The invasive aquatic weevil is destroying the ecological environment and the surrounding economy of Lake Osa in Cameroon. Can the little weevil reverse the fate of the region?
| Dead Lake Osa | Lake
Osa is one of the largest lakes in Cameroon. Dense aquatic plants cover most of the lake, and a group of water birds step on it to find insects to eat. The water plants are densely connected into one piece, which looks like a wide and flat green grassland. The water birds with steady pace shuttle freely on the “grassland”, as if walking on land.
Five years ago, Lake Osa was rich in freshwater turtles, crocodiles, and more than 18 families of fish. Lake Osa has also been a bastion of survival for the African manatee, a vulnerable species on the IUCN Red List. Today, however, Lake Osa is eerily silent, and almost nothing grows in the lake.
The thick layer of vegetation on the lake is Huai Ye Ping, which the locals call Kariba Waterweed, or Huai Ye Ping for short. This kind of aquatic plants is the culprit for the few animals and plants in the lake. The International Union for Conservation of Nature has identified the invasion of Sophora japonica as a “conservation emergency”.
Sophora japonica is a brown-green freshwater fern. The free-floating weed has encroached on 40 percent of Lake Osa’s 4,000-hectare surface, according to the African Marine Mammal Conservation Organization, a non-governmental environmental group in Cameroon.
The rapid spread of Huaiyeping seems to be unstoppable – a large number of wild animals and plants in the lake have died, and the main source of income of the local people has also been affected. Lake Ossa is just one of the bodies of freshwater that has been engulfed by the locust. Efforts to contain it have struggled to keep up with its thriving growth as it has spread across the globe from Brazil to Argentina to Australia.
Fortunately, there is still a glimmer of hope in Lake Osa, and the bearer of this hope is a small aquatic beetle that looks unattractive but is actually very capable. Not far from the shore of the lake, people are raising weevils on a large scale to form an “army” to defend against S. japonica.
Today, Lake Osa is littered with nets tangled in weeds, discarded by discouraged local fishermen. You can see the wooden fishing boats dragged ashore by the lake, and several of them have begun to rot because they have been idle for too long. Of course, there are still fishermen actively fishing the lake, and women who sell their catch, but they say their income has dropped by about 80 percent.
Near noon, I met Dina Marie-Louise alighting from a wooden fishing boat under the scorching sun. She is a fishmonger who lives in Dizengay, a small town by Lake Osa. She has been doing business there for 22 years and often goes to the lake to buy fish caught by fishermen. At this moment, looking at the handful of fish in the basket, Marie-Louise frowned. “Hui Yeping is about to kill us.” She said, “I have 12 children, and seven of them have dropped out of school because Huai Yeping has caused us financial difficulties.”
Roland Lang, who has been fishing in Lake Osa for 12 years Goler also described a similar situation. He said: “There is almost no room for fishing in this lake. If no measures are taken, Huai Yeping will swallow the entire Lake Osa. In the past, more than 100 fishermen came to fish in this lake in one morning alone, but today only Less than 5 came. Everyone was discouraged.”
In addition to fish, Lake Osa was also home to many African manatees. African manatees, one of the least studied species of manatees, are now in dwindling numbers in Lake Osa. Aristide Kamla, founder of the African Marine Mammal Conservation Organization, said that many African manatees swam from Lake Osa to the surrounding rivers in order to forage better.
| Difficult to remove Sophora japonica|
Although it is native to southern Brazil and northern Argentina, it can be scattered to various water bodies by wind, current, animals and humans. “The emergence of invasive plants in lakes in Cameroon is partly due to human factors,” Kamra said.
In addition to humans intentionally or unknowingly taking pagoda from one place to another, such as giving it a “tailwind” boats”, and human activities are also largely responsible for the vigorous growth of S. japonica in Lake Osa.
”We noticed that in 2016, the content of nutrients such as nitrogen and phosphorus in Lake Osa was extremely high, which was twice the historical data in 1985.” Kamla said, “This means that Lake Osa has eutrophication. , that is, the significant accumulation of nutrients in the lake.”
This created perfect conditions for the mass reproduction of Huaiyeping. “Plantia spreads a thick ‘blanket’ on the lake surface, blocking light from entering the water, which in turn impairs photosynthesis of plankton. Most fish, however, feed on plankton.” Cam “As a result, fish production has dropped dramatically,” Ra said.
The growth rate of Huaiyeping is amazing, it can double in size every ten days, so it is almost impossible to curb its spread.
Lum Fonte, an independent botanist working in Cameroon, said: “There are no natural enemies of S. japonica in the new environment, which is conducive to its rapid growth.” There are billboards at every corner, reminding villagers and tourists to pay attention to the invasion of Huaiyeping. Countless signs in the town also read slogans such as “Youth, let us save Lake Osa” and “Let us save Lake Osa from the invasion of Huaiyeping”. This is probably the first time Cameroon has encountered the invasion of Huaiyeping, but the repercussions have been very strong.
There are three main ways to remove Sophora japonica. The first is manual removal, which consumes the most energy. “Manual removal includes manual removal and the use of professional equipment. The former is mainly for low-invasion waters, and the latter is for high-invasion waters.” Fengtai said, “This method is labor-intensive and time-consuming. It can be said to be monotonous and time-consuming. It ’s boring.”
