Hi
Have often wondered the same thing about butterflies since most species are host specific. As caterpillars they can't eat any other type of plant. So if they consume all the food they die also.
In the Monarch example if the milkweed is in short supply the caterpillars will comsume the entire plant even down to the roots. Supposedly this is because the caterpillar extracts the toxins from the plant thus making them safe from predation.But the toxin must be stored in the skin as it seems to be to toxic to the caterpillar also.
Assassin bugs igured this out and will consume everything but the skin lol.Like the caterpillar they will destroy their entire food source.
So why hasn't genetics wiped out all three of these creatures??
it is interesting to me that the entire system is so flawed to be useless yet is copied by non poisonos speciessuch as the queen and Viceroy.
i guess the answer is that there is much more to evolution than evolution?? lol
gary

I think back to all the nature shows I watched as a kid. The lions eat the antelope, yet there are always more antelopes later on. Look at the residential areas that are being overrun with deer because the natural predators have moved away or died off. It's all about checks and balances, survival of the fittest, yada, yada.

I think its a natural control. If the insects didn't cause damage to the plants, the population would become out of control. Think about how many seeds a palm tree can make. Trachycarpus can make close to 100,000 seeds in one year if its a very nice plant.

Turtile,

You're right. In this way populations are kept in check. Generally, food supplies start high, permitting populations to rise. The predator consumes all the food (may be a prey), which subsequently causes a drop in the predator population.

Diseases work the same way, except that the predator is a virus or bacteria.

Herbivores are NOT parasites; they are more like predators of plants. If they kill the plant they are on, they can usually move onto another one. Even sedentary pests like scale usually have an active stage when they can crawl or even fly. It's not much different from a coyote killing and eating a rabbit, then going off to hunt another one.

Another part of the answer is right there in your question: "if left unchecked". In general, critters like aphids, mites, etc. (including rabbits!) have other things that are eating THEM. So while there's no evolutionary advantage to killing one's food, there generally isn't much evolutionary disadvantage to it either.

I don't quite get it either! Here are my thoughts.
An organism exists solely to perpetuate its spp. A plant behaves as if it is the last one of its kind on earth; it must flower, seed and then it can die. We take advantage of this and harvest the fruit (tomatoes, okras etc) regularly, before they mature. The plant 'senses' that it has not completed its mission of life and produces even more fruit as if to compensate. When caterpillars eat up the leaves of a plant, the plant throws out a flush of new, more and greener leaves. I have often thought that, from a shrub's viewpoint, aphids and homeowners achieve one of the plant's cultural practices, tip pruning. But this does not explain the 'plague' type of infestation, like locusts. If they could not fly, they themselves would die when the food source is all eaten up (self limiting). Then there are parasites which must have an intermediate host. If it is not present, then the parasite cannot complete its own life cycle. This 'checks and balances' system in nature is endless in its fascination.

Are you talking about in your HOME environment? That's an articifial one that gives the advantage to the mite/scale. It's not that easy for them on the 'outside'.

If you study geography, you find that this is also true in the human population. Car wrecks, old age, sickness, death of other reasons all happen because there are babies being born every second. If someone is moving in, someone needs to go. LOL

Just think at the bugs and the fact that they lay someones 1000's of eggs just so a few can make it. I guess like you say its all about balance.

I am about to go out and kill some bugs, so today, there will be an unbalance for a few minutes.