CABI News

28 April 2015 – CABI has partnered with the Ol Jogi Ranch in Laikipia, Kenya, to introduce a sap-sucking insect to the region in a bid to control an invasive cactus. The cactus, Opuntia stricta, threatens livelihoods in Laikipia, because it destroys available forage for livestock and wildlife. On 25 April, Ol Jogi hosted an event to officially release the insect, raise awareness about the effects of Opuntia stricta and show the positive results that the insect is already having on controlling the cactus. Officials from Laikipia, together with the Director General of the National Environment Management Authority (NEMA), CABI and members of the community gave presentations and took a field trip on the ranch to view the results.

Communities in northern Kenya are heavily dependent on livestock. In this semi-arid region, pastoralists rely on cattle, goats and sheep as a source of income and struggle with frequent drought and poor pasture. This non-native cactus has invaded the limited amount of good grazing land left. When the livestock eat the cactus fruits, the small spines, called glochids, lodge in their mouths, throats, stomachs and intestines contributing to secondary infections and death. The large spines on the modified stems, called cladodes, often pierce the eyes of livestock, causing blindness, as they try to access forage. Loss of livestock leaves pastoralists in Laikipia without income.

The cactus has also affected the Ol Jogi Ranch, home to many iconic animals, including black and white rhinos, elephants, big cats, wild dogs, zebras and antelopes. Rangers believe young elephants are dying as a result of feeding on the cactus fruit. Opuntia stricta also displaces native plant species and prevents rehabilitation of degraded land. Like their neighbouring pastoralist communities, Ol Jogi has lost good grazing land for resident wildlife to this invasive cactus.

According to the Invasive Species Specialist Group of the International Union for Conservation of Nature, Opuntia stricta is among the top 100 worst invaders worldwide. Until recently, only two means of controlling the cactus were available for pastoralists, farmers and conservationists in Laikipia: chemical control by using herbicides and/or mechanical control by cutting down individual cactus plants. Both of these methods posed challenges in terms of expense, environmental impact and practicality.

In 2012, Dr Arne Witt, Regional Coordinator for Invasive Species at CABI in Africa, suggested using biocontrol: a method of controlling invasives species using living organisms, like insects, which are host-specific and only control the target plant. His recommendation was to use an insect commonly known as cochineal. This sap-sucking bug (Dactylopius opuntiae or ‘dudu’ in Swahili) feeds solely on Opuntia stricta and is unable to feed or develop on any other cactus or plant species in Kenya. The insect has successfully controlled the same cactus species in Kruger National Park, South Africa.

With approval from the Kenya Plant Health Inspectorate Services (KEPHIS) and funding from Ol Jogi Ranch and CABI, the insects were imported from ARC-PPRI in South Africa and placed in quarantine for trials at the Kenya Agricultural Research Institute (now KALRO). The trials confirmed the bug posed no threat to native plant or introduced crop species in Kenya. NEMA gave permission to undertake further field trials on Ol Jogi land, which again confirmed that the insect posed no threat to any other flora. Based on this evidence, NEMA gave permission to release the insect more widely in Laikipia.

Ol Jogi is now partnering with neighbouring communities to release the cochineal into nearby ranches also affected by the cactus, including the community-owned wildlife conservancy of Naibunga. “It is important to acknowledge that we will, in all likelihood, lose more than 70% of our natural grazing lands in Kenya if invasive plant species are not managed,” said Dr Witt. This little ‘dudu’ has huge potential to control the invasive cactus and, in so doing, save costs and restore land to local wildlife and livelihoods to Laikipia’s farmers.

Download a free PDF copy of Dr Witt’s book Invasive Alien Plants and their Management in Africa.

Download a factsheet on Invasive Cactus Species in Kenya.

See a recent article about this work on SciDev.net

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