The causative agents are fastidious phloem-restricted, Gram-negative bacteria in the gracilicutes clade. The Asian form, "Ca." L. asiaticus is heat tolerant. This means the greening symptoms can develop at temperatures up to 35 °C. The African form, "Ca." L. africanus, and American form, "Ca." L. americanus, are heat sensitive, thus symptoms only develop when the temperature is in the range 20–25 °C. Although "T. erytreae" is the natural vector of African citrus greening and "D. citri" is the natural vector of American and Asian citrus greening, either psyllid can in fact transmit either of the greening agents under experimental conditions.