By Gift Briton  

A glimmer of hope shines bright for papaya farmers as the Centre for Agriculture and Bioscience International (CABI)’s biocontrol strategy proves effective in combating the invasive papaya mealybug pest that has wreaked havoc on their crops over the past, jeopardizing livelihoods and food security.

CABI working together with Kenyan partners such as the Kenya Agricultural and Livestock Research Organization (KALRO), the Kenya Plant Health Inspectorate Service (KEPHIS), and the National Museums of Kenya (NMK), introduced a tiny parasitic wasp called Acerophagus Papayae, an environmentally friendly and safe-to-use biocontrol agent, in Mombasa, Kwale, and Kilifi counties to help smallholder farmers fight back against the devastating pest in Kenya.

The deployment of the biocontrol agent yielded promising results in the fight against the menace of papaya mealybugs. Within two years of the first release in these counties, between December 2021 and November 2022, the parasitic wasp demonstrated a remarkable 75% mortality rate of the invasive pest.

According to CABI findings, the average papaya harvests also doubled between treatment and control farms. With higher yields, the average income of farmers on treatment farms increased by almost a quarter.

Dr Selpha Miller, Postdoctoral Research Fellow, Invasive Species Management at CABI, said, “The papaya mealybug is a devastating crop pest with the potential to cause losses ranging from 53-100%. But we have shown that A. Papayae has the ability, as part of an Integrated Pest Management plan, to be very effective with control of the papaya mealybug being achieved within six months of release.”

Papaya mealybug originated from Central America before spreading to the Caribbean and South America in the 1990s. It was first detected in Africa in 2010 in Ghana and in 2016 in Mombasa County, Kenya.

Estimates from CABI show that the value of crop losses due to the Papaya mealybug pest is £2,224/ha annually.

papaya mealybug infestation

Acerophagus Papayae effectively controlled papaya mealybugs on six farms in Kenya’s coastal region. According to CABI, the parasitism rate surpassed 30% within a month of release. The highest parasitism rates were recorded after the release of 1000 parasitoids on a single farm, highlighting the potential of the biocontrol agent as a pivotal tool in the fight against papaya mealybugs.

In light of these developments, Scientists from CABI have recently deployed Acerophagus papaya to curb the papaya pest menace in five more counties in Kenya, including Machakos, Makueni, Embu, Tharaka Nithi and Baringo, where smallholder farmers are affected by the pest. In total, CABI scientists and partners are now fighting the pest in eight counties nationwide.

As part of the comprehensive strategy employed by CABI, farmers are encouraged to reduce their reliance on chemical pesticides, fostering an environment where biological control can flourish and effectively manage pest populations.

The parasitic wasp is mass-reared from the CABI-KALRO rearing facility at Muguga on the outskirts of Nairobi. The parasitoid mummies are then placed on cards and distributed to farmers. The cards are stapled underneath papaya leaves. When the parasitoids emerge, they search for the mealybugs and parasitize them.

Farmers contribute to the rapid multiplication and spread of the parasitoid on their farms by constructing Natural Enemy Field Reservoirs (NEFRs), a technology pioneered by CABI scientists.

The farmers put papaya leaves that may have parasitoid mummies into the NEFRs for 14 days. The mummies on the leaves emerge and parasitize the papaya mealybugs. NEFRs are vital as they help breed other critical natural enemies of papaya mealybugs and other pests.

NEFRs are boxes made using locally available materials and provided with a shade of locally available materials. They allow the biological control agent to be bred in a box in the field.

Dr. Johnson Nyasani, Chief Research Scientist at KALRO, hailed the use of Acerophagus papaya to control papaya mealybug as a sustainable and environment-friendly method, adding, ” It is a safer-to-use and more sustainable way of controlling the pest as part of an Integrated Pest Management plan that reduces the reliance on chemical pesticides.”