D3453: Crop diversification: An agroecological option against the invasive fall armyworm Spodoptera frugiperda (J.E. Smith)

The fall armyworm (FAW), Spodoptera frugiperda, seriously endangers African food security, causing 20-50% yield reductions. The conventional FAW control approach using chemical pesticide may lead to adverse environmental and health issues. Hence, there is an urgent need to develop an eco-friendly and sustainable FAW management alternative. In this study, we hypothesized that odours released by companion crops in a maize-based intercropping system would reduce FAW oviposition responses and attract its parasitoid. In dual choice oviposition assays, we found that the FAW laid significantly more eggs on maize than on beans, groundnut, sweet potato, cassava, greenleaf and silverleaf desmodium. However, significantly fewer eggs were laid on maize in the presence of companion plants except cassava. Wind tunnel bioassays confirmed decreased maize attractiveness to FAW moths when companion plant volatiles were present. Interestingly, FAW larval endoparasitoid Cotesia icipe was attracted to volatiles from the individual companion plants and when they were combined with maize. Coupled gas chromatography-mass spectrometric (GC-MS) analysis detected several potential behaviour-modifying compounds including (Z)-3-hexenyl acetate, (E)-β-ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-β-caryophyllene, camphor, methyl salicylate and (E, E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene in the headspace collection of companion plant volatiles. Field trials validated the results from our laboratory study and provided evidence supporting the effectiveness of potential crop mixtures in reducing fall armyworm infestation and increasing the abundance of natural enemies. Our study demonstrated the potential of crop diversification for ecologically sustainable FAW management.