Scientists have released thousands of tiny wasps across five counties to combat a significant threat to Kenya’s fourth most important fruit: the pawpaw. This fruit is currently under attack from the papaya mealybug, a pest that covers the fruit with thick, waxy secretions, rendering it inedible and unmarketable.
The solution lies in a tiny wasp known as Acerophagus papayae, which targets the mealybug by laying its eggs within the pest, ultimately leading to its death. Researchers are now providing farmers with these beneficial wasps, having successfully introduced them in several counties, including Machakos, Makueni, Embu, Tharaka Nithi, and Baringo.
This initiative is spearheaded by scientists from the research organization CABI, the Kenya Agricultural and Livestock Research Organization (KALRO), the Kenya Plant Health Inspectorate Service, and the National Museums of Kenya. The release of these wasps has previously been successful in Mombasa, Kwale, and Kilifi.
Dr. Johnson Nyasani, chief research scientist at KALRO, emphasized that using Acerophagus papayae as a biological control agent offers a safer and more sustainable alternative to chemical pesticides as part of an integrated pest management strategy.
Pawpaw, or papaya, is a crucial fruit crop in Kenya, following oranges, mangoes, and bananas in importance. In 2020, the total volume of marketed papaya fruit was 120,474 metric tonnes; however, production has been severely impacted by the invasive papaya mealybug, first reported in coastal regions in 2016. Since then, it has rapidly spread to over 21 counties, reaching near-epidemic levels in papaya-growing areas.
While pesticides are an option for control, scientists advocate for biological methods for health reasons. Studies conducted at KALRO have confirmed that Acerophagus papayae specifically targets the mealybug without affecting other species.
Dr. Selpha Miller, a postdoctoral research fellow at CABI, noted the severe impact of the papaya mealybug, which can cause crop losses ranging from 53% to 100%. However, the integration of Acerophagus papayae into pest management strategies has shown effective results, with control achievable within six months of release.
This research and release initiative is funded by the CABI-led PlantwisePlus program, which operates over 150 plant clinics in Kenya, with additional support from the Darwin Initiative project focused on the biocontrol of the papaya mealybug in East Africa.
Originally from Central America, the papaya mealybug spread to the Caribbean and South America in the 1990s and was first detected in Africa in 2010 in Ghana and in 2016 in Mombasa. The introduction of the biocontrol agent in Mombasa, Kwale, and Kilifi led to significant success, with up to 75% mortality of the mealybug within two years and nearly doubled average papaya harvests on treatment farms, resulting in a 20% increase in farmer income.
The adult Acerophagus papayae is pale orange with green eyes and transparent wings. The female wasp lays eggs inside the papaya mealybug, with a developmental cycle from egg to adult taking approximately 13 days. Throughout her life, a female can parasitize up to 100 mealybug hosts.
