Insectory Plants: let Nature manage the pests

It’s a common idea that Nature, left to its own devices, comes to some kind of balance. If one organism gets too numerous, something else will increase to reduce that population. In the case of monocultures created by humans, there is an enforced imbalance that has to be propped up with lots of energy and effort. So in the pursuit of sustainability, humans are opening our eyes to the possibility of biomimicry, imitating Nature. We are coming to the realization that biodiversity is far healthier and less energy intensive than monocultures born out of the aggressive hubris to control Nature. “Let Nature take her course.” But we can stack the deck in human favor first.

         This is the thinking behind growing Insectary Plants. Insectary plants attract and support what we call beneficial insects. These insects are beneficial because they eat other insects that eat our plants (predatory beneficials), or they lay their eggs in or on pest insects that then become food for their developing young (parasitoid beneficials). In both cases, populations of pests are reduced without humans having to spray, spend or lift a finger. Learning to partner with Nature in this way could be very valuable to the health and economics of human life on earth.

         In case you might think this is “pie in the sky”, let me recount a specific example where this approach has worked. A USDA scientist named Eric Brennan worked for 10 years with Salinas California’s $1.3 billion organic lettuce industry. He developed a system of interplanting annual sweet alyssum with the lettuce to attract beneficial syrphid flies (Hover Flies) whose larvae can each eat up to 150 aphids a day. He experimented with the density of the alyssum until he found the right balance where enough syrphid flies were supported to remove the aphids, with no negative competition between the alyssum and lettuce production. This is called Conservation Biological Control. It allows organic lettuce to be competitively priced and saves us from eating pesticides.

         The renowned entomologist Jonathan Lundgren has said that when ag. consultants go into a farmer’s field and use their sweep nets to sample what insects are there, they only identify the pests in the net and recommend the poisons to kill them? Why don’t they identify the beneficial insects in the net and learn how to support their populations? Jonathan is setting out on his Blue Dasher Farm to research and prove that through biodiversity, farmers can grow crops profitably without poisoning the insect life, the soil, water and the rest of us.

         Insectary Plants mainly support beneficial insects through providing nectar which is made up of sugars, carbohydrates, amino acids and more. This is not candy, but natural nutrients vital to the survival and reproduction of many insects, including predatory and parasitoid insects, as well as pollinators. When these nutrients are provided in sufficient quantity and diversity, many kinds of beneficial insects will live, take shelter, lay eggs and over-winter in the adjacent area. Insects are very intelligent, and they know to lay their eggs where there will be food for their offspring.

         Plants provide nectar in two different structures: in the flowers, of course, but also in “extrafloral nectaries.” The floral nectar and pollen attract both pollinators and natural enemies, but the “extrafloral nectaries” in the leaves and stems, etc., mostly support the natural enemies of plant-eating insects. These natural enemies are: wasps, ladybugs, green lacewings, hoverflies, ground beetles, damselflies, assassin bugs, aphid parasites, minute pirate bugs, big-eyed bugs and more, including the reviled earwig. In a diverse ecology, there can be hundreds of different varieties. And wasps alone can parasitize over 200 species of pests. Of course they can kill the larvae of butterflies too, so it’s not all beneficial from a human perspective. But if people spray pesticides, the party’s over; or at least greatly reduced.

         Even scientists have not figured out the best combinations of plants to manage pests in our crops, but the general conclusion is that if we grow a wide variety of plants with differing shapes and sizes of flowers, we will attract a broad diversity of beneficial insects. And if we make sure to pick a variety of different plants that will provide blooms through the whole growing season, our ally insects will stick around and do the pest management for us. It is best to plant groups of the same plant, not just one or two. Insects really understand time-energy management.

         So which plants feed and support these enemies of our pests? Thankfully there are a lot that do. They tend to be plants with tiny flowers in clusters or groups. Large numbers of herbs are insectary plants including: dill, fennel, parsley, cilantro, thyme, rosemary, mints, rue, chamomile, yarrow, mountain mint (and I’m guessing winter and summer savories, oregano, lavender and marjoram). Also a lot of cover crops are good insectary plants: buckwheat, clovers, mustards, turnips, canola (rape seed) and hairy vetch.

         Another major insectary plant group are our native wildflowers. It is reported that these natives support far more native beneficial insects than do non-native plants: gaillardia, goldenrod, yarrow, milkweed, sunflower, penstemon, sulfur flower, greenthread and bee balm. And many native shrubs also support our beneficial insects: rabbitbrush, lead plant, mountain ninebark, fernbush, cacti, wild plum, chokecherry, sand cherry, currants, hawthorn and elderberry.

         For rapid-growing insectary strips in veggie gardens, plant long-blooming annuals like bachelor’s buttons, marigold, cosmos, sweet alyssum, and Rocky Mt. Beeplant. And many garden perennials and biennials support beneficial insects: Basket of Gold, Butterfly Weed, Callirhoe-Wine Cups, Veronicas, Ajugas, Sea Lavender, Rudbeckia, Golden Marguerite, mountain mint, moon carrot, creeping thymes and asters.

         And remember: the predators and parasitoids won’t appear before the pests, so once you see pests, give the beneficials a chance to come and feed, before interfering. If you spray a non-poisonous control like horticultural oil or insecticidal soap to reduce a serious infestation, always leave 10% or so of the pests for food for the beneficials. And don’t clean up too clean in the fall. The beneficial insects need some shelter from the winter, and use dead stems and leaf litter to live over or lay their eggs. And in our hot, dry summers, put out shallow dishes of water. The toads will love you too. Mother Nature is pretty smart, so practice patience and support the good guys. Get the Buzz with your Beauty.

“If humans went extinct tomorrow, nothing too much would happen to the planet, but insect extinction could be cataclysmic.” National Geographic

Resources: Habitat Planning for Beneficial Insects—Xerces Society

Permaculture Research Institute—Insectary Plants

Biological Control Site: Natural Enemies in N. America—Cornell U

Insectary Plant list—Butterfly Pavillion: ayarger@butterflies.org

Enhansing Beneficial Insects with Native Plants—Michigan U