Acentria ephemerella

Life Cycle

Acentria ephemerella, which is commonly known as the watermilfoil moth or water veneer, is a sexually dimorphic aquatic moth species. Males are about 12 mm long with wingspans of 13-17 mm (Water Veneer). Females, however, are smaller and usually have reduced wings, rendering them flightless (Miler et al., 2014) . Females with fully developed wings have been documented, but are much less common than the flightless females. Their life cycle begins when a small, translucent-skinned larvae with no gills hatches from an egg at the base of an aquatic angiosperm. These larvae will create static shelters out of leaves of aquatic plants for which they will use for protection from predators while they are not foraging. The larvae are completely dependent on the aquatic plant they hatched on as it supplies them with oxygen, food, and shelter. A. ephemerella larvae are sensitive to high temperatures, preferring to inhabit water that is below 22 °C, though they can tolerate water temperatures of at least 40 °C for short periods of time. If the larvae sense the water becoming too warm, they will travel farther down the stem of the plant until the water is the proper temperature. Once the larvae becomes mature, it will spin a tightly-woven cocoon in an eaten portion of the stem, which supplies it with an air bubble which keeps the larvae from drowning in the cocoon. Once fully developed from within the cocoon, the adult will emerge and swim towards the surface of the water. If it is a male or winged female, they will take flight and search for a mate; if it is a flightless female, it will swim to the surface of the water, raise their abdomens, and release pheromones to attract males to mate with her. After she has mated, she will grip an aquatic plant and walk down its stem so she can lay her eggs (Buckingham & Ross, 1981) . The adult A. ephemerella will live only two or three days in total, enough time for them to mate and lay eggs. Due to their short development, up to three generations of moths can be bred each year.

Habitat and Distribution

Acentria ephemerella are native to Europe, where it is widespread. It prefers lakes, ponds, and slow-moving streams and rivers due to its dependency on watermilfoil and other aquatic plants for food and shelter. A. ephemerella is also an invasive species in North America, first being documented in Montreal, Canada in 1927 (Johnson et al., 1997). The moth has since spread, now occupying bodies of water in much of the Northeastern and Upper Midwest of the United States (Scholtens & Balogh, 1996). It is unknown how A. ephemerella was brought to North America, but it is hypothesized that its eggs or larvae may have been brought here accidentally along with Eurasian watermilfoil, then spread to other lakes through human activity and boat movement (Mills et al, 1993).

Diet

Acentria ephemerella larvae are considered generalist feeders, meaning that they feed on a wide variety of aquatic plants, not one specific one (Johnson et al., 1997). The feed on a variety of aquatic plants, such as Myriophyllum spicatum (Eurasian watermilfoil), Potamogeton (pondweeds), Ceratophyllum demersum (hornwort), and Elodea canadensis (common waterweed) (Choi et al., 2002). Adults, due to their short lifespan, do not actually feed.

Use as Biological Control

The habitats in which Acentria ephemerella live in Europe are home to Myriophyllum spicatum, or Eurasian watermilfoil. Much like A. ephemerella, Eurasian watermilfoil is also an invasive species in North America, categorized as a noxious weed, and devastates native pond and lake vegetation by outcompeting native species. In their native habitat, A. ephemerella is a common herbivore to the milfoil, earning it one of its common names, the watermilfoil moth. Due to this natural dynamic between the two species, it has been discussed for A. ephemerella to be introduced to areas with invasive Eurasian watermilfoil to be used as a biological pest control agent, along with several other insect species like the larvae of Criscotopus myriophylli and Euhrychiopsis lecontei (milfoil weevil) (Gross et al., 2000). Studies that have been carried out have shown promise to using A. ephemerella as a way to decrease the biomass of Eurasian watermilfoil. In a paper published in Aquatic Ecology in 1997 by Robert L. Johnson, Elisabeth M. Gross, and Nelson G. Hairston, Jr., the authors detail how the biomass of Eurasian watermilfoil drastically decreased in Cayuga Lake in northern New York following the first confirmed sighting of A. ephemerella larvae in the lake. Notably, the biomass of aquatic plants in the lake did not decrease as native plants gained abundance. The authors conclude that this is because although A. ephemerella are generalist feeders, the life cycle is more closely tied to the Eurasian watermilfoil because the larvae will use the apical tips and stems as refuge during the winter and summer (Johnson et al., 1997). However, even though this study seemed to show positive prospects for A. ephemerella being used as a biological pest control agent, it has thus far not been introduced to any areas to aid in controlling the Eurasian watermilfoil population. This could be due to hesitancy from local ecologists to introduce another exotic species to the habitat that could have unforeseen negative effects on the environment. Another factor could be that the moth seems to spread fairly well on its own, having moved into many bodies of water in Canada and the United States over the past 100 years.

Citations

Acentria Ephemerella (Denis & Schiffermüller, 1775). GBIF. (n.d.). Retrieved December 7, 2021, from https://www.gbif.org/species/4531687.

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

Choi, C., Bareiss, C., Walenciak, O., & Gross, E. M. (2002). Impact of polyphenols on growth of the aquatic herbivore Acentria ephemerella. Journal of Chemical Ecology, 28(11), 2245-2256.

Gross, E. M., Johnson, R. L., & Hairston Jr, N. G. (2001). Experimental evidence for changes in submersed macrophyte species composition caused by the herbivore acentria ephemerella (Lepidoptera). Oecologia, 127(1), 105–114. https://doi.org/10.1007/s004420000568

Johnson, R. L., Gross, E. M., & Hairston, N. G. (1997). Decline of the invasive submersed macrophyte Myriophyllum spicatum (Haloragaceae) associated with herbivory by larvae of Acentria ephemerella (Lepidoptera). Aquatic Ecology, 31(3), 273-282.

Miler, O., Gross, E. M., & Straile, D. (2014). Small-scale variation in sexual size dimorphism and sex ratio in the aquatic Mothacentria Ephemerelladenis and Schiffermüller, 1775 (Lepidoptera: Crambidae). Aquatic Insects, 36(3-4), 187–199. https://doi.org/10.1080/01650424.2015.1066015.

Mills, E. L., Leach, J. H., Carlton, J. T., & Secor, C. L. (1993). Exotic species in the Great Lakes: A history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research, 19(1), 1–54. https://doi.org/10.1016/s0380- 1330(93)71197-1

Scholtens, B. G., & Balogh, J. (1996). SPREAD OF ACENTRIA EPHEMERELLA (LEPIDOPTERA: PYRALlDAEIIN CENTRAL NORTH AMERICA. Great Lakes Entomologist, 29(1), 21.

Water Veneer Acentria Ephemerella. UKmoths. (n.d.). Retrieved December 7, 2021, from https://www.ukmoths.org.uk/species/acentria-ephemerella/.