Beetle clears weeds

Press, 18 November 1981, Page 16

Beetle clears weeds

By

Keith Hindley

A tiny Brazilian beetle is proving remarkably effective at . destroying the unsightly rafts of floating Salvinia weed which clog many waterways in tropical countries. The two-millimetre-long Cytobagous singularis is a longsnouted black weevil with a single-minded passion for Salvinia buds. Even its grubs, which hatch from eggs laid under water, bore into Salvinia roots and help to destroy the plants from within. In recent months the bugs’ prodigious appetite has cleared the most rampant infestation in Australia wnere $200,000 worth of herbicides had failed. Salvinia weed was first noticed spreading through the trooics in the 19505.-Bv 1976 it

was a far more intractable problem than the more famous water hyacinth. By 1980, 50,000 tons of weed had clogged 1000 acres of Lake Moondarra in Queensland, turning the lake into a great, green swamp. Biologists from Brazil and Australia noticed in 1978 that the Brazilian weevil was successfully feeding on the same species of Salvinia in Brazil. Some of the beetles were captured and studied carefully to ensure they had no harmful parasites and did not harbour a liking for other Australian plants. A total of 1500 was then released in enclosures on the lake. Within months, the weeds inside the cages were clearly declining. Heartened by these results., a

fresh batch ot 1500 beetles was released last January and the doors of the test cages opened. Faced with a veritable mountain of its favourite food, the beetle then indulged in a reproductive orgy that staggered scientists. By mid-April, the beetle population was estimated at more than 100 million and the Salvinia was turning brown and sinking. By August only a ton of very sickly weed remained and the beetle itself was in heavy decline. Reporting in the journal “Nature,” the group is clearly elated at one of the most successful examples of biological control yet reported. Copyright — London Observer Service.