The influence of colony density , temperature and 1 illumination intensity on the aggregation of fire ant , 2 Solenopsis invicta 3

Aggregation plays a basic role in the organization of social insects, and many factors 20 including environment and individual interaction can influence this behavior. In this study, we 21 investigate the influence of changes in individual density, temperature and illumination intensity 22 on the aggregation time of Solenopsis invicta. Population density has no influence on the 23 aggregation time until it reached 1.5 individuals/cm 2 . Additional results also showed that 24 temperature has negative effect on the aggregation time of fire ant. Along with the fall of 25 temperature, the speed of aggregation increased rapidly. Fire ant required 96.5min to get robust 26 aggregation under strong light intensity (1200lux); which was faster than under low light 27 conditions (10lux). These results revealed that fire ant can shift their cluster behavior under 28 changing environmental conditions. 29