Two insect herbivore species have been found to be commonly damaging duckweeds:
The duckweed weevil Tanysphyrus lemnae (Coleoptera: Curculionoidea) (Figure 4) is one of the most common and widespread duckweed herbivores . This weevil is characterized as having a mottled, black and brown colored elytra, light brown legs and antennae, and having a bilobed third tarsal segment on the hind legs  (Figure 5).
Figure 4 – (a) Adult Duckweed weevil, Tanysphyrus lemnae, feeding on the leaf of duckweed;
(b) adult duckweed weevil walking across a colony of duckweed (Pictures by Carlos Wiggins, 2019).
Figure 5 – (a) Lateral view of the duckweed weevil showing the characteristic mottled black
and brown coloration of the elytra; along with the lighter brown colored legs and antennae;
(b) SEM image of the Duckweed Weevil showing the lateral view in greater details (image provided
by Michael J. Grodowitz: Research Leader – Supervisory Entomologist -USDA).
Figure 6 - (a) Adult duckweed weevil walking across open water between duckweed leaves.
(Pictures by Carlos Wiggins, 2019); (b) SEM image of the thorax and legs of adult Duckweed Weevils,
showing the scales which help in providing the hydrophobic surface of the weevil
(image provided by Michael J. Grodowitz: Research Leader – Supervisory Entomologist -USDA).
The female weevil chews a hole into the surface of a plant and then lays eggs one at a time in the frond parenchyma. Eggs develop in tunnels in the space between the upper and lower surface of the frond, and then plugs the holes with leaf tissue mixed with excrement. After a week, larvae emerge from inside the frond, eating their way out and tunneling while doing so (Figure 7). The first frond is completely consumed in twelve hours (Figure 7 a), then they dig down to the next one or swim to it (but only for short distances) (Figure 7 b,c). Larvae typically leave the fronds to pupate in the soil of the riparian zone shorline. Adults also consume floating fronds, causing characteristic large round holes damaging the plants (Figure 8). The total generation time for T. lemnae from egg to adult is around 16-20 days [12, 13].
Figure 7 - Duckweed weevil larva feeding within the parenchymal tissue of a duckweed leaf.
(Pictures byFlaminia Mariani, 2021).
This weevil species is native to Europe. Currently, the distribution of T. lemnae in the U.S. includes 23 states .
The duckweed weevil can feed and reproduce on several species of Lemnoideae [12, 17]. Observations in Louisiana suggest that weevil larvae and adults can feed on Lemna spp., Spirodela spp. and Ladoltia punctata (Flaminia Mariani personal observations).
The presence of the weevils on duckweed populations may be recognized by the circular holes left in duckweed leaves as a result of the adults feeding externally on the leaves (Figure 8). In addition, feeding damage by the larvae can be recognized by transparent leaves as a result of internal feeding (Figure 7). To date, no study has shown the impact of this insect on duckweed populations .
Figure 7 - (a) Damaged duckweed leaf done by adult duckweed weevil (lower left),
compared to undamaged leaf (upper right). (Pictures by Carlos Wiggins, 2019);
(b) SEM image of the chewing mouthparts of adult Duckweed Weevils.
(image provded by Michael J. Grodowitz: Research Leader – Supervisory Entomologist -USDA).
Lemnaphila scotlandae Cresson (Diptera: Ephydridae) is a dipteran native to America which grows primarily on Lemnoideae. It is the only species of the genus present in the United States . This fly is considered one of the smallest insects that attacks an aquatic plant. Adults are small (1.2 mm) black flies with yellow-tipped legs (Figure 9) .
Figure 9 – (a) Lemna fly adult on duckweed; (b) Feeding damage from Lemna fly larvae
(Pictures by Flaminia Mariani, 2021).
Adult females lay yellowish ovoid eggs in the margin of the upper surface of the frond, usually a single egg per frond. After two days, the larva breaks the egg shell, and begins to burrow a small tunnel into the frond with its mouthparts. From here it feeds on the spongy parenchyma, ingesting the torn tissue. After completely consuming the frond, the larva may move to the adjacent frond to continue feeding. The larval stage lasts 10 days and includes three stages. The pupa stage lasts 4 days, after which the adult fly emerges. Although the adult can fly, it does not take full advantage of this ability: as soon as it unfolds its wings it begins to feed on duckweeds frond parenchyma, digging characteristic parallel tunnels on the upper surface of the plant (Figure 10) [17, 18]. The reduced parenchyma of duckweeds is able to provide enough food to meet all the needs for its survival, which is limited to a time span of only three days .
