The helical wall-free microorganism, Spiroplasma citri, which is associated with citrus stubborn, a disease with no known vector, multiplied in the leafhopper vector of corn stunt but multiplied to higher titer in the vector of aster yellows and decreased the longevity of that insect. Acholeplasma laidlawii and A. granularum also multiplied in both leafhoppers.