shadscale have been used successfully which may ultimately provide shrubs to pollinate bushes of four-wing salt- for soil stabilization on disturbed areas, bush. More than 300 hybrid seedlings beautification of the landscape, screen- have been produced from these crosses ing and cover on recreational areas, and are awaiting maturity for further and the restoration of big-game winter evaluation. This is all new research ranges.

The Snail, the Mermaid, and the Flea Beetle ROBERT D. BLACKBURN and LLOYD A. ANDRES

A fisherman's frustration try- Nature's weapons to maintain the ing to retrieve a lure through a heavy balance of nature between aquatic growth of weeds, or the look of disgust plants include plant-feeding insects, on a boating enthusiast's face as he diseases, fish, snails, and manatees. untangles a mass of weeds from the The role of each varies with the par- fouled propeller of his outboard, best ticular problem. Specialists often seek illustrate the problem of waterweeds. out these organisms in the native home Helping to solve this problem is an of the weed. Each is thoroughly inves- unlikely trio consisting of a snail, a tigated before introduction and cannot flea beetle, and a manatee—a blub- be released in the United States if it bery sea cow once believed to be a will attack any desirable species of our mermaid. But first of all, here is some insects or plants. background. Scientists can often select specific Aquatic weeds interfere with agri- organisms suited to the weed problem culture, navigation, transportation, and the degree of control desired. recreation, and flood control. They Those organisms that feed on a range pose health problems by serving as of plants are especially useful where host sites for disease-carrying orga- more than one weed is involved and nisms. Water skiers and swimmers open water is the desired result. On have drowned in lakes when entangled the other hand, a specific organism in dense -weed growths. may be sought to remove a particular Millions of dollars are spent annually plant without further disturbing the to control waterweeds in the United balance of nature. States. Chemical and mechanical means of control are often successful, but must be repeated frequently. Bio- ROBERT D. BLACKBURN IS a Research Botanist^ logical control, which uses living orga- Aquatic Weed Investigations, Crops Research Di- nisms to destroy pests, may be the vision. Agricultural Research Service, Fort Lauder- economical way to overcome the prob- dale, Fla. lem. This method has proved most LLOYD A. ANDRES is Ö Leader, Biological Control popular against aquatic weeds of of Weeds Investigations, Entomology Research foreign origin which flourish in this Division, Agricultural Research Service, Albany, country free of natural enemies. Calif. 229 In 1962, we teamed up at Fort At Fort Lauderdale, the war of snail Lauderdale, Fla., with a snail to con- versus aquatic weeds was waged in trol aquatic weeds. How fast is a concrete tanks filled with various spe- "snail's pace"? This question was con- cies of weeds. Snails put into the tanks tinually asked by fellow workers. fed vigorously on the submersed weeds : Biological control with the large pondweed, southern naiad, coontail, fresh water snail, Marisa cornuarietis L. elodea, and certain species of algae. (hereafter referred to as marisa) was To our great surprise, marisa ate all intriguing to the scientist. It was a the submersed weeds in 10 weeks. We dual-purpose biological agent. Marisa suddenly realized that the snail did could control waterweeds and as a not eat at a "snaiPs pace." consequence reduce snail- and mos- The snails fed on the roots of water- quito-borne diseases. hyacinth and waterlettuce, but would Marisa is native to the watersheds not move out of the water to consume of the Magdalena and Orinoco Rivers above-water leaves. However, they ate in South America. It has been found up the leaves of the floating weed, in Puerto Rico and many other Carib- salvinia, which could be devoured bean Islands. In 1957, marisa was without emerging from the water. discovered in Coral Gables, Fla. It had Immediately after introducing the been sold in the aquarium trade under snails into the tanks, we observed eggs the name "Colombian snail." Marisa's attached to the aquatic vegetation. plant-eating habits became well known When the snails were removed later in the aquarium trade, and the snail from both series of tanks, the popula- was soon listed as an undesirable tion had increased five to seven times. aquarium pest. Major disadvantage of marisa is it Adult marisa are mostly dark brown, may feed on rice, water cress, and with occasional three-planetary, thin, waterchestnuts. This would restrict its chocolate-colored stripes. Marisa use in some areas. reaches a maximum size of 2^ inches We stocked marisa in three small and is three-quarters of an inch thick. ponds near Fort Lauderdale in 1965 Shells vary considerably; thus, sexes at rates of 8,000 snails per acre. One cannot be differentiated upon the basis year later the ponds were free of sub- of shell characteristics. mersed weeds and remained clean Marisa eggs are laid in smooth, during 1966. Birds, rats, and certain whitish, oblong, gelatinous masses. fishes fed on the snails. However, The masses usually contain 70 to 100 prédation did not prevent the snail eggs and