San Diego Floral Association
See past editorial content: Growing Grounds | Favorite Tool | Friend or Foe | Floral Stories | Roots | Archives
Friend or Foe: Flies
Reprinted from: September/October 2009, Volume 100, Number 5
Flies are pesky and some are annoying and bothersome, but are they harmful to your plants? Next time you pick up a fly swatter to get rid of them, think again. Could these common insects actually be friends instead of foes?
Flies are everywhere - in your home, garden and office; and while some are definitely foes, it may benefit you to leave the majority of them alone. Flies are important pollinators. Some plants pollinated by flies include American pawpaw (Asimina triloba), skunk cabbage (Symplocarpus foetidus), goldenrod (Solidago spp.) and Queen Anne’s lace (Daucus carota). The National Research Council’s “Status of Pollinators in North America” study confirms that flies are economically important as pollinators for a range of annual flowers.
Many flies will attack common garden predators as well. For example, fireflies, well known in other parts of the country for their summer light show, also eat insect pests. They feed on slugs, mites and small crawling insects.
Damselflies attack aphids, leafhoppers and many caterpillars. Robber flies attack bees, beetles, grasshoppers and wasps. Syrphid flies, also called hover flies, eat aphids, thrips and leafhoppers.
Tachinid flies, which are commonly mistaken for house flies, are probably the most helpful of all flies. Their yellow larvae parasitize adult beetles, grasshoppers, caterpillars, armyworms and sawflies.
While you should be happy to have many of these flies in and around your garden, some flies, such as the whiteflies, can cause widespread damage. Whiteflies damage plants through feeding and they are also transmit viruses. Economic losses due to whiteflies are estimated in the hundreds of millions of dollars.
Whiteflies are very difficult to control because they quickly gain resistance to pesticides. Multiple options and applications may be necessary. Washing the plant, including underneath the leaves, also may help eliminate the pest. Beneficial insects such as green lacewings and lady bugs, also will attack whiteflies. —Alyssa Holderbein
Mission: To promote the knowledge and appreciation of horticulture and floriculture in the San Diego region.