Biological Control: Application of Natural Enemies
David Orr and James Baker
Department of Entomology, North Carolina State University
Increasingly, natural enemies of pests are being produced and sold as least toxic pest management tools. As the use of these products becomes more widespread, the need for an understanding of how to best use these products is becoming more acute.
If a decision has been made to use natural enemies to control pests, several considerations need to be made before proceeding. First, find a source of high quality natural enemies (see the publication "
Biological Control: Purchasing Natural Enemies"listed at the end of this article). Second, consideration should be made of how best to apply or release the natural enemies. A number of challenges and limitations are posed when biological control is incorporated into a pest management program. This publication gives tips on increasing the effectiveness of natural enemy applications. The failure of control is not unique to natural enemies.
The use of pesticides also involves challenges and limitations that can lead to product failure or poor performance. For example, it is important to match pesticides with target pests that they will kill, and that the target pest is not resistant to. Pesticides need to be applied at the correct rate. Compounds should be avoided that may affect growth/survival of plants and other non-target organisms (e.g. birds, fish, pets, people). Safety practices should also be carefully thought through since pesticides are poisons. Environmental conditions such as temperature, rainfall, and wind can all affect the quality and undesired effects of pesticide applications. Finally, it is important to make sure the pesticide actually gets to the target pest.
Biological control can be an effective, environmentally sound method of managing pests. However, when using natural enemies in your garden, farm, home, or interiorscape, identify the pest and natural enemies, estimate the population of pests and natural enemies, purchase the correct natural enemies, release them correctly, and monitor the effectiveness of the natural enemies.
Identify Pests and Natural Enemies
Accurate identification of pest problem is even more important with biological control than with insecticides, because natural enemies often will attack only specific types of pests. There are resources available to help you do this. The first is your County Extension Center. The second is the Plant Disease and Insect Clinic at North Carolina State University. Specimens can be sent to the clinic, and for a small fee they will be identified. The clinic address is: Plant Disease and Insect Clinic, 1104 Williams Hall, Box 7613, North Carolina State University, Raleigh, NC 27695; Phone: 919-515-3619.
Are Natural Enemy Releases Appropriate For Your Situation?
As with other pest management methods the success or failure of biological control can be determined by the population levels of pests at the time natural enemies are applied. For example, if a pest population is too high, the natural enemies you release may not be able to act quickly enough to protect your crop. In this case, a pesticide with a short residual life may need to be applied prior to the introduction of natural enemies. If, on the other hand you have a very small infestation in your plants, you may not have to do anything if naturally-occurring natural enemies are already present. Another approach to take in this case might be to spot treat (with pesticide) only infested areas, rather than spending the time and money to treat your entire crop/garden.
Usually, natural enemies work best as a preventative pest management method. That is, if they are introduced into your crop/garden before a pest infestation, they can prevent that population from developing to damaging levels. If you wait until pests have become a problem before releasing natural enemies, they usually will not work. Therefore pest problems must be anticipated and planned for by carefully monitoring for pest population development. There are well-established monitoring or sampling and record-keeping methods developed for a wide variety of pest and crop situations that. Information on these methods can be obtained from your supplier or County Extension agent.
Specific information on when to release natural enemies is provided in the section "Timing of Releases/Applications" of this bulletin.
Selection and Purchase of Natural Enemies
Once you have determined the specific pest problem you are faced with, and the appropriateness of using natural enemies, the next step should be selection of specific natural enemies and a supplier. Like purchasing any product, you as the consumer are responsible for determining the appropriate ones for your specific needs. Names, addresses, and telephone numbers of suppliers can be obtained from the sources listed at the end of this publication. When selecting a supplier, you should ask a number of questions to help you find the best supplier for your needs (see the publication "Biological Control: Purchasing Natural Enemies" listed at the end of this article). A competent supplier can provide you with information on which natural enemies you should use.
