I'm looking for a general (and easy, this is going to be for an undergrad class) protocol to isolate and culture primary cells from fruit flies.
This is the original 1972 paper describing the isolation of the S2 cells from Drosophila. However it would be best if you specify what application you are planning to pursue with the cells, which would make it easier to suggest which ones to isolate. I have personally isolated garland cells, which are visible with the naked eye and highly suitable for endocytic assays. It takes a few minutes to isolate them and all you need are two grade 5 or grade 4 sharp tweezers and 2nd or 3rd instar Drosophila larvae and a dish and some PBS to submerge the larvae in. You don't even need to pin them! If you are interested I can edit this response and write their isolation technique as I can't find a good technique online.
I have not personally isolated S2 cells although I have extensively worked with S2 and S2R+ cell lines (which are embryonic). Garland cells are excellent to work with for endocytic assays using Dextran (fluorescent dye used for bulk endocytosis assays) and Dynasore [dynamin inhibitor] (and infact they were used to characterise Drosophila dynamin homologue, shibire, here and here and its temperature sensitive behaviour in Shi[ts] mutants and shi role in endocytosis) as an example shown here in fig 6 using S2 cells. I have never cultured the garland primary cells so I do not know their PD and how they behave in Schneider+FBS (since I only isolated them and performed andocytic assays with them while they were in schneiders) and I don't think anyone has (but have a look) so it would be a great protocol to stablish and publish in a methods paper. I'm more than happy to share the isolation technique with you, tried looking on jove or youtube for a video but failed to find one, and let you know what to look for if you wish. Just as a cautionary note, garland cells are multi-nucleated (i have seen up to 4) so it might not divide very well or at all so just bear that in mind.