Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 1996
Publication Date: N/A
Interpretive Summary: Spiroplasmas (helical mollicutes) are universally associated with arthropods (especially insects) and cause diseases in plants and insects. We are trying to determine whether these organisms can be used as biological control agents against pest insects by (1) directly acting as disease-causing organisms, or (2) as delivery systems for toxins which will kill insects. For spiroplasmas to be used for biocontrol, a detailed knowledge of their biology and taxonomy will be required. In this study, with the help of a new time-saving technique that we developed, we determined the growth rates of 64 strains, representing all known taxonomic and ecological types, at 10 temperatures. The results led to a better understanding of the biology of microorganisms associated with insects, and will therefore lead to more rational development of biological control organisms. The results will be useful to microbiologist, ecologists, insect and plant pathologists, and workers in biological control and integrated pest management.
A new method was developed for determination of the doubling times of spiroplasmas. Sixty-four spiroplasma strains, representing 24 groups and 11 subgroups, were studied. Nine strains representing putative new groups were also included in the study. Doubling times at 5, 10, 15, 20, 25, 30, 32, 37, 41, and 43 degrees C were determined by observing the time required for diluted cultures to acidify the medium. The range of temperatures for spiroplasma growth was 5-41 degrees C. Of the 64 spiroplasmas tested, 23 had an optimum of 30 degrees C, 29 had an optimum of 32 degrees C, and 13 had an optimum of 37 degrees C. The fastest growing spiroplasma was the MQ-4 strain (group XI), with a doubling time at optimal temperature of 0.6 hours. The slowest was the Jamaican corn stunt strain B655 (subgroup I-3), with an optimal doubling time of 36.7 hours. The DW-1 Drosophila sex ratio spiroplasma (group II) also grew slowly (doubling time of 24.7 hr). Spiroplasma strain B31 (group IV) had the widest range (5-41 degrees C), while the DW-1 strain and some subgroup I-3 strains had the narrowest, growing only at 25 and 30 degrees C. Some spiroplasmas adapted and grew well at 41 degrees C, but none of those tested grew at 43 degrees C. The ability of spiroplasmas to withstand a wide range of temperatures may reflect the conditions to which they are exposed in nature, including the temperatures of the insect, tick, and/or plant hosts in which they are carried and the plant surfaces from which they may be acquired by arthropods.