Regional Gardening Reports :: National Gardening Association

In the Garden:
Lower South
May, 2006
Regional Report

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The brown aphids on this tropical milkweed each contain a parasitoid wasp. There is also a ladybug larva and a syrphid fly larva eating their fill.

Gardening Allies

Ever feel like it's you against them? I mean the hordes of insects out there ready to chomp through your garden like a biblical plague. Well, we are not alone. In fact, we play a very small part in defending our gardens against pests.

It is a common misconception that most insects are garden pests, when in fact only a small percentage of the six-legged inhabitants of our gardens are out to do our plants harm. Most are just part of the complex web of life in the environment and have no direct effect on our plants, may even be beneficial to us.

It is these beneficials that are most interesting and worth getting to know better. They carry the load when it comes to preventing pest damage to plants. Let me explain.

If left unchecked, pest populations would explode into a devastating army of destruction. But weather conditions and beneficial insects are at work preventing such an outbreak.

Take aphids for example. In the spring, female aphids appear, already pregnant and popping out babies like a Pez dispenser. These babies are also females that are born pregnant. They reach sexual maturity in about a week, and the cycle continues. Talk about a reproductive machine!

With babies having babies within a week, the exponential potential is staggering. According to one calculation, a single momma aphid in the course of a summer could produce enough descendants to circle the earth more than four times.

So why do we see so few aphids in our gardens? Even what seems like a big outbreak is a mere fraction of what could occur. There are two primary reasons. Environmental conditions don't always favor, and at times suppress, insect and mite survival. Also, beneficial insects are out there attacking them in a scene reminiscent of Jurassic Park.

Common Good Guys
The most familiar "good guy" -- or perhaps I should say "good gal" -- of the garden is the ladybug. The adults and larvae of ladybugs eat aphids and certain other pests. In fact, a single ladybug larva will consume more than 5,000 aphids in its lifetime.

But aphids are also attacked by other beneficial insects including lacewing larvae, syrphid fly larvae, and my personal favorite: parasitoid wasps.

These tiny wasps lay an egg inside an aphid. The wasp hatches and consumes the aphid's interior, killing the aphid in the process and leaving it a lifeless, puffy, brown shell. The wasp larva then transforms into its adult stage and cuts a hole in the top of the aphid, emerging to continue the process. Way cool! If there were an aphid version of the movie Alien, this would be it.

Welcoming Beneficials
The point of all this is that most of the work in keeping aphids and other pests in check is not up to us. We step in from time to time when nature gets out of balance to shut down an outbreak. If we will conserve, provide for, and protect these beneficial insects, we can greatly reduce the chance of pest problems in the garden.

First, provide food for the adults. Plant the types of flowers that provide beneficials nectar and pollen for energy. Examples include yarrow, fennel, chamomile, autumn aster, and thyme. Some beneficial adults eat pests, so a few pests are a good thing as they will keep the adults around. The larvae also need pests to survive and grow to adulthood. If there are no pests, the adults won't lay eggs on a plant. They look for places where their young will have a good food supply and do their egg laying there.

Finally, avoid spraying needlessly. When spraying is necessary, choose a product such as Bacillus thuringiensis that doesn't affect pest-eating beneficials, or one that breaks down quickly, such as pyrethrum or insecticidal soap. Target the sprays to the pests to minimize unintended consequences.

Remember, if you kill a beneficial insect, you inherit its job.

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