Exploiting Chemical Ecology for Developing Novel Integrated Pest Management Strategies for Africa

Abstract

Push-pull, a novel approach for integrated management of insect pests, weed and soil fertility, was developed through the exploitation of chemical ecology and agro-biodiversity to address agricultural constraints facing millions of resource-poor African farmers. The technology was developed by selecting appropriate plants that naturally emit signalling chemicals (semiochemicals) and influence plant-plant and insect-plant interactions. Plants highly attractive for egg laying by lepidopteran cereal stemborer pests were selected and employed as trap crops, to draw pests away from the main cereal crops. Among these, Pennisetum purpureum produced significantly higher levels of volatile cues (stimuli), used by gravid stem borer females to locate host plants, than maize (Zea mays) or sorghum (Sorghum bicolor). Despite its attractiveness to stemborer moths, P. purpureum supported minimal survival of the pests’ immature stages. Plants that repelled stem borer moths, notably Melinis minutiflora and forage legumes in the genus Desmodium, were selected as intercrops, which also attracted natural enemies of the pests through emission of (E)-β-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene. Desmodium intercrop suppressed parasitic weed, Striga hermonthica, through an allelopathic mechanism. Their root exudates contain novel flavonoid compounds which stimulate suicidal germination of S. hermonthica seeds and dramatically inhibit its attachment to the host roots. We identified and selected new drought- and temperature-tolerant trap [Brachiaria ( B. brizantha × B. ruziziensis ) cv. mulato] and intercrop plants (Desmodium, e.g. D. intortum) suitable for drier agroecologies. The new trap and intercrop plants also have appropriate chemistry in controlling stemborers, a new invasive pest, fall armyworms and parasitic striga weeds. Opportunities for semiochemical delivery by companion plants, including plant-plant signalling and early herbivory alert, are explored for developing future smart integrated pest management (IPM) strategies.