Hummingbirds and Fruit Flies

Each spring I put hanging baskets of fuchsia on my north-facing front porch to welcome the ruby-throated hummingbirds back from Central America! I usually start the hummingbird season with a small sugar-water feeder and add a hanging basket or two. Soon my native plants provide plenty of nectar for the hummingbirds. By mid-May, I put away the feeder. However, this year I’ll relocate the hummingbird feeder to my berry patch to try a new insect management technique.

You may remember Drosophila melanogaster from genetics studies in biology class. This little fruit fly, correctly called a vinegar fly, lays its eggs on soft, overripe, and decaying fruits and vegetables late in the growing season. It is an important member of the recycling team. However, its exotic relative, the Spotted Wing Drosophila (D. suzukii), has a very different agenda. SWD females have robust, serrated ovipositors to lay eggs into firm ripening or ripe small fruit. Egg laying damages the fruit, but after the eggs hatch, the white,1/8-inch-long larvae feed inside fruits before harvest. Its short life cycle repeats frequently during Pennsylvania summers.

SWD larvae in a raspberry. Photo credit: Hannah Burrack, North Carolina State University, Bugwood.org

SWD has devastated berry production since the insect arrived in the mid-Atlantic region in 2011. These tiny flies favor raspberries, blackberries, blueberries, everbearing strawberries, and sometimes cherries and grapes. The good news is that the SWD population is non-existent or very low early in the growing season. June-bearing strawberries are rarely infested. It’s the varieties with ripening fruits later in the season that are most affected.                                                                  

So, what does this have to do with relocating my hummingbird feeder? Our ruby-throated hummingbirds are limitless consumers of small insects and spiders. Tiny arthropods are their source of protein, especially for feeding their nestlings. Cornell University researchers have verified that hummingbirds do help control adult SWD in berry patches! Although hummers are unfamiliar with this new and exotic insect, when a sugar-water feeder is placed in the berry patch, hummingbirds will be attracted to the area. While there, the hummers explore the plants and consume the adult spotted wing drosophila, often before mating and egg laying occur.

Adult SWD. Photo credit: Hannah Burrack, North Carolina State University, Bugwood.org

Why not just grab a spray to manage spotted wing drosophila? Insecticidal sprays will not affect the eggs or destructive larvae as these stages are inside the berries. The tiny SWD adults fly from fruit to fruit within the canopy of the plant leaves. An insecticide with a long residual effect means that it lasts for several days. You would apply this insecticide to fruits that you harvest every day or two. If you decide to use an insecticide, select one that has a short Pre-Harvest Interval, PHI, the time between application and harvest. Bifenthrin, malathion, acetamiprid, spinosad, and pyrethrin are effective. Apply at a time when pollinators are not active. Remember to follow all instructions on the pesticide label.

Sanitation is essential to manage spotted wing drosophila. Always pick all the berries cleanly, including damaged fruits. Do not allow unwanted fruits in the area where SWD reproduction can continue. Either freeze or “bake" the unwanted fruits in clear plastic bags in the sun to kill the eggs and larvae, then bury the fruit in a compost pile. Prune the canes or limbs and reduce weeds so that there is good air circulation and low humidity. Not only will this reduce disease pressure, but also limit SWD populations.

If you decide to place hummingbird feeders in your berry patch, remember that the feeder will probably be in full sun. You must replace the sugar-water and scrub the feeder often, perhaps even daily as temperatures warm. Consider a second feeder as the replacement while you clean the first. Prepare the sugar-water solution using 1-part white sugar and 4 parts tap water. Red coloring is neither needed nor recommended.

For new plantings, select berry varieties that mature early when SWD pressure is low.

While no one likes to see tiny white worms in fruit, these larvae are harmless if we consume them. If your berry crop is late maturing, do consider using the fruit for juice or jelly rather than for whole fruit or jam. Filter the juice through cheesecloth to remove the interlopers. Those berries are too good to give up! Next year I’ll add native flowers to the berry patch to attract the hummers. Adaptation is part of gardening.