From cgl1@CORNELL.EDU Thu Feb 4 14:29:49 1993 Date: Thu, 4 Feb 1993 11:59:01 -0500 From: Chuck Goelzer Lyons Subject: NEWS: Aquatic Caterpillar May Controll Water Weed, Cornell Scientists Say To: Multiple recipients of list BIOSPH-L For Release Jan. 12, 1993 Cornell University News Service Village Green, 840 Hanshaw Rd, Ithaca, NY 14850-1548 Photos available Contact Roger Segelken, (607) 255-9736 Aquatic Caterpillar May Controll Water Weed, Cornell Scientists Say ------------------------------------------------------------------- ITHACA, N.Y.--A tiny caterpillar may be responsible for doing what herbicides and harvesters could not--controlling one of the worst aquatic weeds in the United States, Cornell University biologists say. The leaf-eating larvae of an aquatic moth may be the cause of dramatic declines observed in the weed, called Eurasian watermilfoil (Myriophyllum spicatum), in Ithaca's Cayuga Lake. If so, the moth could be a biological control agent, replacing or supplementing millions of dollars spent annually in the U.S. for artificial control. But more tests are needed to make that determination. "In the early 1970s, Eurasian watermilfoil made up 90 to 99 percent of the plant biomass in Cayuga Lake," said Robert L. Johnson, a Cornell ecology researcher. "The plants were growing from 3 to 20 feet long--and as long as 35 feet--starting from the lake bottom and reaching for light, forming dense canopies at the surface." Cayuga is one of the largest of central New York's Finger Lakes and is typical of freshwater bodies plagued by the fast-growing weed that was accidentally introduced into the United States from Europe sometime before 1900. It spreads from one lake to the next on boat trailers, propellers and even on the feet of migrating waterfowl. Outside the South, where warmer waters favor other species, Eurasian watermilfoil is the most serious aquatic weed problem in this country. "Eurasian watermilfoil was out-competing native plant species," Johnson said. "Boaters and swimmers complained, marinas closed because people thought the lakes were ruined. Only the fish didn't seem to mind." Beginning in 1986, Johnson's annual surveys of Cayuga Lake aquatic plants found a steady decline in Eurasian watermilfoil. By 1992, the nuisance plant had diminished to 10 percent of its biomass in the 1970s. Searching for causes, he looked for the moth, Acentria niveus, which Middlebury College biologists previously reported in milfoil plants of Lake George, between Vermont and New York State. The insect, also an exotic (non-native) species, was identified near Montreal as early as 1927 and has since been collected in Massachusetts and on the Canadian and U.S. sides of the Great Lakes. The Cornell biologist found hundreds of insect larvae--each about the size, shape and color of a grain of rice--eating the tips of Cayuga Lake's milfoil in the summer of 1992. The tiny caterpillars use their silken thread to bind milfoil's feathery leaves into individual nests called larval retreats, effectively halting growth of the plant stems. When the caterpillars are not consuming leaves that hold their retreats, they dine out on other plant parts, Johnson said. The larvae are believed to spend up to 10 months of their lives under water, before emerging as adults. Male moths fly for a few days, then mate at the water's surface with females. Female aquatic moths submerge to lay eggs on underwater plants, and the cycle begins again. Cornell entomologists John G. Franclemont and E. Richard Hoebeke identified the Cayuga Lake moths as the same species or a close relative to the ones found in Lake George. Just because aquatic moths thrive where Eurasian watermilfoil declines does not mean a successful biological control for the weed has been found, cautioned Nelson G. Hairston Jr., a Cornell professor of ecology and systematics. Controlled experiments could determine whether other factors are involved, he said. For example, some disease may be affecting the plants' health, making them more vulnerable to insect predation. Or water turbidity (cloudiness) from algal blooms in the early season (when milfoil plants try to reach for the surface) may retard their growth, he said. At Cornell's experimental ponds, where controlled studies of aquatic weeds and other plants and animals are planned for 1993, biologist Johnson is not ready to ship moths to every lake with a Eurasian watermilfoil problem. But their presence, he said, complicates strategic planning for aquatic weed control. Weed-harvesting machines, which cut the tops of aquatic plants in some lakes, also may remove beneficial insects. The harvesting machines' effectiveness already is in doubt from Cornell studies that found weed-cutting may actually encourage weed growth, Johnson said. Stray pieces of aquatic weeds from the harvesters take root on lake bottoms, the same way gardeners produce new plants from cuttings. Further, the weed cutting only temporarily opens lanes for boating and swimming, Johnson's measurement of plant growth has shown. Like a fresh-mown (and well-watered) lawn, the Eurasian watermilfoil soon rebounds even stronger than before. ------------------------------------------------------------------- Chuck Goelzer Lyons, cgl1@cornell.edu, Ithaca, NY 14853-5001 From x92nca@ESSEX.STFX.CA Thu Feb 4 14:30:49 1993 Date: Thu, 4 Feb 1993 13:50:47 AST From: DAVID SPENCER Subject: water weed To: Multiple recipients of list BIOSPH-L There is a project involving water weed eating bugs in Sri Lanka, also maybe Venice. I don't have any ref. knowledge of both was gained from popular media...(Toronto Globe and Mail) and CBC TV. Seems to me that the Sri Lankian project is well documented and is a coop venture between local group and Austrialian folks...just a passing note David Spencer X92NCA@ESSEX.STFX.CA