A push-pull system has been established for controlling lepidopterous stem borers in African smallholder maize and sorghum production. It involves using repellent plants as intercrops (‘push’) and a highly attractive surrounding trap crop (‘pull’). Some of the repellent intercrops have now been found to have other activities. Molasses grass, Melinis minutiflora, also attracts stem borer parasitoids, and the forage legume Desmodium uncinatum causes a dramatic reduction in infestation by the parasitic witchweed Striga hermonthica. The mechanisms mediating these interactions are being elucidated and the active chemicals identified. Further exploitation by modern plant breeding and biotechnology is being investigated.

Thus production of (E)-4,8-dimethyl-1,3,7-nonatriene by molasses grass is identified as the most valuable trait with regard to the role of this plant as the ‘push’ component of the push-pull strategy. Biosynthesis is by oxidative cleavage of the higher isoprenoid, which is expected to be nerolidol. Therefore, molasses grass cultivars with a higher release could prove even more valuable than those in current use. This could be achieved by a simple breeding program. The genes associated with the enzyme or enzymes involved in the oxidative cleavage of nerolidol from any plant are not known yet. In the longer term, a program of heterologous gene expression, even in maize and sorghum, could be contemplated. However, a more cost-effective and sustainable approach would again be by a breeding program to enhance the natural release of this compound from maize on induction by pest attack. If this induction could be enhanced to the level where oviposition and minor grazing by stem borer larvae resulted in rapidly induced production of the nonatriene, then this could serve to repel further incoming adult stem borers.