Fall armyworm: Menace to Nepalese farming and the integrated management approaches

— Having worldwide spread from its native American distribution to Africa and Asia since 2016, the fall armyworm (Spodoptera frugiperda) is a crop pest species that has entered Nepal in May 2019 and distributed all over in a rapid way. Nepal is an agrarian nation and the majority of the farmers grow maize on a large scale. This pest has found to affect the maize substantially and damages all the crops entirely declining the yield heavily. This is a menace to maize farmers and poses a major threat to food security and agricultural trade. Thus this review focuses on the assessment of biology of the pest and the possible management approaches which the smallholder maize farmers could afford. Integrated pest management approaches, the integration of physical, chemical, and biological method, is adopted by the majority of the corn producers to reduce the impact of the pest on the crops. Different national and international organizations and institutions have been working to develop the strategies for effective control of such a harmful insect in Nepal.


INTRODUCTION
Fall Armyworm (FAW), Spodoptera frugiperda, an insect belonging to class-Insecta, order-Lepidoptera and family-Noctuidae, is native to tropical and subtropical regions of America (CABI, 2017;FAO, 2017) in the western hemisphere (Capinera, 2001). It is a polyphagous natured insect (Hoy, 2013) which feeds on 186 plant species from 42 families (Early et al., 2018). Even though it is ubiquitous in distribution (Dhungel et al, 2019),it is predominantly present in the zones which have a climate of very little frost cover, a minimum annual temperature of 18-26 o C and 500-700 mm rainfall (Early et al., 2018). The record reported that it canfly 100 km per night (Capinera, 2001). Severe damage is seen on plants by FAW at its larval stage, especially on maize, rice, and sorghum (Dhungel et al., 2019). Nepal, being an agrarian nation, the majority of the people depends on farming for their livelihood. GDP from the agriculture sector contributes 27% (Khatiwada, 2019). The major cereal crops--Rice, maize, wheat, millet, etc. contribute majorly in the agriculture sector of Nepal. The temperature range is highly suitable for the establishment of this pest. In this degree, Nepal is considered as vulnerable to this pest. Maize strain and rice strain are the two common strains of FAW (Frerot et al., 2017).Maize is the third most important cereal crop next to wheat and rice globally, known as 'Queen of cereals (Jeyraman, 2017). Particularly, it is cultivated in hilly areas which are used in major food and feed industry. Loss of yield in maize results in higher demand for maize and dependency of it on other countries. Biodiversity is threatened by biotic pollution caused by fall armyworm (FAW).If FAW infestation spreads in this way, there will be major threats for the farmers of Nepal. In Argentina, food security was threatened by the highest yield loss (72%) and 15-73% yield loss is shown by FAW's infestations in maize (Hruska and Gould, 1997). Farming in Nepal is based on subsistence type, the most cultivated product is consumed by a family member and only the rest of them are for selling. The farmers of Nepal would be impacted by damage of FAW if infestation and spreading of this pest increase to a greater extent. Farmers are confronting challenges on "how to control this pest?" In Nepal, there is aninadequate knowledge of pest and Maize cultivation is a way of life for most farmers of Nepal, especially in the hilly region. Maize is the most widely grown crop in Nepal after paddy in terms of acreage and productions and also a staple food for many people of the country. Although the report showed the slight increment in the yield of maize over the past decade, there has been very little improvement in yield when compared to average yield of the nation few years ago. The only plausible explanation behind the statement is probably the expansion of maize cultivation into less suitable terrain, degrading soil fertility status, sluggish adoption of advanced management approaches, and most importantly; the outbreak of severe pests and diseases such as fall armyworm. The 2020 maize crops, ready to be harvested from August onwards, are growing under appropriate weather conditions. The area cultivated is approximated at a high level, enduring the constant increase observed during the past eight consecutive years, signifying the strong demand by the feed industry (FAO, Global Information and Early Warning System, 2020).

Fig.1 Scenario analysis of maize productions in Nepal: 2008-2019
Source: (Knoema, 2020) In 2019, maize production for Nepal was 2,550 tons. Maize production of Nepal increased from 1931 tons in 2008 to 2,550 tons in 2019. Since a few years, the production has not increased as expected though there is advancement in agricultural technologies and the development of new innovations. The crop has been largely affected by the severe outbreak of dangerous insect-like fall armyworm. Maize cultivating areas are also increasing representing 25% of the total field area of cereal. 20% food and energy of people and 80% poultry and animal feed is supplied by maize. Maize productivity is declining year wise due to pest infestation among which FAW is a major pest. Young leaf whorls, ears, tassel and almost all parts are eaten by FAW, which is considered as a major feed for FAW, resulting in occasional total yield loss.

