He said the fast-growing aquatic fern that could double its area from 10sq m to 20sq m in just three days choked lakes and ponds in Kota Belud, Tuaran, Paitan and Papar.
They believed the fern, native to South America, was brought in as an ornamental plant for aquariums and later discarded in drains or lakes where it began to spread rapidly.
He said the department was alerted about the infestation by Kinabatangan villagers in 2015 and were shocked when satellite imagery showed that almost all of the oxbow lakes there were choked with the weed.
The plants dry up the lakes as they displace the water.
“They are upsetting an entire eco system,” Idrus added.
He said the department brought in more than 350 of the Cyrtobagous salviniae weevils from Melaka last year and had been breeding these insects at its research centre in Tuaran and at the Tungog oxbow lake in the Kinabatangan.
“The weevils will take at least another year before we have enough to contain the situation.”
The weevils, originally from Australia, were used to control a similar infestation of the water ferns in the peninsula during the 1980s.
He said there was no fear of the insects – about the size of rice weevils – getting out of control as they were host specific in that they only consumed that particular water fern.
