You're always supposed to stand far away from food when applying bug spray. That's because many bug repellents contain dangerous chemicals that can make you sick if you eat them by mistake.

Keeping bugs away from your body, however, is only half the battle of enjoying a relaxing picnic. How are you supposed to keep the bugs away from your food?

Red flour beetles feed on grains and really enjoy products such as dry pet food.

Rob Flynn, Agricultural Research Service, U.S. Department of Agriculture

Scientists from New Zealand may have a solution. They've made cardboard food cartons coated with a substance called citronella oil, which is extracted from grass.

Perfumes, candles, and some bug repellents already contain the strong-smelling stuff. And past research has shown that bugs avoid the stink of citronella, along with the smells of other plant extracts, such as garlic and pine needles.

Citronella grass belongs to the lemon grass family of plants.

© Robert Soreng. Photo courtesy of Smithsonian Institution, Department of Systematic Biology-Botany.

To find the best formula, the researchers first made a bunch of cartons out of cardboard. Then they treated each box with one of five, bug-repelling plant extracts. They also left a few boxes untreated. Finally, they let loose hundreds of red flour beetles.

Over a number of trials, the beetles avoided the citronella-treated boxes more than any of the others. Further tests showed half as many beetles entered the citronella boxes as entered the untreated boxes.

The effect may be promising, but it's not permanent. After about 8 months, the citronella loses its punch. By then, however, the picnic should be long over.

Even though citronella comes from grass, it's not a good idea to coat your food or even your food containers with it just yet. Scientists still have to show that citronella-treated cartons are safe for people.