Sustainable biological control agent approved to fight papaya mealybug pest across Kenya

Date:01-22-2025

An environmentally friendly and safe-to-use parasitoid wasp has been approved for release across Kenya to help smallholder farmers fight the devastating papaya mealybug which threatens their livelihoods and food security.

The Kenya Standing Technical Committee on Imports and Exports (KSTCIE) approved the widespread use of the biological control agent Acerophagus papayae against papaya mealybug (Paracoccus marginatus) in all of Kenya’s papaya growing counties over the coming months.

The move follows the gradual release of the agent in Machakos, Embu, Tharaka Nithi, Baringo, Mombasa, Kwale, and Kilifi counties where smallholder farmers are affected by the pest which can cause crop losses ranging from 53-100%.

Smallholder farmers, who are encouraged to use the agent as part of their Integrated Pest Management (IPM) plans, are being asked to be patient when using the agent as it can take up to six months to be effective.

Main image: The parasitoid mummies are placed on cards that are distributed to farmers to place on their affected crops (Credit: CABI).

Worked hard to assess the effectiveness of A. papayae

CABI scientists and colleagues from the Kenya Agricultural and Livestock Research Organisation (KALRO), the Kenya Plant Health Inspectorate Service (KEPHIS) and the National Museums of Kenya (NMK) have been worked hard to assess the effectiveness of A. papayae as part of Integrated Pest Management (IPM) plans.

Papaya mealybug originated from Central America before spreading to the Caribbean and South America in the 1990s. It was first detected in Africa in 2010 in Ghana and in 2016 in Mombasa County, Kenya.

CABI, KEPHIS and KALRO, estimate the value of the crop losses to be £2,224/ha annually but the Kenyan authorities are now satisfied that CABI has provided strong evidence of the efficiency of A. papayae against the papaya mealybug and it is safe for national release.

Up to 75% mortality of the papaya mealybug

The CABI scientists, based at its regional centre for Africa in Nairobi, conducted research – published in the journal Crop Protection – which found that within two years of the first release of A. papayae in Mombasa, Kwale, and Kilifi counties, the biocontrol agent was causing up to 75% mortality of the papaya mealybug.

At the same time, average papaya harvests almost doubled between treatment and control farms. With higher yields, the average income of farmers on treatment farms increased by approximately 20%.

These plans included encouraging smallholder farmers to reduce their use of chemical pesticides so that the biological control agents can thrive and control the pests.

A recent survey was carried out at the Coast in August 2024, though not a socio-economic study, to analyse and report well on yields.

All farmers who had received the parasitoids reported almost more than 100% increase in yields compared to before, they also stopped using chemical insecticides because the parasitoid was working.

Dr Selpha Miller, Postdoctoral Research Fellow, Invasive Species Management, said the roll out of the agent is being funded by partners at no cost to smallholder farmers. A. papayae is mass-reared from the CABI-KALRO rearing facility at Muguga on the outskirts of Nairobi.

The parasitoid mummies are then placed on cards and distributed to farmers. The cards are stapled underneath papaya leaves. When the parasitoids emerge, they begin to search for the mealybugs and parasitize them.

Farmers play a role in the rapid multiplication and spread of the parasitoid

Farmers play a role in the rapid multiplication and spread of the parasitoid on the farms by constructing Natural Enemy Field Reservoirs (NEFRs), which is based on technology pioneered by the late CABI scientist Riaz Mahmood in Pakistan.

Dr Miller said, ″The widespread release of Acerophagus papayae is a major step forward in helping to manage the papaya mealybug across the major papaya growing counties in Kenya.

″We are asking smallholder farmers who use the agent to be patient while it gets to work on helping to control the mealybug as part of an Integrated Pest Management plan.″

The work is funded by the CABI-led PlantwisePlus programme, which has over 150 plant clinics in Kenya that assist farmers with their plant health problems. Extra funding is from the Darwin Initiative project ‘Biocontrol of papaya mealybug in East Africa.’

Power of partnership working

Dr Johnson Nyasani, Chief Research Scientist at KALRO, said, ″The nationwide release of Acerophagus papayae further demonstrates the power of partnership working to sustainably tackle a major crop pest while reducing the reliance on chemical pesticides.

″It also follows extensive research conducted together with CABI into the agent’s efficacy and an understanding of smallholder farmers’ willingness to adopt it as part of their sustainable pest management strategies.″

The CABI-led research, published in the journal CABI Agriculture and Bioscience, found that nearly 90% of smallholder farmers surveyed saw the release of A. Papayae positively. They added that they knew biocontrol works best at a combined individual and community level.