PUTNEY — Gardening season is upon us, and as I scrutinize my various garden maps, trying to decide where to plant what, I have been pondering the relationship between insects and gardeners.
Most gardeners I know like bugs, to a degree. They like to see interesting spiders in the garden, for example, because they know spiders feast on a lot of the “pest” species that might otherwise ravage our crops. But gardeners can be a savage lot when it comes to many of these so-called “pests.”
Last summer I was showing some friends around my gardens, and one of them felt compelled to kill any white butterflies he saw flying around my cabbages by clapping them loudly between his hands. The Cabbage Butterfly (Pieris rapae), after all, is the parent of the infamous green cabbage worm, often found dead in your boiling water after you've cooked up some broccoli.
I understand the impulse. After all, we grow these crops for ourselves, and our families, friends, and neighbors. We hate to see insects devouring the fruits of our labors.
The thing is, insects are part of a huge array of living species that we attract to our gardens by virtue of our crops, herbs, and flowers, as well as the weeds that grow despite our best efforts.
Biologists John Vandemeer and Ivette Perfecto, in their book Breakfast of Biodiversity, refer to the “planned biodiversity” present in any agroecosystem (the ecosystem of a cultivated patch of land) and the “associated biodiversity” made up of “all the soil flora and fauna, the herbivorous, carnivorous, and fungus-feeding insects, the birds and mammals, the associated plants (some of which are weeds) and more.”
They point out that if we are interested in biodiversity conservation we should be at least as concerned with both associated and planned biodiversity, since each depends on the other.
In tropical agroecosystems, such as shade-grown coffee plantations, Vandemeer and Perfecto have found an amazing diversity and richness of insect species, including 128 species of beetles and 103 species of wasps just in the shade trees themselves.
So how is it that when we think about shade coffee, we are eager to ensure that farmers conserve all this biodiversity (which feeds “our” winter migrating birds so we get to see them again in the summer), but when it comes to our own gardens, in the temperate North, we try to eradicate all the species we think of as “pests”?
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We might need to revise the whole concept of “pests” and “beneficials” as the two categories into which gardeners tend to divide all the insects, spiders, and other creatures who live among our plants.
We think of the pests as the ones that damage our crops and the beneficials (such as ladybugs, preying mantises, and many predator wasp species) as those that eat the pests.
But, in reality, if there were no pests there would be no beneficials either. The predator species need an adequate supply of prey if they are to stick around. And if you eliminate all the prey and think you no longer need beneficials, just wait until you try a new crop that attracts a different pest, or a new population of the old pest moves into the neighborhood. You'll have no beneficials, and your crop will serve as the main course at a pest feast.
Recently I came across Insects and Gardens, by entomologist Eric Grissell. I found the book fascinating, not only for the gorgeous color photographs by photographer Carll Goodpasture, but also for the insect maven author's evangelical attitude about bugs.
Grissell, despite being an avid gardener, thinks all bugs are good bugs. That's because he's a firm believer in the principle that diversity in the garden is what we should strive for - such that the prey and predator species have what they need to survive - and leave enough of our crop left over for us to fulfill our own needs for food and flowers.
If you don't mind the occasional didactic rant, Grissell's book is a treasure of information about the role of insects in gardens and the value of diversity. He points out that insects provide the nourishment for a vast number of other creatures such as birds, toads, frogs, lizards, and bats. And bats, of course, are enormously helpful in controlling mosquitoes, which even Grissell admits can be problematic.
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The more diverse your garden is, the more likely the “pest” bugs will be kept below a level that really causes devastation to your crops, and the more likely the “beneficial” bugs will stay around to safeguard the garden from new incursions by a new crop of plant-eating insects.
To ensure a diversity of insects in your garden, you need a diversity of plants - not only in, but also around the garden.
The more berry bushes you can plant (such as high-bush cranberry, elderberry, and blueberry) the more birds will frequent the area, keeping in check that diverse insect community you are inviting to the garden. Having water near the garden, such as a small pond, will attract frogs and dragonflies that also feed on plant-eating bugs. Planting a border of flowers and herbs known to attract predator species can also be effective.
The term “agroecology” refers to the science of understanding farms and gardens as ecosystems; within agroecology circles, the latest trend in insect management is called Ecologically Based Pest Management (EBPM), a set of strategies designed to “manage” insects, rather than control or eradicate them. The Sustainable Agriculture Network has a book, Manage Insects on Your Farm, that gardeners will find useful.
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I still find myself squashing asparagus beetles, but more and more I am trying to learn to live with insects in the garden, to value insect life as much as I value any other living thing whose function in the complex world of the garden is most often something I cannot begin to fathom.
Last summer I picked up the tomato hornworm on my pepper plant and walked it down the street. However, the next day it (or someone just like it) was back in the pepper patch. That time I left it there, and I still harvested quite a few peppers. I also spent a lot of time admiring hummingbird moths in my flower beds.
Maybe this year I'll learn to let the asparagus beetles be.