The pyralid moth, Acentria ephemerella, has the potential to
serve as an agent of biological control against the aquatic weed, Eurasian
watermilfoil (Myriophyllum spicatum). Eurasian watermilfoil is an
exotic species of submersed aquatic plant that arrived in North America in
the mid 1900ís. Since its introduction, Eurasian watermilfoil has become a
major nuisance plant, spreading to 45 states and at least 3 Canadian
provinces. Thick beds of Eurasian watermilfoil plants clog canals, lakes
and ponds all across North America while boats continue to carry Eurasian
watermilfoil fragments to new bodies of water where they grow into new
Eurasian watermilfoil infestations. Lake managers try to control Eurasian
watermilfoil by harvesting the plants, adding light (benthic) barriers,
drawing down water levels during the winter, and applying herbicides. These
methods are costly, rarely specific to watermilfoil, and often require
frequent re-application. Using herbivorous insects as a means of biological
control may prove to be a cost-effective and environmentally sensitive
A. ephemerella is widespread in its native Europe where this generalist
feeds on a variety of aquatic plants including Eurasian watermilfoil. The
shipping trade may be responsible for accidentally introducing this species
to North America, where it first appeared near Montreal in 1927. Today,
this aquatic moth appears in waterways from Massachusetts to Iowa.
Researchers associate declining Eurasian watermilfoil populations with A.
ephemerella herbivory in a few Ontario, Canada and New York State lakes,
although rigorous research is just beginning.
A. ephemerella adults are
tiny white moths between 5 and 9 mm long. All males and a small portion of
females develop wings, while most females have rudimentary wings and are
flightless. Eggs are pale yellow-green colored, and round to slightly
oblong in shape. Larvae are almost transparent, greenish colored
caterpillars, usually with a visible ribbon of dark green (ingested plant
material) running through the gut. The head capsule is distinctive with a
dark gray suture dividing it into two eye regions (with simple ocelli) and a
mouth region (with well-developed mandibles). The larvae feed from inside
shelters they build out of plant leaflets, which they tie together and/or
attach to plant stems. This cryptic behavior of the larvae combined with
their small size make them difficult to detect. They are as small as 0.25
mm when they first hatch. If food is plentiful, larvae may measure up to 10
or 12 mm before they pupate. Larvae progress through 4 or 5 larval instars
before they spin their cocoons for pupation. Pupae are the size of large
(late instar) larvae, and are beige/creamy in color with the visible
precursors of adult eyes and wings. Pupae spin themselves a heavy,
air-filled cocoon instead of the light, water-filled temporary shelters that
they construct as larvae.
A. ephemerella live on
submersed aquatic plants in canals, ponds, and lakes throughout the
temperate zones of Europe and much of North America. A. ephemerella
populations are most common in large, deep lakes where aquatic plants are
abundant. In North America, A. ephemerella most often feed and
reproduce on Eurasian watermilfoil plants. Although we sometimes find moths
on native plant species such as Ceratophyllum demersum, Elodea
canadensis, and Potamogeton richardsonii, moths do not seem to
limit the populations of these species as they do the Eurasian watermilfoil
populations in some lakes.
A. ephemerella attacks the invasive weed,
Eurasian watermilfoil (M. spicatum). Eurasian watermilfoil is an
aggressive species, which can quickly dominate an aquatic community, shading
out desirable native species by forming a canopy on the surface of the
water. These canopies of Eurasian watermilfoil also limit human
recreational uses of the water (boating and swimming), and cause shoreline
property values to fall.
Acentria ephemerella is
one of the few moth species with a life cycle completed almost entirely
underwater. The males (and possibly some winged females) emerge from the
water only for a brief (1 to 2 day) courtship flight. Most females are
wingless and float on the surface of the water to attract a mate. After
mating, the female dives into the water and lays a clutch of 100 to 300 eggs
(under 100 for winged females). Females lay their clutches of eggs in neat
rows along the middle or lower leaflets of submersed plants. Larvae hatch
from the eggs and burrow inside the leaflets where they feed until they are
large enough to build resting shelters or retreats made of leaflets and
small branches. Larvae disperse as they move upward on the plants to feed
on the nutritious apical meristems (growing tips). When larvae are ready to
pupate, they build a cocoon, often by removing the plant tip, adding it to a
lower portion of the stem, and spinning a thick cocoon between them. We
observe two generations of A. ephemerella per year. The first
generation adults emerge to mate and lay eggs in June. The second
generation hatches and develops rapidly in height of the summer to lay eggs
near the end of the growing season. These eggs hatch in the late
summer/early fall, and the larvae over-winter in a resting state (diapause),
becoming the next summerís first generation adults.
In laboratory and in lake enclosure experiments, A. ephemerella
successfully controls Eurasian watermilfoil growth by destroying the apical
meristem, preventing canopy formation, and reducing biomass, stem density
and plant height. Long-term monitoring of a natural population of A.
ephemerella in Cayuga Lake, NY, shows a dramatic decline in the Eurasian
watermilfoil population associated with high A. ephemerella numbers.
Ten years after the initial decline in Cayuga Lake, Eurasian watermilfoil
biomass remains at very low levels with no canopy formation. As the
Eurasian watermilfoil population declined in Cayuga Lake, native plant
species returned and they now dominate the plant community.
The direct effects of herbicides on A. ephemerella are unknown,
although any effective herbicide may harm A. ephemerella indirectly
by eliminating their host plants.
herbicide applications, benthic barriers, and water drawdowns all remove
either A. ephemerella individuals or their habitat (aquatic plants)
from waterways. In doing so, these popular control methods lessen the
ability of the moth to control watermilfoil growth biologically.
Not commercially available
Thanks to Dr. Bern Blossey for reviewing this page.
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