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Philosophy on the Biological Control of Insect Pests¹

ABSTRACT

Biological control may be defined as the balance between a species and biological stress factors that limit its potential population. Four major divisions are usually recognized in biological control research programs: (i) parasites and predators; (ii) insect pathology; (iii) radiation and genetics; (iv) host-plant resistance.

Introducing parasites and predators to combat introduced insect pests was vigorously pursued during the early 20th century. Again in recent years this facet of biological control research has received increased emphasis. Successful establishment of many introduced parasitic species has been recorded. Components of biological control agents usually lag in effect when host populations suddenly increase. Each species has its own realm of environmental requirements for optimum survival.

Pathogenic viruses, bacteria, fungi, protozoa, and nematodes may reduce insect outbreaks rapidly under favorable temperature and moisture conditions. Examples include: (i) polyhedral viruses present in many species of Lepidoptera; (ii) milky disease bacteria in the Japanese beetle, and Bacillus thuringiensis in the European corn borer; (iii) fungi of the genera Empusa or Entomophthora, Beauveria, and Metarrhizium in many orders and a wide range of species; (iv) protozoa of the genera Nosema and Perezia in a wide range of hosts. Artificial dissemination has been successful for milky disease against the Japanese beetle and B. thuringiensis against the European corn borer. Male sterility induced genetically or by radiation is a promising approach to insect population control.

Cooperative research programs have yielded significant varietal resistance to several insect species in economically important field crops such as wheat, maize, sorghum, and alfalfa.

Key Words: entomophagus insects • insect pathology • host-plant resistance

¹ Paper presented Aug. 19, 1971, in New York City at the annual meeting of the ASA as part of the symposium "Breeding for Host-Plant Resistance to Insect Pests."

² USDA, Retired Consultant on Insects and Diseases, Dep. of Plant Breeding, Pioneer Hi-Bred International, Inc., Johnston, Iowa 50131.

Received for publication December 12, 1971.