Scientists use wasp to kill papaya pest

By PAULINE KAIRU

Kenya has scaled up the use of the encyrtide wasp to control the papaya mealy bug, which is listed as a major pest affecting papaya and other horticultural crops. Mealybug is also a serious threat to greenhouse farms and can devastate entire crops if left unmanaged.

Scientists from the Center for Agriculture and Bioscience International (Cabi), the Kenya Agricultural and Livestock Research Organization (Kalro) and the Kenya Plant Health Inspectorate Services (Kephis) carried out tests on the parasitic wasp as a means of biological control against mealybug , and say it shows promise for pest control.

The team of scientists said on Tuesday they would mass-produce the wasp from the current 12,000 parasitoids per month to 40,000 per month for region-wide releases.

As a parasitoid, wasps spend their larval stage on papaya mealybugs feeding on the host and eventually killing it.

Farmers on board

Dr Ivan Rwomushana, senior scientist in charge of invasive species management at Cabi, said the study convinced farmers of the suitability and cost-effectiveness of wasps as a viable control of papaya mealybug. According to Cabi, farmers spray their papaya trees up to 16 times per season to control this pest, using very dangerous pesticides.

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He said they would help communities mass-produce the parasitoid and retain those that are released in their papaya fields.

The papaya mealybug (Paracoccus marginatus) – a whitish cottony mass of insects – originated in Central America before spreading to the Caribbean and South America in the 1990s. It was first detected in Africa in 2010 in Ghana and Mombasa in 2016. Researchers say more than half of Kenya has been invaded by the mealybug and its impact has led some papaya growers to abandon cultivation of the fruit altogether.

Papaya is the fourth most important fruit crop in Kenya after oranges, mangoes and bananas, but the mealybug has devastated production in more than 53 percent of producing counties in just four years. Economic damage caused by the mealybug has been estimated at $2,984 per hectare per year, with crop losses ranging from 53 to 100%.

“And even then, spraying is a gamble because the cochineal’s waxy coating makes it difficult for pesticide sprays to penetrate and kill them,” Makale explained.

Also, he says, “the pest tends to develop resistance to pesticides, and pesticides toxic enough to affect mealybugs will impact other beneficial populations.”

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