Insects in the Garden:
Toward a Balanced Insect Ecology
Table of Contents for This Page
I’ve always been an organic gardener. But early on, I thought that meant using an “organically approved” insecticide like rotenone to defeat leaf-eating insects, especially my arch-nemesis, Colorado potato beetle. I dusted several times a season in a desperate struggle to keep the beetle’s exploding population in check, just barely managing to bring in the crop. But as I learned more about the role in the ecology of insects like lady beetles, lacewings, praying mantises, and assassin bugs—didn’t somebody say they’re “the good guys”?—I worried that blasting away with a powder intended to kill might be not be doing them any good either. One spring I took a Great Vow: to use no rotenone at all in the potato patch, even if it meant losing the crop.
Great was my amazement to find only five potato beetles on my potato plants the entire season. I took that as a luck-of-the-draw seasonal fluctuation—until I bumped into my neighbor across the road, her garden not seventy yards from my own. “My, my,” she wailed, “ain’t these potato bugs just awful—I dust, and I dust, and I dust—and I’m still out here every day, picking ’em off by hand!”
That was my epiphany about the true nature of the teeming insect community around me—and my garden’s relationship to it. From that moment, I have never used a granule of toxin, however reputedly benign, to deal with insect challenges in my garden and orchard—yet have continued to find my former nemesis the potato beetle one of the easiest of all insect competitors to deal with.
My avoidance of toxic chemicals more suited to chemical warfare than gardening was sound. American agriculture uses toxic pesticides at rates approaching a billion pounds annually. Perhaps only one percent of those chemicals actually makes contact with a target insect. The remainder is therefore irrelevant to insect control, but constitutes an assault on the rest of the ecology: with suppressive effects on the soil food web, foundation of soil fertility; pollution of ground water and natural water systems; and increasingly critical species loss.
My fundamental mistake was assuming that use of “organically approved” insecticides made any more sense. To be sure, their impacts on the ecology are not quite so drastic. But my story illustrates that they as well actually do more harm than good: They are broad spectrum in their effect, and wipe out great numbers of non-target species. Doesn’t the fact that my greatest success with potato beetles came when I ceased doing anything at all to defeat them call into question the whole strategy of preventing crop damage by killing whole classes of insects? My decision to reject that model—along with the fact that I’m a lazy old gardener who always has plenty of “the wild” coming in around the edges of the garden—made possible a natural, spontaneous, unplanned solution to my problem: Flowering weeds I just hadn’t gotten to yet provided habitat for insects, no longer suppressed by the rotenone, that eat the eggs and larval stage of the potato beetle. And the rest, as they say, is history.
Plants, being immobile, have to make a deal with their insect buddies: food, shelter, and a place to meet and mate in exchange for the service of moving their pollen to others of their species, in order to “be fruitful and multiply.” Thus a fundamental equation: the more flowering plants, the more insects in the ecology. And the more insect species, the more likely that any overly-successful species is going to be targeted as lunch by predator species. This simple law of population dynamics suggests a strategy to establish a balanced insect ecology as a key to preventing crop damage in garden and orchard: Far from engaging in a “war on insects,” it’s just good sense to try to maximize the numbers of insects in our backyards, ensuring the abundant presence of insect species that feed on those insects with a taste for our crops. Toward that end we should make habitat plantings of flowering plants—both annual and perennial, with flowers of all sizes and shapes, and in all parts of the season, from early spring to fall—as “discos” where ally insects can meet others of their kind, feed, and mate. The result is greater insect diversity, and greater natural balance between herbaceous (leaf-muncher) and predator (bug-muncher) species.
We should place habitat plantings throughout the garden, with an ideal ratio of one to one between habitat and crop plantings. That sounds like an extravagant use of garden space, but actually we can weave other plantings into the insect diversity project.
- We should not plant herbs and cut flowers off in their own little fiefdoms, but intersperse them among crop beds.
- Most soil improving cover crops flower abundantly, providing their insect buddies with nectar and pollen: buckwheat, alfalfa and clovers, cowpeas—even small grains shed abundant pollen in preparation for seed-making.
- Fertility plants such as comfrey and stinging nettle, grown specifically for their contribution to mulches and compost heaps, support insect diversity as well.
- Green feeds for livestock such as rape, kale, turnips, and fodder radishes increase insect diversity if allowed to flower before harvest.
- Ground covers in the orchard can be chosen for the profusion and timing of their flowers—mountain mints, yarrow, violets. Ferns do not flower, but they do increase habitat diversity.
- Weeds—weeds!? They unquestionably played a role in my initial success. We need to rethink our ideas about “weeds” entirely. The “arch-fiend” dandelion, for example, is in reality a dynamic accumulator (of minerals from the subsoil, which it makes available to more shallow rooted crops); a nutritious green for people and livestock; a medicine—and supports insect diversity.
Habitat plantings benefit not only predatory insects we want to encourage, they boost populations of pollinator species as well, crucial in setting seed and fruit in crop plants.
Remember the needs of insects for protection through the winter, and don’t go to excess with fall clean-up. My comfrey beds look somewhat messy when their leaves die in the fall, but I leave them in place as winter shelter for insects (and spiders).
What about using purchased beneficials? That’s a great idea—for the CEO of the insectary offering to sell them to you. They are expensive, and they migrate wherever they please after release, not necessarily where we want them to. If our garden ecology is welcoming to helpful insect species, they will come. If it is not, purchased beneficials may give marginal results but will not thrive.
Remember to encourage other players in your backyard ecology as well, not just insects. A small garden pool is a magnet for toads, frogs, and lizards, who eat a lot of insects. Building bird houses for insect eaters like Eastern bluebird is a fun project; but even more effective is provision of as much “edge habitat” as possible—perhaps flowering hedges, or privacy screens made with flowering vines in lieu of manufactured fencing—for protection, shelter, and nesting sites. Bats may or not take up residence in an assembled bat house, but respect their access to habitats (a hollow tree, an outbuilding) to encourage their insect feeding.
