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السلام وعلیکم!
محترم والدین اور عزیز طلباء آپ کو مطلع کیا جاتا ہے کہ ہارورڈ کوچنگ اکیڈمی زاہد آباد میں نئی ٹیوشن اور کوچنگ کلاسیز کا آغاز ہوگیا ہے۔جس میں انتہائی قابل اور مخنتی استاتذہ آپ کے بچو کو انتہائی مناسب فیس پر پڑھائیں گے۔۔ یتیم اور نادر طلباء کیلئے ٹیوشن مکمل فری۔۔۔
کلاسیز کا باقاعدہ آغاز 14 جون 2023 سے ہوگا۔
کلاس کا دورانیہ =صبح 8 بجے سے 11 بجے تک

السلام علیکم !
عزیز طلباء اور محترم والدین آپ کو مطلع کیا جاتا ہے کہ آپ کے گاوں ذاھدآباد میں ہارڈورڈ کوچنگ اکیڈمی کھولی گئی ہے،جس میں اعلی تعلیم یافتہ اساتذہ کرام موجود ہیں ۔اس میں کلاس فرسٹ سے کلاس 8th,9th,10th,1st year اور 2nd year تک تمام مضامین کی ٹیوشن ہوتی ہے اور کوچنگ کلاسز باقاعدہ طور پر لی جاتی ہے۔روزانہ کی بنیاد پر ٹسٹ اور پریزینٹیشن پر فوکس کیا جاتا ہے،جس سے طلباء میں پوشیدہ صلاحیتیں اجاگر ہوتی ہیں۔لہذا آپ جلد از جلد داخلہ لینے کے لئے تشریف لائیں ۔ اوقات کار :شام 4:00 سے 7:00 تک.
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Parasitoid wasps lay their eggs in or on the bodies of other animals. Their larvae hatch out and devour their hosts. Parasitoidism evolved during the Permian era almost 250 million years ago- all parasitoid wasps are descended from the same common ancestor. But a bunch of wasps descended from this ancestor lost parasitoidism and returned to eating plants during development. And maybe some wasps, which evolved from plant-eating wasps which evolved from parasitoid wasps, regained parasitoidism. Evolution often doesn’t go constantly in one simple direction- since evolution involves a lot of randomness and is incapable of planning for the future, it may often wander back and forth.

Last year an interesting article was published about how fruit flies co-evolve with the wasps that parasitise them: https://www.sciencedirect.com/science/article/pii/S2214574522000311
Both hosts and parasitoids have evolved many adaptations as part of their struggle for survival against each other. The parasitoid must kill its host in order to survive, so the host must kill the parasitoid for its own survival as well; this creates a powerful force of natural selection. Scientists have been investigating how this works at the levels of genes, mRNA and proteins. Flies and maggots are alert to the slightest sensation that a parasitoid might be nearby, and they react with terror, going to great lengths to try to avoid or escape from the parasitoid. If they fail to escape from the parasitoid before it injects its eggs into its victim, the host’s immune system will attempt to contain or destroy the parasitoid egg. Of course the wasps have their own ways to suppress or evade the defences of the maggot.

Some wasps in the Ichneumonidae superfamily of parasitoid wasps have a symbiotic relationship with polydnaviruses, which suppress the immune system of the host, thus preventing the immune system from protecting the host from the wasp larva. Multiple times during evolution, polydnaviruses inserted themselves into the DNA of parasitoid wasps, and the wasps domesticated the viruses and used the viruses against their hosts.

A different superfamily of wasps is Cynipoidea, which includes parasitoid wasps but also plant-eating gall wasps, both wasps which make their own galls and wasps which live in galls that other wasps made. Since different Cynipoid wasps eat such different things and live in such different ways, they are an interesting thing for biologists. Evolutionary biologists have proposed several different hypotheses to exploit how Cynipoids might have first evolved. One hypothesis was that the first Cynipoids laid their eggs inside wood-boring insect larvae. Another hypothesis was that early Cynipoids lived in galls produced by other wasps, and that the parasitoidism of some Cynipoids evolved later. When biologists built a family tree of the Cynipoids, that suggested that the common ancestor of all Cynipoids were parasitoid wasps. But regardless, wasps in this superfamily have repeatedly evolved changes in whom they steal their nourishment from during their development.

In Cynipoidea, there is the Figitidae family, which is not well understood. Over 1,400 species in over 130 genera have been described in this family. The largest subfamily in Figitidae is Eucoilinae, which used to be considered a separate family. Eucolines lay their eggs in maggots.

