The integration of chemical and biological control of the spotted alfalfa aphid: Field experiments on the effects of insecticides

Chemical and biological control are regarded as two main methods of suppressing insects and spider mites. These two methods are often thought of as alternatives in pest control. This is not necessarily so, for with adequate knowledge they can be made to augment one another.

Biological control is part of the permanent natural control of population density. Chemical controls involve only immediate and temporary decimation of localized populations and do not contribute to natural control. Natural control may keep a pest species from ever reaching the economic-injury level or it may permit economic outbreaks. The frequency of these pest outbreaks varies from a regular to an occasional occurrence depending upon the level of the general equilibrium position in relation to the economic injury level and the types of fluctuations about the general equilibrium position.

Integrated control combines and integrates biological and chemical controls. Chemical control is used as necessary and in a manner which is least disruptive to biological control. Integrated control may make use of naturally occurring biological control as well as modified or introduced biological control. Thought must be given to the biological control of not only the primary pest under consideration but also other potential pests.

Integrated control is most successful when sound economic thresholds have been established, rapid sampling methods have been devised, and selective insecticides are available. In some situations, the development of integrated control requires the augmentation of biological control through the introduction of additional natural enemies or modification of the environment.

Integrated control of the spotted alfalfa aphid has been achieved in California. Economic thresholds were established so that insecticides are applied only when damage is imminent. Native predators, introduced parasites, and entomogenous fungi now keep the spotted-alfalfa-aphid populations below the economic threshold for most of the year. When population counts in the individual field clearly demonstrate that a field is threatened, Systox is applied at low dosages. These chemical treatments give adequate control, but do not necessarily eradicate the aphids. Most of the predators and parasites survive and persist on the remaining aphids.