Saving the African pod of protein from bugs – the journey so far
7 February 2007
The prospects of a scientific breakthrough in the biological control of the cowpea pod borer, Maruca vitrata are high under the collaborative efforts of the International Institute of Tropical Agriculture (IITA) and the World Vegetable Center (AVRDC).
Under a special project funded by the Gatsby Charitable Foundation, scientists from both organizations have identified potential c andidates that can be deployed from Taiwan to West Africa for the control of this pest. Among the promising beneficial organisms, a small parasitic wasps, 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.
Cowpea, otherwise known as black-eyed pea is a protein rich crop whose value lies in its ability to grow and 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.
he poor yield of cowpea is attributed to a series 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 their efforts did not yield appreciable results. Efforts have also been made lately to develop transgenic cowpea but here there are biosafety regulatory huddles to cross. None of the cowpea producing countries of West and Central Africa has yet regulatory laws on the application of biotechnology tools to improve food crops. To-date, the yield of the crop has not exceeded 400kg per hectare without the application of insecticides. In fact, 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 low level of farmers’ education, lack of capital, high prices of pesticides, lack of input market and access to recommended pesticides.
Maruca vitrata, the pod borer is undoubtedly the most economically important pest affecting cowpea yields. In West Africa, M. vitrata is attacked by various indigenous parasitic wasps, but none of them has been found to be efficient in reducing its population. According to Dr. 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 (NPV) affecting M. vitrata has recently been discovered by 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
In sub-Saharan Africa, a continent often ravaged by civil strives and natural disasters such as drought and soil infertility, malnutrition is common especially among war refugees, rural peasants and the urban poor. Cowpea with about 27% protein comes h andy as a cheap source of protein in the continent. 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 abysmally poor yields of cowpea will be improved to reduce malnutrition in sub-Saharan Africa.
