There's a confined field trial taking place in rural Nigeria. The crop being tested is genetically modified (GM) insect-resistant cowpea, an important, high-protein, drought-tolerant food legume grown widely in the dry savannah regions of tropical Africa.

The gene that has been introduced comes from the soil bacterium Bacillus thuringiensis, or Bt for short. This organism has been used as an insecticidal spray, especially by organic farmers, for years. It produces a toxin that is specific for the larvae of certain insects, including the damaging pod borer, Maruca vitrata, which often devastates cowpeas.

The toxin, which is itself a protein, binds to specific cells in the lining of the guts of the susceptible larvae, punctures them, and leads to the death of the larvae. All other animals, including frogs, birds and humans, lack these gut cells so they are immune to the Bt toxin.

The results are so promising that the African Agriculture Technology Foundation is considering commercialising the crop in the next few years.

But the trial in Nigeria is unusual because few African countries allow them. GM crops are grown commercially only in South Africa, Burkina Faso and Sudan.

Why Africa is reluctant

The main reasons other countries haven't followed suit are political and economic.

The negative attitude to GM crops found in Europe, where they import GM crops such as soybeans for animal feed but do not allow their own farmers to plant it, has had a strong influence on African politicians.

The reluctance of so many African countries to GMOs is also attributed to fears about the impact it would have on trade with other countries, particularly Europe where a number of countries havebanned GM imports.

Cowpeas, cotton and maize

The gene for the Bt toxin has been introduced into cowpeas, cotton and maize. Cowpeas is the most important food grain legume in the dry savannahs of tropical Africa where it is grown on more than 12.5 million hectares of land. This is comparable with the 15 million hectares of maize grown in Brazil. There are only confined field trials in Nigeria, Burkina Faso and Ghana.

About 8% of the world's cotton is grown in Africa, almost exclusively by small holder farmers. Bt cotton is grown commercially only in Burkina Faso (74% of a total area of 648,000 hecatares), Sudan (80% of 109,000 hectares) and South Africa (95% of a mere 9000 hectares).

Maize is the most widely grown food and fodder crop in Africa. But only South Africa grows Bt varieties commercially (81% of 2.5 million hectares).

The high percentages in these three countries is testimony to farmers' preferences for these varieties.

But political resistance remains strong as does public fear about GM crops. The high fence around Nigeria's trial confirms this. Before a GM crop can be grown in any country it has to be tested for safety to humans, animals and the environment. Because, in the minds of much of the public, this is a potentially dangerous crop, the field trial must take place behind high fences. The field trial must not only be fenced but also guarded night and day.

South Africa's been doing it for years

GM crops have been grown in South Africa since 2000. It has the most GM crops on the continent. There are three currently in production - maize, soybeans and cotton. The traits are insect resistance (Bt) and herbicide tolerance (HT).

The percentages of the crops grown at present are approximately 83% white maize, mostly stacked with Bt and HT but some with single traits; 90% yellow maize with the same trait combinations as for white maize - 92% HT soybeans and 95% Bt cotton. Average annual local consumption of maize during the past 10 years has been about 7.5 million tonnes - 4.4 million white and 3.1 million yellow.

Cotton is not widely grown in South Africa. Thus any foods which contain locally produced maize or soybean will most likely have been derived from a GM crop. This may be in the form of, for example, thickeners, proteins or stabilisers.

Other African countries

Burkina Faso has been growing Bt cotton since about 2007. Out of a total of some 648,000 hectares planted in 2014, approximately 73% were GM.

Sudan was the most recent to commercialise a GM crop, namely Bt cotton. In 2014, GM varieties accounted for some 80% of Sudan's approximately 109,000 hectares of that crop.

By growing Bt crops farmers no longer have to spray with insecticides to kill the insect borers as the crops are now resistant to these pests. They may have to spray to kill secondary insects - something that would also need to be done with conventional crops as well.

This reduction in costly. Insecticides save farmers money and is also beneficial to the environment as chemicals used to kill insect borers on conventional crops are indiscriminate and will kill other beneficial insects, such as ladybirds.

By growing HT crops, farmers still spray with herbicides - but can now do this selectively. Previously, they would allow the weeds to germinate, then spray before planting. While they waited for the herbicide to dissipate - and so as not to kill their crops - they would lose valuable topsoil to wind and rain. Now they can plant their crop, allow both weeds and crops to grow, and then spray. The dead weeds can act as a type of mulch.

This is known as conservation tillage. The herbicide to which most GM crops are tolerant is the biodegradable Roundup, which was widely used even before the advent of GM crops. A recent report, which found that glyphosate - the active ingredient in Roundup - is "probably carcinogenic", has been strongly disputed.

It is clear that if such high percentages of maize, soybeans and cotton are grown in South Africa, they must make economic sense tocommercial farmers. But what about small holder farmers? In Burkina Faso, documented farmer benefits include a 20% yield increase compared to conventional cotton, a pesticide use reduction of about 67%, while cotton profits were elevated by US$64 per hectare - a 51% increase in previous income levels.

Jennifer Ann Thomson is Emeritus Professor in Molecular Biology at University of Cape Town.

Disclosure statement: Jennifer Ann Thomson received (in the past) funding from the National Research Foundation, the South African Maize Trust, the Rockefeller Foundation and the Claude Leon Foundation..She is a member of AfricaBio and serves on the boards of the African Agricultural Technology Foundation and the International Service for the Acquisition of Agri-Biotech Applications.