Herbivores and Pathogens:
Animals and microorganisms that feed on duckweeds.
duckweeds serve as a
food source for a wide variety of
animals and microorganisms. These range from familiar birds and
fish that may
duckweeds as part of their diet to little-known
insects and microorganisms
with specialized dependency on these
plants. Aquaculture systems have been designed in which
domesticated fowl or fish are raised on duckweed grown in managed
ponds. In other cases, herbivorous fish or insects are
to control unwanted growth of duckweeds. This page provides
information on just a few of the organisms that feed on duckweeds
Right: Photo of ducks at the Phoenix Zoo, courtesy of Gayla Chandler.
Insects That Feed on Duckweeds
Two small insects are so commonly associated with Lemnaceae that
their names reflect this fact:
Lemnaphila scotlandae Cresson
duckweed fly grows primarily on duckweeds and is one of
insects to attack an aquatic
The eggs are usually yellowish (0.3 mm long by 0.08 mm wide), with parallel ridges running lengthwise and are usually laid singly on the edges of the fronds. The incubation period is about 2 days, and the white larva digs down and feeds on the mesophyll tissue, tearing it apart with mouth hooks and then ingesting the macerated tissue. After completely clearing out one frond, the larva transfers to an adjacent frond to continue feeding. The larvae can also swim to other duckweed plants separated by open water. The larval stage comprises three instars and requires
about 10 days.
Two black-tipped, cone-shaped structures on the posterior end of the abdomen are thrust into the lower epidermis of the frond prior to pupation. The pupa are amber in color and about 1.5 mm long. The pupal stage lasts about 4 days.
The adult emerges by inflating a specialized bladder-like structure that then ruptures the anterior end of the puparium. The emerging adult crawls through this opening and forces apart the epidermal layers of the frond to exit the frond. Feeding begins very soon after, but mating and egg laying are delayed until the second day. Although these insects can fly, their flights are usually low hops of a few inches. Adults probably only live about 3 days.
This fly has since been reported in Illinois, Michigan, Ohio, and Florida, but likely occurs throughout the eastern US.
Tanysphyrus lemnae Paykull
weevil Tanysphyrus lemnae is one of
the most common and widespread duckweed herbivores.
The female lays her eggs one by one directly into the frond through a hole she chews into it. The eggs are inserted through the top surface of the frond and generally fill the space between the upper and lower surfaces. The female then plugs the hole, probably using feces.
Eggs hatch in about a week into nearly transparent larvae about 0.5 mm in length. The newly hatched larvae immediately begin to feed. Each larva eats most of the frond that contained the egg within the first 12 hours. If other fronds are connected to the first, the larva will burrow directly from one to the next, and if not, will swim from one to the next. The larvae consume the green contents of the fronds, leaving most of the epidermis intact. As the larva grows, it takes on a translucent beige color with a yellow-brown head and lengthens to about 3 mm.
Pupation occurs along the shoreline in the soil or under stranded duckweed. The total generation time is about 16–20 days. Adults feed by chewing on the surfaces of the fronds, causing obvious round perforations.
Aphid, Rhopalosiphum nymphaeae (Linnaeus)
In addition to water lilies, this aphid feeds on many other species. It is also known as the “reddish-brown plum aphid”, a name that is derived from its association with fruit trees, particularly during winter. This insect is widely distributed (cosmopolitan), and has long been known as a pest of cultivated aquatic plants. Aphids suck sap from plant leaves, but can also cause damage by transmitting plant viruses. The waterlily aphid is extremely destructive in aquatic gardens and nurseries and is known to transmit at least five plant viruses.
Winged adult females migrate from aquatic habitats to
trees in late fall and lay their eggs on the trees.
overwinter, and, after hatching, subsequent generations
and early summer on the fruit trees.
After colonizing aquatic sites, the aphids reproduce
developmental period from the birth of the first instar to
stage ranges from 7 to 10 days, depending upon temperature
21-27°C). Each female produces up to 50 nymphs at an
of two to four nymphs per day. The nymphs normally
five instars during the course of their development,
although they will
occasionally produce a sixth instar.
Photos above: A, Adult female and
nymphs of the waterlily aphid. B, Relatively
waterlily aphid colony on the
underside of a waterlettuce leaf.
myriotylum, a root and stem rot fungus.
|Rejmankova et al.
from dying duckweeds growing in
affected Louisiana lagoons.
its pathogenicity towards duckweeds in
cultivation tanks and under
conditions in lagoons. The quantity of duckweeds
killed by the
fungus increased exponentially and a whole stand would
die in several
days. Of six duckweed species tested in
gibba, L. minor, and Spirodela
polyrrhiza were the
most susceptible to the fungal infection. Lemna
was more resistant, while L. aequinoctialis and
punctata never showed symptoms
. The optimum temperature for infection was at
Pythium myriotylum is one of the most common species of Pythium found in the soil in damp climates, often causing damping-off of seedlings and root-rot, so this species cannot be said have any special affinity for duckweeds. These fungi produce masses of microscopic, motile zoospores (see drawing) that can swim short distances to attack wet surfaces of plants. The fungi produce enzymes that break down the pectin in plant cell walls. Pectin breakdown results in a soft, watery rot. Pythium can survive indefinitely in the soil as a saprophyte, feeding on soil organic matter. In the soil it can also form thick-walled sexual oospores (see drawing). Oospores are the primary overwintering form. Pythium species are not vigorous competitors with other microorganisms in the soil. The fungi are disseminated in surface-drainage water and in infested soil on farm equipment, tools, and the feet of humans and animals.
Above: Drawings of Pythium, (a) oogonia fertilized with monoclinous antheridia; (b) inflated sporangium (vesicle) containing immature zoospores; (c) typical sporangium; (d) two zoospores. Drawing by L. Gray.
Reference, see Univ. of Ill. RPD No. 922, 1989.
USDA/ARS Insects and Other
Arthropods That Feed on Aquatic and
Wetland Plants. Technical Bulletin 1870 October 2002 http://www.ars.usda.gov/is/np/aquaticweeds/aquaticweeds.pdf
Mansor, M; Buckingham, GR (1989) Laboratory host range studies with a leaf-mining duckweed shore fly. Journal of Aquatic Plant Management 27: 115-118.
Rejmankova E, Blackwell M, Culley DD. (1986) Dynamics of fungal infection in duckweeds (Lemnaceae). Veroeffentlichungen des Geobotanischen Institutes der Eidgenoessische Technische Hochschule Stiftung Ruebel in Zuerich 0(87): 178-189.
Scotland, M.B. 1940. Review and summary of insects associated with Lemna minor. Journal of the New York Entomological Society 48:319–333.
Univ. of Illinois, Dept. of Crop Sci., "Root and stem rots of garden beans." Report on Plant Disease, RPD No. 922, May 1989. http://web.aces.uiuc.edu/vista/pdf_pubs/922.PDF
Wagner, D.T. (1969) Monocentric holocarpic fungus in Lemna minor L. [Ressia amoeboides] Nova Hedwigia 8 (1): 203-208.
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Revised: December 10, 2005