EFFECTS OF TEMPERATURE AND VECTOR AGE ON TRANSMISSION OF 2 OHIO STRAINS OF ASTER YELLOWS PHYTOPLASMA BY THE ASTER LEAFHOPPER (HOMOPTERA, CICADELLIDAE)

Mean latent period and transmission rate of 2 strains (bolt and severe ) of aster yellows phytoplasma in nymph and adult aster leafhoppers, M acrosteles guadrilineatus Forbes, were studied under controlled condit ions at 15, 20, 25, and 30 degrees C. There was a nonlinear relationsh ip between mean latent period and temperature with shorter mean latent periods at higher temperatures (approximate to 20-25 d) than at lower temperatures (approximate to 40-80 d) for both aster yellows phytopla sma strains and both ages of leafhoppers. The proportion of leafhopper s that became vectors was significantly higher for bolt strain when le afhoppers acquired aster yellows phytoplasma as nymphs than as adults. However, there was no difference in the proportion that became vector s of the severe strain by the 2 age groups. Once leafhoppers became in oculative, the rate of transmission remained constant over their life spans when monitored by serial transfers at 48-h intervals. Increases in temperature and access time of leafhoppers increased the proportion of leafhoppers that became vectors after feeding on bolt strain-infec ted plants. Also, the effect of aster yellows phytoplasma exposure on life spans of leafhoppers was studied at 4 temperatures. At 25 and 30 degrees C, leafhoppers exposed to both aster yellows phytoplasma strai ns lived longer than those leafhoppers not exposed. Data can be used i n an aster yellows epidemiological model to evaluate strategies for as ter yellows management.