by Dr. Paula Kleintjes Neff
When people think of insects, they often think of them as pests. Little do they realize that many insects are our garden allies and provide numerous beneficial services free of charge. To the insect enthusiast, insects are priceless jewels, but according to recent research, the ecological services provided by native insects are estimated to be worth as much as $57 billion/year.
Insect ecological services include pollination, pest control (predation and parasitism), and dung burial (decomposition). Insects are also food for other animals, thus contributing to the recreational value of activities such as fishing and birdwatching. Unfortunately, the unaware gardener may spend more dollars trying to prevent or control insects with insecticides. This tends to provide a short-term fix ultimately resulting in more pests! Pest numbers can rise and resurge due to genetic resistance to insecticides and to the loss of natural enemies that normally keep them under control. Moreover, insecticide residuals are potentially toxic chemicals that harm beneficial insects and other wildlife as well as threaten human health.
According to the Environmental Protection Agency (EPA) Pesticide Market Estimate for 2007 (most recent data available), home and garden use of conventional insecticides constituted 15% (14 million lbs.) of total insecticide use in the United States. Garden herbicide use is even higher. The top three insecticide active ingredients were carbaryl, pyrethroids, and malathion. All are toxic to beneficial insects, including the now ubiquitous neonicotinoids, implicated in the rapid decline of native bees and the European honeybee. Use of insecticides in the home garden is unwarranted and unnecessary at such a small scale when non-toxic alternatives exist and the opportunity to grow and eat fresh food without chemicals is literally at your fingertips. You can easily create a diverse, attractive, and welcoming habitat for the very insects that provide beneficial ecological services by just doing what they do best.
To prevent pests, don’t use the archaic DDT-way of spraying insecticides but rather use the “DD3P way” of planting a Diversity of plants for attracting and supporting populations of insect Decomposers, Pollinators, Predators, and Parasitoids. By establishing a variety of herbs and flowers (from annuals to native perennials and blooming shrubs) within and adjacent to your gardens (whether vegetable, fruit, or landscape) you can serve up a rich mix of species that provide the nectar, pollen, and structure required for supporting healthy populations of beneficial insects all season long. Nectar provides energy-rich food for active pollinating and predatory adults, pollen provides protein, amino and fatty acids for reproduction and egg laying, and structure provides protection for resting and nesting sites. If you attract and support them, they will come and stay! As these insects go about their business, the natural enemies will assist with pest control, pollinators will facilitate and increase seed and fruit set, and decomposers will recycle nutrients back into the soil to conserve the ecological health of your garden. You can also enjoy the intricate beauty and behaviors that native insects bring to your garden. There are numerous resources available that provide suggested plant species mixes and methods for attracting and supporting beneficial insects. One of my favorites is www. xerces.org/pollinator-resource-center. Also, learn how to recognize the good from the bad bugs. Identification and monitoring of insects and then having the patience and tolerance to allow them to do their work in your garden are essential steps for natural pest management. Although natural enemies help keep a number of pests in check, they still need some prey to be present. If intolerable, this is when the fool-proof method of hand picking and crushing pests can be utilized.
Who are the primary beneficial players and what services do they provide? Pollinators are the animals that physically transfer pollen between flowers. Successful pollination will result in fertilization and therefore seed and fruit formation. As adult insects are attracted to flowers, they seek nectar and pollen for themselves and/or their larvae (e.g., solitary bees). Examples of effective pollinators include adult native bees including solitary bees and bumblebees, European honeybees, butterflies, moths, and a variety of flies and beetles. Utilize field guides and webs resources to recognize pollinators in your garden both as adults and larvae.
Insect predators are insects that kill and feed on other animals (prey) usually smaller than themselves (i.e., insect adults, larvae, or eggs). Common generalist insect predators found in a garden free of insecticides include the following: larval green lacewings, genus Chrysopa spp.; adult and larval damsel bugs, genus Nabis spp.; assassin bugs, family Reduviidae; bigeyed bugs, genus Geocoris spp.; minute pirate bugs, genus Orius spp.; soldier beetles, family Cantharidae; ground beetles, family Carabidae; and lady bird beetles, family Coccinellidae. Some species have dual roles depending on their lifecycle. As adults, species such as the green lacewings and the “bee mimic” hover flies, family Syrphidae, feed on nectar and/or pollen, but as larvae they are voracious predators of aphids, mealy bugs, other small insects, and insect eggs.
Insect parasitoids are insects that as adults feed on nectar and pollen but lay their eggs in or on an insect host (in the adult, larval, or egg stage) with the latter serving as “food” for the offspring. The host is killed in the process. Common wasp parasitoids are stingless and barely visible to the naked eye due to their minute size. For example many of the Chalcids are smaller than a pinhead and can be generalists or specific in their choice of hosts, such as the egg parasitoids in the genus Trichogramma spp. Larger parasitoids typically belong to the families Braconidae and Ichneumonidae and utilize a variety of hosts, including many caterpillar pests. The Tachinid flies are also well known parasitoids and their large hairy appearance can be easily mistaken for more pestiferous fly species. Numerous parasitoids work out of sight in a garden and, if left to their own devices, can help to keep pests in check. The same applies to pathogens (viruses, bacteria, and fungi) that can cause insect disease and death. Pathogens, such as Bacillus thuringiensis (Bt), naturally occur in the soil and can effectively spread in an insect population under favorable growing conditions.
Mulch, manure, and dead organisms slowly decompose over time with the aid of bacteria, fungi, earthworms, and soil-dwelling insects. Larvae of some flies, such as soldier flies and beetles such as the rove and dung beetles, can be beneficial for aerating soil and breaking down leaves, grass, and manure into compost so that plants can better utilize the basic elements. Healthy soil is essential for growing a dynamic and productive garden. By protecting soil from chemical pesticides or fertilizers, excessive tilling, or compaction, you can also gain the most benefit from insects and other invertebrates assisting with the decomposition of organic matter. Mulch and green manures such as clover, can also provide valuable nectar and shelter for beneficial insects and at the same time suppress weeds.
Again, think DD3P—Diversity of insect Decomposers, Pollinators, Predators, and Parasitoids—as the key ingredients to growing a healthy and beautiful garden. Don’t use insecticides and strive to maintain floral and structural diversity all season long.
A few resources for attracting and conserving pollinators and natural enemies to your garden include The Xerces Society for Invertebrate Conservation (www. xerces.org), www.organicgardening.com, www.finegardening.com, pollinators.beavercreekreserve.org, www.pesticide.org/solutions/home-and-garden-toolbox, and university extension offices and websites. Losey, J. and M. Vaughn. 2006. “The economic value of the ecological services of insect.” Bioscience, v.56.
Dr. Paula Kleintjes Neff is a professor of conservation biology and entomology in the Department of Biology at the University of Wisconsin–Eau Claire.