If I were writing a book (AND I AM NOT!), and this thread were that book, I'd have to call it "The Education of A Gardener". In this thread, I am going to share with you the second-most-important thing I have learned about gardening, and it is called the Volterra Principle. And, it is very long, and I apologize for that....but it is an important life lesson and I want to explain it well.

WHY?

Have you ever wondered WHY pesticides, which have been used for hundreds of years, don't really get rid of pest insects and only decrease their population for a little while? And, have you ever noticed that after you spray a pesticide, you see fewer pests for a few days and then, at some point, you realize you are seeing more and more and more of those pests? I've wondered about those things, and over a period of years, I've finally gotten to the point where I understand that it happens and I think I understand it well enough to explain it.

BACKGROUND INFO:

Back when I was just a kid, my dad grew magnificent tomato plants. The plants were always tall, lush, heavily loaded with fruit and always produced all the tomatoes we could eat plus a great many more to give away. His tomato plants were darn near perfect....until the spider mites arrived in late June and usually killed the plants by late July. The same thing happened to a friend of his who had a vegetable garden just a few blocks away. Sometimes, both their gardens were hit by spider mites in the exact same week, and their tomato plants often completely died by the same week a month or so later. So, I grew up with the thought planted firmly in my mind that, no matter what you did, spider mites would get your plants every summer and you couldn't do one thing to stop it. As as adult, I now know that is not true and I know why it happens and how we can break that cycle.

THE VOLTERRA PRINCIPLE:

The scientific principle that describes this phenomenon is called the Volterra Principle and it was first applied to a fish population, not a plant population. However, it has been studied and found to apply in plant(prey) and pest (predator) populations too. The Volterra Principle basically explains how there is a unique predator-prey relationship and that when something intervenes, that relationship is disrupted. So, essentially, using lady bugs and aphids as an example....in your garden, the lady bug larvae (predator carnivore bugs) prey upon the pest bug, the aphids. Left along, the lady bugs will keep the aphid levels low enough that the plants do not suffer any long-term damage. If you intervene by spraying an insecticide, though, the predator carnivore bugs die along with the pesty herbivore bugs, and you have a situation where your normal predator-prey bug population is out of balance. When that occurs, the prey bugs that eat your plants increase and increase and increase in number because there are not predator bugs to eat them.

HOW IT HAPPENED IN DAD'S GARDEN: Even though we never noticed red spider mites on the plants until about the third week in June, I now know from my experiences as a gardener that they actually usally show up in small numbers in mid-May and their population finally gets large enough to be "obvious" by mid-June. So, when Dad and his gardener friend began seeing spider mites, they reacted in a way typical of the 1960s and 1970s--they vigorously attacked those spider mites with an arsenal of nasty-smelling chemicals--and from what I remember they used DDT, maybe Sevin dust or something similar, and finally, Kelthane. So, what happened? The spider mite population EXPLODED exponentially, the plants declined, and that was the end of tomatoes for that year. (Fall gardening was not practiced back then, as far as I know.) And, it happened every single year. Every single year.

WHY DIDN'T THE PESTICIDES WORK? Well, by now, you've heard me say a billion times that beneficial insects help keep pest populations under control. I doubt the average home gardener in the 1960s and 1970s understood that though. Back then, "organic gardening" was presumed to be a practice used only by "long-haired hippie freaks" during the back-to-the-land movement so popular at that time. So, I don't think we personally knew anyone who gardened organically at that time--perhaps, if we had, that person would have explained all of this good bug vs. bad bug stuff to us.

So, when Daddy and his gardening friends nuked their plants with chemicals, they killed off the beneficial insects who preyed upon the pest insects. Because pest populations always rebound more quickly (more about that in a second), the pest populations rebounded and grew incredibly fast because there were NO beneficials left to eat them and keep them somewhat under control.

Somewhere along the way, Dad stopped using DDT and Sevin, as if he understood that they were making his garden pest problem worse, or at least they weren't making it better. From then on, he only used Kelthane, which was a miticide. And, early in my marriage, I used Kelthane too and saw the same cycle with spraying of pesticides (in my case, Kelthane) seemingly making the spider mite problem worse and not better. Nowadays, I understand that one reason this occurred is because one predator bug that eats red spider mites is, in fact, a beneficial mite. So, when we used a miticide to kill the bad mites, we also were killing the good mites that eat the bad mites. But, we didn't know that, so the red spider mites showed up every year, and the problem continued and continued and continued.

MAKING A CHANGE:

After a couple of years of using Kelthane in my mid-20s and NOT seeing an improvement, I gave up the use of chemicals and began to transition to organic gardening. (And, at some point after that, Kelthane was removed from the market, although I think it came back into the market about a decade later.) So, what happened? The first year I was organic, I had a minor spider mite problem. In subsequent years, we had less and less and less spider mites. Since going organic, I have NEVER lost one single tomato plant to spider mites. For someone who grew up "believing" that spider mites ALWAYS took out the tomato plants, it was a HUGE shock to discover that they didn't necessarily destroy my crops after all.

So, even though I figured this out for myself, I didn't know then that it was an actual scientific principle (with its' own mathematical formulas) that had been, and continues to be, studied extensively.

