The prospects of a scientific breakthrough in the biological control of the cowpea pod borer (Maruca vitrata) are high, thanks to the collaborative efforts of the International Institute of Tropical Agriculture (IITA) and the World Vegetable Center (AVRDC).

Cowpea seller at Dantokpa Market, Cotonou, Benin. Photo: IITA.

Under a project funded by the Gatsby Charitable Foundation, scientists from the two organizations have identified candidate predators and viruses to be deployed from East Asia to West Africa for the control of this pest. Among the promising beneficial organisms, a small parasitic wasp, Apanteles taragamae, has already been introduced to the IITA-Benin insectaries and experimentally released in Benin and Ghana. The adult females of this parasitoid lay eggs in the body of M. vitrata larvae.

Cowpea, otherwise known as black-eyed pea, is a protein-rich crop whose value includes its ability to grow in marginal soils and improve their fertility by fixing nitrogen. It also tolerates drought. Most of the world's cowpea is grown in West and Central Africa, where many people cannot afford other sources of protein such as meat, eggs and fish. Photo IITA.

But cowpea yields are low because of an array of insect pests and diseases, the most devastating being M. vitrata, which attacks cowpea flowers and pods. Over the years, IITA scientists have attempted to improve the crop through host-plant resistance breeding, but with little success. Efforts have also been made lately to develop transgenic cowpea, but this approach entails biosafety regulatory hurdles, as none of the cowpea-producing countries of West and Central Africa yet has regulatory laws on applying biotechnology to improve food crops.

Maruca larva and damage on pod. Photo: IITA.

Without insecticides, cowpea yield never exceeds 400 kilograms per hectare. Synthetic pesticides recommended for use on cowpea can effectively control M. vitrata, but their use is constrained by environmental and human health concerns, farmers' lack of education and capital, high pesticide prices, and the general absence in West and Central Africa of an input market and of the recommended pesticides.

In West Africa, M. vitrata is attacked by various indigenous parasitic wasps, but none has been found to significantly reduce its population. According to Manuele Tamò, IITA entomologist, "an entomopathogenic cypovirus affecting the larvae of M. vitrata has also been discovered here in West Africa, but its sublethal character has been found to be of little practical interest." However, a much more virulent nuclear polyhedrosis virus affecting M. vitrata has recently been discovered by AVRDC scientists in East Asia.

"We are currently studying this virus in controlled experiments at IITA-Benin, and preliminary observations indicate a high potential as a biopesticide for the control of M. vitrata," says Tamò.

In sub-Saharan Africa, a continent often ravaged by civil strive, natural disasters, and endemic drought and soil infertility, malnutrition is common among refugees, rural peasants and the urban poor. Cowpea, which is about 27% protein, is therefore handy as a cheap source of protein. When, in the near future, IITA and AVRDC perfect an environmentally friendly biological control method to check the menace of M. vitrata, the abysmally poor yields of cowpea will improve and so help to reduce malnutrition in sub-Saharan Africa.

Cowpea field at harvest. Photo: IITA.

For more information, contact Taye Babaleye (t.babaleye@cgiar.org).