What Olive Growers Need to Know About the Olive Fruit Fly

Posted by Olivia on Wed, May 30, 2012

What’s been around since for thousands of years, comes from the Mediterranean, and can devastate a perfectly good olive crop? If you guessed the olive fruit fly, you’re right on target. This olive fruit-loving insect spread into the United States just recently, only around 1998, and ever since it’s been mostly documented in California. If you’re an olive grower, whether for commercial or hobby purposes, you need to learn about this pest and how it can affect the fruit of your olive trees.

What is the olive fruit fly?

The olive fruit fly (Bactrocera oleae) is different than your average fruit fly. This one goes for olive trees, as it uses the fruit for larval growth and feeding. Olive fruit flies lay their eggs under the skin of olives, and the larvae feed their way through the flesh, resulting in bacterial and fungal growth. Any damage to your olives increases the free fatty acid levels and causes off-flavors, drastically compromising the quality of the olives (not to mention any olive oil you hope to produce).

Even seemingly unharmed olives are often damaged by the olive fruit flies. During larval feeding, organisms are created in the olives which can encourage rotting and induce undesirable off-flavors. Because of this, any signs of rotting of your fruit indicate that your olives will not produce extra virgin olive oil.

Olive fruit flies are marked with small dark spots on their wings, which may help you tell them apart from other common fruit flies. They typically prefer cooler climates and may die off when temperatures exceed the mid-90s; however, in those hotter periods they have a way of finding cooler places to hide and stay alive.

Should your olives become infested from the flies, you probably won’t notice serious damage until September or October when you’ll see large brown blotches on the surface of olives, and the insides may contain maggots. Telltale signs earlier in the season may be small spots or vague brownish markings. In order to prevent infestation before it starts, the best bet is early prevention.

How to prevent the olive fruit fly

1. Clean up old and fallen fruit from your growing area. Olive fruit flies can live in rotting and dying fruit on the ground and emerge in the spring season, ready to infest the new crop. Always throw any rotten or infested fruit in the garbage, not into your compost.
2. If you grow your olives organically, one of the best options for pest control is the attract-and-kill (also called Magnet OL) olive fly trap, a device used both in Europe and California. It’s basically an insecticide-coated cardboard cone that baits the flies with pheromones and kills them within days. The pesticide doesn’t come in contact with the environment or your food and is an ecological way to keep the olive fruit fly at bay. Find it here.
3. You may also choose to use Spinosad, an organic insecticide spray. To find information on this spray and its regulations, visit this page from Cornell University.

For more information:

http://www.ipm.ucdavis.edu/EXOTIC/olive_fruit_fly_info.pdf