Influence of sticky trap color, host plant species, and weather factors on the population dynamics of thrips species in Southern Ghana.

It is essential to correctly identify and keep track of the abundance of thrips species on infested host crops to understand their population dynamics and implement control measures promptly. The current study was conducted to evaluate the performance of sticky traps in monitoring thrips species in exporters' eggplant and chili farms and to assess the impact of weather factors on thrips population dynamics. Thrips species were monitored using blue, yellow, and white sticky traps on chili and eggplant farms in Tuba, respectively, in 2020 and 2021. Each field was divided into 8 blocks, and in each replicate, all colors representing 3 treatments were randomly tied to stakes at the center of the respective crop. Data loggers were installed to record hourly weather variables. Three thrips species [Thrips parvispinus Karny (Thysanoptera: Thripidae), Franklinella schultzei Trybom (Thysanoptera: Thripidae), and Thrips tabaci Lindeman (Thysanoptera: Thripidae)] were identified from both farms and the different species showed varied attractiveness to trap color for both seasons, with white proving more attractive to T. parvispinus. The population dynamics of the species varied significantly with the season and weather but not with the crop. Optimum temperatures (28-31 °C) and relative humidity (60%-78%) showed a positive linear relationship between the trapped insects with temperature and RH, while extreme temperatures (35 °C) negatively affected their abundance. All sticky trap colors attracted several nontarget organisms; however, yellow colors had higher populations, including the predator, Orius insidiosus. White sticky traps are recommended for inclusion in the country-wide monitoring for thrips, especially T. parvispinus.

First report of Leucinodes africensis and Leucinodes laisalis on Solanum aethiopicum and Solanum melongena in farmer's fields in southern Ghana.

The eggplant fruit and shoot borer (EFSB) is a devastating pest of eggplants (Solanum aethiopicum L. and Solanum melongena L.) in Ghana, causing significant economic losses. Although initially thought to be the Leucinodes orbonalis Guenee species found in Asia, recent European and Mediterranean Plant Protection Organization reports suggest its absence in Africa. However, eight Leucinodes species have been recently described in Africa, including two new species, Leucinodes africensis sp. n. and Leucinodes laisalis Walker, which were intercepted in eggplant fruits exported from Ghana to the United Kingdom. Despite the reported absence of L. orbonalis in Africa, it remains on the pest list of Ghana as a species known to attack eggplants. To accurately determine the identity of the EFSB complex occurring on eggplant in Southern Ghana, molecular and morphological taxonomic tools were employed, and adult male populations were monitored in on-farm conditions. Our results revealed the presence of two EFSB species, L. africensis and L. laisalis, in the shoot and fruits of eggplants, with L. africensis being the dominant species and widely distributed in Southern Ghana. Notably, L. africensis males were attracted to the pheromone lure of L. orbonalis despite the two species being biologically distinct. This study provides crucial information on correctly identifying the EFSB species attacking eggplants in Southern Ghana and has significant implications for developing management interventions against these pests and their effects on international eggplant trade.

Bionomic responses of Spodoptera frugiperda (J. E. Smith) to lethal and sublethal concentrations of selected insecticides.

Since 2016, the invasive insect Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) from the Americas has made maize production unattainable without pesticides in parts of Sub-Saharan Africa and Asia. To counteract this pest, farmers often resort to the use hazardous pesticides. This study aimed to investigate botanicals, microbials, and semi-synthetic insecticides in Ghana for pest control without harming local ecosystems. Under laboratory and on-station conditions, the present study evaluated the acute and sublethal responses of S. frugiperda to: (i) Pieris rapae Granulovirus (PrGV) + Bacillus thuringiensis sub sp. kurstaki (Btk) 5 WP, (ii) Btk + monosultap 55 WP, (iii) ethyl palmitate 5 SC, (iv) azadirachtin 0.3 SC, (v) acetamiprid (20 g/l) + λ-cyhalothrin (15 g/l) 35 EC, (vi) acetamiprid (30 g/l) + indoxacarb (16 g/l) 46 EC, and (vii) emamectin benzoate 1.9 EC. The results showed that at 96 hours post-exposure emamectin benzoate-based formulation has the highest acute larvicidal effect with lower LC50 values of 0.019 mL/L. However, the results suggested strong sublethal effects of PrGV + Btk, azadirachtin, and ethyl palmitate on the bionomics of S. frugiperda. Two seasons on-station experiments, showed that the semi-synthetic emamectin benzoate and the bioinsecticide PrGV + Btk are good candidates for managing S. frugiperda. The promising efficacy of emamectin benzoate and PrGV + Btk on the bionomics of S. frugiperda in the laboratory and on-station demonstrated that they are viable options for managing this pest.

Spodoptera frugiperda in Togo 5 years on: early impact of the invasion and future developments.

