Abstract: In order to reveal the interactions between lac insect Kerria yunnanensis and ant Crematogaster macaoensis, changes in individual body mass and survival of C. macaoensis in three treatments of feeding artificial diet, honeydew excreted by K. yunnanensis and no food (CK), and changes in the brood amount per female, body size, mortality and the duration of life cycle of K. yunnanensis in three treatments of C. macaoensis monopolizing honeydew, ants visiting freely and no ant visiting were tested in a lac plantation in Yayi, Mojiang, Yunnan, southwestern China, from April 2009 to October 2010. The results showed that the honeydew excreted by K. yunnanensis is a kind of high quality food resource like artificial diet, which could increase the body mass of C. macaoensis workers steadily ［the highest percentage of body mass gain was found in C. macaoensis fed by artificial diet (44.55%), followed by C. macaoensis fed by honeydew (25.81%), and then in C. macaoensis with no food supply (-4.13%) (F_{（2, 54）}=18.81; P＜0.01)］ , and improved the survival of workers ［the highest survival rate was found in C. macaoensis fed by artificial diet (85.78%), followed by C. macaoensis fed by honeydew (82.48%), and then in C. macaoensis with no food supply (78.74%) (F_{（2, 55）}=7.31; P＜0.01)］ . C. macaoensis monopolization of honeydew significantly increased the number of K. yunnanensis females ［the highest was under the condition of monopolization of honeydew (80.81%), followed by ants visiting freely (82.48%), and then no ant visiting (75.33%) (F_{（2, 143）}=54.08; P＜0.01)］, and the brood amount per female ［the highest (401.85) was under the condition of monopolization of honeydew (401.85), followed by ants visiting freely (395.73), and then no ant visiting (353.34) (F_{（2, 144）}=4.82; P＜0.01)］, while reduced the mortality of K. yunnanensis population ［the highest mortality (90.82%) was under the condition of no ant visiting, followed by ants visiting freely (89.78%), and then monopolization of honeydew (89.42%) (F_{（2, 146）}=3.45; P＜0.05)］. In the same time, the feeding of C. macaoensis on honeydew exerted metabolic stress on K. yunnanensis, resulting in smaller body size of females ［the largest one was under the condition of no ant visiting (14.90 mm²), followed by ants visiting freely (13.04 mm²), and then monopolization of honeydew (12.92 mm²) (F_{（2, 147）}=10.88; P＜0.01)］, and longer duration of life cycle ［the longest was under the condition of monopolization of honeydew (203.96 d), followed by no ant visiting (202.85 d), and then ants visiting freely (200.00 d) (F_{（2, 71）}=19.77; P＜0.01)］. These results suggest that the relationship between ant C. macaoensis and lac insect K. yunnanensis associated with honeydew is a factulative mutualism.

Key words: Crematogaster macaoensis, Kerria yunnanensis, interaction, food resources, mutualism