Foreign insects turn allies in eradicating invasive aquatic weeds

An exotic beetle, Cyrtobagus salvinia, helps completely eliminate ‘Chinese Jhalaar’ in 18 months from Satpura dam in Madhya Pradesh
The Sarani reservoir has become completely clean following the release of insects on Salvinia molesta.
The Sarani reservoir has become completely clean following the release of insects on Salvinia molesta. ICAR-DWR

An exotic beetle released into a vast (2,800-acre) reservoir in Betul district has successfully eradicated an invasive weed species, Salvinia molesta, within 18 months.

Salvinia molesta, a highly detrimental aquatic fern, had engulfed the entire Sarani reservoir (Satpura dam) built on the Tawa river in the Betul district of Madhya Pradesh. Known locally as “Chinese Jhalaar”, this invasive species was first spotted in 2018 and had completely carpeted the reservoir by 2019.

The reservoir, owned by the Madhya Pradesh Power Generating Company Ltd. (a government-run electricity producer), houses the Satpura Thermal Power Station on its banks. VK Kaithwar, the company’s chief engineer, expressed his delight at the eradication, calling it “nothing short of a scientific marvel.”

JS Mishra, director of the Jabalpur-based Indian Council of Agricultural Research-Directorate of Weed Research (ICAR-DWR), explained that NTPC had previously considered manual removal, which was estimated to cost a staggering Rs 15 crore. 

“However, this method was deemed ineffective due to the high possibility of the weed’s resurgence. Upon learning about the potential of an exotic insect (Cyrtobagus salvinia) for weed control, the company collaborated with ICAR-DWR to initiate the insect’s release into the reservoir in April 2022. Within 15 to 18 months, the insect population multiplied significantly, effectively consuming and destroying the weed,” Mishra said.

Scientists at ICAR-DWR revealed that Cyrtobagus salvinia, a Brazilian bioagent specifically targeting Salvinia molesta, was imported to India after thorough research and with the necessary governmental approvals.

Cyrtobagus salviniae is a bioagent that eats Salvinia molesta, which gets destroyed once the weed is gone
Cyrtobagus salviniae is a bioagent that eats Salvinia molesta, which gets destroyed once the weed is goneICAR-DWR

The Sarani reservoir project represents the scientists’ most extensive and successful experiment to date. Their confidence in the method stemmed from a successful trial conducted in November 2019 on a pond in Padua village, Katni district. Within 18 months, the insect completely eradicated the invasive Salvinia molesta from this 20-hectare pond.

Rajesh Patel, the husband of Padua village’s Sarpanch (village head), described the pond’s previous condition, “The water was smothered by a thick layer of this ‘Chinese watercress,’ making it impossible to even draw a cup of water.” 

He elaborated on the devastating impact this invasive species had on the pond’s biodiversity, leading to the complete depletion of fish due to a lack of oxygen.

Sushil Kumar, a former chief scientist at ICAR-DWR and a pioneer in insect-based weed control methods in central India, recommended a release density of 22,500 insects per hectare for optimal weed eradication within 15 months. 

“The insect solely feeds on Salvinia molesta and dies naturally once the food source is exhausted, posing no threat to the environment,” he said.

The elimination of Salvinia molesta from the Sarani reservoir has brought immense relief to fishermen in dozens of surrounding villages. For the past five years, these communities have faced a livelihood crisis due to the weed infestation. Many fishermen were forced to migrate and find work as labourers in nearby areas.

Raju Dyer, president of the Sarani Fish Committee, expressed his optimism. “We secured a ten-year fishing contract in 2018. While Salvinia molesta was present in some areas back then, it had completely taken over by 2019, suffocating the fish population due to lack of light and oxygen. Now that the reservoir is clear, the fishermen can look forward to regaining their livelihoods. With the reintroduction of fish fingerlings, we expect their income to return to normal levels by next year,” he said.

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