R help - May 2011 - time series comparison

Hi
 
I have 2 time series consisting of  sequence of data points measuring flies 
activity at time intervals of 20 min over a period of 24 hrs. One time series is
from control flies while the other is from flies treated with a drug. My 
question is to find out if the drug has a significant effect on fly activity. 
What is the appropriate R packages to compare the 2 time series?
Thank you for your help
Joseph
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