By Marlene Angir

Centre for Agriculture and Bioscience International (CABI) in collaboration with the Kenya Agricultural and Livestock Research Organization (KALRO) are stepping up the fight against the devastating papaya mealy bug (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 papaya– a parasite used in the biocontrol of the mealybug pest in papaya-  at three sites in Mombasa County as part of its work under the CABI-led global programme PlantwisePlus.

Since its first report in 2016, the papaya mealybug pest has spread to over 53% of papaya producing counties in a span of just 4 years. Farmers spray up to 16 times in a season to control this pest by using highly hazardous pesticides which could negatively impact native insect biodiversity e.g. pollinators and natural enemies of pests.

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.

Economic damage as a result of the papaya mealybug has been estimated by the Kenya Plant Health Inspectorate Services (KPHIS), CABI and KALRO in selected counties on pawpaw production, and has seen crop losses range from 53-100%. Other losses are incurred through increased production costs and the psychological effects upon the 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. Prior to the first 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 program of papaya mealybug in Kenya. A report on the laboratory performance of 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. The objectives of these arrangements were to create awareness of the introduced biological control agent and share the findings of the performance in quarantine to enable stakeholder buy-in in anticipation of the field release.

“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 of papaya mealybug,” said Dr. Ivan Rwomushana, Senior Scientist, Invasive Species Management at CABI in a statement.