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March 09, 2007

Cowpea : possible breakthrough in biological control of pod borer pest

Cowpea (Vigna unguiculata), otherwise known as black-eyed pea or niebe among other names, is a protein-rich legume crop whose value lies in its ability to fix nitrogen to improve soil fertility in marginal areas. It is also tolerant of drought. Most of the world’s cowpea is grown in West and Central Africa, where many people cannot afford protein foods such as meat, egg and fish. Cowpea with about 27% protein comes in handy as a cheap source of protein.

The yield of the crop has not exceeded 400kg per hectare without the application of insecticides. The poor yield of cowpea is partly attributed to a series of insect pests and diseases, the most devastating being Maruca vitrata which attacks the flowers and bores through the pods.

Synthetic pesticides recommended for use in cowpea can effectively control M. vitrata in the field. However, apart from environmental and human health concerns, there are also socio-economic implications that make the use of chemical pesticides problematic. Among these are the low level of farmers’ education, lack of capital, high prices of pesticides, lack of input market and low access to recommended pesticides.

In West Africa, M. vitrata is also naturally attacked by various indigenous parasitic wasps, but none of them has been found to be efficient in reducing its population. Over the years, International Institute of Tropical Agriculture (IITA) scientists have attempted to improve the crop through host plant resistance breeding, but their efforts have not yielded appreciable results. Efforts have also been made lately to develop transgenic cowpea but, none of the cowpea producing countries of West and Central Africa yet has regulatory laws on the application of biotechnology tools to improve food crops.

According to Dr. Manuele Tamò, IITA entomologist, “a virus affecting the larvae of M. vitrata has been discovered here in West Africa, but its sub-lethal character has been found to be of little practical interest. However, a much more virulent virus affecting M. vitrata has recently been discovered by World Vegetable Center (AVRDC) scientists in Taiwan. 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 Manuele.

Under a special project funded by the Gatsby Charitable Foundation, scientists from both organizations have identified potential candidates that can be deployed from Taiwan 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 into the body of M. vitrata larvae, which are subsequently killed as the parasitoid develop and emerge to form a cocoon.

It is expected that in the near future when IITA and AVRDC perfect the environment-friendly biological control method to check the menace of M. vitrata, the poor yields of cowpea will be improved to reduce malnutrition in sub-Saharan Africa.

source : The Vanguard

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