BAD BUGS VS. GOOD BUGS

There are two basic kinds of bugs: plant eaters (herbivores) and bug eaters (carnivores). (Some plant eaters do eat some other bugs too, so I guess they'd be omnivores.) For example, spider mites, grasshopper, aphids and Japanese Beetles all eat plants. On the other hand, ladybugs, spiders, hornets, assasin beetles, green lacewings, cicada killers and parasitic wasps (like Trichogamma wasps) and other wasps eat bugs OR kill them in some other way (cetain predatory wasps lay their eggs on caterpillars and that eventually kills the cats, for example).

Your herbivores almost always appear first and in large populations....it takes a lot of little bugs, after all, to eat a significant part of a plant. On the other hand, one carnivore insect will eat many, many herbivores, so you never have beneficial insects in the same numbers you have plant-eating insects. And, the beneficial insects you DO have will not reproduce and create baby beneficial insects until there is ALREADY a large-enough population of bad bugs to feed all the beneficial baby bugs.

From a gardener's perspective, then, we want and need those carnivore insects in our gardens to eat the herbivore insects that show up. To have them, we have to do a couple of things. First, we cannot use ANY pesticide or similar product (whether it is of chemical or organic origin) that disrupts the population of carnivore insects. Secondly, we can help establish populations of good (carnivore) insects in our gardens in several ways. Third, when we feel we must use some sort of pesticide because we have a problem pest that is doing a large amount of damage, we need to use a pesticide that selectively targets THAT pest.....Bt is such a pesticide.

ENCOURAGING BENEFICIALS: Most beneficial insects are extremely attracted to plants with very, very small flowers, like alyssum, yarrow, catnip, catmint, basils, etc. If you plant these around and in your garden, they will help attract beneficials. Also, you can buy and release certain beneficial insects to help establish a population of them in your garden and yard. Finally, you never, ever use pesticides or you wipe out your beneficials.

You NEVER have the equivalent of one predator insect for every herbivore insect because one carnivore insect has to eat many, many, many herbivore insects to sustain life AND reproduce more beneficial insects. But, if you make your garden and yard a safe, attractive place for beneficial insects, they'll keep the pests under control for you. THAT is the way nature is intended to work.

So, when you use any pesticide in your garden areas, you have set in motion the law of unintended consequences and are putting yourself in a dangerous cycle. Every time you spray, the herbivores rebound and develop a little more resistance to the pesticide sprays, and the carnivores have to start all over again so they are always "behind" and struggling to catch up.

When your garden is in balance, the predator bugs (the ones I've referred to as carnivores) WILL gobble up the prey (the herbivore insects who damage your plants). Sometimes it is hard to wait for this natural process to occur, but if you are patient, it will occur.

For the first few years that we lived here in Oklahoma, we always had lots and lots of pest bugs: aphids, spider mites, Japanese beetles, etc., but I never lost many plants to them because we had a good population of beneficial insects. Gradually, too, I noticed that my beneficial bug populations was increasing quite a bit. And, of course, I have done everything I can to attract the beneficial predator bugs and to discourage the prey (carnivore insects).

WHY, THEN, ARE MY BENEFICIAL INSECTS "DISAPPEARING"?

Every year, for at least the last 3 or 4 years, I have been seeing fewer and fewer and fewer beneficial insects and I have worried about that. Was I doing something wrong? Where had my green lacewings gone? Why are the spiders fewer and fewer in number? Why is my ladybug population DECREASING every year? Why are my "good bugs" disappearing and where are they going? (sigh) I probably worried about this far too long...but, then, finally I got it!

NOT ALWAYS A DUMB BLONDE: I have pondered the questions in that last paragraph for years and, for some reason, this year I suddenly had a "Eureaka!" moment. My population of good insects is decreasing because I no longer have tons and tons of bad insects for them to eat. Remember, the carnivore-type insects only show up if there are herbivores for them to eat. Whew! Having finally figured that out, I feel better now.

Having said all of the above, keep in mind that there are some things you do in your garden that WILL contribute to having lots of carnivore insects. One of those things is over-fertilization, especially with nitrogen. For some reason (and this is a scientifically proven fact) plants that have been fed an abundance of nitrogen are more attractive to herbivore insects and to other "predators" like bacteria, viruses and fungi. And, plants that are overwatered are also overly attractive to herbivores. So, if you overfeed and overwater, you are essentially turning on a neon light to attract herbivore insects.

Well, that's it. That's one of the most important things I have learned about gardening in my lifetime (probably the second most important thing).....and if I had only read about it, I might have been prone to dismiss it and feel like it wasn't a big deal. However, having experienced all the above in real life, I know that understanding the Volterra Principle and how it happens in your garden is VERY IMPORTANT to your success as a gardener, and it doesn't matter if you are growing flowers, trees, herbs, shrubs, veggies, etc.

And, I know that I mentioned three chemicals by name, simply because they were the ones we used when I was a kid, and one of them I even used as an adult. By mentioning those three chemicals, I do not mean to single them out as being worse than any other chemical product--just that they are the ones we used.

Dawn