When I was learning to garden (admittedly, a long time ago) any insect that we found in our garden was viewed as a threat. We might give a pass to bees, although we worried about their potential to sting. Likewise, we might take the time to identify the intruder’s species before we reached for the sprays. However, judging from what passed as pest control then — so-called “broad spectrum” insecticides that killed indiscriminately — the general attitude was clearly that a garden devoid of insects was best.
Unfortunately, that attitude still persists in much of commercial horticulture. We still see a reliance by nursery growers and many commercial landscape maintenance crews on neonicotinoid insecticides, nerve toxins that are absorbed by plant roots and turn the whole plant toxic to virtually any creature that may feed on its leaves, nectar, or even pollen.
Recently, though, I spoke to a person who is working hard to change attitudes toward insects, horticulturist Jessica Walliser. Walliser confesses to a fascination with “bugs.” (A popular term for insects in general that can be a misnomer as, scientifically speaking, only one order of insects qualifies for this name). Had Walliser delved into insects earlier in her career, she told me, she might have focused on them and become an entomologist rather than pursuing horticulture.
Recently, Walliser has published an updated and revised edition of her award-winning book, whose title bespeaks her enthusiasm: “Attracting Beneficial Bugs to Your Garden.” The subtitle indicates the pay-off: “A Natural Approach to Pest Control.”
To put things in perspective, Walliser notes in the first chapter that just 1 percent of the insects we come across in the course of our lives are harmful to our plants or us and our pets. The overwhelming majority (99 percent) are benign or actively beneficial to our landscapes, providing such services as pollinating flowers or preying on the insects that want to eat our plants. Of course, all species, including the plant-eaters, have an essential role to play ecologically. If you want your garden to function in a healthy and sustainable manner, you have to host all of them. The key, according to Walliser, is to arrange your garden so that it attracts and retains abundant populations of the insects that prey on the plant-eating ones so that their damage is minimized.
This means avoiding, for the most part, the use of insecticides. These are largely counter-productive, Walliser explained to me. To the extent that they kill the plant eaters, they rob the predatory insects of their prey and, if the toxins don’t kill the predators, too, they rob them of their incentive to remain in your garden.
Instead, make sure to provide all the resources the predators need, to keep them abundant in your landscape. Because most of the predators also feed on nectars and pollen at some point in their life cycle, planting appropriate flowers is essential. Walliser includes an in-depth gallery of such plants in her book, with each entry featuring information about what beneficial insects that particular species of flower supports.
An essential characteristic for the gardener who pursues this path, according to Walliser, is patience. That’s because typically when a plant-eating insect population increases — if your roses experience a plague of aphids, for example — it takes time for the population of their predators to increase to a corresponding level and beat back the pests.
Once a natural balance among the insects has been established in your garden, the need for the gardener’s interference should become minimal. Although, Walliser adds, this rule applies only to native insects. Invasive insects that have been introduced from abroad such as Japanese beetles or emerald ash borers have no predators in North America that have evolved to prey on them, so these invasives can proliferate without control. For these, Walliser recommended to me the use of biocontrols, organisms that prey on the introduced pests in their native lands. Such biocontrol organisms must be carefully and extensively screened to make sure that they won’t also prey on native North American insects. If managed properly, though, they can be quite effective and make unnecessary a resort to insecticides. For example, I myself introduced milky spore, a disease of Japanese beetle grubs, into my Berkshire garden and found that an outbreak of those pests was reduced to virtually nothing.
To learn more about Jessica Walliser’s work and her book, “Attracting Beneficial Bugs to Your Garden,” listen to our conversation on the Berkshire Botanical Garden’s “Growing Greener” podcast at thomaschristophergardens.com/podcasts/attracting-beneficial-insects-to-your-garden.