Wasps help farmers fight mealybug pest

The mealybug, native to Central America, is a rapidly spreading crop pest that has been wreaking havoc on papaya crops in Kenya since 2015, causing significant economic losses for smallholder farmers.

A farmer holding papaya fruits from his pest-infested farm. Photo: CABI.ORG

The mealybug pest is native to Central America.

In Africa, it was first reported in Ghana in . It is believed to have invaded East Africa between 2015 and 2020, causing severe losses to smallholder farmers. CABI estimates that in East Africa the pest is responsible for destroying 57 – 91 per cent of crops and costing farmers £2,224 (US$ 2,854) per hectare every year.

In 2019, scientists from CABI, along with the Kenya Plant Health Inspectorate Service, Kenya Agricultural and Livestock Research Organization, and Kenyatta University, identified the wasp, Acerophagus papaya, as a prospective candidate for biological control.

They say it offers a natural and safe solution to the problem of papaya mealybug.

The Kenya Agricultural and Livestock Research Organization then imported Acerophagus papayae, a parasitic wasp from Ghana, and introduced it on Alfred Bolo’s farm in March, 2023. Alfred Bolo is a papaya smallholder from Kwale, in coastal Kenya.

“It took about one month for the parasitoids to spread around the farm. They did not eliminate the mealybug but controlled their numbers to the extent that they could not cause economic losses to me,” Bolo told.

He has since increased his plant production and saved on pesticide costs. “I am now harvesting about 400kgs per week, which is a good harvest.”

Selpha Miller, Post-doctoral research fellow, invasive species management based at CABI, says the Kenya Standing Technical Committee on Imports and Exports gave CABI and its implementing partners, The Kenya Agricultural and Livestock Research Organization and Kenya Plant Health Inspectorate Service, an approval to release the parasitoids at the coastal counties where the pest was first reported.

Following successful management of the pest at the coast, she says, the Kenya Standing Technical Committee on Imports and Exports has approved the release in five more counties, including Baringo.

“Based from the experience at the coast, where the pest was able to be managed after six months, it is also expected it will be efficient in other regions,” Miller told.

She says the parasitoid is expected to manage papaya mealybug to levels they will not cause economic damage to the farmer, “just like the parasitoid has successfully managed the pest in Ghana, where we got the parasitoid”.

“It is very safe and efficient,” she added.

Miller urges African governments to invest in classical biological control of papaya mealybug using the parasitoid.

“Papaya mealybug is a very devastating pest that can lead to huge crop losses if not controlled,” she said.

Vincent Abuje, Baringo county director of agriculture, tells that the Acerophagus papaya is a welcome relief as the mealybug pest has caused massive losses for farmers in the county, with many not knowing how to manage it.

“Papaya farming is a major horticultural enterprise here and a source of livelihood for many households,” Abuje says.

He added that farmers tried using pesticides, but the pest would “go away but resurface after about two weeks”. (SciDev.Net)

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