnet in the Ising machine represents the position of a city in a particular path.