Host suitability of poaceous and broad leaf plants for Fall armyworm (Spodoptera frugiperda) (Lepidoptera: Noctuidae)
Spodoptera frugiperda is native to the Americas but invaded the African continent in 2016, causing damage to maize and sorghum. Reports from literature indicate that larvae of S. frugiperda can feed on 353 different host plant species belonging to 76 plant families, indicating that it is highly polyphagous. Several strategies such as chemical control, host plant resistance, biological control and cultural control can be implemented in an Integrated Pest Management (IPM) system to manage S. frugiperda populations. Chemical control (mainly synthetic insecticidal sprays) and genetically modified crops (mainly Bt maize) are the primary tools used to manage S. frugiperda. However, alternative methods to insecticidal sprays and genetically modified crops are essential for subsistence farmers in Africa to control S. frugiperda in a more cost-effective and sustainable manner. These control methods can include cultural control practices such as intercropping and crop rotation. It is necessary to identify crop and non-crop hosts that are cultivated in Africa on which S. frugiperda larvae can survive and complete their lifecycles. Through this, crops that can serve as ‘’bridging’’ crops for S. frugiperda during off seasons when no maize is cultivated, can be identified and classified as having a high or low risk of suffering infestation and damage. Also, pest management strategies can be developed if poor larval hosts can be identified and used as trap crops. The aim of this study was to evaluate the host suitability of 22 poaceous and broad leaf plant species that are potential hosts of this pest, and which are cultivated in South Africa, for development of S. frugiperda larvae. Spodoptera frugiperda larvae were reared in petri dishes under laboratory conditions on tissue of the different plant species and their life history parameters were recorded. Results showed that the Poaceae species were more suitable larval host plants compared to broad leaf plant species. Maize, oat, forage sorghum and grain sorghum were the most suitable poaceous hosts for S. frugiperda. Development of larvae reared on maize was the optimum, compared to the other poaceous and broad leaf species. The superior performance of larvae on maize and sorghum may indicate that larvae used in this study were from the maize strain of S. frugiperda. However, there is a possibility that some larvae may be interstrain hybrids since larvae reared on rice also performed very well. Spodoptera frugiperda is composed of two morphologically indistinguishable strains, namely the rice strain and the maize strain, and recent reports showed the presence of an interstrain hybrid in in Africa. Brachiaria grass, Panicum grass, as well as Napier and Vetiver grass have the potential to be used as trap crops in a push-pull system to control S. frugiperda. The broad leaf species evaluated in this study, especially Indian mustard, woolly pod vetch and pumpkin, can possibly be used in habitat management strategies (e.g. crop rotation, trap cropping and intercropping systems) to reduce the extent of S. frugiperda infestation of maize. Oat was the only winter crop identified as a high-risk crop which can serve as a bridging crop for S. frugiperda during off seasons when no maize is cultivated in South Africa. However, although some winter-crops could be regarded as suitable hosts, temperature will ultimately determine if S. frugiperda larvae can overwinter in a particular area. Other winter crops such as wheat, cultivated radish and Japanese radish was identified as low-risk crops to sustain S. frugiperda during winter months.