Ag Tech and Research News

Natural enemy fight increased against papaya mealybug in Kenya

22 February 2022, Kenya: CABI in collaboration with the Kenya Agricultural and Livestock Research Organization (KALRO) are busy stepping up the fight against the devastating papaya mealybug (Paracoccus marginatus) which has been ranked high in the top pests affecting papaya and other horticultural crops.

Invasive species experts from CABI’s centre for Africa based in Nairobi have performed a second field release of the encyrtid wasp Acerophagus papayae at three sites in Mombasa County as part of its work under the CABI-led global programme PlantwisePlus.

They also took the opportunity to train farmers on a pilot farm about the use of classical biological control of papaya mealybug using the parasitoid and how they need to avoid insecticides when doing so. An upcoming study on knowledge, attitudes and perceptions of farmers with regard to classical biological control of papaya mealybug revealed that 85% of farmers viewed the release positively, and most (94%) would support the biological control programme in their community.

Since its first report in 2016, the papaya mealybug pest has spread to over 53% of papaya producing counties in a span of just four years. Farmers spray up to 16 times in a season to control this pest, using highly hazardous pesticides which could negatively impact native insect biodiversity such as pollinators and natural enemies of pests. A more ecologically sound approach for management is the use of biological control.

Economic damage as a result of the feeding activity of papaya mealybug has been estimated by the Kenya Plant Health Inspectorate Service (KEPHIS), CABI and KALRO in selected counties on pawpaw production, and has seen crop losses range from 53-100% and economic losses of £2,224/ha annually.

Other losses are incurred through increased production costs and the psychological effects upon farmers themselves.

From the first release of A. papayae, the scientists were able to record 14 parasitoids on three papaya trees and a number of mummies were also present. In Kwale, they were also able to see eight parasitoids on two papaya trees as well as a number of mummies.

Checking for the presence of emerged parasitoids on the papaya tree released in December (Credit: CABI).

Prior to the release, the performance of A. papayae had been evaluated under laboratory conditions for its efficiency as a potential agent for use in the classical biological control programme of papaya mealybug in Kenya.

Laboratory parasitism of 77.5%, 72.5% and 47.5% in adult females, third and second instars respectively was obtained. Consequently, a dossier on the laboratory performance of the parasitoid and formal application for field release was presented to the Kenya Standing Committee on Imports and Exports for consideration.

Following this process, a conditional release permit for the biocontrol agent was granted and among the conditions stated were mass awareness and farmer and extension training before release of the parasitoid. Elaborate plans to engage different stakeholders in the selected counties were put in place and stakeholder awareness meetings were held in Mombasa, Kwale and Kilifi.

This involved the top leadership of the county agricultural department, local authority, farmers, KEPHIS, National Museums of Kenya, ICIPE, KALRO and CABI. The objective of these engagements was to create awareness of the introduced biological control agent, Acerophagus papayae, and share the findings of the performance in quarantine to enable stakeholder buy-in in anticipation of the field release.

During the engagements, the background of the papaya mealybug biocontrol works and findings of the biological and socio-economic surveys and performance of biocontrol agent in quarantine were shared. A way forward regarding further engagement was also agreed between participants.

Dr Ivan Rwomushana, Senior Scientist, Invasive Species Management at CABI, said, “Through PlantwisePlus, we seek to cultivate a mutually beneficial partnership with this approach, by tackling a significant threat to the sustainable production of papaya and, therefore, the livelihoods of smallholder farmers in Kenya.

“The second release of A. papayae reinforces our research into the efficacy of the classical biological control while at the same time teaching and convincing the farmers of its suitability and cost effectiveness as a viable control for papaya mealybug.”

In the coming months, mass production of the parasitoid will be scaled up from the current 12,000 parasitoids/month to reach a target of 40,000 for area-wide releases. Post release monitoring and farmer engagement is also continuing with the longer-term goal of supporting communities to mass produce the parasitoid themselves and conserve those that are released on their papaya fields.