Eucoilinae live all around the world and include over 1,000 known species, but probably there are many more Eucoiline species out there which no one knows about. It can be hard to figure out which wasps belong in Figitidae, but it’s obvious that eucoilines are all closely related to each other, because they have all inherited a common feature: Eucoilines have a plate on the top back part of their thorax, with a glandular pit in it. Female Eucoilines have 13 segments in their antennae, and male Eucoilines have 15 segments in their antennae. Female Figitids have a clip at the end of their egg-laying organ. Eucolines can be 1 to 5 millimetres long. Their bodies are shiny and dark.

In Eucoilinae, there is a parasitoid genus called Leptopilina. Leptopilina uses virus-like particles to suppress the host’s immune system and prevent the host from maturing. Unlike the symbiotic viruses used by Ichneumonids, the virus-like particles of Leptopilina don’t seem to actually be produced by virus DNA: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758193/

One Leptopilina species is Leptopilina heterotoma. L. heterotoma can parasitise a bunch of different hosts, mostly various species of fruit flies.

There are over a thousand species of fruit flies. Fruit fly species can eat a lot of different things, although usually rotting things. Of course some fruit flies eat fruits- others eat flowers, tree sap, cacti or mushrooms. Fruit flies often eat the bacteria in rotting things, in addition to eating the rotting thing itself. Some fruit fly species have evolved a generalist strategy, in which they can eat and lay their eggs on many different things. Other fruit fly species have evolved to be specialists which are highly adapted to eating only one specific thing. Drosophila phalerata eats only rotting stinkhorn mushrooms. D. sechellia eats only rotting morinda fruit, which are poisonous for other fruit fly species. L. heterotoma mostly attacks maggots in rotting fruits and in tree sap, but it can also attack maggots in fungi and in other rotting plant matter.

Although L. heterotoma can parasitise many different species, it does much better with some species than others. D. immigrans is the species most likely to be able to defend itself from L. heterotoma. If L. heterotoma lays its egg in a D. immigrans maggot, the wasp offspring will die in at least 49 out of 50 attempts. We have a lot of D. immigrans flies in Europe, but they are rarely parasitised. But maybe D. immigrans can defend itself so well, not through its immune system, but because it has really thick skin, which the wasp cannot pe*****te, so the wasp fails to actually get its egg through the tough skin of the maggot. When wasps lay their eggs on D. ananassae, D. biarmipes, D. paralutea and D. busckii, all of their eggs might die.

Drosophila suzukii, the spotted wing fruit fly from Asia, is another species where the vast majority of wasp eggs laid in the maggot die. Humans consider D. suzukii to be a pest, because it eats delicious fruits such as cherries, raspberries and blueberries, and ornamental plants, although it also eats wild plants. D. suzukii is different from and more annoying than other fruit flies because it lays its eggs, not on rotting fruit which we don’t want anyway, but on the freshest, juiciest fruit which is most appealing to humans. We can’t safely kill D. suzukii using pesticides, because that would contaminate the fruit we want to eat, so we want to harness the deadly power of nature and exploit other animals to kill it.

Unfortunately for us, we cannot use L. heterotoma to kill D. suzukii for us, because D. suzukii can defend itself against L. heterotoma. Fortunately there are hundreds of thousands of different parasitoid wasp species. We could instead send other parasitoid wasps, such as Trichopria drosophilae or Pachycrepoideus vindemmiae, to kill this maggot. Wasps, such as Isobar japonica and Ganaspis brasiliensis, which co-evolved with D. suzukii in its native land, might be especially effective at parasitising this maggot.

Drosophila kuntzei is a great host for L. heterotoma. If L. heterotoma can lay its egg in a D. kuntzei maggot, in almost 9 out of every 10 attempts, the baby wasp will survive to adulthood. D. suboscura, D. hydei and D. pseudoobscura are other fly species which tend to be good hosts for L. heterotoma.

Drosophila melanogaster, the most widely studied fruit fly species, is a good host for L. heterotoma, and L. heterotoma is happy to lay its eggs in this species. The exact success of L. heterotoma at parasitising a particular species varies based on the individual biology of both the wasp and its victim. In some studies, almost 3 out of 4 of wasp eggs laid on D. melanogaster die, but in other studies, nearly 19 out of 20 wasp eggs laid on D. melanogaster survive to adulthood. It makes a different whether the maggot and wasp were collected from the same area at the same time. Populations of wasps and flies which live together co-evolve, so even within the same species, a population will have special adaptations aimed at the specific population of the other species which lives in the exact same environment with it in nature, while a distant population will lack those adaptations.

