I ran 10 traps a day for 7 years when living in Africa....and have experienced several weeks trapping in South and Central America...and over all that time I experimented with different baits...some of you may like to consider the following points to the recipes. Everyone has their own favourite recipes...this is what I came up with.
All sorts of evil potions including rotting meat, faeces, urine etc have been used...but they are really unpleasant and could make you ill....so be careful. The best and easiest all round bait in my opinion is to get some rotten bananas. ...put them in a bucket with a loose fitting lid...add a teaspoon of sugar and a teaspoon of bakers yeast. Keep at around 70f/20C and in 24 hours you will get a foaming mass of the best bait possible.
Return bait to bucket each night and stir it up...and change bait every week. You can add beer if you want...but I found it better to drink it when putting the traps up! It's just not really worth it. Do be careful on the amount of sugar you use...the butterflies are after the alcohol and not the sugar...too much sugar produces a jam...which prevents alcohol being produced...it is great for attracting wasps and bees though!
Filling any bait container to the top with bananas...adding sugar and yeast will cause it to overflow as it ferments...so do be careful. I have used yeast in the past...but in the end I found natural banana fermentation better...supplemented with only a small amount of sugar...a sprinkling. Sugar does tend to turn bait into jam...too much will kill the yeast as it is a preservative...and as it dries out in the traps it becomes sticky ...and this sticks to wings and spoils them. I only use sweet bananas...the blacker the better...sprinkle in a little sugar and then put a loose fitting lid on top. I always leave the last quarter empty as the initial fermentation causes the banana to froth up and pressure will build if sealed. I never add any water. Yeast will speed the process up if time is important.
After a couple of days the bait is ready...it only remains effective for three or 4 days ... when just like all other fermentations without an airlock...the mixture will start to produce vinegar and go sour. As long as it remains pungent and not acid...the fermented fruit and alcohol content will draw in the butterflies. Other baits...like rotting fish, dung etc also can work well...but only attract male butterflies the females ignore it! When trapping in the rainy season you may like to consider sticking a plastic cover over the top of the trap to keep as much rain off the bait as possible...if it overflows inside the trap it can be really annoying to see a prized specimen happily feeding off the drips outside the trap!