Kalro step up fight againt papaya disease

Kenya Agricultural and Livestock Research Organisation (Kalro) and CABI are stepping up the fight against the devastating papaya mealybug (Paracoccus marginatus). Papaya mealybug has been ranked high in the top pests affecting papaya and other horticultural crops.

Invasive species experts from CABI’s centre for Africa in Nairobi have performed a second field release of the encyrtid wasp Acerophagus papayae at three sites in Mombasa County. They also trained 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. An upcoming study on knowledge, attitudes and perceptions of farmers with regard to classical biological control of papaya mealybug revealed that 85 per cent of farmers viewed the release positively, and most (94 per cent) would support the biological control programme in their community.

Since its first report in 2016, the papaya mealybug pest has spread to over 53 per cent of papaya producing counties in 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, CABI and Kalro in selected counties on pawpaw production, and has seen crop losses range from 53 to 100 per cent and economic losses of £2,224/ha annually.

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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. 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 per cent, 72.5 per cent and 47.5 per cent 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.

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