Greenhouse Project > Natural Enemies for Suppression of Greenhouse Pests
I. How to Use Living Organisms for Pest Control

When insecticides are used to suppress insects, they often are used in a curative manner. Used in this way, nothing is done until insect numbers become high, at which time a pesticide is applied. Insecticides are capable of quickly suppressing high pest numbers, in many cases. Fungicides, for control of plant diseases, are not used in the same way. They are used in a preventative manner because the fungal pathogen, once inside the plant, cannot be killed. Fungicides act by preventing infection, and hence must be applied before disease develops to high levels.

Biocontrol agents differ from insecticides in that they must be used in a preventative manner, rather like the way we use fungicides. For example, whiteflies on poinsettias are easier to control if wasp releases are begun very early in the crop, at a time when whitefly numbers are low and do not yet present a damaging problem. Wasp releases are unlikely to work if growers wait until numbers are high before starting to release wasp.

Compatibility with Pesticides
Natural enemies are living organisms that can be killed by pesticides. Many natural enemies will fail if growers also make pesticide applications to the same set of plants before, during, or after natural enemies releases. In general, insecticide use is incompatible with the use of all types of predators and parasites, but ok with nematodes, whereas fungicides are incompatible with the use of insect-killing fungi (Table 1). More precise information is available on the compatibilities of particular products and natural enemy agents.

Product Quality
Because biological control agents are living organisms, they must be handled and stored more carefully than pesticides to keep them alive and able to be effective when applied. The following are some steps growers can take to increase the quality of the biocontrol agents they use.

Fast shipment. Be sure you are receiving your agents from your supplier quickly (2-4 days), and that the material is kept cool during shipment (ice pack in carton when you get it?). Check you shipment when you get it to see if the material is alive on receipt. If you have problems, call your shipper and ask them to change shipping procedures. Keep at it until it works.

Proper storage. After you have received your biocontrol agents you must kept them under favorable physical conditions until they are used. Some agents cannot be stored and should be used immediately. Others can be stored for days, weeks or months, depending on the product:

1. Parasites and predators. Use immediately in most cases. If these must be stored, hold them at 55-60 F and high (70-90%) relative humidity. Do not refrigerate, as temperatures in refrigerators (35-45 F) will injure these agents. Do not hold in warm places (70-90 F), as the organisms will emerge and may die if not provided with water and food. One of the common sources of mortality in storage is desiccation. This can easily be avoided by placing the container of natural enemies in a plastic bag along with a wet sponge, and closing up the bag.

2. Nematodes. These can be stored for up to 10 weeks, but need to be kept refrigerated and humid. Store at 40 F; overpack containers in plastic bags with a wet sponge to maintain moisture.

3. Bacillus thuringiensis. This material is very stable and can be stored like an insecticide. Refrigeration is not needed, but it is best (as with chemicals) to avoid high temperatures (over 90 F).

Right species. Natural enemies differ one from another in very important ways. To use them successfully, you first must have a recommendation from a reliable source that a certain species is able to provide control of your pest in your crop. Second you must be sure that the supplier is selling you the species you want, not merely a related species.

Verification Upon Receipt
If is important that you verify that you are receiving what you order and that it is healthy. You should verify the number received by counting a small sample of the product and multiplying as needed to calculate the number per package. If you are not receiving full measure, contact your supplier for compensation or change suppliers. Your should verify quality by observing the agents to see that they are moving about. For some agents, like whitefly parasitoids, you can count the number that emerged after release by retrieving the release cards and determining the proportion bearing the right type of holes to show that a wasp emerged.

Release Number and Pattern
Biological control has worked best in systems in which the use pattern and release rate have been scientifically evaluated by an impartial scientist, not employed by the producer of the biocontrol agents. Testimonials are not reliable. Ask about the basis for recommended rates supplied by producers.

Prepared by:
Roy Van Driesche and Mark Hoddle
Greenhouse IPM Program
University of Massachusetts
Amherst
August 1995

Selected IPM Articles
2001 Annual Report
IPM Scouting and Decision Making
Western Flower Thrips: Biology And Control
Fungus Gnats and Shore Flies
A Grower's Guide to Using Biological Control for Silverleaf Whitefly on Poinsettias in the N.E. United States
Pointsettia - IPM Guidelines
Pest Management for Herbs
Pest Management for Vegetable Bedding Plants
Botrytis Blight of Greenhouse Crops
Managing Weeds in Your Greenhouse
Natural Enemies for Greenhouse Pests
Part I: How to Use Living Organisms for Pest Control
Part II: Parasites and Predators
Part III: Selection and Buying of Natural Enemies Species