Identification of insect
Eggs of FAW can be recognizedon the basis of the clustered laying nature of the eggs ranging from few to hundreds in numbers (Sparks 1979;Sharanabasappa et al., 2018). Eggs are laid on single or multiple layers creamy colored with anal tuft of hairs or sometimes without hair cover (Firake, 2019, p. 9). Eggs are usually spherical in shape and laybeneath the leaves, near the base of the plant, close to the junction of the leaf and the stem (CABI, 2019, p. 21). Identification of larvae in the field needs expertise and skills as FAW is easily confused with similar species such as the African armyworm (Spodoptera exempta), and the cotton leaf worm (Spodoptera littoralis), as well as species of other noctuid genera. First instar larvae are greenish with a black head capsule, and later turned greenish-brown in the second instars. Larvae darken in color as they feed and appear greenish (Luginbill, 1969) .The third instars are brownish with three dorsal and lateral white lines. Fourth to the sixth instars are brownish black and had three white dorsal lines and alight lateral line (Sharanabasappa et al., 2018). The mature larva has a dark head with an upside down pale Y-shaped marking in head area and black four spots arranged in square in last abdominal segment (CABI, 2017). In male moth, the forewings generally shaded grey and brown, with the triangular white spot at the tip and near the center of the wing while the forewings of the females are less distinctly marked, ranging from the uniformly greyish brown to fine mottling of grey and brown (Prasanna.et.al., 2019).

Biology of the pest
The lepidopteron pest, fall armyworm has four stages in life cycle; viz: egg, larva, pupa, and adult. The fall armyworm feeds on leaves and stems of more than 80 plant species, causing significant damage to maize, rice, sorghum,

Larva:
There are six larval instar of fall armyworm. The duration of the stage of larva tends to be almost 14 days during the summer and 30 days during cool weather. The mean development time was estimated to be 3.3, 1.7, 1.5, 1.5, 2.0, and 3.7 days for instars 1 to 6, respectively, when larvae were reared at 25ºC. The larvae in the back consists of 3 yellow stripes followed by a black and again yellow stripe on the side whereas on the second to last segment, four dark spots are seen that forms a square(FAO,2018).

Pupa:
The larva binds the particles of soil together to form a loose, oval and 20-30 mm long cocoon inside which a reddishbrown pupa measuring 14 to18 mm in length and 4.5 mm in width resides. The duration of the stage of pupa is nearly eight to nine days during the summer, but reaches 20 to 30 days during the winter (CABI, 2019). Adult:

Threats of fall armyworm: Farmer's nightmare
An intrusive pest, fall armyworm (Spodoptera frugiperda) was first recorded in Nepal from Nawalpur district which are presumed to have entered from India . As the world is confronting the perils of climate changes in agricultural productions, the outbreak of detrimental insect, fall armyworm, has added the challenges in farming sector. Fall armyworm is a hazardous trans boundary insect with a high likelihood to spread expeditiously due to its natural distribution capacity. ( The fall armyworm (FAW) has harshly affected maize production across the country this year, 2020, as compared to previous year, 2019, hitting farmers who have already had to confront the burden of the coronavirus pandemic (The Himalayan Times, 2020). The catastrophic outbreak of the pest has threatened many small to large maize producers of the country. It has destroyed over thousands of hectares of maize fields from different districts across the country. In 2018, the Democratic republic of Congo reported that 45% of maize harvest losses occurred due to FAW attacks that resulted in a loss of 0.89 million tons of maize during harvest season (FAO, 2018).Similar cases were recorded in Nicaragua; yield loss of over 70% (Hruska and Gould , 1997), America; yield loss of 39% ( Ivan et al., 2012), and Argentina; yield loss of 72% (Chamberlain et al., 2006). It causes substantial damage to maize by feeding on leaf whorls, ears and tassel which sometimes results in total yield loss (Sarmento et al., 2002). Although the direct foliar damage in maize from the attacks of fall armyworm is menacing too many farmers, the damage in many cases doesn't result in dramatic yield reduction (Hruska , 2019).The larvae, being voracious in nature, consume almost all the vegetation in their path. The consumption rate is high and the major damage is due to the feeding on the foliage. At the beginning, young larvae feeds on leaf tissue from one side and second or third instar larva make series of holes in the leaves and feeds on the edge of the leaves inwards. The older larva makes a huge damage leaving only ribs and stalk of corn. Because of its cannibalism nature, one or two larva is found per plant. Larvae also burrow the growing parts such as buds, whorl, etc. and hindered the growth of corn. It often infests ears as well. Such ears aren't consumed by humans. That's why the fall armyworm doesn't directly affect the food safety of maize; rather it can make the maize more susceptible to aflatoxin presence (Zanolli, 2018). The pest will consequently affect natural capital through economic yield losses and the capacity of farm lands to respond to shocks, and through increasing the cost of production which will ultimately affect household's social and physical capital (the household's assets). The pest also impact the import and export of the maize within or outside the country as it carries the risk of introducing pests to areas where the pests are not yet present. For the reasons, it has become a great nightmare particularly to maize crop farmers. The alarming pest has a voracious appetite for corn and other cereal crops and its impact would be noteworthy for the Nepalese farmers and country's economy ( Beshir et al., 2019). The insects prefer maize -a key food crop in Nepal -as well as rice, sorghum, millet, potato, sugarcane, vegetable crops and cotton.

