ASNS African Science News
Food security, livelihoods at risk as destructive pest invades Tanzania
Written by Isa Chuki
A new, destructive pest is rapidly spreading through the coastal areas of Tanzania around Dar es Salaam and Zanzibar attacking important food crops such as papaya and cassava, and ornamental plants like hibiscus and frangipani. It has been identified by scientists at the International Institute of Tropical Agriculture (IITA) as the Papaya mealybug (Paracoccus marginatus).
In the recent years, this highly invasive pest has also been spreading and causing damage in many Asian and West African countries. With its origin in Mexico, it was first observed on the African continent in Ghana in 2010 from where it spread to Benin, Nigeria, Togo, and Gabon. The discovery of the papaya mealybug in Tanzania means that the rest of East Africa is now likely to be affected as well.
According to Dr James, Legg, IITA entomologist, and one of the scientists who is leading the efforts to contain the pest after first noticing the pest’s damage in his home garden, the papaya mealybug is currently one of the most destructive and rapidly spreading invasive insect species.
“In Tanzania we have observed the pests along the coastal belt around Dar es Salaam and its environs, mostly on papaya, cassava, and ornamental plants such as hibiscus and frangipani. But we need to carry out a survey throughout the country to determine the full extent of spread and the range of plants affected,” he says.
The papaya mealybugs appear as white fluffy spots on the undersides of leaves, branches, and fruit, and are often accompanied by an unsightly black, sticky substance coating these surfaces―this is a result of a sugary excretion by the pests which attracts mold. The affected plants don’t grow properly, and farmers are unable to sell the often misshapen, discolored, and in severe cases, completely shrivelled fruits.
These mealybugs are tiny, white, flat insects which sap the life out of the plants. Their preferred host are papayas, but the insects also affect a wide range of crops including cassava, bean, coffee, pepper, melon, guava, tomato, eggplant, cotton, and jatropha. Therefore, if not controlled, the pest may result in massive damage and loss of livelihoods for many farmers in the country.
“Samples sent to IITA’s Biological Control Center for Africa, located in Cotonou, Benin, have been positively identified as the papaya mealybug by the Institute’s entomologist Dr Georg Goergen. Now that we know what we are dealing with we need to act fast. The pest can easily spread throughout the East African region causing major damage and threatening the food security and incomes of tens of thousands of Tanzanian farmers,” he said.
The mealybugs are easily blown by the wind or transported by ants from one plant to another, and are transported longer distances by people who unknowingly carry infested plants or fruit from one part of the country to another, or from country to country.
Efforts are underway from IITA, the Ministry of Agriculture, Food Security and Cooperatives (MAFSC), and the United Nations Food and Agriculture Organization (FAO) to mobilize funds to use biocontrol agents to contain the pest before it gets out of hand. This involves introducing natural enemies of the pest such as parasitoids―extremely tiny insects that lay their eggs inside the papaya mealybug. As the eggs hatch, tiny worm-like “larvae” emerge, which then eat the mealybug from the inside out!
According to Mr Elibariki Nsami from the National Biological Control Programme (NBCP) of the Ministry of Agriculture, Food Security and Cooperatives, using biological control is the only effective way to manage the pest menace as most pesticides are not effective since these mealybugs coat themselves with a protective wax. “The biocontrol mechanisms are safe as they are very specific and only attack the papaya mealybug. They are also cheap, cost effective, and safe for the environment.”
It will also be important to set up a surveillance system to track the spread of the pest in the country and the wider region and to create awareness among the farmers and general public on how to control it.