No one knows exactly when the Opuntia Stricta, an attractive prickly plant with yellow flowers and edible purple-reddish fruits was introduced in Kenya.

But the old men of Il-Pulei Village of Laikipia North, a constituency in Kenya’s Rift Valley say the invasive species, which has colonised their land, was introduced by a white colonial farmer in the 1940s.

Today, the once cherished cactus (valued for its use as a barrier fence and is a succulent fruit) is the cause of many of their problems.

A native of the Americas, the Opuntia Stricta, also known as the Australian prickly pear, has destroyed the environment, brought diseases to livestock, displaced people and impoverished the economy of the pastoralist community of Laikipia North.

Now cattle lack pasture because the landscape is dotted with the cactus. When ingested, the small spines on the fruit, called glochids, get lodged in the throat, stomach or intestines of the animals.

This causes abscesses (a collection of pus, often accompanied by swelling and inflammation) and mouth ulcerations/inflammations, are painful particularly when the animal is feeding, and which lead to secondary infections and eventually, death.

Mzee Jonathan Ranam, a village elder said that the digestive tracts of the animals that eat the fruit get damaged too.

“When you slaughter the animal, you will wonder what ate up its intestines,” he said.

Wilson Sintaroi, a pastoralist from Munishoi village in Il-Pulei is a devastated man. Although he is still in his mid-20s , he appears much older.

Most of the cattle, goats, sheep and donkeys he inherited from his father have died due to complications caused by eating this cactus, and now he is afraid the remaining will soon be dead.

“I am as good as dead,” he said. “My goats are sick and could die any time.”

The situation is worse during the dry season when livestock feed is scarce, causing the animals to turn to the prickly cactus.
The robust spines on the stems of the plant also cause blindness when they pierce the eyes of the animals.

“It happens when the animals try to reach the grass underneath the cactus,” said Sintaroi.

For a community whose mainstay is livestock keeping, the invasion of the O. Stricta is significant, requiring urgent attention. A herd of cattle is a bank, a source of income, and a status symbol for the pastrolalists who live in a harsh environment where drought occurs frequently.

“About 10 years ago, we realised there was a problem with this plant and we tried to uproot it but we were unsuccessful; the situation was turning catastrophic and we had to find a solution,” said John Weller, the general manager of the Ol Jogi wildlife conservancy in Laikipia North.

“On the ranch, we have lost more than 10 per cent of our grazing land to the cactus, which is not only a threat to the 3,000 cattle we keep but also the 1,500 more owned by the community that have sought refuge here.”

The 58,000 acre conservancy, is home to the black and white rhino, elephant, big cats, wild dog, Grevy’s zebra as well as many species of antelope and smaller mammals.

Mr Weller said that people contribute to the spread of the cactus when they use it for ornamental purposes or as a hedge to keep wild animals out of their homesteads. Elephants too, which feed on the succulent fruit, disperse fragments of the plants to other parts of the expansive grazing lands of Il-Pulei. When they eat the fruit, the seeds spread through the animals’ droppings.

The cactus reproduces by seed and vegetative reproduction via its cladodes (leafpads), which become dislodged from the plant and produce roots.

Initially, Mr Weller’s team partnered with other commercial ranchers and the local community to find ways to get rid of the cactus. But when the project failed, they sought help from the Centre for Agricultural Biosciences International (CABI) — an international not-for-profit organisation with a focus on agriculture and the environment.

That was how the cochineal, a sap-sucking insect, was introduced to the region as a biological control mechanism to rid it of the invasive cactus. Biocontrol is a method of controlling pests using other host-specific living organisms — a method that is effectively controlling the same cactus species in the Kruger National Park in South Africa.

Arne Witt, the co-ordinator of invasive species at CABI, said that more than 20 per cent of plant-eating insects on the planet are “monophagous” — meaning that they can only feed on one or a few closely related plant species. Cochineal is one such insect, making it an effective control for the Opuntia Stricta.

“The fact that the cacti can reproduce vegetatively through their leaves, which root when they come into contact with the ground, means that their management is considerably more difficult than that of other species,” said Dr Witt.

“A biocontrol method is effective in controlling the cacti.”

Biocontrol insect

According to Geoffrey Wakhungu, the director general of the National Environment Management Authority (Nema), the introduction of the biocontrol insects was the only solution to the growing problem in the area.

“We issued a license to Ol-Jogi ranch after three years of trials and we are convinced of the success of the cochineal insect,” said Prof Wakhungu, while acknowledging that the O. Stricta case was unique and had taken too long to find a solution.

The cochineal sucks sap from the Opuntia Stricta and once the plant is dead, the insect migrates through wind dispersal to the next. When all the plants are eradicated, the insect dies.

With approval from the Kenya Plant Health Inspectorate Services (Kephis) and funding from Ol Jogi Ranch and CABI, the insects were imported from quarantine in South Africa, and placed in quarantine at the Kenya Agricultural Research Institute in Nairobi.

After successful quarantine tests, permission was sought from Kephis and the Nema to undertake field trials at Ol Jogi some two years ago to confirm that the insect did not pose a threat to native plants.

The field trials confirmed that the cochineal bug posed no threat to other crops, which prompted Nema to grant permission to release the insect on a wider scale in Laikipia.

The Ol Jogi ranch has been multiplying the cochineal insects in greenhouses.

“The ranch has 13 greenhouses of the insects for all group ranches in Laikipia North which will be released immediately to the respective villages to tackle the Opuntia plant,” said Harun Kamau, the Deputy County Commissioner of Laikipia North.

Ol Jogi is now partnering with neighbouring communities to release the cochineal to the nearby ranches that are also affected by the cactus. This includes the community-owned wildlife conservancy of Naibunga.

Prof Wakhungu said that after the successful eradication of the plant in northern Kenya, Nema will upscale it to other parts of the country ravaged by the prickly plant.