Maize, Zea mays L (Cyperales: Poaceae), is one of the major cereal crops grown worldwide including in sub-Saharan African countries [1, 2, 3, 4]. It is the third most important agricultural commodity worldwide after rice and wheat in terms of cultivated area and consumption, being used for human consumption, animal feed, and as input for industrial processing [1]. In the sub-Saharan Africa alone, more than 300 million people depend on maize production [2]. Similarly, it is one of the major cereal crops in Ethiopia, being major stable food and feed source for millions of people in the country [5, 6, 7, 8, 9]. The country produces more maize than other crops, accounting for more than 27% of crop production [10]. Maize is widely produced in almost all agro-ecologies with both rain-based and artificial irrigation systems and smallholder farmers accounting for the largest share of its production.
Although the crop plays a leading role in maintaining food security for the growing population, productivity remains low with an average yield of 3.24 tons ha− 1 compared to the world average of 4.5 tons ha− 1 [11]. Both biotic (mainly diseases, weeds, and insect pests) [5, 8] and abiotic factors such as inefficient production methods, low soil fertility, drought, and small landholding attribute to the low productivity of maize in the country is attributed to [7, 10, 12].
Among the biotic factors, pests such as the fall armyworm (FAW), Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), different species of stem borers like Chilo partellus Swinhoe (Lepidoptera: Crambidae), Busseola fusca Fuller (Lepidoptera: Noctuidae) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae), and the notorious weed Striga, Striga hermonthica B (Lamiales: Orobanchaceae) are predominantly affecting maize production and productivity [2, 3, 13]. Among these, FAW has become one of the major challenges of maize production mainly threatening smallholder farmers in the country [9, 10, 14, 15, 16, 17].
In the case of Africa, FAW has become an invasive species in the last few years with outbreaks reported in western and central Africa in 2016 [2, 14, 15, 16, 18, 19, 20]. Further spread of FAW was observed in Eastern and Southern African countries in 2017 [13, 19]. By late 2018, it had been confirmed by virtually every country in sub-Saharan Africa [13, 15, 21]. The spread of FAW within a country and among African countries was rapid. For instance, within Ethiopia, FAW infestations were reported in the Southern Nations, Nationalities, and Peoples` State on March 2017 and spread fast to all states to become an epidemic pest by June 2017 [15]. Since then, the FAW has already become a major pest of maize in all states of Ethiopia. Future forecasts predicted for a high possibility of this insect pest to become and remain a regular pest in Ethiopia and the continent [14, 16, 19].
The FAW believed to be originated in the tropics and subtropics of America, causes damage to almost 100 plant species [19, 20, 21, 22, 23]. It mainly prefers maize. In addition, it is also a common pest of sorghum, rice and millet. It also sporadically affects vast arrays of additional crops and plants, including cotton and vegetables [21]. It reproduces during the rainy season, when the moths lay their eggs on crops. Their larvae march in groups, devouring food sources they come across. They subsequently pupate to form moths, each of which can fly up to 1,000 km and lay 1,000–2,000 eggs in their 10-day lifetime [24, 25, 26, 27].
Given its voracious feeding habit, long-distance migration behavior and high reproductive rate, FAW might substantially and persistently affect millions of smallholder farmers in the African continent unless cost-effective integrated pest management approaches are in place to keep the pest below an economic threshold. While most farmers affected by FAW in developed countries have large-scale farm operations with access to international market prices, risk-transfer mechanisms and the benefits of government subsidies [21], the overwhelming majority of farmers in Africa are smallholders [9, 13, 21] without access to those conditions [21]. This dramatically different context means that different management approaches must be sought. Therefore, developing effective and smallholder-farmers-friendly integrated FAW management strategies is of paramount. Among the management methods believed to be affordable by smallholder farmers is a push-pull system [3, 13, 28, 29].
The push-pull system is a novel tool for integrated pest management programs that uses a combination of behavior-modifying stimuli to manipulate the distribution and abundance of insect pests and/or natural enemies [3, 13, 28, 30, 31, 32, 33, 34]. It involves intercropping target crops like maize with a repellent plant, such as silver-leaf desmodium, Desmodium uncinatum J (Fabales: Fabaceae) (a push-plant) that repels or deters insect pests, and planting an attractive trap plant which is highly apparent and attractive to a pest, such as Sudan grass, Sorghum sudanense P (Cyperales: Poaceae) or Napier grass, Pennisetum purpureum S (Cyperales: Poaceae) (pull-plants), as a border crop around the intercropped field, thus, facilitating their accumulation and control [3, 13, 19, 35, 36, 37, 38, 39]. Recent findings reported that the push-pull system reduces FAW infestation in maize fields [2, 3, 4].
However, instead of using a push-pull system as a stand-alone control method of FAW, integrating it with other monitoring and control mechanisms might enhance effective control of all life stages of FAW. An integrated pest management (IPM) approach would be more effective in sustainably containing and controlling the FAW in maize by smallholder farmers. Previous findings reported that moths (both male and female) of many lepidopteran species including FAW are characterized by their rapid positive responses to light during the night-time [40, 41, 42]. Night-time light traps can be used for monitoring and mass trapping of lepidopteran moths such as FAW [41, 42]. As a FAW IPM approach, we hypothesized that integrating night-time light-traps and the push-pull system could enhance the control of different FAW life stages (adults, eggs, and larvae). Therefore, this research aims to: (1) determine the effect of integrating night-time light-traps and push-pull system on deterring FAW moths, (2) evaluate the effect of integrating night-time light-traps and push-pull system on FAW eggs and larvae infestation on maize plants, and (3) determine the proportion of maize plants damaged by FAW larvae in maize plants treated with night-time light-trap and push-pull integrated system relative to maize monocrops or maize plants treated with a push-pull or light-trap alone.