The infestation of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in Africa since 2016 has been a major threat to maize production. Previous studies in Togo and Ghana from 2016 to 2018 did not correlate FAW infestation to yield losses. Thus, the aim of this study which assesses the impact of FAW infestation by inspecting 150 maize farms throughout the five Agro-Ecological Zones (AEZs) of Togo for FAW plant damage, and third instar larvae were used to infest 10-day-old maize plants in netted plots under controlled conditions at an experiment station (Station d'Expérimentations Agronomiques de Lomé) in 2019 and 2020. As control plots at the experiment station, plots were both netted and treated with emamectin benzoate, simply netted, or open to natural infestation. The number of larvae, egg masses, percent damaged plants, and damage proportions of leaves and ears were scored until harvest. Infestations and damages on maize plant throughout Togo were similar between the two years but were higher in the southern part of the county (AEZ5). At the experiment station, the yield losses were significantly considerable and increased from 25% infestation. The losses were 0.37 t ha-1 for 25% infestation, 0.34 t ha-1 for 30%, 0.59 t ha-1 for the open plots, 0.70 t ha-1 for simple netted and 50% infestation, 1.03 t ha-1 for 75%, and 1.27 t ha-1 for 100% infestation. This current study suggested thorough inspection on maize farms to set off management practices from 25% of infestation.

Differential effects of weather, plant phenology and predators on the seasonal variation of aphids on cabbage.

The aphids Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) pose serious threats to the production of cruciferous crops in the tropics. Understanding their population dynamics is important for developing integrated pest management programmes to minimize their damage to crops. This study investigated the effects of climatic factors, natural enemies and plant age on the population dynamics of these pests. The population density of aphids and their natural enemies in 20 cabbage plants, and weather conditions were monitored for five cropping seasons from 2019 to 2021 in two agroecological zones of Ghana (Coastal Savannah and Deciduous Forest zones). The highest population density of L. e pseudobrassicae was recorded in January (dry season) in both agroecological zones, while the highest population density for M. persicae occurred in September (minor rainy season) and August (dry spell) in the Coastal Savannah and Deciduous Forest zones, respectively. The highest aphid densities were noted to occur during periods with low relative humidity and low rainfall. The population density of L. e. pseudobrassicae was significantly negatively related to plant age, air temperature and relative humidity, and positively related to syrphids (Paragus borbonicus) and spiders in the Coastal Savannah zone, while in the Deciduous Forest zone, it was significantly positively related to coccinellids. On the other hand, M. persicae population density was significantly positively related to syrphids and coccinellids in the Deciduous Forest zone. Rainfall negatively affected syrphids in the Coastal Savannah zone, while air temperature positively affected syrphids and negatively affected spiders in the Deciduous Forest zone. Coccinellids had a significant positive relationship with relative humidity in the Deciduous Forest zone. This study provides important insights into the key factors that regulate aphid population densities on cabbage and will support development of timely interventions to manage these pests.

Assessing the Potential of Inoculative Field Releases of Telenomus remus to Control Spodoptera frugiperda in Ghana.

In response to the threat caused by the fall armyworm to African maize farmers, we conducted a series of field release studies with the egg parasitoid Telenomus remus in Ghana. Three releases of ≈15,000 individuals each were conducted in maize plots of 0.5 ha each in the major and minor rainy seasons of 2020, and compared to no-release control plots as well as to farmer-managed plots with chemical pest control. No egg mass parasitism was observed directly before the first field release. Egg mass parasitism reached 33% in the T. remus release plot in the major rainy season, while 72-100% of egg masses were parasitized in the minor rainy season, during which pest densities were much lower. However, no significant difference in egg mass parasitism was found among the T. remus release plots, the no-release control plots and the farmer-managed plots. Similarly, no significant decrease in larval numbers or plant damage was found in the T. remus release fields compared to the no-release plots, while lower leaf and tassel damage was observed in farmer-managed plots. Larval parasitism due to other parasitoids reached 18-42% in the major rainy season but was significantly lower in the minor rainy season, with no significant differences among treatments. We did not observe significant differences in cob damage or yield among the three treatments. However, the lack of any significant differences between the release and no-release plots, which may be attributed to parasitoid dispersal during the five weeks of observation, would require further studies to confirm. Interestingly, a single application of Emamectin benzoate did not significantly affect the parasitism rates of T. remus and, thus, merits further investigation in the context of developing IPM strategies against FAW.

Trapping Spodoptera frugiperda (Lepidoptera: Noctuidae) Moths in Different Crop Habitats in Togo and Ghana.

The economic impact of the invasion of Spodoptera frugiperda (J.E. Smith, Lepidoptera: Noctuidae) into Africa has so far been limited to maize agriculture but could potentially impact many other crops. Trapping based on pheromone lures provides a cost-effective method for detecting this important pest (commonly known as fall armyworm) and will be essential for large-scale monitoring of populations to determine its geographical distribution and migration behavior as the species equilibrates to its new environment. However, the effective use of pheromone trapping requires optimization for a given location. An earlier report demonstrated that two commercial lures (one 3-component and the other 4-component) that were effective for trapping S. frugiperda in maize fields in Togo, Africa. The current study extends these findings to agricultural areas that differ in plant host composition (maize, pasture grasses, rice, and sorghum) in multiple locations in Ghana and Togo. In two seasons, significantly higher numbers of moths were found in maize, and in one season, higher numbers were found in rice than in sorghum and pasture grass systems. The results confirm the effectiveness of pheromone trapping and identify pheromone lures and trapping methods best suited for the different agroecosystems common to West Africa and that are at risk of infestation by S. frugiperda.

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

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.