Parasitoidism creates strong natural selection on maggots, because maggots which cannot resist wasps will die and will not pass on their genes. When many parasitoid wasps have been living in an area for generations, the natural selection caused by the wasps increases the rate of parasitism resistance in the maggot population. L. heterotoma is very virulent, but some fly species have managed to resist it by evolving new genes, such as lectin-24A which is involved in the immune response to parasitism. Genes like this only tend to evolve when parasitoids are creating strong natural selection because they come at a cost to the maggots: maggots which build stronger defences against parasitoids also weaken themselves in ways which would make them more likely to die from other causes or less likely to successfully compete against other maggots if there were no parasitoids.

Some parasitoid wasps paralyse their hosts so that the hosts can do nothing to try to protect themselves from the wasp larvae devouring them. Other parasitoid wasps let their hosts continue moving, but freeze the development of the host- the host can no longer grow, and no matter how much it eats, all of the nutrition that it takes in goes to feed the wasp larva that will eventually kill it. But L. heterotoma allows its host to not only keep on eating, but even keep growing, as the wasp larva which will eventually kill the host develops inside it. Ten days after the wasp egg was laid in the host, the young wasp will burst out of the host’s body.

After L. heterotoma injects its eggs into maggots, the eggs float around in the maggot’s blood:https://deepblue.lib.umich.edu/bitstream/handle/2027.42/28608/0000417.pdf
In Drosophila melanogaster, part of the maggot’s immune system are the lamellocytes. Lamellocytes are the maggot’s cells which gather together to build capsules around dangerous things inside the maggot’s body, to protect the rest of the maggot’s body from being harmed by these invaders. When the lamellocytes surround something dangerous, the lamellocytes use phenoloxidases to produce melanin. By surrounding the parasitoid egg and producing melanin, the lamellocytes prevent the egg from hatching, killing the egg and saving the life of the maggot. When a wasp injects an egg into a maggot, the maggot responds by producing more lamellocytes to try to save itself. Other fruit fly lineages have independently evolved their own blood cell types which defend the host in a similar way to lamellocytes.

But usually if a wasp manages to get her egg into the body of the maggot, the maggot’s lamellocytes and immune system are not able to kill the egg- the wasp embryo defeats or evades the immune system and develops successfully. When L. heterotoma injects her egg into the body of a maggot, she also injects venom which destroys the lymph gland where lamellocytes are produced:https://deepblue.lib.umich.edu/bitstream/handle/2027.42/30167/0000551.pdf

The venom is made up of a bunch of chemicals, including kinases, esterases and hydrolyses. An important part of the venom is aspartylglucosaminidase. Other parasitoids use aspartylglucosaminidase to paralyse their hosts. In order for the blood cells of the maggot to surround and imprison the wasp egg, they must attach carbohydrates to proteins. Aspartylglucosaminidase reverses this, so maybe it can prevent the blood cells from imprisoning the egg. Another chemical in the venom is lymph gland apoptosis related protein or Lar. Lar destroys the lymph gland of the maggot.

Like the venom of many parasitoid species, the venom of L. heterotoma includes virus-like particles, which she produces in her venom gland and then matures in a special reserve in her reproductive system. Virus-like particles suppress the immune system of the host by preventing the lamellocytes from sticking to the egg, by destroying the lymph glands which produce lamellocytes, by killing blood cells which could produce lamellocytes, and by directly invading the lamellocytes and making them explode.

Virus-like particles are made of proteins but, unlike real viruses, do not contain any RNA or DNA. A protein called p40 is abundant on the surface and spikes of the virus-like particles. The genes which code for the proteins in the virus-like particles are in the wasp’s DNA. Maybe these genes came from a virus which infected the ancestors of the wasps once in the distant past. Or maybe these genes evolved, brand new, in the wasp, have no shared ancestry with any virus, and are only similar to viruses because of convergent evolution- they need to do the same thing that viruses do, so maybe natural selection has shaped them to be like viruses, the way that similarities have evolved between birds and bats or between dolphins and seals, despite them not being closely related.

Some fly species, such as Drosophila suzukii and D. algonquin, have stronger immune responses than most species. Probably the ability of the maggot to survive depends on how many defensive blood cells similar to lamellocytes it has. Species with more defensive blood cells are more likely to survive.

