A healthy and well-maintained Drosophila (=fruit fly) culture will typically have a total average lifespan of 50 to a maximum of 90 days at the perfect temperature and humidity conditions.
The Drosophila Melanogaster is a smaller fruit fly than the Drosophila Hydei that reproduces a little slower.
It takes about two weeks for a Drosophila Melanogaster to complete the lifecycle and reach adulthood, while it takes around 3 weeks for a Drosophila Hydei to reach the adult stage.
The life cycle of a fruit fly includes the following stages: Egg, larva, pupa, and adult. During the larva stage, the fruit fly goes through several stages, which are called instars.
The life cycle starts with the egg. The fruit flies lay their eggs on the surfaces of rotting food found in the kitchen, sinks, and trash cans.
After a few days, the larvae hatch. The larvae will feed on the decomposing surface where they hatched, making the food decompose even faster. Once the larvae are ready to pupate, they will attach to a dry surface and evolve into flies after approximately 48 hours.
There are several changes that can be observed when fruit flies get older. They change their behavior by eating less, being less interested in courtship, and sleeping more. An older fruit fly is also less stress resistant, is not as reproductive as younger fruit flies, moves less in general, and has a weaker immune system.
Why are My Fruit Fly Cultures Dying?
Fruit fly cultures can die for a variety of reasons. The most common reasons are age, temperature, humidity, a high CO2 level, mites, and diseases.
Fruit flies don’t have a very long lifespan. The common fruit fly usually lives 2 to 3 months.
When they are kept in cultures, the cultures are usually disposed of after one month to avoid mold and mites spreading.
The older fruit flies are, the slower they get. They reproduce slower, move slower and less, eat less, and the immune system gets weaker.
The perfect temperature for fruit fly cultures to thrive is between 70 and 80° F (approx. 21 to 26,7° C).
Anything higher or lower can reduce the lifespan of the fruit flies.
Short temperature drops or increases are not an issue for fruit flies (as long as the temperature change is not too extreme).
But constant temperatures below 70°F will decrease the reproduction rate, temperatures below 60°F will decrease the lifespan, and temperatures below 53°F will stop their development altogether.
A constant temperature above 85°F will make fruit flies sterile, which will also eventually kill a colony.
The perfect humidity level for fruit flies is between 60% and 80%. Lower temperatures can lead to a dried-out media on the bottom which can affect both larvae and adults and kill the culture.
A higher humidity level is better for fruit flies than a low humidity level.
Fruit flies are able to detect humidity and will choose a space that offers them the best humidity.
All fruit fly species prefer a humidity level that is in accordance with the climate of their native habitat.
When Drosophila Melanogaster was free to choose between an area with a humidity of 70% and a humidity of 80%, almost all flies flew to the side with 70%.
Fruit flies are very sensitive to CO2. Even though fermenting food creates CO2 and one would expect that fruit flies are therefore attracted by some CO2, they will avoid places with a higher CO2 level.
Overpopulation, as well as the wrong temperature, humidity, diseases, mites, malnutrition, and some other factors, can lead to a higher stress level in a fruit fly culture. And stress will lead to a higher CO2 production of the fruit flies.
Especially very young flies show a high mortality level when they are exposed to a high level of CO2. Pupae that are exposed to a high level of CO2 (20%) over a period of 4 days reach a mortality level of 95%.
Older fruit flies have a much lower mortality rate when it comes to a higher CO2 level, but it still stresses them out, and can eventually kill them if the CO2 level stays high.
Mites are a common issue in fruit fly cultures. They are hard to detect in the beginning, but when they start spreading, they are almost unstoppable and you might have to toss away the infected fruit fly culture.
There are mite species that are not such a big problem, such as the common white-grain mites. As long as the fruit flies are doing well, they won’t be prone to suffering from mites. A few mites in a culture are usually not a problem.
But if the fruit flies are weakened by low temperature, low humidity, diseases, or other disturbing factors, the mites might become a huge issue due to the lowered immune system of the fruit flies.
If you detect a large number of mites in your fruit fly culture, do not use these flies to create new cultures anymore. You can feed as many flies as you can but you should toss the rest of the culture away after euthanizing them in the freezer.
Mites are often already in the medium that you use in the cup. You can store the medium in the freezer to kill of mites before putting the fruit flies in.
It is also important to move your fruit flies to a new cup every month. This will also prevent fruit fly invasions.
Mites and their eggs can be killed with ethanol. If you used any of your equipment that you want to keep using, in a fruit fly culture that was infested with mites, you should disinfect everything you used with ethanol.
Every fruit fly culture will also be home to some bacteria. That is completely normal, and as long as the fruit flies appear to be healthy, and you exchange the cup every month, you should not have issues with diseases.
If you notice that more fruit flies than usual are dying or they are even discolored, or the larvae is dark-colored, you should toss away that culture after euthanizing them in the freezer to prevent any diseases to spread. Do not feed infected fruit flies to other pets. In some rare cases, they can transmit diseases.
Lisa is one of the two founders of Animal-Knowledge. She has been very interested in animals and insects from a very young age and has owned different kinds of pets such as snails, ants, fish, turtles, mice, rats, hamsters, rabbits, a dog, … you get the idea 🙂