New Predatory Fly May Help Control Greenhouse Insect Pests
by Scott W. Ludwig and Kim Engler
A new insect is showing up in Texas greenhouses and for once this is not an
insect you will need to control. Coenosia attenuata, an old world hunter fly, was
first identified in 2004 at Nortex Greenhouses in Collin County. Since that time,
this beneficial fly has also been identified in Cherokee County. In North America,
this hunter fly was previously known to occur in New York, California and
Ontario, Canada. In California, C. attenuate is associated with gerbera, roses,
poinsettia and chrysanthemum production.
Coenosia attenuate resembles a small housefly. They range in size from 2.5 mm
to 4 mm. The female has a dark grey body and black legs while the male has
pale yellow legs. You can observe the adult flies perched on plants, pipes, or
other objects in the greenhouse. These predators actually wait to fly out and
grab any flying insect of suitable size. The prey is then subdued by stabbing
them with specialized mouthparts. Hunter flies prey on insects such as fungus
gnats, shore flies, whiteflies, winged aphids and leafminers. Once prey is
stabbed, they return to their perch to feed. Each adult occupies a defined
territory and sometimes territorial "dogfights" can be observed when boundaries
are compromised.
Adult flies lay their eggs in the soil and the developing larvae are predators of
fungus gnats and shore flies. Research conducted at Cornell University indicates
that this is an effective predator of fungus gnat larvae.
We sampled fly populations at Nortex Greenhouse for a year. It appears from
these results that this predator is capable of managing fungus gnat populations,
especially in pot plants.
If you see a new fly showing up in your greenhouse do not automatically reach
for the nearest bottle of insecticide. Have the fly identified. Coenosia may prove
to be a valuable biological control agent. Even more importantly, one you do not
need to purchase!
This research was funded in part by the USDA-ARS Floriculture Research
Initiative Agreement Number 58-6204-0-106.
