Crack the Case at Its Core

By Erin M. Walker
Special to The Washington Post
Thursday, October 11, 2007

The good news: It's early fall and farmers markets still are overflowing with ripe produce. The bad news: Insects are just as happy about the late-season abundance as we are, and none more so than the annoying fruit fly.

These tiny irritants are like cockroaches, says University of Maryland entomologist Mike Raupp: If you see one or two, you've got a hundred. But with a bit of vigilance, you can prevent them from establishing a base camp in your kitchen.

Start outside. Keep your yard or other outdoor area clear of decomposing vegetables or fruit; if you have a compost pile, keep it away from the house. That way, fruit flies will be less likely to stray into your home by accident. It also helps to install window and door screens that are 16 mesh (that means 16 wires in each direction per square inch) or finer, and properly sealed. Fruit flies are small but they're not that small, and other insects will have a hard time getting through that mesh as well.

Be merciless about weeding out bruised or battered fruit -- whether it's the produce you bring in from the farmers market or in that bowl on the kitchen counter. Fruit flies are not attracted to healthy skin; they like the yeasty decomposition of rotting fruit or vegetable flesh . . . ah, paradise! Eggs laid on rot spots should be visible to the naked eye, but later molting stages may not. It's best to get rid of overly soft or damaged fruit immediately, or cut out the bruised parts and just eat the rest right away. And remember, washing produce is never a bad thing.

If the fruit flies get past your multi-pronged prevention campaign, you'll need to identify their breeding site and eliminate them there. Here are a few of their favorite locations and some ways to clear them out in a hurry:

¿ Drains and disposal areas can contain a moist fermenting film that fruit flies find irresistible. While this tends to be more common in restaurants and markets, here's how to make sure it's not your breeding site: Tape a sandwich bag over the drain overnight, and if it contains fruit flies the next morning, bingo! That's your source. Thoroughly clean the drain with a new bristle brush and a food-safe cleaner.

¿ Bottles, cans and other containers in recycling bins usually hold small amounts of beer, fruit juice, wine and other fermenting matter. If you see flies buzzing there, get the whole bin out and away from the house. To prevent flies from returning, thoroughly clean the bin and rinse empty bottles before recycling them.

¿ Even a lone grape at the bottom of the fruit bowl or an apple core in a bedside wastebasket can be an attraction. Again: Get rid of the fruit, and remember to throw away the trash, too. As for the remaining fruit, rinse it off and put it in the fridge.

So what can you do if you've eliminated their breeding site, but a few (or 400) flies remain? Start by thoroughly cleaning their area of origin -- scrub the counters, clean the floors, vacuum, the works. Once you've eliminated the breeding ground, you need to make sure they don't have a new place to go. Any standard disinfectant or antimicrobial should do the trick.

Setting a Trap

You know the old saying that you catch more flies with sugar than with vinegar? When it comes to fruit flies, the reverse is true.

There are a few fruit-fly catchers on the market, but a simple homemade version using a paper funnel and cider vinegar is one of the most effective. It's a cunning contraption, Raupp says, because it lures the insects to behave exactly as evolution decrees: Their hard-wired instinct to breed in a fermenting substrate becomes their undoing.

You'll need:

A drinking glass. A sheet of paper. Scissors. Tape. Cider vinegar or other sweet fermenting liquid or fruit.

Step 1: Roll the paper into a funnel shape that will rest in the mouth of the glass, leaving a small opening about the size of a pea at the bottom of the cone. Cut off the excess paper.

Step 2: Fill the glass with cider vinegar just up to the level of -- but not touching -- the cone. Use tape to seal cone against glass.

Step 3: Leave the trap wherever you see flies. The liquid lures them down the funnel, but they can't fly back out; they either drown or die trying in a couple of days, most within the first 24 hours.

"They're very good on the locating thing, Raupp says, "but they're not very clever on the escaping thing."