Biopesticide Information > Section 3: Successfully Using Biopesticides

Biopesticides need not be reserved for organic crop production. Biopesticides can be particularly effective when incorporated into integrated pest and disease management programs and when used in conjunction with conventional pesticides. Biopesticide products typically have no pre-harvest intervals and very short reentry intervals, which permits a crop to be harvested immediately after the biopesticide is sprayed. This is particularly important in export crops that are shipped globally and are subject to international maximum residue levels.

Biopesticides can be used successfully:

• to manage for pesticide resistance;
• in rotations with other products, as a stand-alone and in tank mixes;
• early in the growing season when pest pressure is low;
• late in the season when a short preharvest interval is needed;
• during critical field events such as multiple harvests;
• to manage or eliminate pesticide residue;
• and to reduce labor costs when it is important to have a short reentry interval.

The use of biopesticides can be an effective tool in managing for pesticide resistance. According to Extension recommendations for orchards in the Pacific Northwest, pesticide resistance management will extend the useful life of valuable IPM-compatible pesticides. In order for resistance management to be successful, orchardists and others need to:

• routinely monitor pests;
• use reasonable treatment thresholds; and
• make full use of nonpesticidal methods, such as biological and cultural control, sanitation and host plant resistance.

For well-developed IPM systems, like those used in Pacific Northwest tree fruit production, resistance management programs are key. The lack of registration of new pesticides, coupled with a loss of registered pesticides to the regulatory process or to resistance, will leave growers with few or no registered products that adequately control key pests. With good IPM practices, the efficacy of key pesticides can be prolonged considerably and, in some cases, maintained indefinitely.

Biopesticides can be used as a management tool in rotations with other products to reduce pesticide resistance. Biopesticides contain multiple modes of action which makes them well-suited for rotation in pest management programs to help prolong the efficacy of conventional pesticides.

Biopesticides help with resistance management in two ways. When a biological is substituted for a conventional pesticide, the cycle of repeated applications that leads to pest and disease resistant populations is broken. This, then, extends the efficacy and lifespan of the most critical synthetic materials. Also, because of the complex chemical nature of biopesticides, it is difficult for pests and diseases to easily mutate and build resistance to biopesticidal compounds.

Rotating biopesticides with conventional pesticides has been termed "absolutely critical" in the fresh-market vegetable industry in California . Using biopesticides on a regular basis to break the cycle of using harder chemicals and to prevent resistance development is highly recommended.

The most widely used biopesticides for resistance management are Bacillus thuringiensis or Bt -based products. There are thousands of strains of Bt, many of which have been used to manufacture microbial insecticides.

Bt is a naturally occurring bacterium, discovered nearly 100 years ago, that is found throughout most regions of the world. It occurs naturally in soil and in other common environmental habitats where insects are found. It has pesticidal properties when consumed by the larvae of specific insects.

The primary toxic component of Bt is a crystalline protein (toxin). Bt must be eaten by the insect larvae to cause mortality. Bt has no effect on adult insects. When ingested, the Bt toxins dissolve in the insect gut and become active in the presence of highly alkaline conditions. The toxins then attack the lining of the insect gut, rupturing the cell walls and allowing the gut's contents to spill into the insect's circulatory system. After ingestion of a lethal dose of Bt, the insect stops feeding and plant damage is halted. Death of the insect follows within three or four days. If larvae survive the toxin, they may be more susceptible to other environmental stresses, such as cold temperatures or low levels of biopesticides.

C.	D.
Bt bacteria	Bt mode of action ruptures gut cell lining
E.	F.
Pest starved by exposure to Bt	A graphic from http://www.bt.ucsd.edu/how_bt_work.html demonstrates how Bt toxin is ingested by an insect then binds to specific gut receptors, breaking down the gut wall and allowing bacteria to enter the body, causing death.s

Certain strains of Bt affect members of three insect Orders: Lepidoptera (butterflies and moths), Diptera (mosquitoes and biting flies), and Coleoptera (beetles). Commercially available, EPA-registered Bt products include:

B.t. aizawai (Lepidoptera) - used for wax moth larvae in honeycombs and for diamondback moth caterpillars.