Drosophila suzukii is one of the species that is most successful at killing L. heterotoma. Probably this is because D. suzukii has a lot of blood cells. When L. heterotoma lays an egg in D. suzukii, the egg usually develops fine at first, but two or three days later, when the wasp larva hatches out of the egg, the maggot’s blood cells surround and kill the wasp larva.

Maggots which can defeat wasps, such as Drosophila euronotus and D. algonquin, also have other immune responses to defend themselves: they produce antimicrobial proteins and peptides which might prevent the egg or wasp larva from developing. One example is nitric oxide. Nitric oxide is a gas and a free radical which is used as a signaling chemical by animals. Along with carbon monoxide, it is one of the few gases which acts as a neurotransmitter. Maggots change the amount of nitric oxide they release when they are attacked by a wasp.

Immune responses vary a lot from one individual to the next. The strength of the immune response partially depends on the characteristics of the individual, like their age, and partially on aspects of their environment, like the temperature or the amount of alcohol they are bathing in. Maggots crawl around in rotting fruit, and alcohol is a byproduct of rot, so maggots are constantly swimming in alcohol, among other things, but the amount of alcohol can be very different from one rotting fruit to the next.

Not all innate biological characteristics of an individual come from their own genes either, because in early development there is no clear dividing line between the mother’s biology and the offspring’s biology. Maternal effect genes encode mRNAs from the mother which are already present in the egg before fertilisation, and which control early embryonic development, especially before the embryo’s own genes are activated. Over eighty maternal effect genes in mammals are known. We don’t usually think much about maternal effect genes, but they can be important because variants in maternal effect genes are linked to miscarriages (or “spontaneous abortions”, as doctors and scientists call them), stillbirths and birth defects: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8756509/
So maternal effect genes are one way that biological factors from the mother may be part of the offspring, even if the offspring didn’t inherit the DNA of a maternal effect gene which is part of its biology (the mRNA from the maternal effect gene will never become part of the embryo’s DNA- see the central dogma of molecular biology for more information). Epigenetic changes that occur in early development might also affect the offspring for a long time to come. For example, people whose mothers were starving during their pregnancy are more likely to suffer from heart disease, schizophrenia and diabetes, comparing to siblings from pregnancies which did not occur during starvation, because how well-fed or hungry the mother is permanently alters the DNA methylation state of the embryo: https://www.cdc.gov/genomics/disease/epigenetics.htm
When maggots react to parasitoids, they are also influenced by maternal effects like these. If a fruit fly lays her eggs near L. heterotoma, her babies will produce more lamellocytes, even if the L. heterotoma leave and the maggot never encounters them again after hatching- somehow the mother’s experience shortly before egg-laying alters the biology of her offspring.

Spiroplasma are bacteria which build colonies that look like fried eggs, have little DNA, have a simple metabolism and tend to be parasites. Spiroplasma live inside fruit flies, and these bacteria protect maggots from parasitoids. Spiroplasma produce ribosome-inactivating proteins, which block the ribosomes that the parasitoids use to make proteins. But Spiroplasma can only protect the maggots when the temperature is right. At 18 degrees Celsius (65 degrees Fahrenheit), Spiroplasma cannot help the maggots.

Wolbachia are bacteria which live inside the cells of invertebrates, often as parasites- it is one of the most common parasites in the world, since it infects arthropods, and arthropods are by far the most common animals- almost 85% of known animal species are arthropods. Up to 70% of insect species may be infected by Wolbachia: https://www.karger.com/Article/Abstract/104228
Wolbachia also protects maggots against parasitoids a bit, although not very effectively.

If L. heterotoma lays multiple eggs in the same maggot, only one of these eggs will be able to survive to grow into a wasp. So L. heterotoma is a solitary parasitoid. Every L. heterotoma mother is capable of laying hundreds of eggs, so she can parasitise many maggots.

Both the wasps and the flies can have multiple generations per year. In summer, warm temperatures cause insects to develop faster, and the fly population explodes, which allows the wasp population to boom as well. Whenever the populations of vulnerable fly species fall, the wasp population also crashes. If the area has a lot of other parasitoid wasps of a different species, which there could well be, since there are hundreds of thousands of different parasitoid wasp species, the L. heterotoma population may die out because the vulnerable hosts are all being parasitised by other wasp species. In order to avoid this sort of dangerous competition, L. heterotoma tries to stay away from locations where other parasitoid wasp species are active:https://www.jstor.org/stable/pdf/4601069.pdf

To find victims, parasitoid wasps must hunt down maggots. If the wasp lays her egg in a maggot which is already parasitised, her egg will probably die, since another wasp larva is already feeding off the maggot. When multiple wasp larvae are inside the same maggot, only one wasp will be able to survive- the others will die, and the younger, smaller, weaker larva is more likely to be the one that dies, rather than the older, bigger, stronger larva which got a head start. Maggots which already have a wasp larva inside them are unhealthy, or may be paralysed depending on the wasp species, so they are the most obvious potential victims- unable to escape or flee from other wasps.

