Tanysphyrus lemnae
Paykull/Fabricius, 1792
Common Name:
Duckweed/aquatic weevil
Synonyms and Other Names:
duckweed weevil, aquatic weevil
Identification:
Adults of this aquatic weevil or rhynchophorous beetle exhibit a mottled or dull black elytra that is wider than the thorax by half. They display brown antennae and tarsi. The hind legs have bilobed third segments. In adults at rest, the cylindrical beak curves back into the prosternum. The anterior coxae are contiguous. There are various widely spaced hair-scales for protection upon occasional immersion. Larvae are transparent to translucent beige with yellow-brown heads in older individuals (Leconte and Horn 1876; Scotland 1934; Tanner 1943; Thorpe and Crisp 1949; Pennak 1978; Merritt and Cummins 1984; Center et al. 2002).
Tanysphyrus lemnae adults are around 1.2–1.5 mm long by 0.6 mm wide, while neonates are 0.5 mm long, and larvae are 3 mm long right before they pupate (Scotland 1934; Pennak 1978; Center et al. 2002).
Size:
1-3 mm
Native Range:
Tanysphyrus lemnae is native to Europe (Mills et al. 1993).
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This map only depicts Great Lakes introductions.
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Great Lakes Nonindigenous Occurrences:
The earliest record of T. lemnae in the Great Lakes basin is from 1934 in Ithaca, New York, which is located on Cayuga Lake, part of the Lake Ontario drainage. It is known from a large area in the Lake Ontario and Lake Michigan watersheds, including parts of Wisconsin, New York, and Michigan (Scotland 1934; Tanner 1943; Bayer and Brockmann 1975; Mills et al. 1993; Duggan et al. 2003).
Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Tanysphyrus lemnae are found here.
Table last updated 5/2/2024
† Populations may not be currently present.
Ecology:
Tanysphyrus lemnae is an herbivorous shredder of floating hydrophytes. It requires a host plant and is usually associated with duckweeds (Lemna spp.) and duckmeats (Spirodela spp.). However, it can also be found on other species. For example, in Florida it is specifically associated with exotic water lettuce (Pistia stratiotes) (Merritt and Cummins 1984; Lillie 1991; Dray et al. 1993; Center et al. 2002).
This weevil lays off-white to yellow eggs one at a time in the thalli of floating hydrophytes. Eggs develop in tunnels in the space between the upper and lower epidermis, in holes plugged with frass (macrophyte pieces mixed with excrement). When emerging from the tunnels, larvae eat their way out, consuming the first thallus in 12 hours then burrowing and/or swimming short distances to the next. Adults also consume floating thalli, eating large holes into them. Larvae typically find their way to the riparian zone and pupate in the soil or under clumps of macrophytes. The total generation time for T. lemnae is around 16–20 days (Scotland 1934; Center et al. 2002)
Adult T. lemnae are not able to swim and live on their host plant species. However, occasional submersion does occur, and they can survive (Thorpe and Crisp 1949).
Means of Introduction:
Unknown.
Status:
Established where recorded.
Great Lakes Impacts:
Current research on the environmental impact of Tanysphyrus lemnae in the Great Lakes is inadequate to support proper assessment.
There is little or no evidence to support that Tanysphyrus lemnae has significant socio-economic impacts in the Great Lakes.
There is little or no evidence to support that Tanysphyrus lemnae has significant beneficial effects in the Great Lakes.
Management:
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
There are no known biological control methods for this species.
Physical
There are no known physical control methods for this species.
Chemical
There are no known chemical control methods for this species.
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.
Remarks:
The small size of this beetle (1.5 mm) and its life-history, in and on tiny floating plants of the genus Lemna (duckweeds) mean that this insect is probably frequently overlooked. Recent reports of this insect are rare, probably reflecting its inconspicuousness rather than its abundance.
References
(click for full reference list)
Author:
Kipp, R.M., J. Larson, and A. Fusaro
Contributing Agencies:
Revision Date:
12/6/2019
Citation for this information:
Kipp, R.M., J. Larson, and A. Fusaro, 2024, Tanysphyrus lemnae Paykull/Fabricius, 1792: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatLakes/FactSheet.aspx?Species_ID=2363&Potential=N&Type=0&HUCNumber=DGreatLakes, Revision Date: 12/6/2019, Access Date: 5/2/2024
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.