Questions and Answers for the Home Gardener

What is Biological  Control?

Tired of picking, squashing and spraying garden pests? Let someone else do the work!  Biological control is the use of a specially chosen living organism to control a specific pest.  This chosen organism might be a predator, parasite, or disease that will attack a harmful insect or weed.
Biological control is a form of manipulating nature to achieve a desired effect.  Biological pest control programs may range from choosing a pesticide that will be least harmful to beneficial insects, to raising and releasing one organism to have it attack another, almost like a "living insecticide".

What are the Advantages of Biological Pest Control?

Biological control methods can be used as part of a broad-based program to reduce the environmental, legal, and health hazards of chemicals in the garden.   In addition, biological control may be a less expensive alternative to certain insecticides.  Some biological control measures can actually prevent economic damage to plants.  Unlike
most insecticides, biological controls are often very specific against a particular pest.  People, animals or helpful insects may be completely unaffected or undisturbed by their use, and there is no impact on the environment and water quality and it is fun watching bugs do the work for you!

What are the Disadvantages?

Biological control takes a little more management and planning.  It can take patience and record keeping.  Successful use of biological control requires knowing the biology of the pest and its enemies.  Many natural enemies are also susceptible to pesticides, so using them successfully requires care.  In some cases, biological control may be more costly than pesticides, but the long-term  advantages often outweigh the cost. Most natural enemies attack only one type of insect, but this can also be an advantage.
 

What is a Beneficial Insect?

A beneficial insect used for biological control would be any insect that preys upon a harmful insect that could otherwise damage the garden. These commonly take the form of a predator insect which eats another. The eating may take place immediately, or the harmful insect may be paralyzed and eaten later, or it may even be consumed by the insect's offspring.  Examples are lacewing larvae that eat aphids, paper wasps that catch caterpillars and feed them to their young, and tiny parasitic wasps that sting and have offspring that eat the pest insect from within.

How can I protect the Beneficial Insects already in my garden?

The first step is to identify the common insects in the garden.   The identity of the insect reveals whether the insect is eating the plant, looking for an another insect to eat, just seeking shelter, or merely passing through.  If it is a harmful insect, one can estimate how much further damage it could cause and whether a chemical is needed. A small caterpillar will grow into a large one that will do a lot of eating. A large one may have already done most of its eating.  Some chemicals can also kill beneficial insects so they must be used wisely and only if needed.  Proper use includes, choosing the correct chemical, using it at the correct strength, at the correct time, and at the correct place.
When chemicals are necessary, there are often special ones that may kill the pest, and not harm the beneficial insect.   Killing all the insects present may allow the pest population to recover more quickly than the predator population.  Consequently, outbreaks of harmful insects sometimes occur following certain chemical treatments.

How can I identify an insect?

        Field guides and gardening reference books can be helpful. Gardeners should learn to identify beneficial insects in any life stage.  However, if you are uncertain, you may contact your County Cooperative Extension Center for help.   Trained and experienced agents and specialists should be able to assist.  Helpful online guides to insects (both pests and beneficials) found in North Carolina are located at the following addresses:
http://www.ces.ncsu.edu/depts/ent/notes/
http://www.cals.ncsu.edu/course/ent425/library/compendium/index.html
http://ipm.ncsu.edu/current_ipm/otimages.html
 

What are the safest sprays to use?

        The three most common compounds used that have the least harmful effects on beneficial insects contain B.t., horticultural oil, or insecticidal soap. They are all available as ingredients in different brand-name products.
* B.t. is an abbreviation for Bacillus thuringiensis, which is a bacterium that attacks only specific insects and makes them sick.  It will not harm the beneficial ones.  Be sure that the pest you wish to kill is listed on the label.  Because not all strains of this bacterium work on all pests.
* Horticultural oils are specially refined oils that can be sprayed on insects and kill the more susceptible pests, doing less harm to the beneficials.
* Insecticidal soaps are special formulations of soap (not the same as dishwashing detergent) that will only kill fragile pest insects (such as aphids) that it contacts.

Can I add beneficial insects to my garden?

