Culturing fruit flies

Introduction

Successfully maintaining fruit flies in the lab can be surprisingly easy or ridiculously labour intensive, or anywhere in between. This largely depends on the species and how long they have been kept in the lab. Some species will happily live with a standard food, being tipped onto fresh vials every week or two with great fecundity. Others require dedicated attention, with freshly cut mushrooms on a daily basis, just to get enough flies to keep the stock going; not to mention trying to get enough flies for an experiment. 

The best resource I found when I started culturing Drosophila was Drosophila: A Guide to Species Identification and Use by Patrick O’Grady and T.A. Markow (2005). Please comment below if there are any others you can recommend. Some of the details below, I have learnt from this book, others I have discovered from colleagues or through trial and error.

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Containers: Vials, bottles, cages and closures

Drosophila are most commonly reared in vials (small or large) or bottles; glass or plastic. The choice mostly depends on:

• The number of adults you need- bottles make it easier to culture large numbers of flies without taking up as much space as you would need for the equivalent in vials.
• The type of stocks you have – for example, if you have isolines, vials are better to help reduce ‘outbreeding’ of the isoline.
• The cleaning facilities you have – if you have a large team or sufficient time to autoclave and wash a lot of glassware, then glass would be the better option, if only from a sustainable environment point of view. It can have a large initial cost but assuming you are working on Drosophila for several years (at least) then the cost will easily pay off. If, however, you are working on anything particularly nasty (e.g. viruses) you may prefer plastic for its sterile, disposable nature.

In our laboratory, we use 23ml (small) flat-base plastic vials for our isoline stocks (D. subobscura and D. pseudoobscura), and 200ml glass bottles (we bought 1000 bottles for £200) for most of our other stocks. We also use the 23ml vials in all our experiments. Other colleagues use 28.5 x 95 mm (large) vials so stocks can be left in the vials for a longer duration, meaning less time spent tipping flies.

There are other useful rearing techniques for experiments too. For example, using petri dishes for collecting larvae. Or egg laying pots for collecting eggs. 

Closures for these vials, bottles or cages are also a key component to consider. The most common types are cotton wool, flugs and plugs. We primarily use cotton wool balls because they are a perfect size to sit snuggly in our vials and only costs about 1 pence each. However, it is much easier for mites to get into stocks through cotton wool (no matter how tightly you squash it in). On the Tips and Tricks page there is a video of how easily a mite can walk through cotton wool. Droso Flugs are a lot more expensive, around 15 pence each, but make it much more difficult for mites to get into the vial because of it’s highly dense weave. Droso Plugs are a type of foam closure, which are the only ones advertised are reusable, including being autoclavable. These cost about 35 pence each, but if they are used at least 35 times, then they would match the cost of cotton wool.

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Recipes for culturing

We had over 40 species in our laboratory at one time. All of these are kept on one of four recipes we have for fly food. Below are the recipes for making 1 litre of these. In the Gallery section for each species I have included which food we used for each species.

Nipagin is made as 10% methyl 4-hydroxybenzoate in ethanol.

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Recipes for experiments

There are some recipes we only use for experiments. Sugar yeast is great for fattening up flies and maintaining stocks. We often use these for keeping virgins on until they are sexually mature. The main reason for not using this food for stocks is the larvae can struggle to chew its much firmer mixture. Also the food is drier and may require tipping the adults more often. The other main recipe we use for experiments is grape juice food or grape ASG. These are used primarily for egg counting and harvesting because the darker colour makes it much easier to see the white eggs.

Please see this link here for the methods to make each food on protocols.io. Included is a list of the ingredients/brands we use and where we buy them (UK).

https://www.protocols.io/workspaces/drosophoto.com

You can also buy premade food mixes, where you just add water, or have vials delivered with freshly made food, although these are not available in all countries.

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