are attached to vegetation, from controlling weeds. concrete, rock, or wood surfaces. Aver- Snail populations appear to fluctu- age hatching time is 13 days. ate with the weed population in a The snail is exceptionally hardy. It closed body of water. Snails survived can survive at temperatures of 48° to in ponds free of submersed weeds by 110° F. It can tolerate highly polluted feeding on the algae that are attached water and water with a salinity of to rocks and soil. 2,500 parts per million. Stocking of snails into small lakes Marisa will not move out of water may need to be done before the weeds and is confined to this environment. become extremely dense. If the weed If streams dry up, the snail survives by population is dense, a combination of remaining tightly closed in its shell. chemical and biological control may The U.S. Public Health Service in be needed for satisfactory control. Puerto Rico found marisa can control Several aquatic herbicides are not other snails. Its indiscriminate feeding toxic to the snail ; however, water con- habits allow it to eat the eggs of taining low rates of copper sulfate and disease-carrying snails. Marisa carries insecticides will kill it. It should not be no disease of man and has actually stocked into waters containing any of been used as food in Puerto Rico. these chemicals. 230 Research initiated in 1967 under di- logically similar to our gulf coast. rection of Agricultural Research Serv- Lagunilla, the common name for alli- ice scientists at Fort Lauderdale will gatorweed in South America, was determine if the snails can be pro- found over much of this area, but duced in numbers sufficient for large never in the luxuriant abundance stocking programs. We feel a "marisa with which it has flourished in the factory" is the main objective of this United States. research program. Over 30 species of insects were found In contrast to the indiscriminate aflecting the weed. Massive attacks by feeding of marisa is the fastidious taste the Agasicles beetle had forced the of a flea beetle, Agasicles n. sp. The plant from its aquatic habitat and beetle is the entomologist's answer to onto the shores in many areas. It was the problem of controlling the im- the first candidate for study. ported alligatorweed {Âlternanthera phi- Argentine agricultural officials pro- loxeroides). In nature, this small beetle, vided laboratory space at the modern which obtained its name by the way Instituto Nacional de Technologia it hops, feeds only on alligatorweed Agropecuaria at Castelar (Buenos and will starve in its absence, a fact Aires) for testing the beetle. A study uncovered through careful scientific program was carried out by Donald sleuthing. It enabled the introduction Maddox, another Agricultural Re- of this insect to the United States with search Service entomologist. Failure assurance that the insect would attack of the beetle to feed or develop on only its host plant. over 40 species of plants assured its Alligatorweed arrived in the United safe introduction to this country. States via the gulf coast ballast dumps The quarter-inch-long beetle is color- of old sailing ships. Freed from its fully marked with black and yellow natural enemies, it crowded out the longitudinal stripes and is easily native aquatic flora, eventually spread- spotted on growing plant tips. Eggs ing from North Carolina to Texas. The are attached to the undersides of the Army Corps of Engineers, unable to leaves in symmetrical clusters. The keep all waterways open to navigation, dark-colored larvae begin feeding on called upon Agricultural Research the lower epidermis, but soon cut Service scientists for help. Since the irregular holes through the leaves. The plant was introduced in this country mature larvae enter the hollow stems from abroad and several successes had to pupate. The entire life cycle requires been recorded using insects to control approximately 25 days. similarly imported rangeweeds, the Adult feeding and egg laying are Entomology Research Division's spe- linked to alligatorweed by chemical cial parasite introduction research unit stimulants, apparently peculiar to the was called in. plant. Pupation in the hollow stems of Entomologist George Vogt was di- alligatorweed automatically eliminates rected to find the home of alligator- plants of dissimilar structure as possibly weed and determine what natural hosts for the beetle. enemies could be used to control the Some 260 beetles were placed on the plant in the United States, if such Ortega River, Jacksonville, Fla., in natural checks existed. April 1965. By November, the flea A search of the botanical literature beetles were well established, feeding and an examination of over 1,400 and laying eggs normally. dried plant specimens indicated alli- By the spring of 1966, the hundreds gatorweed originated in the river of beetles had multiplied to thousands. courses and coastal regions from north- What was once a solid stand of alli- ern Argentina to the Guianas. Vogt gatorweed began yellowing under the concentrated his early exploratory ef- feeding onslaught of larvae and adult forts in Paraguay, southern Brazil, and beetles. The leaves were cut from the northern Argentina, an area meteoro- stems. A second wave of the beetles 231 Flea beetle, left, and marisa, right, feeding on waterweeds. Below, a manatee, or sea cow.

