CABI News

Natural Enemies Field Reservoirs – technology created by the late CABI scientist Riaz Mahmood – play a crucial role in the sustainable management of the papaya mealybug pest according to new CABI-led research in the journal Biological Control.

The researchers found that the establishment of farmer-managed Natural Enemies Field Reservoirs (NEFRs) led to an increase in the absolute and average count of the natural enemy parasitoid Acerophagous papayae used to manage the papaya mealybug (Paracoccus marginatus) in Kenya.

Indeed, the rise in A. papayae populations per leaf elevated parasitism rates, leading to an overall reduction in the infestation levels of the papaya mealybug per leaf. The presence of NEFRs, the researchers argue, resulted in an increase in the type (species) and number (abundance) of predatory arthropods in the respective treatments.

Severely impacts the livelihoods of smallholder farmers

Papaya mealybug invaded East Africa between 2015 to 2020. The pest causes 57-91% yield and £2,224/ha household economic losses annually and severely impacts the livelihoods of smallholder farmers.

As a means of control, nearly 51% of farmers manage the pest using pesticides which harm insect biodiversity in addition to other non-target effects. However, biological control is an ecologically friendlier approach that has controlled papaya mealybug elsewhere around the globe.

The rationale behind NEFR technology is rooted in the ecological principle of biological control, where natural enemies play a crucial role in suppressing pest populations. The idea is to reduce the need for synthetic pesticides, thereby promoting sustainable pest management practices.

Enhancing the proliferation of A. papayae

Dr Belinda Luke, an author of the research, said, “The natural enemies field reservoirs constructed in the farmer fields, with an aim of enhancing the proliferation of A. papayae in the coastal region of Kenya, demonstrated the potential of such low-cost technologies in the management of papaya mealybug in papaya orchards.

“Our results show that the natural enemies field reservoirs led to a significant reduction in the populations of papaya mealybug coupled with an increase in the populations of A. papayae in the orchards. In addition, there was an influx of other natural enemies, mainly generalist predators, in the natural enemies field reservoirs treatments feeding on papaya mealybug.”

The researchers say that coupled with the low cost involved in its construction, using materials available to the farmer, incorporation of NEFR in Integrated Pest Management of papaya mealybug leads to reduced usage of pesticides, thereby revitalizing biodiversity and promoting sustainability in farming ecosystems.

Dr Ivan Rwomushana, a co-author of the study, said, “NEFR can be thought of as an elegant, self-sustaining, non-polluting, and inexpensive technology with a great potential to manage papaya mealybug.”

Increase in the parasitism rates

The establishment of farmer managed NEFRs across the three coastal counties led to an increase in the absolute count and average populations of A. papayae per leaf in the respective farms. This in turn led to an increase in the parasitism rates in the farms resulting in an overall decrease in the infestation levels of papaya mealybug in these farms.

“In addition, there were more predator species and higher abundance of predators in the NEFR treatments suggesting the effectiveness of this low-cost technology not only in conservation of these natural enemies but also its significant role in the management of papaya mealybug.”

The research suggest that further studies are recommended to establish the relationship between these generalist predators and the host-specific parasitoids such as A. papayae.

Additional information

Main image: A papaya fruit affected by papaya mealybug (Credit: CABI).

Full paper reference

Stephen T.O. Othim, Selpha Opisa, Ivan Rwomushana, Belinda Luke,
Unleashing nature’s defenders: Farmer-managed natural enemies field reservoirs (NEFRs) enhance management of the invasive papaya mealybug (Paracoccus marginatus) in coastal Kenya, Biological Control, Volume 193, 2024, DOI: 10.1016/j.biocontrol.2024.105528.

The paper can be read open access here.

Funding acknowledgement

This study was conducted as part of CABI’s PlantwisePlus programme, which is funded by the Foreign, Commonwealth and Development Office (FCDO), UK; the Directorate- General for International Cooperation (DGIS), Netherlands, the Swiss Agency for Development and Cooperation (SDC), Switzerland; the European Commission Directorate-General for International Cooperation (DG DEVCO); the Australian Centre for International Agricultural Research (ACIAR); and the Ministry of Agriculture and Rural Affairs of the People’s Republic of China. Additional co-funding was provided by the Darwin Initiative funded project “Protecting biodiversity through biocontrol of papaya mealybug in East Africa” Ref 29-012.

CABI is an international intergovernmental organization, and we gratefully acknowledge the core financial support from our member countries (and lead agencies) including the United Kingdom (Foreign, Commonwealth and Development Office), China (Chinese Ministry of Agriculture and Rural Affairs), Australia (Australian Centre for International Agricultural Research), Canada (Agriculture and Agri-Food Canada), the Netherlands (Directorate-General for International Cooperation), Switzerland (Swiss Agency for Development and Cooperation) and Ireland (Irish Aid, International Fund for Agricultural Development-IFAD). See https://www.cabi.org/what-we-do/how-we-work/cabi-donors-and-partners/ for full details.