Two munches by a feeding insect on the tiny leaves of plants just emerging from the seed and it’s all over—while plants with more developed leaves can shrug off a lot more feeding. That's why I start as transplants, rather than direct sowing, as many crops as possible.
Healthy plants are less vulnerable to insect feeding pressure than weak, sickly ones; so garden sanitation and boosting soil fertility help crop plants thrive despite the presence of herbaceous insects.
I have argued that the solution to crop damage must not be a “war on insects.”” But my sharp-eyed reader may raise an obvious question: “So what did you do with those five potato beetles you found?” The answer is: Squish! To which the logical response is: “But I thought you said that the solution isn’t killing insects.” A practice of Squish! (otherwise known as handpicking), however, is a purely local event, and does not have the devastating impact on the insect ecology as “going nuclear” with broad-spectrum insecticides. Leaf-eating insects, like the rest of us, are opportunists—their reproductive prowess can be awesome. Handpicking can keep their populations from surging to damaging levels before their competition—our insect buddies in the garden—have time to catch up. Handpicking is a lost cause if initiated after a population surge is well under way. But if we’re doing every day what we should be doing in any case—just strolling through the garden to see how everybody is doing—it can be quite effective. As has been said, “The best fertilizer is the gardener’s shadow.”
If extensive planting of insect habitat is our basic alternative to making war on the insect community, here are some additional strategies for dealing with particular crop crunchers in acceptable “local skirmishes”:
- Physical barriers can limit our competition’s opportunities as well. Cutworms wrap around the slender stems of new transplants such as broccoli and cut them off at the knees, as it were. A strip of cardboard pressed into the soil as a collar around each transplant will deter the cutworms until the stems are larger and tougher. Row covers of spun-bonded fabric—which allow entry of rain, air, and sunlight—block access by insects until new plantings are less vulnerable. Finely crushed egg shells scattered in a wide band around transplants or tender crops like lettuce help deter slugs, for whom crawling over the sharp fragments is like walking over gravel barefoot for us. (The shells feed the planting with calcium as well.)
- Accommodation: Some exceptionally prolific competitors are simply going to be a factor in the garden, whatever we do (including the “nuclear” option); so the better part of wisdom is trying to accommodate their presence while bringing in the harvest anyway. An example in my garden is Mexican bean beetle, which reliably emerges in my early planting of bush beans in great hosts. I get numerous pickings of beans in spite of them, and simply accept that the plants eventually succumb to the beetle’s feeding pressure. The hungry beetles move on to my pole beans, but for some reason they are able to shrug off any amount of feeding pressure and still produce abundantly until frost.
- Succession planting is a variant of this strategy. Squash bug is another garden competitor with impressive reproductive capability. But I get many cuttings of yellow crookneck and zucchini before the plants succumb. Since cucurbits are so fast growing, I simply make another planting elsewhere in the garden (perhaps protected by row cover), timed so flowering occurs about when the planting under assault succumbs. There is little interruption of the flow of squashes into the skillet, despite the persistence of the squash bugs.
- Dodgeball: We might time planting of a crop to miss a critical “window of opportunity” of a problem species. The squash vine borer gets its start from a winged female who lays her eggs on the stems at soil line. Planting before or after the two or three week period when the gravid females are active gives borer-free crops.
- Planting resistant varieties deters some potential problems—for example, varieties of corn with tighter husks are likely to have less earworm damage. Pay attention to references in seed catalogs to insect resistance. If you save seeds from individual plants that seem to do better under pressure from herbaceous predators, you will over time be rewarded with more resistant varieties.
- Poultry power: Guineas, confined to the winter squash patch with a temporary fence, provide one hundred percent organic, one hundred percent effective control of squash bug (and help as well with insects that feed on tall crops such as corn, sunflowers, sorghum, and trellised cucumbers). Chickens are not good candidates for that job—their constant scratching would destroy the planting. However, chickens can be used in the garden in the preseason to reduce presence of slugs and snails. In some crops ducks are great for slug patrol. Almost all domestic fowl with access to the orchard help prevent insect damage—it’s a thrill to see a guinea take a coddling moth right out of the air! Geese break the life cycle of fruit damaging insects by cleaning up dropped fruits.
It is not the basic insect diversity strategy which is difficult, but the discipline to avoid “going nuclear” with toxic responses even if a particular insect surges temporarily beyond acceptable levels of feeding. For a couple of years in my garden harlequin bug, which had never been a problem for me, shut down production of radishes and turnips—one hundred percent. Even at that level of damage, I refused to jeopardize garden diversity in an attempt to gain temporary relief from the harlequin bug. The next season, some balance re-asserted itself—the harlequin was still present, but only in modest numbers—and I was eating radishes and turnips again. Meanwhile, populations of other competitors such as cabbage worm had continued their decline each season.
Manufacturers can sell us poison sprays only if they convince us to see insects as a big threat. I hope you will instead see a kaleidoscopic diversity of insects in the backyard as the key to sustainable, chemical-free gardening—and a thing of beauty.
It helps to remember that healthy plants may actually be stimulated by loss of up to ten percent of leaf mass to insect feeding. Remember as well that our great-grandparents grew lots of their own produce, thank you, long before poison merchants such as Monsanto and Cargill arrived on the scene.
Vegetable gardening without pesticides is not a fairy tale, but a practical, effective program. I have used no broad spectrum pesticides whatever in my garden for well over two decades. I still have problems with some insect species in some crops in some seasons. But every season, without exception, I grow more beautiful, residue-free produce than we can eat and give away.