A tiny parasitic wasp, Acerophagus papayae, is helping Kenyan farmers recover from the devastation caused by the papaya mealybug, an invasive pest that arrived in Kenya in 2016. Within a year, the pest had spread rapidly across papaya-growing regions, damaging leaves, stems, and fruits, and forcing many farmers to abandon their fields.
Papaya is Kenya’s fourth most important fruit crop, providing income and nutrition to thousands of households. The widespread infestation led to reduced harvests, loss of income, and declining local supply. In response, scientists at the Centre for Agriculture and Bioscience International (CABI) began searching for sustainable control methods and turned to a model developed in Ghana, where the wasp had already been used successfully.
Dr. Selpha Miller, an invasive species scientist at CABI, explained that Kenya imported the wasps from Ghana and adapted the process for local use. “We learned how to produce and distribute the wasps while they are still in their ‘mummy’ stage,” she said. “That allowed us to produce more and reach about 995 farms so far.”
The wasps are reared in laboratories on potato sprouts. Once developed, the mummified wasps are attached to small glue-coated cards and placed under papaya leaves. When the wasps emerge, they begin parasitizing and killing mealybugs, helping reduce pest populations without chemical input.
Farmers who had struggled with the pest now report improvement. “We were struggling to control the pest because nothing worked at that time,” one farmer said. “The extension officers told us not to spray chemicals since they were harmful. When I heard about biological control using natural enemies, I was excited. It’s good news for us farmers.”
Another grower, Mary, who produces papaya, citrus, and bananas, said, “The mealybugs destroyed about half of what I was supposed to harvest. I used to spray chemicals every week, and it was very expensive. It was like we were sharing the yield 50-50. Since using this biological control, I’m now saving a lot. Buyers come to my farm to buy fruits directly. I plan to expand, grow more pawpaws, and support my children’s education.”
Dr. Miller explained that biological control is a gradual process. “Unlike pesticides that give instant results, this method takes about six months for the wasps to build up and control the pest population,” she said. The wasps also disperse naturally to nearby farms, spreading the control effect without additional releases.
CABI worked with Kenyan institutions, including KALRO, KEPHIS, the National Museums of Kenya, and local county governments to coordinate the intervention in regions such as Machakos, Makueni, Embu, Tharaka Nithi, and Baringo. The same model is now being replicated across East Africa. “We’ve already supported Uganda, Tanzania, Rwanda, South Sudan, and Burundi,” Dr. Miller said.
The biological control programme has restored production for papaya growers across Kenya, supporting the sector’s recovery and reducing reliance on chemical pesticides.
