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 growers’ livelihoods and food security.

The Kenya Standing Technical Committee on Imports and Exports (KSTCIE) approved the widespread use of the biological control agent Acerophagus papaya 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 that can cause crop losses ranging from 53 to 100 per cent.

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 could take up to six months to be effective.

American roots

CABI (Centre for Agriculture and Biosciences International) 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 working 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 (Sh371.81) per hectare annually, but the Kenyan authorities are now satisfied that CABI has provided strong evidence of the efficiency of A. papayae against the mealybug and it is safe for national release.

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 per cent 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 per cent.

There are plans, including 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 Kenyan coast region in August 2024, though not a socio-economic study, to analyse and report on yields.

All farmers who had received the parasitoids reported almost a doubling of their yields compared to previous seasons. 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. papaya is mass-reared from the CABI-KALRO rearing facility at Muguga on the outskirts of Nairobi.

Wild card

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 parasitise them.

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.

 “The widespread release of Acerophagus papaya 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,” Dr Miller said.

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.’

The nationwide release of Acerophagus papaya 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” Dr Johnson Nyasani, chief research scientist at KALRO, said.

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