Control/management
Sensing Fall Armyworm infestation before it causes heavy damage is the key to their management and control. Its management should be done cautiously as it is a dangerous pest. Only one method is not sufficient for the control of this pest. Different system should be integrated to control effectively.

Integrated management of fall armyworm
The best and most effective strategy to control FAW is taking preventive measures and immediate actions when the fall armyworm is detected. IPM focuses on the growth of a healthy crop with the least possible disruption to agroecosystems and encourages natural pest control mechanisms. Management of this pest should be done in such a way that sustain for eco-friendly environment, causes low risk to human environment, and also should be cost effective. Control of this pest is possible through many physical, biological, chemical, cultural means.

Early warning system
By warning farmers earlier on the futurerisk of FAW outbreaks, they have the likelihood to prevent crop damage.
On the basis ofrisk level, farmers are encouraged to scout their fields routinely for eggs and larvae and take precautionary measures where possible. Food security and food safety are very important for day-to-day life but outbreaks of harmful diseases and pest has imperiled farmer's life. Along with diagnosis-controlling, early forecasting is crucial which is known as Early Warning System (Li et al., 2007).
Consolidating the principles of biology, ecology and mathematics is the basis of early warning system (Wang et al., 2013). It is a process in which collection and sorting of data, and generation of early warning information is done (Wang et al., 2013). Android application -"Fall Armyworm Monitoring and Early Warning System(FAMEWS)" was used in Madagascar and Zambia and successfully applied by African country which was developed by FAO (FAO, 2018c). Similar application can be developed in Nepal to monitor FAW effectively.

Fig 4 Framework of Early Warning System
Source: (Wang, 2013)

Physical method of control
It is the simplest method of pest control where FAW eggs and larvae are killed mechanically. During first week after planting, eggs which are laid on mass on maize leaves are immediately crushed. Young larvae are picked off the leaves, before invades inside whorl. Hand picking and destruction of egg masses during monitoring is done which helps to control the pest. In Ethiopia, 15% of the farmers practiced only handpicking for FAW management (Rwomushana, 2018)  and crushing or immersing of larvae in masses. Application of dry sand in whorl is another method of controlling FAW by disturbing them. Soil application inside the whorl is done to control somehow.

Cultural method
Cultural control is an effective component of a pest control strategy for FAW. Deep ploughing has shown effective for controlling eggs and pupal stages of FAW. Planting of legumes as a trap crop and ploughing field rightly before planting the field can be an effective possible cultural method for managing the pest. Cultural practices like clean cultivation and proper use of fertilizers, grown of maize hybrids with tight husk cover will reduce ear damage by FAW (Firake, 2019

Conservation agriculture
Combined use of no tillage, residue retention, and rotation increases and diversifies biological activity of macro-(spider, beetles, and ants), meso-(fungi), and micro fauna (bacteria). These practices also lead to improvement of soil health, which contributes to more vigorous growth of the crop. a) predatory insects and mites, which eat their prey; b) Parasitoids, which are insects with a free living adult stage and a larval stage that is parasitic on other insects. c) Parasites and microbial pathogens, such as nematodes, fungi, bacteria, viruses and protozoa, which cause lethal infections. (FAO, 2018).

Predator:
Predators of the Fall Armyworm kill several individuals either as eggs, larvae, pupae or adults. The predators include earwigs, ladybird beetles, ground beetles, assassin, flower bugs, and predatory wasps. Birds, skunks, and rodents also feed on larvae and pupae of FAW among the vertebrate predators. Pair and Gross found 73% FAW pupal mortality mainly due to predators. Generally,they are non-selective or generalists, so they feed opportunistically on more than one host species, often even on their own kind. The most preferred site of FAW in maize is the whorl inside which a predatory earwig, Doru luteipes (Scudder) lays its eggs (Reis et al., 1988) and occurs throughout the maize crop cycle. Nymphs of D. luteipes consume 8-12 larvae daily, while in the adult stage they consume 10-21 larvae of S. frugiperda daily (Reis et al., 1988).

