Food security in sub-Saharan Africa is increasingly at risk due to the rapid spread of maize pests in the region, which are destroying crops and causing significant losses to farmers. Each year, between 20 and 40 percent of global crop yields are reduced due to plant pests and diseases.

“Up to very recently, maize growers have been at peace with insect problems in their crop, apart from sporadic attacks by stem borers. Then, spittlebugs started to emerge, possibly due to climate change,” said Manuele Tamò, insect ecologist at the International Institute for Tropical Agriculture (IITA) in Benin.

“Just last year, a new brutal invader landed in Africa, the fall armyworm, destroying thousands of hectares of maize crops. There is hence an urgent need to develop and deploy ecologically sustainable, economically profitable, and socially acceptable control measures against these new bio risks attacking maize in Africa.”

Spittlebug

Spittlebug (Poophilus costalis) is the most widespread and damaging species observed on maize in Togo and Ghana. Although maize farmers are aware of the damage made by the spittlebug, most of them do not apply any control measures. Infestation rates vary from one season and from one region to another, but are generally higher in the coastal and moist savannas; with peak densities of over three adult spittlebugs per maize plant. With up to 40 percent yield loss, economic damage can be substantial. Diverse host plants assure the survival of the spittlebug during the off-season, with preference for shady and moist environments.

Some natural enemies are found to be associated with the pest, but their impact is presently still unknown. Eight isolates of the entomopathogenic fungus Beauveria bassiana – which can act as a parasite of insects – have shown promising results as biocontrol agent against the spittlebug. Studies to assess their endophytic competence in the maize plants – the degree to which these isolates increase the resistance of the maize plants to the spittlebug – are underway. The CGIAR Research Program on Maize (MAIZE) is also funding a project to develop bio pesticides for the control of spittlebugs on maize crops in Togo together with the Laboratoire de Biosécurité et de Biotechnologie at the Institut Togolais de Recherche Agronomique (ITRA).

Fall armyworm

A new, highly destructive, maize pest, the invasive fall armyworm (Spodoptera frugiperda), has suddenly appeared in West, Central and southern Africa, causing panic among maize farmers. It was first reported in West Africa in January 2016 and had assumed epidemic proportions by the first quarter of 2017 in several southern African countries, including Mozambique, Namibia, South Africa, Zambia and Zimbabwe. To date, Zambia has confirmed reports that almost 90,000 hectares of maize have been affected, Malawi reports some 17,000 hectares have been hit, Zimbabwe reports a potential 130,000 hectares affected, while in Namibia, approximately 50,000 hectares of maize and millet have been damaged, according to the FAO.

Scientists are in intensive discussions with various research and development institutions based in Africa, as well as integrated pest management (IPM) experts to identify the best possible short-, medium- and long-term solution to this major menace. Control of the fall armyworm will require a multi-pronged approach, following the principles of IPM, including chemical control, biological control, host-plant resistance, agronomic management at different scales (field, farm and landscape), and a community- and GIS-based tracking and early warning system. Scientists will undertake experiments to screen elite maize germplasm to identify potential sources of even partial resistance to the insect pest. MAIZE agronomists will also be experimenting on suitable agronomic management practices to minimize the damage from the fall armyworm in maize-based cropping systems.

African stem borer

Nearly all of sub-Saharan Africa is affected by Busseola fusca (Fuller), an indigenous stem borer that occurs at higher altitudes. Various control strategies have been tried, but all have limitations and none has provided a complete solution. The four general approaches to stem borer control are chemical, biological, cultural, and host plant resistance. Chemical control is costly and risky to human and the environment and using systemic insecticides provide only protection at early attacks but not against the borers feeding in the cob. Biological control requires trained personnel, and the disruption of natural enemies due to extensive pesticide use has often led to resurgence and pest population explosion besides the concern of pesticide residue on the marketable produce. Cultural methods are only good when combined with other methods and involve the manipulation of aspects of crop agronomy to make the habitat less favourable for the pests or more favourable for their natural enemies. Farmers often do nothing but to bear the losses.

MAIZE and partners have emphasized on host plant resistance, whereby resistance developed through conventional breeding or through transgenic technology is availed to farmers encapsulated in the seed, a fact that ensures the technology is affordable, safe, easy to use, and that farmers need not purchase more than the seed. Use of stem borer resistant maize increases efficiency of farming through reduction or elimination of the cost of insecticides and reduction of yield losses from stem borer damage.

Bt maize provides a new management tool for small scale farmers and has the potential to increase yields where stem borers are a major constraint. Bt maize represents genetically modified maize that is capable of producing an insecticide – Bt protein – that can kill certain chewing insects. MON810 is a genetically-engineered, stem borer insect-pest resistant maize event that carries the Cry1Ba Bt gene from a common soil-dwelling bacterium, Bacillus thuringiensis. The gene helps Bt maize to resist damage by major stem borers in Africa. As demonstrated in several countries globally, Bt maize can reduce significantly losses of maize yield due to stem borers without unfavorable effects on non-target insects, mammals, livestock humans and the environment.

The Bt maize event MON810 was first tested against stem borers in laboratories and greenhouses. Recently, confined field trials of MON810 took place in 2011 in Kitale in the Kenyan highlands. Maize plants with and without MON810 were artificially infested with larvae of the respective stem borer species and data was taken on leaf damage score, number of exit holes, tunnel length and grain yield. Preliminary results of leaf damage scores indicate complete control of the species. Similar trials were conducted in Uganda and more are planned in Tanzania and Mozambique in 2017.