By Karim Gharbi
While I appreciate the advances in horticulture that have allowed us to feed 8 billion people, that appreciation does not extend to the pesticide industry. This idea that we can dominate nature with “quick fixes” like insecticides or herbicides is hubris. Mother Nature developed the tools to self-regulate long ago, we need only to follow her lead.
This pesticide industry arose from the colonialist mindset that the land and its inhabitants are ours to conquer and that this conquest is even possible! And we’ve packaged and bottled the “solution” for only $19.95. But the profiteers of the pesticide industry have forgotten (or ignored) that indigenous communities have long known how to enlist the services of naturally occurring organisms to control garden pests. More recently, we’ve named this indigenous practice “conservation biological control,” and I want to share that you can easily do it too.
Biological control is the practice of using one organism to control another. This usually involves mass releases of captively bred organisms to target specific pests (e.g. aphid mummy wasps to control aphids). But these organisms are costly and usually do not present a long-term solution to our pest problems.
In contrast, conservation biological control involves modifying the landscape to attract naturally occurring beneficial organisms from nearby areas. And most of you are already doing this, whether you realize it or not!
Flowers
- Simply planting flowers (especially natives) attracts beneficial insects. The protein/carbs in pollen/nectar are a valuable meal to a diversity of predators and parasitoids. Lured to your garden by the smell of your floral appetizers, they begin to patrol in search of a main course. For many parasitic wasps, pollen and nectar are filling enough. But their young can only gestate inside the many soft-bodied insects that inhabit our gardens. After filling their bellies, they look for a suitable “nursery.”
- Just like us, insects have favorite foods. Some beneficials prefer the aesthetics and flavor of blanketflower, coneflower, and black-eyed susans. Meanwhile, others prefer the spire-shaped flowers of gayfeather, goldenrod, and penstemon. The larger parasitic wasps need somewhere large and flat to land, like the heli-pad created by the umbel flowers of common yarrow, milkweed, and the like.
- Not only do these beneficials have different palates, but they also have different sleep schedules! Some insects are more active in the early morning hours, while some can only be found at dusk. Similarly, different flowers have their peak nectar flow at different times of day. Encouraging floral diversity also ensures a continuous nectar supply, attracting beneficial insects from dawn till dusk.
Native Bee Habitat
There are over 1100 species of native bees here in Colorado (and counting). This astounding diversity arises from the plethora of meso-climates created by the various valleys and canyons strewn across the Rockies.
- As important as they are, flowers are not the only resource our beneficial insects require. There are some very simple ways you can create habitat for our astounding diversity of native bees.
- Of these 1100 species, about 30 percent are cavity-nesters. Those are the bees nesting inside of holes in dead/dying trees. If the wood is soft enough, these bees can excavate their own nests. But they are not so proud to pass up the holes excavated by wood-boring beetles. Unfortunately, we often view dead/dying trees as eyesores, hacking them down. This is understandable, as dead/dying trees can be thought of as fall risks or disease reservoirs. But if your snag is neither of those things, leave it be for the bees. Besides serving as habitat to native bees, they provide food/shelter for a slew of organisms different from those it supported while alive. If it is a fall risk, consider cutting it into smaller pieces but keep those logs on site! Moving wood around isn’t a great idea anyways.
Unfortunately, we often view dead/dying trees as eyesores, hacking them down. This is understandable, as dead/dying trees can be thought of as fall risks or disease reservoirs. But if your snag is neither of those things, leave it be for the bees. Besides serving as habitat to native bees, they provide food/shelter for a slew of organisms different from those it supported while alive. If it is a fall risk, consider cutting it into smaller pieces but keep those logs on site! Moving wood around isn’t a great idea anyways.
- Cavity-nesting bees will also inhabit those “bee hotels” people build. But the tubes in these hotels must be replaced every year or two to prevent accumulating populations of parasitic organisms (pollen mites, fungal diseases, etc.)!
- Consider installing plants with hollow, pithy stems, as many solitary bees nest there as well. Annual sunflowers are the most popular choice, but joe pye weed and umbellifers can also work! If you go this route, please wait until mid-spring to cut back those plants. Prematurely composting plant material with native bees overwintering inside can affect their survival.
- The other 70 percent of those 1100 species are ground nesters, excavating burrows in undisturbed patches of bare, sandy soil. Despite the abundance of these types of native bees, that sort of habitat is in short supply in urban areas. We gardeners cannot bear to see bare soil, always covering it with plants, mulch, or rocks. But if you have the right place for a bare spot amidst your garden, digger bees are a treat to observe!
- Many of these bees line their nests with sections of leaves/flowers that they cut themselves. If you’ve seen C-shaped cut from the edges of your leaves, now you know who’s responsible. These bees prefer plants with soft, pliable leaves/flowers, such as ash, buckthorn, lilac, lambsquarters, roses, alfalfa, serviceberry, hostas, and more!
Despite the few species that plague our gardens, the overwhelming majority of insects are a gardener’s best friend. They are working behind the scenes not only to control pests, but to enrich the soil and plant microbiome. They enrich our lives as well. It is an egregious disservice to oneself to deprive yourself of the joy of observing the myriad beings that call our gardens their homes. I hope that this sermon has convinced you of that!
Karim Gharbi is a Horticulture Specialist with CSU Extension, Denver Office.