By Fred Birdsall, Colorado Master GardenerSM, and Carl Wilson, horticulturist, Colorado State University Cooperative Extension
Just as human babies eat different food from adults, the same is true with many beneficial insects.
Adult lacewings, flower (syrphid) flies and parasitic wasps, for example, feed on flower nectar and pollen. Their young devour some of the insect pests that can make a gardener's life miserable. Maintaining this workforce, however, means providing food for both.
Research shows that ample flowers not only sustain adult beneficial insects, but also allow longer survival and production of more progeny, thus increasing the biological control of undesirable insects.
Most insects go through four very different life stages: egg, larva, pupa and adult.
Only the larval and adult forms are active feeders.
The larvae of lacewings (above), called aphid lions, use hooked jaws to pierce and kill aphids. Flower fly larvae (below) look like maggots as they crawl over foliage, feeding on dozens of soft-bodied insects.
Predatory pirate bugs are a little different in that the larval stage is a miniature version of the adult insect and both eat the same food: spider mites, thrips and insect eggs. Only one-eighth of an inch long when mature, predatory pirate bugs are one of the most important controls of these undesirable insects.
What flowers are most often used to sustain adult beneficial insects? To answer this question, Whitney Cranshaw, Colorado State University entomologist, surveyed Front Range flower collections, including the Denver Botanic Gardens. The accompanying list shows flowers that are most visited and relied on as nectar or pollen food sources.
Including early blooming flowers such as Basket of Gold (Aurinia saxatilis) followed by midseason bloomers such as English lavender (Lavandula augustifolia) and late blooming goldenrod (Solidago virgaurea) you'll have a season-long food source for beneficial insects.
If you don't provide food for adult beneficials, it's likely they won't inhabit the garden and you'll inherit their work. Plant a wide range of plants that bloom throughout the growing season to gain the benefits of natural insect control in your garden. Note that this approach must include minimal pesticide use or at least use of pesticides "friendly" to beneficials.
Flowers used by beneficial insects:
Basket of Gold Aurinia saxatilis
Rocky Mountain penstemon Penstemon strictus
Native potentilla Potentilla verna
Creeping thyme Thymus serpyllum
Sweet alyssum Lobularia maritima
Columbine Aquilegia x hybrida
Carpet bugleweed Ajuga reptans
Common yarrow Achillea filipendulina `Coronation Gold'
Dwarf alpine aster Aster alpinus
Spike speedwell Veronica spicata
Wine cups (Poppy mallow) Callirhoe involucrata
Cilantro (Coriander) Coriandrum sativum
English lavender Lavandula angustifolia
Sulfur cinquefoil Potentilla recta `Warrenii'
Edging Lobelia Lobelia erinus
Mint Mentha sp.
Stonecrop (various) Sedum sp.
Fernleaf yarrow Achillea millefolium
Lavender globe lily Allium tanguticum
Dill Anethum geraveolens
Dyer's camomille Anthemis tinctoria
Fennel Foeniculum vulgare
Sea lavender Limonium latifolium
Wild bergamot Monarda fistulosa
European goldenrod Solidago virgaurea
The Denver Botanic Gardens has taken an active approach to natural pest control. They have released a number of beneficial insects into the newly re-opened conservatory in an attempt to control many different types of pests including aphids, spider mites, whitefly, mealybugs and thrips. The beneficial insects released include lacewings (Chrysoperia rufilahris), the "Mealybug Destroyer" (Cryptolaemus montrouzierei), and several types of parasitic wasps including Aphidius colemani. The "Mealybug Destroyer", a beetle native to Australia, has now established itself in the conservatory and is doing an excellent job of controlling the mealybug population.
To learn more about beneficial insects, request CSU Fact Sheets, "'beneficial insects in the yard and garden--5.550" and "Friendly pesticides for home gardens--2.945" from any county office of Colorado State University Cooperative Extension.
Photos: Judy Sedbrook, CSU, Agriculture Western Australia
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010