The fly can feed and reproduced on several species of Lemnoideae . Observations in Louisiana suggest that fly larvae and adults can feed on Lemna spp., and Ladoltia punctata (Flaminia Mariani personal observations).
The duckweed fly was first reported from Ithaca, New York. It has since been reported from Illinois, Michigan, Ohio, and Florida, but it likely occurs throughout the eastern United States .
Unlike most ephydrids, the adults feed on the plant. They rasp the upper surface of duckweed thalli with spines located on their mouthparts, creating distinctive parallel gouges. To date, no study has shown the impact of this insect on duckweed populations.
 Landolt, E., 1986. Biosystematic investigations in the family of duckweeds (Lemnaceae) Vol. 2: The family of Lemnaceae: a monographic study. – Morphology, karyology, ecology, geographic distribution, nomenclature, descriptions. Zürich: Eidgenössische Technische Hochschule Zürich.
 Keddy, P.A., 2010. Fertility. Wetland Ecology: Principles and Conservation (2nd ed.). Cambridge: Cambridge University Press.
 Dussart, G., Robertson, J., and Bramley, J., 1993. Death of a lake. Biololgical Sciences Review 5 (5), 8–10.
 Janes, R.A., Eaton, J.W., and Hardwick, K., 1996. The effects of floating mats of Azolla filiculoides Lam. and Lemna minuta Kunth on the growth of submerged macrophytes. Hydrobiologia 340 (1-3), 23–26.
 Weakley, A.S., 2020. Flora of the southeastern United States. University of North Carolina Herbarium, North Carolina Botanical Garden, Chapel Hill, NC.
 Men, B., Ogle, B., and Lindberg, J., 2002. Use of Duckweed as a protein supplement for breeding ducks. Animal Bioscience; 15(6), 866–871.
 Gupta, C., and Prakash, D., 2013. Duckweed: an effective tool for phyto-remediation. Toxicological & Environmental Chemistry, 95(8), 1256–1266.
 Ceschin, S., Crescenzi, M., and Iannelli, M.A., 2020. Phytoremediation potential of the duckweeds Lemna minuta and Lemna minor to remove nutrients from treated waters. nvironmental Science and Pollution Research 27, 15806–15814
 Dial, N.A., Bauer, C.A., 1984. Teratogenic and lethal effects of paraquat on developing frog embryos (Rana pipiens). Bull. Environ. Contam. Toxicol. 33, 592-597.
 Rzymski, P., Klimaszyk, P., Kubacki, T., Poniedziałek, B., 2013. The effect of glyphosate-based herbicide on aquatic organisms – a case study. Limnol. Review 13 (4), 215-220.
 Ceschin, S., Della Bella, V., Piccari, F., Abati, S., 2016. Colonization dynamics of the alien macrophyte Lemna minuta Kunth: a case study from a semi-natural pond in Appia Antica Regional Park (Rome, Italy). Fundam. Appl. Limnol. 188 (2), 93-101.
 Center, T.D., Dray, F.A.Jr., Jubinsky, G.P., and Grodowitz, M.J., 2002. Insects and other arthropods that feed on aquatic and wetland plants. USDA/ARS Technical Bulletin 1870.
 Kipp, R.M., J. Larson, and A. Fusaro, 2021. 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: 8/4/2021
 Mills, E.L., Leach, J.H., Carlton, J.T., and 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.
 Thorpe, W.H., and Crisp, D.J., 1949. Studies on plastron respiration. IV. Plastron respiration in the Coleoptera. Journal of Experimental Biology 26:219-260.
 Buckingham, G., 1989. Lemnaphila scotlandae (Diptera: Ephydridae) and three of its parasites discovered in Florida. The Florida Entomologist, 72(1), 219–221.
 Scotland, M.B., 1934. The animals of the Lemna association. Ecology 15 (3).
 Scotland, M.B., 1940. Review and summary of studies of insects associated with Lemna minor. Journal of the New York Entomological Society, 48(4), 319–333.