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Acentria ephemerella

(Lepidoptera: Pyralidae) 

        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 alternative.   

        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.   

Appearance

        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.
 

Habitat 

        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.

 Pests attacked

         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. 

 Life cycle 

        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.   

Relative effectiveness

        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.

 Herbicide susceptibility 

        The direct effects of herbicides on A. ephemerella are unknown, although any effective herbicide may harm A. ephemerella indirectly by eliminating their host plants.

Conservation

         Mechanical harvesting, 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.   

Commercial availability

          Not commercially available

 Acknowledgements

           Thanks to Dr. Bern Blossey for reviewing this page.

 References 

Aiken, S.G. 1981.  A Conspectus of Myriophyllum (Haloragaceae) in North America.  Brittonia. 33(1) pp. 57-69. 

Batra, S.W. 1977.  Bionomics of the Aquatic Moth, Acentropus niveus (Oliver), a Potential Biological Control Agent for Eurasian Watermilfoil and Hydrilla.  New York Entomological Society LXXXV(3) pp. 143-152. 

Berg, K. 1942.  Contributions to the Biology of the Aquatic Moth Acentropus niveus (Oliver).  Vidensk Medd Dansk Naturh Foren 105:59-139 

Buckingham, G.R. and B.M. Ross, 1981.  Notes on the Biology and Host Specificity of Acentria Nivea (=Acentropus niveus).  Journal of Aquatic Plant Management.  19:32-36. 

Gross, E.M., R.L. Johnson, and N.G. Hairston Jr.2000.  Experimental Evidence for Changes in Submersed Macrophyte Species Composition Caused by the Herbivore Acentria Ephemerella  (Lepidoptera).  Oecologia 127 (2001) 1 pp 105-114.  http://link.springer.de/link/service/journals/00442/bibs/1127001/11270105.htm

Johnson, R.L., P.J. Van Dusen, J.A. Toner, and N. G. Hairston, Jr. 2000.  Eurasian Watermilfoil Biomass Associated with Insect Herbivores in New York.  Journal of Aquatic Plant Management. 38 (2) 82-88. 

Johnson, R.L., E.M. Gross, and N.G. Hairston JR.  1998 Decline of the Invasive Submersed Macrophyte Myriophyllum spicatum (Haloragaceae) Associated with Herbivory by Larvae of Acentria ephemerella (Lepidoptera).  Aquatic Ecology 31:273-282.

Newman, R.M., D.C. Thompson, and D.B.Richman. 1998b.  Conservation Strategies for the Biological Control of Weeds.  P. Barbosa (ed.) Conservation Biological Control.  Academic Press, NY, NY pp. 371-396. 

Smith, C. S. and J.W. Barko. 1990.  Ecology of Eurasian Watermilfoil.  Journal of Aquatic Plant Management. 28:55-64. 

 

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