Yes, but there is limited value in general and frequently an unnecessary expense.   Beneficial insects may be transported to your garden from nearby sites where they are found.  Some are also available for sale from supply houses.  When purchasing beneficial insects and predators, it is "buyer beware".  Due to the lack of regulation of this industry, the quality of material consumers receive varies widely among producers and suppliers.  Consumers should try to become well informed before choosing a supplier of beneficial insects.  More information about biocontrol and suppliers can be found at http://cipm.ncsu.edu/ent/biocontrol/.
Some commercially available beneficial insects may not be suited to this climate, may not be appropriate for release in a garden, or are very specific regarding which insects they attack.  For example, praying mantids are commonly sold as natural insect controls.  However, mantids ambush anything that passes in front of them that they can subdue (including beneficials).  In other words, they do not seek out insects such as caterpillars, aphids, thrips that are typically pests in our gardens. Mantids are of little use for effective pest control, but still retain their value as entertaining and watchable insects.
Ladybeetles, adults or larvae, can consume many aphids.  But when hundreds of them are collected into a container and released, they tend to fly away and disperse in order to avoid competing against each other for the same food.  Don't forget that there has to be a lot of food to support a lot of beneficial insects. So if your garden is not full of harmful insects, it won't support large numbers of beneficial ones.  It is best to strive for a balance of low levels of both harmful and good insects.

What else can I do?

Better options for home gardeners than purchasing beneficial insects are:

* Don't overlook handpicking and destroying insect pests.  In addition, some insects may respond to traps, baits, or sticky cards placed in or near the garden.
* Avoid over fertilization.  Too much nitrogen promotes vegetative growth and stimulates an increase in aphid and mite populations.
* Provide a diverse habitat.  Most natural enemies do better with a diversity of hosts or plants.  Annual or perennial flowering plants provide an alternative food source of pollen and nectar for many beneficial insects such as syrphid flies, robber flies, lady beetles and parasitoid wasps.  They can also provide shelter and humidity. Create a diverse landscape with different plants and different micro-habitats.
* Employ cultural practices.  Trap cropping may attract a pest away from the desired plant but toward a plant that is not important in the garden. Appropriately timed applications of pesticides may then be applied to the trap plant.
* Supplement the needs of the beneficial insects.  Similar to planting flowers for additional food, undisturbed natural areas either within or around the garden can provide nesting and over-wintering sites for beneficial insects such as lady beetles and parasites.

How do I start ?

1)  Develop a plan.  Biological, cultural, chemical, and mechanical controls can all be assembled into a pest management plan for the home garden.  First identify and inventory the pest(s) with which you are dealing.
2)  Determine if control measures are necessary.  (What are your priorities?  Are you interested in using less chemicals? Can you tolerate a few holes in leaves?  Do you want to spend less money?)  If you can identify your goals ahead of time, you will be able to evaluate your success later.
3)  Determine which beneficial insects would be helpful against your pests by working with an Extension agent or a supplier. Learn what you can expect from any of the parasites or predators you purchase. When should you release them? Will they fly away when you open the container, or be dead the next day? How much will they cost?
4)  Purchase and/or deploy the beneficial insect.
5)  After allowing enough time for beneficials to act, decide if a pesticide is still needed. If so, make the best choice from a bacterial (B.t.), insecticidal soap, horticultural oil, botanical chemical, or traditional insecticide.  Choose the lowest rate of application.
6)  Evaluate results. During the off season, decide if cultural practices, such as  planting dates, spacing, or sanitation could help you avoid the pest problem next year.
7)  Design habitat for beneficials and continue adjustments until the plan is successful.
Biological control takes motivation, patience, and knowledge, but the rewards can be great.

Sources of Additional Information

* Your local North Carolina Cooperative Extension office

* Biological Control Virtual Information Center (on the WWWeb)
http://cipm.ncsu.edu/ent/biocontrol/

* NCSU Extension Service Publications Biological Control: Purchasing Natural Enemies (AG 570-1), Biological Control: Application of Natural Enemies (AG 570-2) and AG 571

* List of Producers of Natural Enemies of common Pests.

*Some Suppliers of Beneficial Organisms

The Green Spot                                            Koppert USA
93 priest Rd.                                                 28465 Beverly Rd.
Nottingham, NH 03290-6204                       Romulus, MI  48174
(603) 942-8925                                            (734) 641-3763

       Recommendations for the use of chemicals or suppliers are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative
Extension Service agent.

Prepared by Stephen Bambara & David Orr, Extension Entomology, NCSU, 5/2000      last reviewed 6/6/2008
AG 570-3