Acentria

Distinguished from other Crambidae by the combination of aquatic habitat and extreme female wing dimorphism. Males resemble small white pyralid moths but are identified by association with water and swarming behavior at lights. Flightless females are unique among moths: small white insects found on or just below water surface with stubby non-functional wings. Winged females larger than males. Larvae recognized by aquatic habitat, light olive-green color, and case-building behavior in late instars.

Adult males are small white moths with wingspan approximately 12 mm; forewings whitish with obscure brownish veins and costa, hindwings whitish. Females exhibit pronounced wing dimorphism: most are brachypterous with rudimentary non-functional wings and remain aquatic, while a minority possess longer wings up to 23 mm and are capable of flight. Aquatic females possess swimming hairs on second and third legs and modified compound eye structure adapted for underwater vision. Larvae are light olive-green with light brown head.

Freshwater lentic habitats including ponds, lakes, and marshes. Larvae inhabit submerged aquatic macrophytes. Adults occur at water surface or in terrestrial environment depending on sex and female morph.

Native to Europe where widespread; introduced to North America with established populations in northeastern United States and Canada. Documented in New York State lakes, including Cayuga Lake and Seneca Lake.

Adult males active in summer, attracted to light and capable of swarming in thousands on warm humid nights. Larval stage lasts approximately 42 weeks with pupation and emergence in summer. Larvae overwinter in cocoons on macrophytes.

Larvae feed on aquatic macrophytes including pondweeds (Potamogeton spp.), Canadian waterweed (Elodea canadensis), and Eurasian watermilfoil (Myriophyllum spicatum). Not a specialist feeder; laboratory studies demonstrate consumption of wide variety of submerged macrophytes.

• Myriophyllum spicatum - primary host for life cycle refuge and feedingLife cycle closely tied through use of apical tips for summer refuge and stems for winter refuge; preferred over other plants
• Potamogeton spp. - host plant for feeding and oviposition
• Elodea canadensis - host plant for feeding and oviposition

Egg masses laid on aquatic plants by females diving from surface. Larvae emerge and bore into plant stems, constructing shelters from glued plant material. Late instars build cases. Larvae girdle stems while feeding, causing plant damage. Pupation occurs inside underwater cocoons filled with air. Adults emerge and swim to surface; males and flighted females fly away, flightless females remain aquatic.

Adult males live 1-2 days solely for breeding, mate with aquatic females at water surface. Males strongly attracted to light, forming large swarms on warm humid nights. Aquatic females possess swimming hairs on legs for underwater locomotion. Larvae construct protective shelters and cases from plant material. Cryptic habits make detection difficult.

Herbivore of aquatic macrophytes. Contributes to decline of invasive Eurasian watermilfoil biomass, with associated increase in native macrophyte abundance. Used as biological control agent, though lacks host specificity and will attack native plant species.

Employed as biocontrol agent against invasive Eurasian watermilfoil (Myriophyllum spicatum), but requires careful management due to non-specific host range. Potential to reduce watermilfoil infestations in northeastern United States documented.

• Nymphula nitidulataBoth are aquatic crambid moths with semi-aquatic larvae; distinguished by N. nitidulata larvae living on wetland plants above water line rather than fully submerged, and by lack of extreme female wing dimorphism
• Bellura spp.Both have aquatic caterpillars; Bellura larvae breathe by periodic surfacing and lack the extreme sexual dimorphism and fully aquatic adult females of Acentria

• freshwater
• sexual dimorphism
• brachypterous
• biocontrol
• invasive species management
• aquatic insect
• case-building larva
• monotypic genus

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Comparative Cytogenetics | Blog - Part 2
• The Lepidopteran Life Aquatic
• Decline of the invasive submersed macrophyte Myriophyllum spicatum (Haloragaceae) associated with herbivory by larvae of Acentria ephemerella (Lepidoptera)
• The genome sequence of the Water Veneer, Acentria ephemerella (Denis & Schiffermüller, 1775).