DDT spread way too broadly in the ecosystem, to species it had never been tested on, and it persisted a long time. It was known to interfere with critical species such as nitrogen-fixing bacteria. This is not something you want to mess around blindly with, which is what we did by putting DDT into widespread use without adequate testing.

There are three effective ways to control insects.

1. Poison them with something that is dangerous to a wide variety of life.

2. Poison them with something that is narrowly targeted to the species you are trying to control and is harmless to other species.

3. Deal with them mechanically, such as by crushing them or tearing them apart.

DDT and similar pesticides take the #1 approach. To do that safely you have to carefully control the spread of your pesticide so that it doesn't spread to species you do not want to harm. You can do this by being very careful in how it is applied, and designing it to break down quickly and not spread beyond the application area. We failed in this aspect with DDT.

The #2 approach is quite feasible. The way it works is that you base your pesticide on hormones of your target species. Insects are essentially biological robots running conceptually simple and very inflexible state machines. Various hormones control this, triggering various programs that run on the state machine. For instance, there might be a particular hormone that activates in the males when the weather changes, triggering in males a flight to find a female, and after that program runs the male dies. A different hormone might trigger female mating behavior.

Entomologists can study that species, and identify the various behavior programs built into the insect state machine, and figure out what hormones active which programs. Then a pesticide can be designed that mimics the hormone that starts the male mating subroutine. Spray that on them when it is not the right time of the year, so the females are not having their mating program trigger, and the males will go do their (now futile) mating flight and die.

The best part about this is that it is safe for other species, because these program control hormones for one species are almost always harmless to other species up the food chain. (To be up the food chain from something, you kind of need to have evolved to not be bothered by its hormones).

Another nice thing about the #2 approach is that the pests do not develop immunity. If an insect develops immunity to, say, the hormone that triggers its mating flight, then it is not going to mate when that trigger fires naturally, and so whatever mutation provided that immunity dies off.

The #3 approach is also quite feasible...and no, I don't mean importing cheap migrant workers to go out with tweezers in the fields and crush insects. :-) I'm talking about finding an insect the preys upon or is a parasite to the insect you want to control, and using it. Entomologists can study a pest species and identify what its enemies and parasites are (and there usually are some), and then you can introduce those to control the pest species. Unlike higher forms of like, like reptiles and birds and mammals, insects tend to be very picky about what they prey upon or what they are parasites to. If you've got a particular species of invasive insect from Florida destroying your California citrus crop, and you import the species of parasitic wasp that kills the pest, when it kills them it does not turn to some other species for hosting services. It dies.

The big problem with #2 and #3 is that there are a lot of insect species, and a lot of predator and parasite species, and not a lot of entomologists. This is discussed in the excellent book "Life on a Little Known Planet" by Howard Ensign Evans [1]. He was one of the worlds leading experts on parasitic wasps. There are hundreds or thousands of species of them, most very small (the size of pinhead or smaller). In the book, he tells the story of that pest destroying the California crop. Officials did try to import the parasitic wasp from Florida that kept the pest in control there.

It failed. Eventually, after the crop was destroyed, they found out why. It turns out that what was thought to be one species of parasitic wasp was actually two, which are almost identical, except one of them was NOT a parasite for the particular species they were trying to control. With hundreds of species of parasitic wasps and very few parasitic wasp experts in the world, no one had looked at this one species close enough to have noticed that there were really two species.

The kind of observation and experimentation is takes to learn enough about the insect state machines to make the hormone mimicking pesticides, or to learn enough about an insect's predators or parasites to effectively and safely control the pest biologically, takes a long time. Industry is not interested in funding that. They want entomologists to work on type #1 poisons, not to spend 20 years in the lab studying one species to identify a key hormone.

Academic entomologists who want to pursue these studies aren't pulling in the big grants, either. Evans tells of having to advise a graduate student to NOT specialize in parasitic wasps, despite the student's interest in and talent at it, because he would not be able to get funding for research in that area.

[1] http://www.amazon.com/Life-Little-Known-Planet-Biologists/dp...