Drosophila are annoying, so just put some small pieces of fruit (e.g. banana or apple) inside. 

Don't waste time with mixing any attractant (sugar/vinegar/wine etc. )- They are made to find rotten fruit so this is the best way to attract them. 

The big open area allow the scent to lure them with maximal efficiency and guide them to the center opening. But only 1% will find a way out again. 

For ∅ 55mm bottle (top cut away) but the script is customizable with parameter.

If your bottle doesn't has a ring notch - carefully heat the rim so it will curve a little inward so later the prints protrusion can clip in. (e.g hold close over a hot (~150°C) plate)

Print

• Use vase mode / spiral mode
• Bottom need to be 1.5mm so the fillet meet when the single wall starts

 The rim is reinforced (thicker) with a protrusion to clip into a bottle/glas notch.

You can also scale  this for bigger diameter. (if you scale to much the flies will escape through the bigger slits)

example:  for 64mm =  64/55 = 1.164 = scale 116.4%