Bird populations in French countryside have fallen by a third in fifteen years

Could some of that be due to you paying more attention to insects and birds when you were growing up? Kids tend to spend more time outdoors than adults, especially more unstructured time, and so might be expected to have more time to notice things like insects and birds, and more time to indulge curiosity about them.

But to do so, we have to seriously understand the target species, bit there aren't anywhere near enough entomologists for that.

Briefly, what you have to do is extensively study the life cycle of the target. Insects are the biological equivalent of simple robots that follow a bunch of pre-programmed behaviors triggered by their inputs. Hormones are associated with this various behaviors.

Get a few PhD entomologists who make it their career to understand a particular insect, and they can figure out what pre-programmed behavior that insect has, and what triggers them, and most importantly what hormones are involved with which trigger.

You can then make a pesticide based on one of that insect's hormones that will trigger the associated behavior.

For example, suppose you have an insect that in its juvenile form causes a lot of damage to crops. Later, in its adult form, when certain weather changes occur, the females look for a particular plant growing in a still pond, and lay their eggs on the leaves. The males, when that weather change occurs, also seek those plants in still ponds, and fertilize any eggs they find. The adults then die.

If you can find the hormone that triggers the "go lay/fertilize then die" behavior, then you maybe can make a pesticide with that which you can spray on the juveniles. It triggers the "reproduce and die" program, even though the juvenile females cannot yet pay eggs and the males cannot yet fertilize eggs. That doesn't matter. They are essentially biological automatons, and they are running that program now. They find the pond, find the plant, go through the motions, and die.

The cool thing about hormones is that the hormones for one species usually are highly specific to that species. The hormone based pesticide probably will not do anything to other insects. It also probably won't do anything to whatever eats the target insect--things that eat insects and are not unharmed by insect hormones tend to evolve away from eating insects. Another cool thing about using hormones as the basis for pesticides is there is not much the target can do to evolve resistance. An insect that evolves resistance to its own "go and mate" hormone, for instance, is not going to be passing those genes on.

Another thing you can do when you have enough entomologists to actually seriously study insect life cycles is try biological control. For many pest insects there are predator insects that kill the pest. There are also often parasites that can control the pests. If the pest is also a predator, there are often other predators that compete with the pests for food. If you know enough about this complex web of predator/prey/parasite, you can reasonably safely try things like boosting the predators of your pests, or bringing in non-pest competitors for the pest's prey.

But you need to really understand a lot about all the involved species to do that safely, so it suffers the same problem as does hormone based pesticides, but more so.

* Varroa mite - a Chinese mite that spread to Europe and then the by cross species breeds. It bites into the side of a bee. Adult bees are usually strong enough withstand the bites. But the mite's feeding leaves holes in the shell that never really heal and makes it easy to contact diseases like Fowl Brood Hive Disease.

When the mite hit the brood (aka larva) they'll grow up in cell with the brood. Regular brood will have the mites cleaned off or the brood and mite larva will be removed as soon as possible. But drones have a longer gestation period and deeper cells. By the time the drone emerges the mite has already gone through it's full life cycle and is ready to restart the process attaching to nurse bees. Ohio would have eradicated it by now but neighboring states don't regulate their hive.

* Fowl Brood Hive Disease - It's bacterium that spreads on contact between bees. Since bees are very social it spreads very easy. Remember when a bees stings something it dies, so why fight when you don't have to? Plus queens prefer to breed with other hives to prevent genetics stagnation.

When a brood has been infected it forms scales on it's shell and begins to for scales similar to Harlequin Ichthyosis in humans. If they die in the cell the nurse bees will remove the decaying brood. In the process the nurse bees also get the spores on them spreading the disease in them. At the point the only good way to stop the disease is to kill the whole hive, clean out the hive, and boil everything. Again Ohio would have eradicated it by now but neighboring states don't regulate their hive.

* Genetically altered crops - We have enough floral diversity in our wetlands, open fields, forests, and private gardens to feed our bees. But we sees build-up of genetically modified pollen that has a pesticide in it. The first couple years of a hive theirs no issue. But around year 3 we can almost count on total hive collapse. Its because the pesticide builds up in the wax they keep rebuilding for the brood, nectar, and honey storage. Eventually to get so strong it poisons the brood or the hive swarms to find a better location.