Buzz kill: Auburn researcher offers advice for ridding homes of pesky fruit flies

As many people prepare for cookouts and fun gatherings for the Fourth of July weekend, those celebrating could be doing so not only with family and friends, but also an unwanted seasonal pest–the fruit fly. Auburn University’s Laurie Stevison, an assistant professor in the Department of Biological Sciences, is an expert on the tiny, airborne nuisance. She offers the below information about how you can rid your home of them and how in some ways they can actually be beneficial.

What causes fruit flies in the house?

Drosophila melanogaster found typically in your home is a human commensal, meaning that they live wherever humans are present, except Antarctica. Just like humans, their origins trace back to Africa. In our homes, they are typically attracted to our foods–fruits and vegetables. This is partly why they are in higher abundance in summer months, like now. Our crops are increasing their numbers outside, and we bring those crops into our homes for eating and cooking.

Why are fruit flies so attracted to fruit?

Interestingly, the flies are attracted to rotting fruit, not fresh fruit. So, it is fruit that has been in your house over a week that attracts fruit flies. As fruits age, the fermentation process begins to break them down. This process creates alcohols and vinegars that attract fruit flies, but also makes them less appealing to us. Just like humans, the flies select an environment that is best for their children. So, think of rotting fruit like the hunt for the best schools! This provides a rich source of nutrients for them to lay their eggs.

How do I rid my home of fruit flies?

Much like getting rid of mice, I recommend setting a trap for the fruit flies. They are drawn to rotting fruit, so vinegar, a byproduct of the fermentation process, sets a perfect trap. Apple cider vinegar is probably best, but in a bind, beer or wine will work well, too! Mix about two ounces, a full shot glass, of the vinegar with some dish soap and place it in a container. The soap keeps the flies stuck in the liquid, and they ultimately drown. For the container, I recommend something with a narrow opening and a wide base, like an empty soda or beer bottle. You could also use a covered casserole dish and make small openings to give the same effect. Leave it open, or even add a funnel, and watch the flies come to you!

You may also see them in your sink a lot. For this problem, you can pour hot water down your drain, then cover it and fill it with water as if you were going to wash dishes. Leave the water in the sink overnight to kill the flies by depriving them of oxygen.

A few extra tips if you have a big infestation is to set multiple traps up in your house. The flies are attracted to the smell, so the stronger the smell, the better. But make sure you don’t have something else that smells even stronger somewhere in your house, as this will draw attention away from your traps. You should also look around your home carefully for forgotten fruit or vegetables that flies could breed on. If you find maggots, get rid of them before they become adults!

Can fruit flies pose a health hazard to humans? And conversely, is there a benefit to fruit flies?

For the most part, fruit flies in the genus Drosophila are relatively harmless. There is only one species that is known to be a crop pest, Drosophila suzukii. Because fruit flies are attracted only to fruit that is rotting, they pose no major health risks to humans. Still, research in fruit flies has had a major benefit to innovations in human health. For example, research in fruit fly development has helped map out gene networks to guide efforts in humans to study novel developmental disorders. Similarly, being able to mutate these genes and see how development is altered has helped identify the genes involved. Once these genes were found, genetic screening has become more precise and custom treatments have been developed.

Are fruit flies seasonal? Why are they only in my house this time of year and not others?

One of the funny things about fruit flies is we know very little about where they go and what they do when they are not infesting our homes. They are known to be able to survive for a long time at very low temperatures–similar to hibernation in bears. This is known as “diapause.” In the summer months when it’s warm and many plants are fruiting, they come out of diapause and breed in high numbers. We also have many crops we produce in summer months, as well as fruits and vegetables we bring into our homes. A single mated female can lay over 100 eggs. These take about 10 days to hatch as adults. This means if you miss trash day, then you can expect a big swarm of fruit flies before the next week. Also, if you ignore a few fruit flies because you are busy, it can become a BIG problem very fast.

Beyond their small size, how do fruit flies differ from other types of flies? 

Most fruit flies are the species Drosophila melanogaster, though there are more than 2,000 described species of fruit fly. Fruit flies are known to entomologists as “true flies,” meaning they have one pair of wings as compared to other insects that have two pairs or four wings. The second set of wings in flies have been converted into a structure they use to navigate, similar to a pilot flying a helicopter. Interestingly, mosquitos and gnats are also considered flies and have these same structures. But for the most part, fruit flies are not particularly special among flies and mainly differ in how they look, as far as size, shape and coloration.

Why do scientists study fruit flies?

In the early 20^th century, a group of scientists were looking for an organism they could study in the lab that breeds very fast and has large numbers of offspring. All the things that make fruit flies annoying pests make them perfect for scientists to study how traits are passed down from one generation to the next. It may seem like this doesn’t have relevance for humans, but many of the genes found in humans are also found in fruit flies.

In addition, we have the ability to mutate any gene in fruit flies and study its impact. While it is unethical to do controlled breeding experiments in humans, doing this in fruit flies is easy and fast. Now, more than 2,000 labs across the world study fruit flies and have found amazing discoveries that have helped understand humans and other species. For example, their short life span makes them an excellent model for aging in humans. With all these efforts, many scientists assume we have figured out everything we can about fruit flies, but the truth is, there is still a lot that is unknown. My lab uses fruit flies to understand how the environment, and particularly increased temperature due to climate change, alters the genes important for cell division during reproduction, which is important for understanding reproductive and environmental health.

About Laurie Stevison:
Laurie Stevison is an assistant professor of biological sciences at Auburn University. Like many fruit fly researchers, she can trace her academic pedigree to the founder of fruit fly genetics, TH Morgan.