I am doing Sf9 cell work now. I got the virus and I wanted to titer it. I did three times plaque assay already, but all three times I didnot get the "clear spot" as described in the mannual. Instead, I always get more cells accumulate together, more like colonies. I am sure that there is virus because from the small dilution: 10-1 and 10-2, I can almost see nothing , only a clear well, but when it comes to 10-3 diultion, I see a lot of white spots compare to the background, and under the microscopy there shows more cells also. I dont understand why. Anybody had experience?