Beneficial Bug Spotlight: Syrphid Flies-Important Aphid Predators

Veronica Yurchak, Vegetable Specialist, UMD; vjohnso4@umd.edu

One of the earlier natural enemies to emerge during spring, the syrphid fly (aka hoverfly), has been spotted out and about. Syrphids are beneficial to farmers because they can reduce the severity of some insect pest outbreaks. Syrphid larvae are important predators of several soft-bodied insect pests including thrips, small caterpillars, leafhoppers, and especially aphids. Depending on the species, a single syrphid larva can consume up to 400 aphids, and when abundant, larvae can reduce aphid populations by 70 to 100%. They are also typically more effective than other predatory insects in cooler weather. Adult syrphids are not predatory and instead feed on nectar, pollen, and aphid honeydew.

Appearance: Larvae are maggot-like with translucent bodies and no true legs (Figure 1, left). Their coloration ranges from brown, greenish, pinkish or whitish depending on the species and color of recently consumed prey. Mature larvae of most species are 5-20 mm long. Pupae are brown, teardrop-shaped and around ½ in long (Figure 1, right). Syrphid flies will pupate either in the soil or on the plant.

(Figure 1, left). Their coloration ranges from brown, greenish, pinkish or whitish depending on the species and color of recently consumed prey. Mature larvae of most species are 5-20 mm long. Pupae are brown, teardrop-shaped and around ½ in long (Figure 1, right).

Figure 1. (Left) Syrphid fly larva feeding on aphid & (Right) Syrphid fly pupa

Adult syrphids (Figure 2) are often mistaken for “sweat bees” due to their resemblance to bees and behavior of hovering around a person’s arms and legs. Unlike bees, however, syrphid fly adults do not possess stingers and have only one pair of wings (bees and wasps have two pairs). Their resemblance to bees and wasps is a form of mimicry to ward off predators. Eggs are whitish, 1mm or less in length, and often laid singly inside or near an aphid colony.

There are a wide variety of syrphid species found in the Delmarva region, many of which can be found in field crop, vegetable, and orchard habitats. So far this season I have spotted them in cover crops and along shrubby field edges. Understanding and promoting the presence of syrphid flies in agricultural settings can improve pest control and crop pollination, making them valuable contributors to sustainable agriculture.
Adult syrphids (Figure 2) are often mistaken for “sweat bees” due to their resemblance to bees and behavior of hovering around a person’s arms and legs. Unlike bees, however, syrphid fly adults do not possess stingers and have only one pair of wings (bees and wasps have two pairs).

Figure 2. Adult syrphid flies