Often parasitoid wasps can recognise if a maggot already has the larva of another wasp of the same species inside it, and then she will probably refuse to inject her egg into the maggot. But if the maggot already has the larva of a different wasp species inside it, often the wasp will fail to recognise that and will inject her egg into the maggot. Also, although laying an egg in an already parasitised maggot usually dooms the egg to die, not laying an egg at all will also result in the wasp’s genes not being passed on, so sometimes a wasp intentionally chooses to take the risk and lay an egg in a maggot that she knows is already parasitised; when she does that, she is putting her baby in a very dangerous situation, but maybe babies are cheap enough that the mother will still come out ahead.

L. heterotoma are drawn to the rotting things that maggots eat. They fly to the smell of yeast and of the byproducts of rot, such as alcohol. They also hunt down maggots by tracking the smell of the pheromones that flies use to attract other flies. In some fly species, flies like to lay their eggs in the same place, to build a little community of maggots, like a maggot kindergarten, so when they lay eggs, they also spread an aggregation pheromone which attracts other flies to lay their eggs there as well. But this same pheromone also attracts parasitoids.

Once a wasp finds some food which is good for maggots, she walks on the food, searching for maggots by scanning the air with her antennae (the insect equivalent of sniffing the air) and probing the rotting thing with her egg-laying organ. If her egg-laying organ pierces a maggot, she has found a potential victim. If scientists cut off the wasp’s antennae, she can still find victims, so the use of the antennae is not completely necessary.

After the wasp has pierced a maggot with her egg-laying organ, she makes the decision to either go ahead and lay her egg or to pull her egg-laying organ back out (especially if she senses that the maggot already has another wasp’s larva inside it) and continue searching. The process of injecting her egg into the maggot may last for up to thirty seconds. If the maggot is at all healthy, it will not lie there passively and wait as the wasp injects her egg. The maggot twists and turns and tries to escape. L. heterotoma has a clip on her egg-laying organ which pins the maggot in places and prevents it from escaping while the wasp injects her venom and her egg. To celebrate successfully laying an egg, the wasp then preens her egg-laying organ and her ge****ls; if she pierces a maggot but decides to just withdraw her egg-laying organ without laying an egg, she does not preen afterwards.

Pheromones help the wasp find the maggot-infested rotting thing, but then they don’t help the wasp track down maggots within the rotting thing. To track down maggots within the rotting thing, the wasp searches, not pheromones which flies intentionally release, but rather the maggot’s body odor. Scientists call this “kairomones”, which are the smells of animals, which do not benefit the animals producing them, but are exploited by predators and parasites searching for the animals. If your body odor does not attract other humans, but only attracts mosquitoes and ticks, that’s the same thing. The body odor of maggots which the wasp tracks might be the maggot’s cuticular hydrocarbons, the chemicals in its skin which protect it from drying out. The wasp may also follow the scent of the maggot’s f***s. These scents are not very strong, so they cannot be detected from far away and cannot guide the wasp all the way to the rotting thing from a distance, but once the wasp is already standing on the rotting thing, they can help her find where the maggots are within it.

Parasitoid wasps learn from their experience, how to find their victims. If a wasp has successfully injected an egg into a maggot while smelling a particular odor, she will seek out that odor again in the future. She can learn to tell the difference between fruits, fungi, etc, for example the difference between pears versus apples or between yeast versus mushrooms, and she can learn to prefer some over others. However, wasps can’t learn to tell the difference between different apple varieties. Experienced wasps can find fly food faster and more accurately than inexperienced wasps. Wasps remember the kinds of food where they have successfully injected eggs into maggots, and seek out that same food again if they get the chance.

In past decades, scientists often called L. heterotoma “Pseudeucoila bochei”. Actually scientists have mistakenly given L. heterotoma a dozen different names, including six different genus names. But L. heterotoma was actually the first name given to this species, in 1862, and in science, the first name given is the name that is supposed to get used.

