I don't know much about drosophila, but here is some advice from my experience with co-IPs of calcium dependent proteins:

If you are looking for an interaction that you don't know much about (ie, does the interaction take place in the presence or absence of calcium, etc), then you want to try conditions that have calcium or are calcium-free (preferably with a calcium chelator to further reduce free calcium from your buffers). The detergent is also important--increased concentration or harsh detergents will reduce the chance of seeing the interaction, but too little will lead to problems with nonspecific binding. I usually start with a couple of different detergent condtions (maybe 0.2 and 1% DDM and 1% digitonin). And of course physiological salt and pH. Then modify the conditions based on the results (especially if you have a positive control interaction to test for). Good luck!