Premier Presentation: Exploiting plant behavior and chemical ecology for developing new crop protection strategies for Africa

To develop novel approaches for integrated pest and weed management for resource poor African farmers, appropriate plants were selected that naturally emit signaling chemicals (semiochemicals) and influence plant-plant and insect-plant interactions. Plants highly attractive for egg laying by lepidopteran cereal stem borer pests were selected and employed as trap crops, to draw pests away from the main cereal crops. Of these, Pennisetum purpureum (Schumach) produces significantly higher levels of volatile cues (stimuli), used by gravid stem borer females to locate host plants, than maize or sorghum. Despite its attractiveness to stem borer moths, P. purpureum supported minimal survival of the pests’ immature stages. Plants that repelled stem borer moths notably, Melinis minutiflora P. Beauv., 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 (Del.) Benth., through an allelopathic mechanism. Desmodium root exudates contain novel flavonoid compounds which stimulate suicidal germination of S. hermonthica seeds and dramatically inhibit its attachment to host roots. We identified and selected new drought and temperature tolerant trap (Brachiaria cv mulato) and intercrop plants (desmodium, e.g. D. intortum) suitable for drier agro-ecologies. The new trap and intercrop plants also have appropriate chemistry in terms of stem borer control and striga suppression. Opportunities for semiochemical delivery by companion plants, including plant-plant signaling and early herbivory alert, are being explored for developing future smart IPM strategies for Africa and beyond.