Use of wasps to fight papaya mealybug pests

Papaya fruit in one of the farms in Wajir

The fight against the devastating papaya mealybug has been stepped up in the country in four counties with the release of a natural enemy known as Acerophagus papayae.

A papayae is a small parasitic wasp that only attacks the papaya mealybug by laying eggs on the pest.

Centre for Agricultural and Biosciences International (CABI), together with Kenya Agricultural and Livestock Research Organisation (KALRO), the National Museums of Kenya and Kenya Plant Health Inspectorate Services (KEPHIS), is preparing to unleash A papayae against the papaya mealybug in Machakos, Makueni, Tharaka Nthi and Embu.

There are plans to cover all of the 10 major papaya-growing counties in Kenya with hopes that future releases will be carried out in Meru, Murang’a, Kitui, Homabay, Busia and Baringo.

The work is being carried out by CABI’s invasive species experts based at its Regional Centre for Africa in Nairobi as part of work under the CABI-led global PlantwisePlus programme.

Papaya mealybug is a serious pest of papaya fruit, which originated from Central America before spreading to the Caribbean and South America in the 1990s. The pest was first detected in Africa in 2010 in Ghana and in Mombasa County, in 2016.

According to CABI researchers, more than half of Kenya has been invaded by papaya mealybug and its impact has led some papaya farmers abandoning farming the fruit altogether. CABI, KALRO and KEPHIS have seen crop losses ranging from 53 to 100 per cent and economic losses of Sh406, 612 (£2,224) per hectare annually.

A papayae offers a classical biological control remedy for the papaya mealybug pest. This reduces the overreliance on more harmful and more damaging for the environment pesticides – as part of an Integrated Pest Management (IPM) plan.

Before the release, the performance of A papayae had been evaluated under laboratory conditions for its efficiency as a potential agent for use.

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 before approval was granted.

Senior Scientist, Invasive Species Management at CABI, Dr Ivan Rwomushana said the papaya mealybug is a significant pest which can devastate a whole crop if left unmanaged. He added that not only does it have a severe impact on the livelihood of a smallholder farmer but also the ability to contribute to local, national and global food security.

“It is hoped that following the releases of A papayae, Natural Enemies Field Reservoir (NEFR) technology, pioneered by the late CABI scientist Riaz Mahmood in Pakistan, will also prove fruitful in mass-rearing the parasitoid against papaya mealybug in Kenya,” said Dr Rwomushana.

NEFRs used in Pakistan as part of a separate USAID-funded Phytosanitary Risk Management programme in Sindh, Balochistan, Gilgit and Skardu where the conservation of important biocontrol agents of papaya mealy bug, apple pests, fruit flies and the giant mealy bug are being carried out.

Under the release programme for A papayae, CABI is working with KEPHIS and KALRO to increase awareness about the classical biocontrol of papaya mealybug and build the capacity of farmers, extension officers, researchers, input suppliers and policymakers to manage the pest.

Furthermore, CABI is training and helping farmers to establish NEFRs in farmers’ fields that would act as a natural home for the Acerophagus papayae parasitoid at the farmers’ fields and help in conservation of the parasitoids in communities when the project ends.

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