Handling of Natural Enemies After Arrival
Specific handling instructions should be provided prior to or at the time of arrival of your natural enemy shipment, and should be followed carefully. In general, it should be kept in mind that many natural enemies are tiny living insects and mites. They should be kept under relatively cool conditions (room temperature) and out of direct sunlight. If the material arrived in an insulated container, it should probably be kept there until you are ready to apply/release it. Usually, the sooner material can be applied after arrival, the better. For example, some predatory mites are shipped with a small food supply. Once that food supply is exhausted, they feed on one another or starve.
How Many Natural Enemies to Release
Here again, your supplier should provide detailed instructions regarding the "rate" that natural enemies should be applied at. Usually this is expressed as a number of natural enemies per a given "unit" such as: infested leaf; plant; square ft.; or acre. As with traditional pesticides, the recommended rate should be followed very closely. Any questions that may arise regarding application numbers can be directed to your supplier or County Extension Service agent.
Timing of Releases/Applications
Timing of natural enemy releases is critical to the success of biological control. Since natural enemies work better as a preventative rather than curative pest management method, it is important to release them when pest infestations are just beginning. Sampling methods and materials for specific pests are often readily available from suppliers (see Directory of Least Toxic Pest Control Products, listed at the end of this publication), but if they are not your County Extension agent can assist with the design of a sampling program.
Some natural enemies are affected by the time of year, and can be less effective as a result. The time of day can also be important, especially if the release is to be made outdoors or in a greenhouse. When the temperature is high during the middle of the day, natural enemies tend to be more active and may disperse or leave the area they were released in. Higher temperatures during the release can cause increased mortality of the enemies, reducing the number available to attack your pest problem. Other weather conditions, especially rain, may also have an impact on natural enemy survival during release. As a general rule, releases should be made in a cool part of the day (early or late), under favorable weather conditions, and at a time of year that the specific natural enemy finds favorable (your supplier can provide you with this information).
If you have selected a reliable and knowledgable supplier of natural enemies, then the quality of material you receive should be consistently high. However, there are some factors, such as shipping conditions, that are out of the suppliers control. Therefore, it may be helpful to work with your supplier to develop a quality assurance protocol since the condition of natural enemies you receive can have a dramatic effect on the results you obtain (see "Biological Control: Purchasing Natural Enemies" listed at the end of this publication).
Environmental Conditions in Area of Release
Like all living organisms, natural enemies have specific requirements and limits for life. The conditions present in the area you plan to release natural enemies in should be taken into consideration prior to making releases. For example, some species of predatory mites will do better under hot, dry conditions while still others will perform better under cooler high humidity conditions.
Lighting can also have a dramatic impact on natural enemies. For example, the mealybug destroyer beetle will slow or stop its reproduction, feeding and growth if supplemental lighting is not sufficient in winter months.
If releasing a mobile stage of a natural enemy (e.g. adults that can fly), it may sometimes be advisable to cage the natural enemies on infested plants for a day or two to allow them to become accustomed to their new surroundings. The presence of pest insects will also encourage reproduction, and reduce the likelihood that they will leave the area.
In some cases, the presence of nectar-bearing plants or other food sources (e.g. aphid honeydew) may also encourage natural enemy populations.
Pesticide use may be the most important consideration when including natural enemies in a pest management program. Spraying for pests other than those being targeted by natural enemy releases may interfere with or eliminate the natural enemies. Care should be taken to avoid spraying materials harmful to natural enemies directly before, during and after release. If spraying must be conducted, it is important to find out which pesticides have the least effect on natural enemies. Again, your supplier or CountyExtension agent can help you gather this information.
What Should be Done After the Release?
It is extremely important with natural enemies to make sure that sufficient numbers have been established following release in your crop to control a pest problem. The sampling program you establish for monitoring for your pest population(s) (see "Are Natural Enemy Releases Appropriate For Your Situation?" section in this article) can be modified to help you monitor natural enemy populations as well.
Information About Suppliers and Purchase of Natural Enemies
There are many companies that sell natural enemies, and several reference sources that provide general information about both the companies and natural enemies. Two reference sources are listed below:
Directory of Producers of Natural Enemies of Common Pests. Bio-Integral Resource Center, P.O. Box 7414, Berkeley, CA 94707. Annual. Cost: approximately $10.00
Biological Control Virtual Information Center
Members of the Association of Natural Bio-control Producers