Maize Infestation of Fall Armyworm (Lepidoptera: Noctuidae) Within Agro-Ecological Zones of Togo and Ghana in West Africa 3 Yr After Its Invasion

Abstract

The fall armyworm Spodoptera frugiperda (J. E. Smith) invaded several West African countries in 2016 causing severe injury to maize plants and economic damage. This study assesses variations in the occurrence of this species in different Agro-Ecological Zones (AEZs) in Togo and Ghana during the 3 yr following its discovery. The surveys were conducted on 120 farms in Togo and 94 farms in Ghana by collecting larvae from 200 maize plants per hectare. Infestation levels were 68.46% in 2016, 55.82% in 2017, and 17.76% in 2018. The number of larvae recorded per hectare and infestation levels were higher in Togo than in Ghana. The lowest number of collected larvae and infestation levels of S. frugiperda were in 2018, compared to the other 2 yr. Larvae per hectare and the infestation level varied regionally inside the two countries. The southern part of Togo (AEZ five) contained higher numbers of larvae and higher infestation levels during the 2 yr following the invasion of the pest. We concluded that infestation levels of S. frugiperda are much lower in 2018 than the two previous years and it is therefore necessary to determine the factors that affect the population dynamics of S. frugiperda in the field, which is a perquisite for developing management interventions.

The fall armyworm strain associated with most rice, millet, and pasture infestations in the Western Hemisphere is rare or absent in Ghana and Togo

“…Specifically, significant differences were observed between the mean TpiR frequency found in Florida-Texas corn versus both Ghana-Togo rice (P = 0.009) and Ghana-Togo corn (P = 0.002), but not between the Ghana-Togo rice and corn collections (P = 0.3485). These findings are consistent with previous observations that TpiR frequencies at corn sites in Africa are consistently lower than what is typical for Western Hemisphere corn site collections [22,30]. [14].…”

“…In both Ghana and Togo, rice is grown in lowlands where adequate water for most of the year allows multiple crops to be grown contemporaneously and in proximity. Because the farms in this western African area are usually small, less than two hectares in size, the rice habitat collection sites were unavoidably located within 1-2 kilometers of corn and other crops [30,31]. These factors make it possible, if not likely, that fall armyworm collected in the rice field pheromone traps originated from nearby corn or other hosts.…”

“…Specimens from 2016 and 2017 were limited to larval collections from corn and were previously described (Table 1). Collections from October 2018 to January 2019 were from pheromone traps in habitats represented by corn, rice, or pasture grasses [30,31]. Attempts were made throughout the 2018-9 survey period to collect larvae from rice and pasture grasses, but observed infestations were rare and only a small number could be processed for genetic analysis.…”

“…To address these issues, we obtained specimens from systematic surveys of fall armyworm from pasture, rice fields, and corn fields located in the western African countries of Ghana and Togo [30,31]. Because many specimens were collected from pheromone traps in rice, we performed a meta-analysis of genetic studies of fall armyworm collected from rice in South America to ascertain the strain and genetic marker composition we should expect for this host plant.…”

First report and distribution of the South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Togo

“…Zone II: The Dry-Savannah zone, covering the South of Kara region and the North of Central region, is characterized by mix of dry forest and savannah plants; the zone is dominated by cereal production. Zone III: The Humid-Savannah zone, covering the South of Central region and Eastern to South-West of Plateaux region is characterized by woody plants, the predominant crops are cereals and yam (Akpagana and Bouehet 1994;Koffi et al 2020). Zone IV: The Semi-Deciduous Forest covering the Western of Plateaux region hosts dense and semideciduous forest, and dominated by tree crops of coffee, cocoa and fruit, but also, rice, maize, yam, cassava and vegetables including tomatoes.…”