BACTERIA, SPIROCHETES, AND RICKETTSIA AS INSECTICIDES

Most bacteria pathogenic to insects are classified in the families Pseudomonadaceae, Enterobacteriaceae, Lactobacillaceae, Micrococcaceae, and Bacilliaceae; spirochetes and rickettsia are in the families Spirochaetaceae and Rickettsiaceae, respectively. Except for Bacilliaceae, these families contain nonsporulating microorganisms. Most spore-forming bacteria pathogenic to insects belong to the family Bacilliaceae. The identification of microorganisms associated with insects is inadequate because of inaccurate descriptions. A comprehensive evaluation of bacterial classification and identification can be found on the sixth and seventh editions of Bergey’s Manual of Determinative Bacter i~ logy .~ ,~ However illogical the existing scheme may be, we feel strongly that it should be adhered to by the insect pathologist, and the use of generalized names without reference to the specific causative disease agent should not continue. The incorrect hypothesis among insect pathologists that insects harbor special microorganisms is probably the main cause of misnamed bacterial species. Often, microorganisms from diseased insects are named for the insect from which they are isolated and are incriminated as pathogens. This practice should be discouraged. The procedures outlined in Koch’s canons for demonstrating that a disease is caused by a microorganism are as follows: finding the specific microorganism in all cases of the disease; isolating it in “pure culture” (description of the pure culture isolate should be by established taxonomic procedures) ; inoculating (or feeding) the isolate into the host insect and experimentally producing the original disease; and finally, reisolating the microorganism from the experimentally diseased insect and demonstrating it to be the same as the pure culture isolate previously inoculated. In this communication, we shall, when possible, ignore unauthenticated bacterial species claimed to be insecticidal. Bucher7z9 classified bacterial insect pathogens as either obligate, facultative, or potential. We shall discuss, according to Bucher’s categorization, nonsporulating bacterial pathogens, including true bacteria, spirochetes, and rickettsiae and sporulating bacterial pathogens, including “crystalliferous” types.