U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



The U.S. Government Workers


Ann. Rev. Entomol. 1981. 26:49-73


Protozoa have been recognized as important factors in the natural regula­tion of the densities of certain insects. However, they have been given little consideration as applied microbial agents because entomophilic species cause chronic or debilitative infections in a narrow range of hosts. From a control standpoint, and ultimately from an economic standpoint, they could not compete with the more rapid, broad spectrum action of chemical insec­ticides or the more virulent pathogens such as bacteria, viruses, and certain fungi. Protozoa appeared useful only when low levels of pests could be tolerated, as in forests.

Gradually, interest in protozoa as potential biological control agents has been increasing (98). Primarily, this is a result of pest management concepts that emphasize conservation and augmentation of existing natural control agents. This has been demonstrated by an increase in published research reports on applied use of protozoan microbial agents, along with some excellent reviews of certain aspects of protozoa (8, 9, 77, 78, 98). The body of literature dealing with natural and applied control by protozoa now is so extensive that no single review can provide a fully comprehensive treat­ment of the subject. Since the review by McLaughlin (77) provided a fairly complete assessment of the subject prior to 1970 it seems appropriate that it should serve as a starting point for this review in order to demonstrate the progress over the past decade.

A comment is necessary on the systematics of this very diverse group. In several recent schemes the Microsporida were given phylum rank as Micros­pora, thereby removing this group from Protozoa (36, 97). Although there are basic differences between the Protozoa and Microspora, many research­ ers use the traditional nomenclature of Microsporida or Microsporidia; for the purpose of continuity with prior reviews, microsporidia will be treated here as part of the Protozoa.