Abstract
Invasive alien species (IAS) continue to shape the global landscape through their effects on biological diversity and agricultural productivity. The effects are particularly pronounced in Sub-Saharan Africa, which has seen the arrival of many IAS in recent years. This has been attributed to porous borders, weak cross border biosecurity, and inadequate capacity to limit or stop invasions. Prediction and early detection of IAS, as well as mechanisms of containment and eradication, are needed in the fight against this global threat. Horizon scanning is an approach that enables gathering of information on risk and impact that can support IAS management. A study was conducted in Ghana to establish two ranked lists of potential invasive alien plant pest species that could be harmful to agriculture, forestry, and the environment, and to rank them according to their potential threat. The ultimate objective was to enable prioritization of actions including pest risk analysis, prevention, surveillance and contingency plans. Prioritisation was carried out using an adapted version of horizon scanning and consensus methods developed for ranking IAS worldwide. Following a horizon scan of invasive alien species not yet officially present in Ghana, a total of 110 arthropod and 64 pathogenic species were assessed through a simplified pest risk assessment. Sixteen species, of which 14 were arthropods and two pathogens, had not been recorded on the African continent at the time of assessment. The species recorded in Africa included 19 arthropod and 46 pathogenic species which were already recorded in the neighbouring countries of Burkina Faso, Côte d’Ivoire, and Togo. The majority of arthropod species were likely to arrive as contaminants on commodities, followed by a sizable number which were likely to arrive as stowaways, while some species were capable of long distance dispersal unaided. The main actions suggested for species that scored highly included full pest risk analyses and, for species recorded in neighbouring countries, surveys to determine their presence in Ghana were recommended.
Highlights
The spread of invasive alien species (IAS) has been increasing exponentially over the years, greatly facilitated by international trade and the global transport industry (Perrings et al 2005; Meyerson and Mooney 2007)
63 arthropods and 77 pathogens/nematodes determined to be irrelevant to this exercise were removed, such as those that already occur in Ghana but were not listed as occurring in Ghana in the Crop Protection Compendium (CPC), or those that were unanimously considered by the SMEs as not important for plants in Ghana, e.g. species that are specific to a plant genus that does not occur in the country
The full results of the assessments are provided in the Suppl. material 2 while the 40 species with the highest scores are provided in Table 1 and Table 2, which presents the most suitable actions to be taken against them
Summary
The spread of invasive alien species (IAS) has been increasing exponentially over the years, greatly facilitated by international trade and the global transport industry (Perrings et al 2005; Meyerson and Mooney 2007). Sub-Saharan Africa (SSA), a region dominated by resource-poor farmers, has suffered from an increasing number of invasive plant pests. The pest causing the highest yield losses (USD 9.4 Bn) was the fall army worm (Spodoptera frugiperda). This American pest was first recorded in Africa in 2016 and has since spread to SSA, threatening smallholder maize and sorghum production (De Groote et al 2020; Tambo et al 2020). Other plant pests recently reported in the region with devastating effects include tomato pinworm (Tuta absoluta) (Mansour et al 2018), Cassava brown streak virus (Ferris et al 2020), wheat stem rust (Puccinia graminis f. sp. tritici) (Fetch et al 2016) and potato cyst nematodes (Globodera rostochiensis and G. pallida) (Mwangi et al 2015; Mburu et al 2020)
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