Acentria nivea, Acentropus niveus

Adult females are usually brachypterous, or with shortened, non-functional wings. They have hairy second and third legs for underwater swimming, and exhibit a plastron, or an incompressible gill full of hydrofuge hairs that traps gas on the ventral surface. Winged males, flightless females, and winged females (which are rare but occur occasionally) have a short, under-developed proboscis (Dierl and Reichholf 1977, Merritt and Cummins 1984, Munroe 1947, Pennak 1978).

Egg laying often occurs twice a year, resulting in A. ephemerella emergence coinciding with two peaks in the biomass of milfoil (Myriophyllum spp.), one of its typical host plants. The latest generation of hatched larvae typically overwinters until spring of the following year. Not all North American populations produce two generations though, and when only one occurs, larvae usually overwinter in cocoons on macrophytes, then create new feeding shelters on plants the following year (Batra 1977, Johnson and Blossey 2002, Judd 1953, Painter and McCabe 1988).

The larval stage can last around 10.5 months and larval development generally requires temperatures below 22ºC, although higher water temperatures can be tolerated for short periods of time. Larvae that are ready to pupate cut the apical tip of their host plant and spin a cocoon between this piece of plant material and the main stem. Metamorphosis and adult reproduction both occur sometime in the summer. Adult males only live one or two days solely to breed and they copulate with females at the water surface. Wingless females are mostly nocturnally active and float on the water surface until they mate. Wingless females lay 100-300 eggs on host plants, while winged females usually lay fewer than 100 (Batra 1977, Buckingham and Ross 1981, Johnson and Blossey 2002, Judd 1953, Painter and McCabe 1988, Pennak 1978).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Beneficial

Current research on the environmental impact of Acentria ephemerella in the Great Lakes is inadequate to support proper assessment.

Potential:
Acentria ephemerella is a generalist feeder, reportedly consuming a variety of macrophytes in North America and Europe, including Elodea canadensis, Ceratophyllum demersum, and Potamogeton spp., which are native to many of the Great Lakes states (Buckingham and Ross 1981, Gross et al. 2002, Johnson and Blossey 2002, Johnson et al. 1998). While feeding activity could suppress native macrophyte populations, A. ephemerella generally avoids feeding and building cocoons/retreats on the apical tip of these species, limiting damage to these plants (Johnson and Blossey 2002, Johnson et al. 1998). Furthermore, A. ephemerella appears to prefer the nonindigenous pest plant, Eurasian watermilfoil (Myriophyllum spicatum) over many native species (Gross et al. 2001, Johnson et al. 1998, Johnson and Blossey 2002). For instance, in Cayuga Lake, New York, the introduction of A. ephemerella resulted in significant declines in M. spicatum populations, while native macrophyte populations experienced recovery and growth.

However, native pondweeds (Potamogeton spp.) may also be a preferred resource of A. ephemerella (Johnson and Blossey 2002). In Europe, A. ephemerella heavily colonized both P. perfoliatus and M. spicatum, damaging, altering, and reducing P. perfoliatus populations (Gross et al. 2002, Miler and Straile 2010). A study at Lake Constance, Germany found A. ephemerella to be an ecosystem engineer through its control of the macrophyte communities (largely of P. perfoliatus) that many species, including young-of-the-year (YOY) and adult perch, stickleback, and pike, used as habitat (Miler 2008).

There is little or no evidence to support that Acentria ephemerella has significant socio-economic impacts in the Great Lakes.

Acentria ephemerella has a moderate beneficial effect in the Great Lakes.

Realized:
Acentria ephemerella has had some success as a biological control agent of M. spicatum in the Great Lakes region. In Lakes Buckhorn and Scugog, part of the Trent Canal system flowing into Lake Ontario, populations of introduced Eurasian watermilfoil were decimated in the 1980s, likely due to grazing by A. ephemerella (Painter and McCabe 1988). In Cayuga Lake, the introduction of A. ephemerella was associated with a decline in M. spicatum populations and the recovery of native macrophytes (particularly Elodea canadensis) during the 1990s (Gross et al. 2001, Johnson et al. 1998, Johnson et al. 2000). The biocontrol ability of A. ephemerella is attributed to its feeding and building activities, which damage the apical meristems of M. spicatum and seriously hamper the plant’s growing ability. Milfoil can resist four A. ephemerella larvae per ten apical tips, but eight or more larvae or per ten tips causes very severe impacts (Johnson et al. 1998, Johnson et al. 2000, Painter and McCabe 1988).

Potential:
Outside of the Great Lakes Basin in Brownington Pond, Vermont, herbivory by A. ephemerella and the weevil Euhrychiopsis lecontei was associated with declines in M. spicatum. Entire stands were pulled underwater as damaged plants with reduced buoyancy weighed down proximate healthy plants (Creed et al. 1992, Creed and Sheldon 1994). Experiments designed to test the ability of A. ephemerella as a biocontrol agent indicated that it can significantly reduce milfoil stem length and prefers to feed on M. spicatum over E. canadensis despite being a mainly generalist grazer (Creed and Sheldon 1994, Gross et al. 2001). A review on the biocontrol of Eurasian watermilfoil in North America agrees that A. ephemerella, along with E. lecontei and Cricotopus myriophylli, has the potential to be an effective control agent; however, populations in many study sites were lacking the densities of A. ephemerella needed to be fully effective (Newman 2004).

Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
Acentria ephemerella is used for biological control of Eurasian watermilfoil (Myriophyllum spicatum).  Its population is best controlled by elimination of its host plants – which are predominantly Eurasian watermilfoil but also may, to a lesser extent, include a variety of other native and nonindigenous plants (Cornell 2004).

Physical
Mechanical harvesting, herbicide applications, benthic barriers, and water drawdowns all remove either A. ephemerella individuals or their habitat (aquatic plants) from waterways (Cornell 2004).

Chemical
This species is susceptible to herbicide control of its host plants (Cornell 2004).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

In spite of the documented strong negative effects of high densities of A. ephemerella on M. spicatum, this aquatic moth probably only has a weak negative effect on many host plants in general. Such macrophytes as M. spicatum, T. natans, and P. crispus generally experience such low costs in acting as hosts to A. ephemerella that the relationship can even be classified as commensal (Ricciardi 2001). Moreover, it is possible that herbivore damage to milfoil stems causes fragmentation and aids dispersal of some fragments that are still viable (Creed and Sheldon 1994).

In ITIS, Acentropus niveus and Acentria niveus are both listed as valid but unverified species names (citing 1996 Code). Bernd Blossey (Cornell U., pers. comm.) advised that Acentria ephemerella is the correct, valid name per:  Passoa, S. 1988. Systematic positions of Acentria ephemerella (Denis & Schiffermiiller), Nymphulinae, and Schoenobiinae based on morphology of immature stages (Pyralidae). J. Lepidopt. Soc. 42: 247-262.