232 stripped the young shoots put out by Only a few thousand are believed to the floating mat. Finally, to everyone's exist. Meat of the manatee is of high surprise, sections of the mat began to quality, which may explain its near sink and rot, leaving patches of open extinction. It is protected by law in water. By November 1966, the entire many countries. area was free from floating alligator- Unofficial reports collected from all weed, and the shore was lined with areas of the world indicate the manatee dead stems. probably could clear some of the Floating mats had torn loose from world's lakes, canals, and waterways the banks and drifted downriver, of aquatic weeds. In British Guiana, carrying the beetles to new weed sites. two manatees 7.5 feet long cleaned a A survey of Florida in 1967 indi- canal 22 feet wide and 4,800 feet long cated that almost all alligatorweed in 17 weeks. The manatee was so sites are now infested with the flea promising that 46 animals were col- beetle. In some areas, they were so lected and distributed in weed-infested thick that adults crawled from the canals in the country. plants into the survey boat by the A 3-year study of manatees and their hundreds. A concentrated efl'ort is con- usefulness in controlling aquatic weeds tinuing to collect and ship beetles to was completed by Florida Atlantic other States where the weed exists. University (FAU) of Boca Raton in Despite the startling success in Flor- 1966. The study was supported by the ida, the flea beetle failed to damage Central and Southern Florida Flood alligatorweed on the National Wildlife Control District (FCD). and Game Refuge at Savannah, Ga. FCD officials became extremely con- Entomologists feel other insects may cerned with aquatic weeds when they be needed. They have already released noted the rapidly rising cost of weed a species of thrips and are studying a control in the district. In 1968, this stem-feeding moth in Argentina. cost is budgeted for $275,000, and it The marisa snail and the flea beetle is expected to be a half million dollars are small and effective, but consider by 1970. FCD is supporting research the manatee: Five hundred to 2,000 to find more and less expensive pounds of plant-eating mammal! methods of aquatic weed control. Aquatic plants not relished by her FAU's study was conducted to deter- counterparts are considered a delicacy mine how many weeds manatees can by the manatee. eat, to study their rate of reproduction, This animaPs history is lost in antiq- and to learn whether or not the beast uity. It passed through a mythological can be employed practically and eco- era in which manatees were believed nomically as a means of biological to be mermaids. Sailors long at sea weed control. fancied that this fishtail animal was a This study was conducted under the sea maiden, thus the name mermaid. leadership of Dr. P. L. Sguros. The They also are called sea cows. Scien- Miami Seaquarium was employed by tists know very little about them. FCD to capture seven manatees used The manatee has a small head and in the 3-year study. They weighed brain, almost hairless hide, a hori- from 384 to 2,170 pounds, and their zontally flattened tail or fluke, and size was soon found to be a problem subcutaneous blubber. when moving them to test sites. There The number of young born in cap- was no noticeable period of adaptation tivity is very small. Probably only one after the manatees were introduced calf is born every 2 years. Many scien- into the sites. Feeding commenced tists still question the ability of the immediately and appeared to be a manatee to survive and reproduce in continuous process. fresh water. Some have associated salt Weeds in test areas were primarily water with mating activity. submersed types (coontail, naiad, and The manatee is near extinction. bladderwort). Cattail, arrowhead, 233 Water hyacinths, a major waterway pest, clog a creek in the Ocala National Forest, Fla.

pickerelweed, and several species of The name "sea cow" became very aquatic grasses were also growing meaningful during the study. A strong along the canal bank and in the water. bovine resemblance was noted with Sguros estimated that 5,000 pounds regard to herbivorousness, herding of manatee, the total weight of five, instincts, and passivity. can eat the submersed weeds in a half Manatees cannot tolerate water tem- mile section of canal in 3 weeks. An peratures below 65° F. Three test ani- equivalent weight in manatees would mals in the study died from respiratory clear the same canal of water-hyacinth infections associated with low water in 8 weeks. Test sites were free from temperatures. vegetation for 6 to 8 months after the The manatee has no peer, based on manatees were removed. current knowledge, as a harmless, Manatees remained in several test rapid, economical, and otherwise fea- sites after the submersed and floating sible means of controlling obnoxious aquatic weeds were consumed. They aquatic weeds. then ate all bank vegetation extending Successful use of the manatee as a into the water and grubbed the canal weed-controlling agent depends on bottom for roots of the weeds whose additional knowledge to be applied in upper parts they had already eaten. sea cow husbandry procedures. 234 Growing Nations and World Trade

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