Beneficial insects are those that consume or parasitize insect pests.
They include wasps, flies, beetles, true bugs, thrips (who knew!), spiders and mites. The good news is that that they are already active in the landscapes you manage, helping to keep pest species in check. But there is more that designers and landscape managers can do to make landscapes more welcoming for these hard working pest managers.
A study by John Losey and Mace Vaughn in 2006 estimates that the pest control services provided to agriculture by beneficial insects is worth roughly 13.60 billion dollars annually. They focused on agricultural crops because they could easily assign a dollar value to crop loses caused by pests. If you consider the additional services that beneficial insects provide in natural areas and managed landscapes, the figure would be much higher.
Diverse landscapes that incorporate a variety of flowering plants with native and non-native trees and shrubs of varying sizes (tall trees, understory trees, shrubs, and ground covers) are less likely to have major pest problems than simpler landscapes comprised of a limited selection of plants and few species, such as a traditional suburban lawn with a handful of conifers or deciduous trees. Variety in the size of plants creates microclimates that offer beneficial insects protection from harsh weather and predation by other insects or birds. Researchers from the University of Maryland conducted a study in 2006 that examined controlling azalea lace bug without the use of pesticides. They found that landscapes comprised of different species of plants and a variety of sizes had vastly lower lace bug populations than simple landscapes containing few species with little variation in the size of plants. The main difference was that the diverse landscape had more natural enemies to keep the lace bug population in balance.
Flowering plants provide pollen and nectar that many species of beneficial insects require in addition to their preferred prey species. Try to select flowering plants so that something is in bloom from as early in spring to as late in fall as possible. Remember that simple flowers provide better floral resources than double flowers because double flowers typically replace reproductive structures with petals that do not offer pollen and nectar. Some flowering plants especially attractive to beneficials include:
- Dill (Anethum graveolens) – Annual
- Coriander (Coriandrum sativum) – Annual
- Fennel (Foeniculum vulgare) – Perennial
- Blanket Flower (Gaillardia spp.) – Annual/Perennial
- Coneflower (Echinacea purpurea) – Perennial
- Tickseed (Coreopsis spp.) – Perennial
- Goldenrod (Solidago spp.) – Perennial
- Sunflower (Helianthus spp.) – Annual/Perennial
- Yarrow (Achillea spp.) – Perennial
- Clustered Mountain Mint (Pycnanthemum muticum) – Perennial
- Basket-of-Gold (Aurinia saxatilis) – Perennial
- Sweet Alyssum (Lobularia maritima) – Annual
- Milkweed (Asclepias spp.) – Perennial
- Joe-pye Weed (Eutrochium spp.) – Perennial
- Golden Alexanders (Zizia aurea) – Perennial
- Hairy Beardtongue (Penstemon hirsutus) – Perennial
- Anise Hyssop (Agastache foeniculum) – Perennial
- Cosmos (Cosmos bipinnatus) – Annual
When pest problems do arise that are not being managed sufficiently by beneficials, it is important to choose products that target the pest without killing the good guys as much as possible. Products such as B.t. kurstaki target caterpillars without impact on other species. Soaps and oils might take out beneficial insects present when the application is made without harming those that come in after the sprays dry. Many botanical insecticides break down quickly on exposure to sunlight, which limits how long they are harmful to beneficials.
Fertilize landscape plants based on soil testing rather than guessing. Plants that receive too much high nitrogen fertilizer are more susceptible to pest outbreaks. Since nitrogen can be a limiting factor in insect reproduction, over-fertilized plants are more nutritious for pests and result in higher rates of reproduction.
The next point may be a tougher sell to your customers: try not to clean up fallen beneficial insects. Perhaps you can shred those leaves up into mulch for landscape beds, which benefits the plants as well as the beneficials.
1. Losely, J. and M. Vaughn, 2006. The Economic Value of Ecological Services Provided by Insects. BioScience (2006) 56 (4) 311-323.
2. Shrewsbury, P.M., and M.J. Raupp. 2006. Do top-down or bottom-up forces determine Stephanitis pyrioides abundance in urban landscapes? Ecological Applications, 16(1): 262-272.
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