How to Manage Pests

UC Pest Management Guidelines

When natural enemy populations are not present or are not high enough to reduce pests, they can sometimes be augmented with releases of commercially reared natural enemies. There are two types of augmentative releases: inoculative releases and inundative releases.

Inoculative releases are made when pest populations are low and relatively few natural enemies are released, usually just once or twice a season. The introduced predators or parasites reproduce, and it is their progeny, not the released individuals, that are expected to provide biological control. Releasing the mealybug destroyer lady beetle (Cryptolaemus montrouzieri) in the spring to control mealybugs is an example of inoculative release. The mealybug destroyer is effective in killing mealybug species that feed openly on foliage or stems, but it overwinters poorly outdoors in California and needs to be reintroduced to target areas in spring.

Inundative releases involve releasing large numbers of natural enemies often several times over a growing season. The released natural enemies are expected to provide biological control. Although they may reproduce, progeny of release individuals generally are not relied on for control. Periodically releasing Trichogramma species (parasitic wasps) to destroy moth eggs is an example of inundative biological control.

A good place to start with augmentation is in situations similar to those where researchers or other pest managers have previously demonstrated success. Guidelines for releasing natural enemies are given for many pests in the individual pest sections of this guideline. Desperate situations where pests are already abundant or damage is common are not a good opportunity for augmentation. Because pest presence is necessary to sustain natural enemies, choose crops where some levels of the target pests and their damage can be tolerated. Begin making releases early in the production cycle. Consider what other pests may occur in the crop and how they can be managed in ways that are compatible with biological control. Make other necessary changes in production practices, for example, by avoiding use of pesticides that harm natural enemies (Table 1).

Increase the likelihood that natural enemy releases will be effective by accurately identifying the pest and its life stages. Parasites and many predators attack only certain pest stages; release the beneficial species when the pest is in its vulnerable life stage or stages. The pest life stage that can be effectively controlled with natural enemies may be different from the pest stage that damages plants. For example, Trichogramma species kill only eggs of moths and butterflies; they are not effective against caterpillars. Trichogramma must be released when moths are laying eggs, before the caterpillars become abundant.

The quality of commercially available natural enemies is not regulated and may sometimes be poor because of production practices, inadequate packaging, or unsuitable conditions during shipping. Evaluate the quantity and quality of each shipment of natural enemies. If beneficials arrive in parasitized hosts, count parasite exit holes in a small sample immediately after parasites arrive. Keep the sample in a suitable place and recount and compare the number of emergence holes about 10 days after deploying the parasite. If natural enemies (typically predators) arrive in a shaker-type container, estimate their numbers and calibrate your application rate by making one shake over a sheet of white paper and counting the number of apparently alive or active natural enemies. Repeat this several times to estimate the average number of predators per shake. If predators or parasitized hosts arrive on leaves, use a hand lens or dissecting binocular microscope to examine the underside of several leaves and estimate the natural enemies per leaf. Contact the supplier immediately if natural enemy quality is unsatisfactory.

Remember that natural enemies are living organisms that require water, food, shelter, and suitable growing conditions. Natural enemies may be adversely affected by extreme conditions such as hot temperatures. Residues of certain pesticides can persist for weeks or months, harming natural enemies long after losing their effectiveness against pest species. Overhead irrigation may drown natural enemies. Many beneficial species stop reproducing under short day length or prolonged cool conditions. Supplemental light may be necessary for some predators and parasites to be effective year-round. Environmental conditions required by natural enemies (such as long days) may not be compatible with production needs of certain crops.

Many natural enemies are commercially available (Table 2) through mail order. A publication listing sources, Suppliers of Beneficial Organisms in North America, can be obtained from the Environmental Monitoring and Pest Management Branch of the California Department of Pesticide Regulation online at www.cdpr.ca.gov or as a printed publication by calling (916) 324-4100 or writing the Department of Pesticide Regulation, Environmental Monitoring and Pest Management Branch, 830 K St., Room 200, Sacramento, CA 95814.

PUBLICATION

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Insects and Mites
K. L. Robb, UC Cooperative Extension, San Diego Co.
H. S. Costa, Entomology, UC Riverside
J. A. Bethke, Entomology, UC Riverside
M. P. Parrella, Entomology, UC Davis
Acknowledgment for contributions to the insects and mites section:
R. S. Cowles, Connecticut Agricultural Experiment Station, Windsor, CT

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