Papaya farming is an important horticultural industry in Kenya. However, the cultivation has very frequently faced a growing threat from the papaya mealybug, Paracoccus marginatus, an invasive pest that has spread rapidly through papaya-growing regions causing substantial crop losses. Farmers who depend on papaya for their livelihoods, largely suffered every time with the arrival of the pest because of poor yields and pest management costs.
Papaya mealybug is particularly damaging because it reproduces rapidly and can establish large populations on plants within a relatively short period. It started with serious infestations in Kenya from around 2015 onwards. According to estimates cited by the Centre for Agriculture and Bioscience International (CABI), severe infestations can result in crop destruction ranging from 57-91%, with losses estimated at approximately £2,224 (US$2,854) per hectare each year. Such losses are particularly significant for small-scale producers.
As long as control is considered, chemical pesticides have been in use very commonly, but their efficacy has not been promising. It was reported by the farmers, despite repeated applications, mealybug populations would return in short periods. In Baringo, agricultural officials observed that pesticides could repel or suppress the pest for approximately two weeks before infestations recurred. This created a cycle of repeated chemical applications, rising production costs and continued uncertainty over the final harvest. Some growers reported that their expected harvests had fallen by more than half compared with previous seasons.
The limitations of chemical control therefore increased interest in biological methods that use the pest’s natural enemies. One of the most promising alternatives came out to be a tiny parasitic wasp, Acerophagus papayae,. The relationship between the two insects is very specific: the female wasp lays an egg on the mealybug, and the developing parasitoid feeds on its host before emerging as an adult. As A. papayae populations become established, they can gradually outnumber mealybug populations without requiring farmers to repeatedly treat the crop with insecticides. Finally, researchers identified A. papayae as a potential biological control agent in 2019, and the Kenya Agricultural and Livestock Research Organization (KALRO) subsequently imported the parasitoid from Ghana. The wasps were introduced on a farm in March 2023 to establish the natural enemy in Kenyan papaya-growing areas. It was then since the experience of farmers provided an indication of the potential value of this approach. Alfred Bolo, a smallholder papaya farmer in Kwale County, observed that the parasitoids took almost a month to spread across his farm. Although they did not eliminate the mealybugs entirely, they reduced their numbers enough to keep the pest below levels that would cause significant economic losses. The reduction in pest pressure was accompanied by increased papaya production and much lower dependence on chemical treatments. Similar observations was made in Baringo, where Vincent Abuje, then county director of agriculture, described A. papayae as an important biocontrol agent for protecting farmers against the invasive pest. The results highlight an important principle of biological control: the aim is not necessarily to eradicate a pest, but to suppress its population below the level at which it causes economically significant damage.
For Kenya’s papaya farmers, this transition could be crucial. Instead of depending entirely on pesticides that provide temporary suppression, farmers can incorporate natural enemies into broader integrated pest-management programmes. The establishment of A. papayae therefore represents a shift from repeatedly reacting to mealybug outbreaks towards maintaining a biological balance within the crop. If the parasitoid continues to establish and spread effectively, it could help reduce production losses, lower farmers’ dependence on chemical pesticides and provide a more sustainable means of protecting Kenya’s papaya industry.
To read more about papaya mealybug biocontrol in Kenya, reach out to the International Pest Control Magazine at https://international-pest-control.com/wordpress/control-of-papaya-mealybug-in-kenya/
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