After two years of experiments, the results obtained by Dr Guèye have proved to be enlightening. When spread by means of fumigation in a confined environment such as an airtight silo, Boscia effectively protects cereals and leguminous plants against five insect species reputed to be among the most devastating ones, in particular, the strong Prostephanus truncatus. This insect, known in French as Le grand Capucin du maïs, was accidently introduced into Africa at the end of the 1970s and was discovered by Dr Guèye himself in Senegal in 2008. Known for the extensive damage it causes to maize and dry cassava chips, Prostephanus truncatus can be effectively controlled by chemical pesticides. However, as is often the case, farmers do not have the proper skills to use these pesticides correctly.

What is the most effective dosage of Boscia leaves and fruits? According to Dr Gueye: “When used at a rate of 2% (in weight), this plant from the west of the country (the Dakar region) can cause a 100% mortality rate in the five insect species studied (Prostephanus truncatus, Caryedon serratus, Callosobruchus maculatus, Tribolium castaneum and Sitophilus zeamais). The higher the latitude, the higher the content of the precursor of the active molecule (glucocapparin) and thus the smaller the quantities of the plant required to make the treatment effective. This might be called the “local effect”: the toxicity of the product for insects is linked to various factors (climate, pedology, ecology, etc.). Furthermore, the physiological state of the plant is highly important: the glucocapparin content reaches its peak in December and January. During the rainy season (from the end of July to November), contents can drop by a factor of 30! The fruit is almost always more effective than the leaf even though it often contains less of the secondary metabolite.”

However, the work of Dr Guèye has gone even further by showing that fumigation with Boscia can attack not just the pests themselves, but in some cases their larvae and eggs. The larvae of cowpea and peanut weevils, for example, live inside the grains and consume them before emerging as adults. The grains can then certainly still be used as seeds, but they may also wither very quickly due to a lack of sufficient nutrients. “In order to destroy the larvae and eggs, it is imperative to double or even quadruple the dose of Boscia when compared to the amount used for adults”, Dr Guèye explains. “It has been possible to demonstrate this recognisable deadly effect, thanks to three years of research complementary to that of Dr Dogo Seck. The outcome has been the development of a dosage protocol for methyl isothiocyanate, produced in collaboration with Dr Joeri Vercammen (Intersciences, Louvain-la-Neuve). This research has also demonstrated that this penetrative ability of Boscia does not alter the germination potential of the grain. This establishes Boscia as a very serious alternative to chemical pesticides for the storage of seeds in a closed environment.” A practical application of Boscia use has already been planned: a data sheet will soon be designed that will target farmers directly. The doses to be used will be explained in the sheet based on resources available in the farmer’s workplace: pots, various utensils, etc.