But it’s inconvenient to use scientific names all the time, especially when talking to non-scientists. So recently some scientists proposed that L. heterotoma be called the amber wasp in English, because it is amber coloured: https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.9625
I guess feel free to translate that into whatever language you want, since the wasp does not already have any common names that I know of. In German maybe we could call it die Bernsteingelbwespe. Maybe in French you could call it la guêpe ambre jaune. It seems that in both German and French, all wasps are grammatically feminine. For most eusocial insects, it makes some kind of sense to talk as if female is the default, since the females do all the interesting stuff, all the work of building and maintaining the colony, and the drones just mate and die. Parasitoid wasps are not eusocial, though. In parasitoid wasps, the females are the ones who lay their eggs in their victims- to biologists, that’s much more interesting than whatever male parasitoid wasps do. However, grammatical gender never makes any sense anyway. In German, die Bahn is feminine but der Zug is masculine: both of those words mean train.
Copied from dear Erica Ehrhardt

Adaptations and counter-adaptations in Drosophila host–parasitoid interactions: advances in the molecular mechanisms Both hosts and parasitoids evolved a diverse array of traits and strategies for their antagonistic interactions, affecting their chances of encounter,…

Sensory neurons encode information about the world around us, as detected by our sense organs. Motor neurons activate muscles to make our body parts move, creating our behaviours. Neurons which are neither sensory neurons nor motor neurons are interneurons, and their functions are harder to figure out. Interneurons which inhibit other neurons nearby often regulate the function of neural circuits. One example are the local interneurons or LNs of the insect antennal lobe, the brain region which first receives information about smells from the olfactory receptor neurons or ORNs of the antenna.

ORNs send signals to projection neurons or PNs, which carry the information to higher brain centres. The antennal lobe is organised in glomeruli, round, tangled balls of axons and dendrites- which is interesting because the olfactory bulb of our brain is organised in the same way.

When an insect is exposed to a smell, molecules of the odor bind to olfactory receptor proteins in the ORN dendrites in the antenna. This opens ion channels, allowing positively charged atoms to flow into the ORNs, changing their electrical potential and exciting them. The spike travels down the axon of the ORN, then causes the ORN’s axon terminals to release neurotransmitter, which binds to receptors on PN dendrites, causing ion channels to open in the PN cell membrane and thus exciting the PNs. LNs can regulate the connection between ORNs and PNs by inhibiting both sides.

The inhibition from the LNs is important for how smells are encoded in the insect brain. Without inhibition from LNs, the ORNs would be too active and would be worse at encoding information. With inhibition, the ORNs respond to weak smells with weak activity, and only respond to very strong smells with their strongest possible activity. Without inhibition, the ORNs would respond to all sorts of smells with their strongest possible activity, and thus the brain would not be able to tell the difference between a very strong smell and a weaker smell. Also, most smells do not activate only one type of odourant receptor or ORN, but rather bind to a bunch of different odourant receptors and activate a bunch of types of ORNs, only with different intensities. Without inhibition, this would result in similar smells all producing basically the same broad pattern of activity in many ORNs. Inhibition suppresses the activity in the ORNs which do not respond as strongly to the smell, leaving the strongest activity in only one or a few ORNs which are particularly sensitive to that smell. Thus inhibition creates more specific different activity patterns in response to similar smells.

Not much is known about the shape of LNs in the fruit fly. Different LNs seem to be connected to a bunch of different neurons, but no one really knew what different LNs are doing. When scientists study our olfactory bulb, they can tell the difference between different classes of LNs based on their shape and their location in the layers of the olfactory bulb, but not so much was known about the LNs of the fly antennal lobe. Insect LNs are harder to identify because the insect antennal lobes are not organised into layers like our olfactory bulb, and the location of a cell body in an insect kind of randomly varies between individuals. We can see that different LNs have different patterns of activity, and thus might have different functions, but it was not clear how the activity of LNs are related to their shape. Usually we study fly neurons by genetically modifying flies so that we can control gene expression in just one cell or subset of cells, but there were not many genetically modified flies where gene expression is controlled in the LNs.

In many species of insects, one class of LNs is interesting in terms of activity in that these LNs do not fire spikes. The non spiking LNs can still be excited, in that positively charged atoms flow into the neuron and change the electrical potential, but they don’t have the big chain reaction where the change in electrical potential triggers the opening of a bunch of ion channels which let more ions flow in. No one knew what the function of this class was.

A recent study investigated some fruit fly LNs:https://www.eneuro.org/content/eneuro/early/2023/01/06/ENEURO.0109-22.2022.full.pdf
They studied patchy LNs, which get their name because they each extend their branches through patches of glomeruli. This study showed that patchy LNs are non spiking.

www.eneuro.org