Parasitoid:
Parasitoids are organisms whose adults lay eggs either inside or attached to a single host organism. To enable development, the resultant larvae feed on the tissues of the host until they are fully grown and pupate. Parasitoid larvae always kill their host as the outcome of their development.
The majority of parasitoids known to be associated with the FAW are wasps, and less frequently flies (FAO, 2018). The parasitoid Cotesia icipe (Hymenoptera: Braconidae) found to parasitize 33-45% of FAW larvae (Global Fall Armyworm Management , 2019). Use of Parasitoids for the control of pest is effective for the environment and human health.

Pathogen:
Pathogens are everywhere. Entomopathogens are those which affect insect. Pathogens are viruses, fungi, bacteria, nematode and protozoans. Mostly, virus, fungus, and bacteria play important role in controlling FAW. They are farmerfriendly pathogen which can be recycled by farmers easily in this process, dead-decayed larva which are found in field and contain full of viroid particle of fungal spore are taken from field and then they are grinded by kitchen blender. The liquid strain from these are taken and mixed with water. Then they are sprayed in infected plants. Nuclear polyhedrosis virus (NPVs) and Spodoptera frugiperda multi capsid nucleo polyhedrosis virus (Sf MNPV) are reported lethal to the FAW. The host-specificity of pathogens is quite high, usually restricted to a few closely-related insect species (FAO, 2018). The larvae of the Fall Armyworm infected by a pathogen change the color with increasing paleness and decreasing movement, especially, when touched. However, the best way to identify a diseased larva is when it is already dead. Particularly for FAW larvae infected with Baculovirus the dead larvae will generally be observed in the upper parts of the maize plant and will hang upside down. Dead larvae covered with a powdery white or greenish mass suggest fungal infection (Prasanna et.al., 2019, p. 78). The major entomopathogens helpful for management of FAW are listed below in table.

Botanical:
Natural pesticide that is derived from plants having defensive properties is known as Botanical pesticides. More than 6000 plant species from at least 235 plant families have been screened for pest control properties.According to the laboratory studies neem seed powder is found to be the effective in killing FAW larvae causing over 70% of mortality (Maredia, 1992

Host plant resistance
The most effective and ideal method of combating insects that attack plant is by developing insect-resistant varieties (Luginbill, 1969

Fall armyworm management efforts in Nepal
Most of people in Nepal depend on agriculture for their livelihood. Farmers of Nepal have been combatting the threat of devastating pest for long; however attack of fall armyworm across the field of maize raises the serious concern threatening food security to millions of people. In Nepal, the fall armyworm has the potential to cause maize yield losses of 20-25%, which translates to the loss of more than half a million tons of the annual maize production estimated at around $200 million (Pradhan, 2020). If the pest is left unrestrained, its impact will be huge for farmers and the economy.At present major problems affecting FAW management efforts in Nepal islack of knowledge about the plant disease and pest, their diagnosis and management practices the farmers, lack of sound contingency, lack of proper coordinated plans and policy, scientific research, surveillance, laboratory and adequate practices for management of pest which may be result of low financial status. However NGO  IV. CONCLUSION Nepalese farmers, especially maize producers have encountered the problem of fall armyworm infestations on a large scale in different parts of the country. Furthermore, the environmental condition of Nepal is found very favorable for the introduction, establishment, and spread of FAW. The colossal majority of farmers in the country are smallholders. These farmers have limitations to access to infrastructure which restrict their options for management of FAW. Due to very rapid spreading capacity its complete control is very difficult. Its entry in Nepal may bring up to 100% yield decline in maize as warned by FAO. Although the loss assessment of the pest in Nepal has not been estimated yet, CIMMYT has constantly been working to manage the pest in Nepal through evaluation of push-pull strategy in which Napier grass and Desmodium are cultivated with maize crop. Integrated pest management approach is practiced by most of the farmers which include; physical, chemical, botanical, and biological method. Biological approach of management is most effective as it uses different parasitoids, pathogens, and predators to control the best. Chemical method of control is not generally preferred as it is expensive and environmentally toxic. Plant quarantine has been established in India-Nepal border to check the entry of such harmful pest. Different related institutions and organizations have been supporting the government and the smallholder farmers to help in managing and controlling the fall armyworm in Nepal.