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How to identify it
- Adults are about 2 mm long with a nearly straight snout that has an obvious constriction at its base. They range from golden-brown to bluish-gray, and bare patches where the scales have rubbed off the wing covers give them a chevron-like pattern. Females are usually slightly larger than males.[1]
- The surest signs are on the leaves: a distinctive larval mining trail, clearly visible through thin leaf tissue, and the round feeding holes chewed by adults, which sometimes bite on into the spongy tissue. Other insects feed on water lettuce now and then, but their damage is inconsistent and sporadic.[1]
- Larvae are white or yellow with a brown head and up to 3 mm long; pupae are cream-colored and only up to 2 mm; eggs are small, oval and cream. All live inside the leaf.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Water lettuce moth (Spodoptera pectinicornis) | A leaf-feeding moth from Thailand released in Florida and Texas from 1990 as a second water lettuce agent; its mottled brown adults have a 19 to 23 mm wingspan and its larvae reach 25 mm, far larger than the weevil. Its populations dwindled and it can no longer be detected.[1] |
Where it lives
Weevils originally collected in Brazil were released in Australia, and from Australia they were redistributed to Florida beginning in 1987 and then to other southern states. A 2013 attempt to move weevils from Louisiana to California failed when waterfowl compromised the release site. The weevil is established in three US states and disperses well.[1]
Biology and life cycle
In warm locations both the weevil and water lettuce develop all year round, with adults and pupae the stages most often found over winter. In its native range there are three generations a year.[1]
The female chews holes in the upper surface of a leaf near its margin and lays a single egg in each. The larva mines into the leaf and feeds toward the spongy tissue through three stages, then pupates inside the leaf. The emerging adult feeds on the leaves, leaving round holes.[1]
The weevil develops fastest and feeds most actively in warm weather and on large, nutrient-rich water lettuce plants.[1]
Damage and signs
- Larval and adult feeding destroy the leaves' buoyancy, and at high weevil densities the attacked plants sink and die; NAISMA documents a 10-acre pond at Torry Island on Lake Okeechobee, Florida, cleared this way.[1]
- Within 18 to 30 months of release, water lettuce was eliminated from three of the four original Florida release sites, and the weevil has proven effective at many sites in the southeastern United States. Establishment has not been universal, though, and long-term suppression of water lettuce has not been achieved. No nontarget effects have been reported.[1]
Health risk
A weevil that feeds only on water lettuce leaves; neither source describes any risk to people.[1][2]
Control
Traps and physical control
Water lettuce can also be raked or seined off a pond's surface; Texas A&M lists physical removal and herbicides alongside the insects.[2]
Biological control
The weevil is a water lettuce control, not a pest; Texas A&M lists it, with the water lettuce moth, among the insects that feed on the plant. Where it is present, leave it alone and let it work, remembering that it does best in warm weather on large, well-fed plants and that suppression has not lasted everywhere.[2][1]
Common questions
- How do I know if the weevil is in my water lettuce?
- Hold a leaf up to the light and look for the larval mining trail through the thin tissue, or check the leaves for round adult feeding holes. Finding the 2 mm golden-brown or bluish-gray adults or the white leaf-mining larvae confirms it.[1]
- Will the weevil get rid of water lettuce on its own?
- Sometimes. It cleared three of its first four Florida release sites within 18 to 30 months and has worked at many sites in the Southeast, but it has not established everywhere and has not kept water lettuce down over the long term.[1]
- Does it attack other pond plants?
- No nontarget effects have been reported; its known feeding is on water lettuce.[1]
Sources
- North American Invasive Species Management Association (PDF hosted on Bugwood), “Dray and Madeira (USDA-ARS Invasive Plant Research Laboratory). Waterlettuce Biocontrol Agents: History and Ecology in North America. In: Winston, ed., Biological Control of Weeds in North America, NAISMA-BCW-2022-23-WATERLETTUCE-A (2022).” bugwoodcloud.org/resource/files/23230.pdf (accessed 2026-11-10)
- Texas A&M AgriLife Extension, “How to Control Water Lettuce. AquaPlant: Management of Pond Plants and Algae.” aquaplant.tamu.edu/management-options/water-lettuce/ (accessed 2026-11-10)
- iNaturalist, “Neohydronomus affinis taxon page (order and family).” www.inaturalist.org/taxa/677444 (accessed 2026-11-10)