Euhrychiopsis lecontei (Coleoptera: Curculionidae)
The aquatic weevil, Euhrychiopsis lecontei, has the potential to serve as an agent of biological control against the aquatic weed, Eurasian watermilfoil (Myriophyllum spicatum). Eurasian watermilfoil is an exotic species of submersed aquatic plant that arrived in North America in the mid 1900ís. Since its introduction, Eurasian watermilfoil has become a major nuisance plant, spreading to 45 states and at least3 Canadian Provinces. Thick beds of Eurasian watermilfoil plants clog canals, lakes and ponds all across North America while boats continue to carry Eurasian watermilfoil fragments to new bodies of water where they grow into new Eurasian watermilfoil infestations. Lake managers try to control Eurasian watermilfoil by harvesting the plants, adding benthic barriers, drawing down water levels during the winter, and applying herbicides. These methods are costly, rarely specific to watermilfoil, and often require frequent re-application. Using herbivorous insects as a means of biological control may prove to be a cost-effective and environmentally sensitive alternative.
E. lecontei is a weevil species which is native to North America. This weevil, a watermilfoil specialist, traditionally feeds on the native northern watermilfoil (Myriophyllum sibiricum), and now feeds on Eurasian watermilfoil as well. Many scientists believe that large weevil populations contribute to Eurasian watermilfoil decreases in some lakes in Vermont, New York, and Minnesota.
E. lecontei adults are smaller than most terrestrial weevils, measuring only 3 mm in length. This weevil is generally dark-colored with a pattern of dark brown/black and yellowish stripes on the dorsal half, fading to a lighter, yellow-beige underbelly. However, some weevil individuals vary in color from almost completely black to mainly tan or beige. The eggs are round and opaque yellow in color, with a diameter of 0.5 mm. The larvae are a translucent greenish or whitish color with a dark purple-black head capsule. As the larvae age, they begin to turn a purplish gray color, indicating that they are nearing pupation. Pupae take on an immature adult form: a head with a long snout and closely jointed thorax and abdomen with wings (elytra), although they are immobile and the exoskeleton is still soft. The pupae develop mature color patterns just before emerging from the pupal chamber as adults.
E. lecontei inhabit temperate lakes and ponds where watermilfoils (Northern and/or Eurasian) are abundant. Both species of watermilfoil (and the weevils that feed on them) thrive in lakes with varying sediment types, water chemistries, and flow rates. Weevil populations are largest in small, shallow lakes where watermilfoil grows near the shore. Each fall, adult weevils migrate to shore where they spend the winter in loose soil, plants, and leaf-litter. Because of this yearly migration, weevil populations may be restricted in lakes where watermilfoil beds are far from the shore (increased fish predation), or where shorelines are highly developed (no leaf-litter).
E. lecontei attacks the invasive weed, Eurasian watermilfoil (M. spicatum). Eurasian watermilfoil is an aggressive species, which can quickly dominate an aquatic community, shading out desirable native species by forming a canopy on the surface of the water. These canopies of Eurasian watermilfoil also limit human recreational uses of the water (boating and swimming), and cause shoreline property values to fall.
E. lecontei adults swim and climb from plant to plant, feeding on leaflets and stem material. After mating, the female lays an average of 1.9 eggs a day, usually one egg per watermilfoil apical meristem (growing tip). One female may lay hundreds of eggs in her lifetime. The eggs hatch, and the larvae first feed on the apical meristem, and then mine down into the stem of the plant, consuming internal stem tissue. Weevils pupate inside the stem in the pupal chamber, a swelled cavity in the stem. Adults emerge from the pupal chamber to mate and lay eggs. In the autumn, adults travel to the shore where they over-winter on land. In the laboratory, E. lecontei take from 20 to 30 days to complete one life cycle, depending on water temperatures. For complete development, weevils require about 310 degree-days with temperatures above 10 degrees C. In the field, we generally observe 2 to 4 generations per year.
In laboratory and lake-enclosure experiments, as well as in natural lake systems, we find high levels of damage to Eurasian watermilfoil plants associated with large numbers of E. lecontei. However, the high levels of seasonal damage that we observe in the field, may not translate into long-term declines in Eurasian watermilfoil populations (measured as plant biomass, stem density, and/or plant height). E. lecontei seem to be contributing to some short-term declines in Eurasian watermilfoil in some Vermont, Minnesota, and New York Lakes, but not in others. Current research is focusing on the roles of fish predation and over-wintering habitat on E. lecontei populations and their possible biological control properties.
The direct effects of herbicides on E. lecontei are unknown, although any effective herbicide may harm E. lecontei indirectly by eliminating their host plants.
Mechanical harvesting, herbicide applications, benthic barriers, and water draw-downs all remove either E. lecontei individuals or their habitat (aquatic plants) from waterways. In doing so, these popular control methods lessen the ability of the weevil to control watermilfoil growth biologically.
E. lecontei populations rely on natural shorelines with dry shelter (leaf-litter) for overwintering habitat. Loss of natural shorelines may reduce winter survival of E. lecontei.
For more information about E. lecontei biology please visit: http://www.fw.umn.edu/research/milfoil/milfoilbc/weevil.html.
Eggs and larvae are available from EnviroScience, Inc.at:
Thanks to Dr. Ray Newman and Dr. Bern Blossey for reviewing this page.
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R.M. Newman and D.D. Biesboer. 2000. A Decline of Eurasian Watermilfoil in Minnesota Associated with the Milfoil Weevil, Eurychiopsis lecontei. Journal of Aquatic Plant Management, 38 (2).
Newman, R.M., D.C. Thompson, and D.B.Richman. 1998b. Conservation Strategies for the Biological Control of Weeds. P. Barbosa (ed.) Conservation Biological Control. Academic Press, NY, NY pp. 371-396.
Smith, C. S. and J.W. Barko. 1990. Ecology of Eurasian Watermilfoil. Journal of Aquatic Plant Management. 28:55-64.
Solarz, S.L. and Newman, R.M. 2001. Variation in Hostplant Preference and Performance by the Milfoil Weevil, Euhrychiopsis lecontei Dietz, Exposed to Native and Exotic Watermilfoils. Oecologia 126 (1) , pp 66-75. http://link.springer.de/link/sercive/journals/00442/bibs/1126001/11260066.htm.