That's probably not practical, but in practice it is also not really needed. Usually when someone has a problem with insects they just need to kill a few particular species. Doing that is actually feasible.

There are three broad approaches to killing insects.

#1. Mechanically disrupt them. E.g., rip their heads off or squish them or similar. This may seem impractical at first, bringing to mind images of immigrant laborers crouching over the crops with magnifying glasses, identifying the bad insects and crushing them between thumb and forefinger.

That would indeed be impractical. The way you implement #1 is to find another insect that preys upon the pest insect, or that is a fatal parasite to the pest insect.

This can be a very safe method for dealing with the pest insect, because predator and parasite species are often very specific when it comes to their prey or hosts, often only going after a single species.

So why don't we use this method more? I'll cover that later.

#2. Disrupt their life processes chemically by using a pesticide that attacks some fundamental aspect of life.

This is risky and hard to get right, because most of the fundamental aspects of life that insects depend on are also the fundamental aspects of life that other life forms depend on. This means those pesticides are almost always harmful to far more species than just the pest you are trying to get rid of.

Insects are small, so you can sometimes work around most of the danger to other species by keeping the doses small enough so that they are huge in insects, but are small in other animals that eat the poisoned insects, or in animals and people that eat the crops that that the residue lingers on.

You can also try to design the pesticide so that it breaks down quickly. Insect lives are often on regular and predictable schedules, so for many species there will only be a short, predictable time when they are attacking crops. In that case, a pesticide only needs to stay effective for that time frame.

#3. Disrupt their life cycles chemically by using something that only affects the particular species that you wish to get rid of.

This is actually feasible! Insect behavior is essentially controlled by biological state machines, and state transitions are triggered and controlled by hormones. Suppose you've got a pest insect that hatches at a certain time of year, then spends a couple months living in the ground eating grubs, then on the first warm evening of summer emerges, finds a pond, and then swarms 2 to 3 meters above the north side of the pond, swarming until it finds a mate in the swarm, mates, and then lays eggs on your crop plants and then dies, and when the eggs hatch the larva eat the crops.

Each of those events will be controlled by a hormone. There will be a hormone that triggers the "leave the ground and fly to find a pond" behavior. Another will trigger the "find the north side of the pond" behavior. Yet another will invoke the "swarm at 2 to 3 meters" action, and the "find a mate action" after that. After the mating, another hormone will trigger the "lost in time, like tears...in...rain. Time to die" behavior in the males, and the "lay eggs and die" behavior in the females.

If you can make a synthetic version of that hormone that triggers the the start of the sequence, and expose the insects to it a few weeks before that first warm evening of summer, you can make them do everything early. If that is early enough that they have not yet become sexually matured, they will go through the motions, but nothing useful (from the insect point of view) will happen. You'll have effectively wiped out that whole generation in that area.

But what happens to other insects that get exposed to that hormone? Won't we also be triggering bees and other useful insects into doing things out of sequence? Nope! It turns out that hormones from one species generally don't affect other species, nor do they affect non-insects that might eat the insects.

So why do we do #2 instead of #3? The same reason we rarely do #1.

We rarely do #1 and #3 because to do them requires actually understanding the pest insect. If you want to bring in a predator or parasite for a pest insect, you need to know enough about the natural ecosystem of the pest to identify its predators and parasites, and understand their effects on it.

Similar for #3. Someone has to study the life cycle of the pest sufficiently to reverse engineer its behavior state machine to identify the behaviors that we'd like to fiddle with, and study the pest sufficiently to identify which hormone controls that behavior.

From what I understand, these studies aren't particularly easy. Someone may have to spend many years studying a particular insect to understand it enough to start hacking it's biological programming. The big pesticide companies aren't particularly interested, because #2 is a lot easier...that just takes formulating new chemicals that are generally hostile to life, and then figuring out what restrictions have to be placed on their use to kill insects without doing too much collateral damage.

Academic researchers don't do much for #1 or #3 either, because there just isn't the funding.

There is a good illustration of this in the book "Life on a Little Known Planet: A Biologist's View of Insects and Their World" by Howard Ensign Evans. He was one of the world's leading experts on parasitic wasps. Before reading his book, I did not even know that there were parasitic wasps, but in fact there are many species of them, most very tiny (head of a pin size).

He tells of an incident where there was an invasive pest, from Florida if I recall correctly, that was attacking California citrus crops. In Florida there was another insect that was either a predator of or a parasite of (I forget which) the pest. This was imported in an attempt to control the pest.

This attempt failed, and California's citrus crop suffered large losses. Many years later, researchers figured out why the imported predator/parasite did not work. It turned out that the predator/parasite species turned out to actually be two species. According to everything that scientists had observed and measured at the time, they appeared to be one species, but it turned out to be two closely related species. There were only a couple of observable differences, both subtle. One was something like one species mated slightly earlier than the other. That was easy to miss, because unless you've watched a lot of them mating, you won't be able to tell the difference between two populations whose mating windows overlap, and one population with a wider mating window. Unfortunately the other difference was that only one of the two was a predator/parasite to the California pest. All of the ones they collected to send to California were from the wrong population.

I believe (but don't recall for certain) that this predator/parasite species was a parasitic wasp. The reason no one had studied it enough to realize that it was two species was that in the US there were only two parasitic wasp experts, and they were busy with the thousands of other parasitic wasp species.

(There are a lot of species science has not gotten around to studying, or even cataloging. Evans mentions early in the book that every summer he'd set out an insect trap on his property in New England, and would routinely catch insects that were unknown in the scientific literature. He would even occasionally catch parasitic wasp species that he did not recognize).

Why were there only two parasitic wasp experts? Evans mentions that he had a promising graduate student who was interested in specializing in parasitic wasps, and Evans advised the student to find another specialty. Industry was not interested in hiring parasitic wasp experts, and universities entomology departments weren't growing so the only way he'd get an academic position as a parasitic wasp expert was to replace an existing retiring expert, and neither Evans nor the other US parasitic wasp expert were anywhere near retiring.

Personally, I find this ridiculous. Pest insects cause a tremendous amount of economic damage. Methods #1 and #3 are effective and environmentally safe ways to control them. I would think it would be well worth our while to fund anyone who is interested and willing to make a career out of studying the ecology of pest insects and of predator/parasite insects that might affect pest insects. Even if most do not lead to controlling pest insects, some would, and that should justify the cost.

As far as I have been able to find, no one keeps track of how many entomologists there are, but the Entomological Society of America has about 7000 members. If every member of the ESA was an expert in a dozen species, they would still not come close to covering all the species that are probably economically relevant in the United States.