Since 2019, the “African Marine Mammal Conservation Organization” has mobilized local people to remove S. japonica to reduce its infested area, but progress has not been smooth. “Manual removal is too laborious because this invasive plant multiplies very quickly,” Kamla said. “We removed more than 200 tons of A. saponica from Lake Osa in 2019 and 2020, but it didn’t feel like it was doing anything.” ”
Feng Tai said that this is because manual removal alone is not enough to curb the spread of Sophora japonica. Sophora japonica left in the lake grows rapidly and will soon fill the vacancy.
The second method is the chemical control method, using herbicides to eliminate Sophora japonica. However, this method itself has ecological disadvantages, because the herbicide also poses a threat to other plants and may also harm other microorganisms in the lake. So far, no chemical control has been tried at Lake Ossa, and scientists, including Fonte, have warned against it.
| Weevils That Do the Heavy Duty |
Luckily, there is one last option — sending out a small, brown-black aquatic beetle native to Brazil. This small beetle feeds almost exclusively on saffron, and is known as the “saccharomyces weevil”. They may be able to rid Lake Osa of syringa and rebuild its own ecosystem. The adult weevil is only 2 to 3.5 mm long, and although it has a short body, it has a long and strong nose. However, it is the larvae of the weevil that can deal a devastating blow to Huaiyeping. They will burrow into the rhizome of Sophora japonica and cause fatal damage to it.
From 1978 to 1982, Wendy Forno, a scientist of Australia’s Commonwealth Scientific and Industrial Research Organization, visited South America. During this time, she discovered the weevil japonica. In 1980, people first used this weevil as a biological control tool to eliminate S. japonica, and introduced it to Lake Mundara in Mount Isa, Australia, and the final effect was remarkable.
”Today’s Mundala Lake basically has no pagoda. At the beginning, 400 hectares of the lake were infringed, and weevils wiped out 50,000 tons of pagoda on the lake.” Matthew Purcell, director of the Australian Biocontrol Laboratory Said. The laboratory is jointly operated by the US Department of Agriculture and the Australian Commonwealth Scientific and Industrial Research Organisation.
”Whether it is an adult or a larva, the weevil does not eat other aquatic plants and only feeds on this aquatic plant.” Purcell said, “With the seasonal growth of the weevil, the number of weevils also increases. It will grow. Throughout the year, the two continue to increase or decrease, and the overall balance is maintained.” Purcell also said that weevils have never completely wiped out S. japonica, but they help restore the balance of the ecosystem.
Arnold Peters was a retired senior researcher at the Royal Netherlands Institute of Tropical Science. He said that the Senegal River also introduced the weevil weevil to the Senegal River at the beginning of this century, and the effect was also significant. He also emphasized that it is precisely because of the strong preference for the diet that weevils have become a popular choice in the field of control of Huaiyeping. “It has been proven that this small beetle does not cause any harm to the environment or crops,” Peters said.
South Africa has also been successful in controlling the anthropogenic weevil, as the weevil has been introduced to freshwater ecosystems in South Africa since 1985. Julie Coetzee, deputy director and project manager of the “Aquatic Weeds Biological Control Program” at Rhodes University in South Africa, said: “Sophia japonica grows and spreads in many water bodies in South Africa, mainly in small reservoirs and rivers.” This part Depending on the nutrients in the water and the climate, it takes one to three years for the water to regain its clarity. “There are still infested waters,” Coetzee said, “but as long as weevils are introduced, we can usually clean them up in a quarter.”
Although Huaiyeping is helpless against bollworms, weevils also have weaknesses. “We didn’t notice the defect at first, but recently we found that some waters still have the invasion phenomenon of S. japonica, especially in sheltered waters.” Coetzee said, “A parasitic algae transmitted the bacteria to the weevils. ’” The algae, called Helicospora, impairs the weevil’s ability to reproduce.
Still, Coetzee remains optimistic that the weevils will be able to clean up the weevils in Cameroon’s Lake Osa. “In Cameroon, biological control is the most environmentally friendly and economically sustainable option to curb P. coedifolia,” Coetzee said. It may take some time for the weevils on the control mission to grow their team to destroy Huaiyeping and weaken their power. This process will not be fast, and patience is the key.”
Purcell also hopes that the weevil can bring Lake Osa back to life. “Weevils should work in Cameroon. Most of the removal will be done within three years,” Purcell said. “The control can go on indefinitely, which is much better than spraying. If you choose to spray, every year , need to be re-sprayed every quarter, and it will have a negative impact on the aquatic environment.”
Maybe it won’t be long before Lake Osa, which is crowded with S. japonica, will become another water body that welcomes weevils. A task force involving several government ministries in Cameroon has been formed to oversee the introduction of weevils to eradicate Ossa.
Lake Osa locals, however, have been disappointed by the speed of the removal. Fisherman Jean-Pierre said: “Fishing is our only source of income. We are running out of patience.” Dora Seeh, who has been a fish trader for 25 years, agrees: “There is no progress.”
In the town of Dizengay Weevil populations are steadily increasing at dedicated sites by the African Marine Mammal Conservation and its partners. “As soon as we get the authorization from the government, we will put the weevils in the lake,” Kamla said. “Hopefully in two or three years, we will be free of this invasive plant.”