A joint biological control study conducted by IITA and the University of Ghent – Belgium has found that certain species of nematodes could be used against crop pests in Sub-Saharan Africa (SSA). The study, carried out in the humid forest zone of South Cameroon, identified and isolated native species of entomopathogenic nematodes (EPNs) that could be effectively deployed as biological control agents against a wide range of insect pests of crops in the region.
EPNs are microscopic roundworms similar in morphology to plant parasitic nematodes but differ in their target hosts. They are termed ‘entomopathogenic’ as the nematodes kill the insect host from within. EPNs also rapidly kill their pest hosts, usually within 48 hours. They reproduce until the resources in the cadaver are depleted, then they migrate in search of new hosts.
The project included isolation of local EPN species, characterization of isolates and associated bacteria, matching of EPN species with the insect pests, development of suitable application strategies, determination of nematode/bacterium associations for commercial production, mass production of EPNs for distribution to farmers, and conduct of training on the effective use of EPNs.
According to Ir. Françoise Kanga Messiga, coordinator of the project, “EPNs are more effective when they are incorporated as a component of an on-farm integrated pest management (IPM) system. Within limits, EPNs are compatible with the use of chemical pesticides since their virulence is not affected. More importantly, using EPNs is safe for users and the environment as their associated bacteria poses no threat to vertebrates or plants”. However, she cautions that EPNs may affect some beneficial insects such as pollinators.
She adds that in SSA, many families of insect pests could be potentially targeted by EPNs. These could include pests of major crops such as banana, cowpea, coffee, cotton, cocoa, cassava, cocoyam, yam, taro, groundnut, maize, oil palm and certain fruits and vegetables.
For years, pesticides have been the mainstay of crop protection against insect pests. Many large farms and companies in SSA producing cash crops such as banana, cocoa, coffee, cotton, oil palm, plantain and tomato routinely and intensively use chemical pesticides. For example, from 1992 to 2000, Ethiopia imported an average of 1452 tons of pesticides annually. In Ghana, about a million liters of Lindane (a neurotoxic insecticide) were estimated to be in store in 2001.
Unfortunately, not only are pesticides harmful to the environment but pests also develop strong resistance against them. Millions of farmers have also been exposed to hazardous chemicals because of inadequate awareness or training on their correct choice and use. Their use is also costly for small-scale farmers – as much as US$ 97 per ha in West Africa. As such, classical biological control using natural enemies of pests presents a better alternative especially if deployed as part of an IPM strategy.
Worldwide, EPNs have been successfully used to control insect pests, especially in tropical regions. In Brazil, Venezuela and in the tropical areas of Australia, they have been applied to manage banana weevil. In Colombia, native EPNs are used against the coffee berry borer. In Egypt, larvae of the diamond back moth succumb to the bacteria of at least two EPN species. The cotton bollworm, which also attacks chickpea and tomato, has been shown to be susceptible to EPNs. Most of the EPNs used are native to the countries mentioned. To obtain high efficiency, EPNs must be adapted to local environmental conditions.
However, information on indigenous EPNs in Africa is still limited, especially in SSA. Currently, documented studies are available only from Kenya and Ethiopia. The IITA – University of Ghent project addressed this by prospecting for populations of EPNs indigenous to SSA and suitable for biocontrol of pests in the region.
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