Insect pests in your garden are not enemies, they’re symptoms; symptoms of poor soil.
Most simply put, insect pests are predators, and predators go after the weak, the stressed, the infirm. The more organically fertile your soil, the stronger your plants well be, and the fewer pest problems you’ll have.
Case in point is our experience with Colorado potato beetles. Our neighbor used to be plagued with them and finally gave up growing potatoes, whereas we had none in out potato bed — well, maybe two or three, looking lost. He came over one day, saw this, and inquired. I explained that, first, our soil was about as rich as it could be in compost and other organic matter, meaning our potatoes had all the nutrients they could want. Second, we hilled ours up with leaves and straw, not bare dirt. Potatoes get highly stressed with the wet-dry cycles of moisture found in the upper levels of bare soil, and become fodder for beetles. The leaves and straw level out these changes, so the soil is always just moist enough. No stress
A more scientific explanation lies in the fact most pest populations remain low in fertile earth because, while there is plenty of food around, there is not enough nitrogen in that food for insect nutrition. Stressed plants are a richer source of nitrogen, so your garden becomes a pot luck for bugs. In the words of Eliot Coleman, author of “The New Organic Grower” (Chelsea Green Publishing, VT, 1989) and other books, “Scientific evidence indicates that the effect of stress on a plant–whether from lack of nutrients, excess or deficiency of water, soil compaction, temperature, or other soil or environmental factors–is to inhibit the synthesis of protein by the plant. When protein synthesis is inhibited, the plant accumulates increasing levels of free amino acids (also called free nitrogen) in its arial parts, especially the phloem. Under nonstressful conditions, those amino acids would have been used by the plant to form protein. Insects thrive on plants high in free nitrogen and are thus attracted to and feed upon those plants. When protein synthesis proceeds normally, the nitrogen is locked up in completed protein. The insects are not attracted to unstressed plants because they cannot feed successfully on them.”
(Be aware that that’s about as much scientific discourse as you’ll find on this blog.)
An interesting sidelight is that a poor growing year, such as with a drought, results in abundant plant stress, and just as abundant bug pest pressure. Their overwintering offspring will be out in force the following year, so your soil (and therefore your vegetables) had better be ready.
A little bug pressure is a good thing, though, because plants produce antioxidents as a natural pest repellent – and antioxident levels are much higher in plants grown in organicaly rich soil than with chemical agricultural products.
What a system, huh?