Syrphid Flies: Interesting Allies in Floriculture

In our region, we have over 800 species in about 100 genera, and worldwide there are some 6000 species in the family Syrphidae. Not only do these insects serve as effective pollinators, but in some situations, they have been shown to be more effective pollinators than honeybees. The adults are excellent fliers, and as their common name implies, they can actually fly in place or hover. Adults of most species will feed on nectar and pollen, and so in an outdoor production of floricultural plants numbers of these insects will naturally congregate. When the greenhouse vents are open, they can also visit greenhouse interiors.

The adults resemble small yellow jackets of many of the species found in PA, although not all species exhibit the distinct yellow and black markings. The larvae of these species are maggots and feed on small insects, although with some species the food source for the larvae is decaying organic material. The species that consume insects, such as aphids, thrips, and other plant-sucking insects are already active this year and are working hard on cleaning up insects in flowering plants.

Syrphid fly adult (left)and Syrphid fly larvae (right) Photo: Sinclair Adam, Penn State

Aphids can build up rapidly on flowering plants, and many species of aphids can reproduce without mating, producing clones of the mother aphid. Clones that are resistant to a chemical can build up numbers in a short period. Some aphid species are monophagous feeding on one species like Chrysanthemum aphid, but potato aphid is an example of a polyphagous species and feeds on many different plants.

Syrphid flies will consume numbers of aphids and can eat up to 1,200 aphids in their development. These excellent flies do a considerable amount of aphid control in the Penn State Flower Trials, and control around 50-70% of aphids in the trials. Florida researchers concluded that 75-100% aphid control occurs with high larval populations of syrphid flies.

Potato aphid has appeared every year in the Penn State Flower Trials but is not a serious problem due to the syrphid fly larvae population. Syrphid flies suck the body contents out of the aphid, and while this is happening, the aphid loses its color along with its body contents. The larvae will often rise uplifting the prey from the leaf while feeding.

It is helpful to conserve naturally occurring biological control agents. Syrphid flies are very good allies in aphid and thrips control. Growers should scout for the syrphid fly larval stage on foliage where aphids are found (especially on plants being produced outdoors) before applying chemicals and should use lower toxicity chemicals for insect control if syrphid flies are already present. Aphid populations that seem large can be controlled effectively and fairly quickly when syrphid fly larvae are in good numbers as well.

Left: Macrosiphium sanbornii (Potato aphid), giving birth to live young on Iris 4/6/20. Right: Syrphid fly larvae consuming aphid on 4/6/20. Photos: Sinclair Adam, Penn State