B.t. israelensis (Diptera) - frequently used for mosquitoes and blackflies.

B.t. kurstaki (Lepidoptera) - frequently used for gypsy moth, spruce budworm, and many vegetable pests such as diamondback moth and cabbage looper. It is also used for fruit pests such as leafrollers on apples and peach twig borer.

B.t. tenebrionis (Coleoptera) - used for elm leaf beetle, Colorado potato beetle

B.t. kurstaki is the most commonly used Bt formulation, as it will kill many leaf-feeding larvae on vegetables, shrubs, fruit trees and conifers.

To effectively use Bt microbial insecticides, consider the following:

• T iming of application is critical. Make the initial Bt application immediately before or just after egg hatch while the larvae are still small. Monitor plants for worm eggs and use pheromone traps to determine when adult moths are in the area and when egg laying is likely to occur.

• The larvae must eat Bt -treated foliage. Therefore, good spray coverage of the plant is essential for satisfactory control. Use adequate spray volume and pressure. Small droplet size is best; too much water dilutes the active ingredients (protein crystals and spores) and reduces efficacy.

• Properly identify the target insect species and select the Bt strain with activity against that insect. The product label will indicate the Bt strain contained in the product, and will list pest insects controlled.

• Bt products offer an effective alternative to conventional insecticides for control of certain pest insect species. It is also useful to alternate or tank mix Bt s with conventional insecticides to delay the development of insect resistance to any one material. For example, tank mix Bt with chemical pesticides to control tomato fruitworm.

• Bt activity is affected by environmental factors including temperature, rainfall, pH, and sunlight. Bt applied to leaf surfaces, for example, can be degraded by solar UV or washed off by irrigation or rainfall.

• Bt is considered to be "practically nontoxic" to humans and other vertebrates. It has been extensively used for many decades in biopesticidal formulations because of its safe environmental and human health records.

Like any other pest control method, Bt works best as part of an integrated management plan. The goal of an IPM plan is to reduce pests to acceptable levels, not to eliminate them completely. Bt has become a cornerstone of IPM programs, accounting for more than 90 percent of the biological insecticides currently used. Though Bt has been used successfully alone, the practice of IPM generally incorporates Bt with the following control methods:

Cultural: Crop rotation; minimum tillage; shelter strips

Mechanical: Removal of pest (eggs and larvae); removal of infested materials

Biological: Parasitoids; pathogens, including Bt , fungi, granulosis virus and nucleopolyhedrosis virus; predators

Biochemical and Chemical: Botanical insecticides such as neem and pyrethrins; pheromone baiting/mating disruption; and pyrethroids, spinosads and other chemicals.

Effective IPM programs frequently incorporate the use of pheromones as a method of insect control. Pheromones are chemicals emitted by living organisms used to send messages to individuals - usually of the opposite sex - of the same species. Pheromones of hundreds of insect species have been chemically elucidated, including the sex pheromone of the codling moth.

When used in combination with traps, sex pheromones can be used to determine what insect pests are present in a crop and what plant protection measures or further actions might be necessary to assure minimal crop damage. If the synthetic attractant is exceptionally effective and the population level is very low, some control can be achieved with pheromone traps or with the "attract and kill" technique.

Generally, however, mating disruption is more effective. Synthetic pheromone that is identical to the natural version is released from numerous sources placed throughout the crop to be protected. The male moths are then unable to locate the females and the number of matings and offspring are reduced.

Mating disruption has been successful in controlling a number of insect pests. More than 20 percent of the grape growers in Germany and Switzerland use this technique and produce wine without using insecticides. In the United States, mating disruption has proven effective in codling moth, navel orangeworm, pink bollworm, Oriental fruit moth, European grape moth, and grapevine moth, to name a few. More than 40 percent of the fruit tree acres in the western U.S. are treated with mating disruption for caterpillar control.