Back to top

Greenhouse Updates: Jun 23, 2015

Natural Enemies - Hover Flies
June 23, 2015

Now that you are scouting your outdoor herbaceous perennials, it is important to keep an eye out for native beneficial insects and mites. If they are present in sufficient numbers, they can do your work for you! These good guys may be either generalist predators that feed on many pests during their lifetime or more specialized host specific parasitic wasps that may parasitize aphids.

Hover flies (syrphid or flower flies) are an example of naturally occurring beneficial, predatory insects. Adults are small (3/8 to 3/4 inch long) and resemble small bees or wasps, but as a member of the fly family, they only have two wings. Hover flies also have short antennae and large eyes.

At this time in June, these pollen feeders are often seen near perennials in flower (sedums, veronica) or around aphid colonies where they lay eggs that resemble a small grain of rice. The eggs hatch into small legless larvae that feed upon aphids as well as thrips and small caterpillars. Larvae vary in color, are legless and have a tapered head. Sometimes, you will see a tar-like excrement that the larvae leave.

Adult syrphid flies feed on pollen and nectar, while the larval stage feeds on insects. They lay eggs on leaves and stems of plants infested with aphids or other suitable prey. Eggs hatch in 3 to 4 days into soft-bodied maggot-like larvae. Larvae feed and develop through several stages (instars) over a period of 2 to 3 weeks before pupating (tan-brown color), either on the host plant or in the soil. A life cycle from egg to adult is completed in about 16 to 28 days with overlapping generations. A single syrphid larva can consume hundreds of aphids in a month. There are many species of syrphid flies and while most are predators, some are not predaceous, and feed on fungi.

Hover flies get their name from ability of the adult fly which hovers in midair, can dart a short distance very quickly and hover again. They can also fly backwards.

Photo Library by UConn and UMass Extension (scroll down): Hover fly adults, larvae, eggs and larva feeding on aphids

More info on naturally occurring hover flies:

http://www.biocontrol.entomology.cornell.edu/predators/syrphids.php (Cornell University)

http://www.ipm.ucdavis.edu/PMG/NE/syrphid_flies.html (University of California)

http://mint.ippc.orst.edu/syrphid.htm (Oregon State University)

http://www.canacoll.org/Diptera/Staff/Skevington/Syrphidae/Syrphidae.htm#General (Canada National Collection - good photos of many species of adults)

Leanne Pundt, UConn Extension and Tina Smith, UMass Extension