Kenya: Tiny insects help eradicate ‘killer’ cactus, save pasture

Dr Arne Witt, Regional Coordinator for Invasive Species at Centre for Agriculture Biosciences International (CABI) in Ol Jogi Ranch in Laikipia County explain to the members of the public how cochineal controls the invasive cactus. (PHOTO: NANJINIA WAMUSWA)

Joshua Simel has always struggled to find pasture for his livestock. “During extreme cases of drought, l lose tens of livestock. I suffer huge losses,” he says.

For Simel and other pastoralists in Naibor, Laikipia County, livestock is their livelihood. Livestock is everything to them: it provides food, income, and, most importantly in these parts of Kenya, status.

But climatic changes are no longer their worst fear. The emergence of an invasive killer cactus, also known as Opuntia Stricta, has multiplied their woes. Simel says Opuntia stricta, which has invaded huge tracts of grazing lands, thrives during dry spells.

“Our livestock eat the cactus for lack of better pasture, resulting in many deaths,” he says.

Simel says he lost between 15 and 20 cows, sheep and goats in one of the worst months in 2013. Some pastoralists lost more.

So invasive is the cactus that it has literally taken over the area. John Weller, the owner of Ol Jogi Ranch, says not even elephants are spared by the wild fruit.

“The elephants feed on the cactus fruits, especially during drought when there is little to eat. The thorns prick their mouths, causing massive ulcerations and make it too painful to continue feeding,” he says.

Worst Invasive Alien Species

According to International Union for the Conservation of Nature (IUCN), Opuntia stricta has been listed in the top 100 of the World’s Worst Invasive Alien Species.

Dr Arne Witt, the regional co-ordinator for invasive species at the Centre for Agriculture Biosciences International (CABI), says the cactus has small spines called glochids on the surface of its fruits that can lodge in the throat, stomach or intestines of any animal that eats it.

“This causes abscesses (a painful tender infection), which can lead to secondary infections and death. The more robust spines on the stems can also pierce the eyes of livestock trying to access grass underneath the cactus, causing blindness,” explains Dr Witt.

For more than five years, pastoralists, farmers and conservationists in Laikipia County have tried in vain to control the cactus by spraying the unwanted plant with herbicides or cutting and burying them to avoid further spread.

Mark Tonkei, a pastoralist from Dol Dol, told The Standard on Sunday they joined hands to buy herbicides to try and get rid of the cactus.

“But the invasive plant had spread so much that buying chemicals became very expensive for us,” he said.

They also tried removing the plant manually by clearing the bushes, but this too failed.

“We have combated the invasive cacti without success,” said Weller.

His 58,000-acre conservancy and cattle ranch is home to many spectacular plants and animals, including black and white rhinos, elephants, bug cats, wild dogs, gravy zebras, antelopes and other smaller mammals, most of which are at the mercy of the cactus.

Dr Witt says it is difficult to control Opuntia stricta using mechanical or chemical means. “The mechanical method is only effective on isolated plants or small infestations. But for cactus, any plant parts dropped during clearing will root and establish new plants,” he said.

Using chemicals, on the other hand, is expensive because high concentrations of herbicides need to be applied. Besides, the chemicals pollute the environment.

Natural enemies

He says for Opuntia, two natural enemies are known to be effective: the cactus moth and cochineal bug.

Yet there is light at the end of the tunnel.

Two years ago, Dr Witt learned of the invasive cacti in parts of Laikipia County, and offered to control the plant using biological strategy by introducing ‘cochineal’, a sap-sucking insect that feeds solely on cactus.

Cochineal has helped control the same cactus species in South Africa’s Kruger National Park.

With approval from Kenya Plant Health Inspectorate Services (KEPHIS) and funding from Ol Jogi Ranch and Cabi, the insect was imported from South Africa and placed in quarantine at the Kenya Agricultural Research Institute (KARI).

Dr Witt says more trials were taken at Kari to ensure the cochineal poses no threat to other plants. “Cochineal can only feed on one or a few closely related plant species. It is in fact so host-specific that it will not even feed or develop on any other cactus species in Kenya,” he said.

The trials confirmed that the cochineal bug poses absolutely no threat to any other plant.

After successful quarantine tests, Witt sought permission from Kephis and the National Environment  Management Authority (Nema) to undertake field trials in Ol Jogi. The results were overwhelming.

But how does this strategy work? The cochineal sucks the sap from the plant, leaving the cactus dry and eventually killing it.

Waxy white threads

Although the nymphs of the cochineal are very tiny and cannot easily be seen with a naked eye, one can see the waxy white threads secreted by the females on the plants.

Females attach themselves to the plants, and remain in that position for their whole life. But beneath the fluffy balls, they produce eggs which hatch to produce red nymphs known as crawlers.

These crawlers are dispersed to new plants by the wind using their waxy threads for buoyancy. However, the male crawlers pupate and emerge as winged adults, which never feed, and are very short-lived.

Keen monitoring

Nema Director General Geoffrey Wahungu, who has toured Ol Jogi ranch, says they will keenly monitor the progress of the bug and will scale it up to other areas with similar problems if it succeeds. “We are releasing them in clusters. If it does not work, we quarantine the area and eradicate them,” he said.

Ol Jogi is now partnering with local communities to release the cochineal bug into nearby ranches.

The locals are already celebrating.

“The cochineal is going to restore our land,” they say.