Prediction of High-Risk Probability Areas under Current and Future Climate Scenarios in India for the Establishment of Fall Armyworm

— The Fall Armyworm (FAW) or Spodoptera frugiperda, is an endemic and agriculturally important insect pest in tropical and subtropical regions of the Americas causing severe impact estimated at millions of dollars. FAW has been recently identified for the first time in India and is also a first record in Asia threatening the food security and livelihoods of millions of farmers. The insects are affected by climatic factors, and climate change may affect geographical distribution, abundance, growth rate, survival, mortality, number of generations per year and other characteristics. These climate change effects on insects are difficult to project due to complex interaction among insects, hosts and predators. Moreover, agricultural pest management may become more challenging under future climate change and variation. The present study aims to project the impact of climate change on future suitability for the expansion of FAW as well as highlight the high risk probability areas due to the pest using the historical and future climatic conditions. The modelling was carried out using CLIMEX model, GIS, the known distribution of the species and the CliMond meterological database. The analysis has indicated high climatic suitability for FAW occurrence in India with Eco-climatic Index (EI) values above 20. Further, the high risk probability areas for the FAW establishment up to district level were also identified for the major maize growing states. The areas where the pest is currently reported in the country are coinciding with the predicted potential areas in India validating the current analysis. The analysis using two general circulation models (GCMs), CSIRO MK3.0 and MIROC-H, for 2030 and 2050 under the A2 Special Report on Emissions Scenarios (SRES) indicated the possible reduction of climatically suitable areas for the FAW establishment in India. This kind of analysis assessing the possible impacts of FAW under future climate conditions is essential for the future economic production of crops.


INTRODUCTION
The fall armyworm, Spodoptera frugiperda (J.E.Smith) is an agriculturally important insect of more than 80 plant species, causing damage to economically important cultivated cereals such as maize, rice, sorghum, and also to vegetable crops and cotton with a particular preference for maize, a main staple crop around the world threatening food security and biosecurity. This highly-destructive and invasive pest has been seen in the Americas since several decades, but its prevalence outside was noted for the first time in West Africa in early 2016 (IITA 2016; IPPC 2016), and it has subsequently been recorded in most sub-Saharan countries (ACAPS 2017). It has spread to 44 countries across the continent, barring North Africa (CIMMYT 2018). Sightings of damage to maize crops in India due to fall armyworm mark the first report of the pest in Asia in 2018. In India it was reported for the first time from Karnataka (ICAR-NBAIR, 2018a) and Andhra ISSN: 2456-1878 https://dx.doi.org/10.22161/ijeab.62. 2 8 Pradesh (EPPO, 2018). The pest has also been reported in Telangana, Tamil Nadu, Maharashtra and Gujarat.
Fall armyworm (FAW) causes major damage to economically important crops. In sub-Saharan Africa, where fall armyworm is devastating maize crops, estimates indicate 13.5 million tons of maize valued at $3 billion are at risk in 2017-2018, which is equivalent to over 20 percent of total production for the region (CABI, April 2017). In America, FAW is listed as one of the major pest of maize and causing severe economic losses, with infection level up to 70%. According to the International Maize and Wheat Improvement Centre (CIMMYT) at Mexico, FAW has, over the last two years, damaged more than 1. Fall Armyworm is native to tropical and subtropical regions. However, it may also be found in temperate regions (Luginbill 1928;Sparks 1979;Clark et al. 2007). FAW does not possess a capability to enter diapause, due to this; FAW cannot survive extended periods of freezing temperature but must migrate northwards each spring if it is to re-infest cropping areas in temperate regions (Luginbill 1928).
The life cycle, behaviour, survival and spread of insects are affected by climate factors, especially temperature, which has a strong influence on all ectothermic organisms (Rosenzweig et al. 2001;Fhrer 2003;Diffen). Outbreaks of FAW are closely related to climatic conditions, and migrant adults can move northwards up to 483 km/generations with good winter and spring conditions (Sparks 1979

OBSERVATIONS:
The parameter values from the hypothesis of Hannalene Du Plessis et al., relevant to species biology under "Wet Tropical" species condition were considered to project potential distribution of FAW. The parameters are explained in detail below- • The heat stress temperature threshold (TTHS) and its accumulation rate (heat stress accumulation rate, THHS), were used to limit the survival of FAW at high temperatures. When the average maximum temperature is below TTHS, the heat stress is equal to zero (Sutherst et al 2007). The threshold of 39 °C is the same as the upper temperature limit for development.
• CLIMEX accumulates dry stress when soil moisture is lower than the dry stress threshold (SMDS). This stress is accumulated weekly and is multiplied the dry stress rate (HDS) (Sutherst et al 2007). There is evidence that during a dry season, few adult moths are trapped and the population peaks are delayed (Andrews 1988). The dry stress was set at SMDS= 0.1 to avoid the persistence of FAW. Dry Stress was given by using the lower soil moisture growth threshold and adjusting the rate to limit the distribution to tropical and subtropical regions where it has been reported.
• Wet stress accumulates when soil moisture exceeds the wet stress threshold (SMWS The resulting maps show areas that are likely to be at different level of risk of FAW as determined from the climatic suitability range (Fig 1). The current climate conditions modelled for FAW showed suitability for FAW occurrence in India.
• Tropical regions were found to be more suitable for its establishment which is similar to the observations of Luginbill 1928. High risk suitability areas with EI=>20 for FAW occurrence in India are projected in Fig 2. • Currently, infestation of FAW is reported in twelve states in India viz., Andhra Pradesh, Bihar, Chhattisgarh, Goa, Gujarat, Karnataka, Madhya Pradesh, Maharashtra, Odisha, Tamil Nadu, Telangana and West Bengal (CABI, 2020). The current analysis with Compare locations (Species 1) application has also indicated high climatic suitability in the above states with 20-95 EI values validating the present study (Fig 2).
• Climate is not the only factor limiting species geographical distribution (Brown et al., 1996). Host availability is also important in actual determination of potential geographic areas.  (Table 2).
• High risk suitability areas are mostly noticed in South India and North east India. High risk potential areas were noticed in eight major maize growing states viz., Andhra Pradesh, Bihar, Jharkhand, Karnataka, Madhya Pradesh, Maharashtra, Tamil Nadu and Telangana while risk potential was medium to low in states of Rajasthan, Gujarat and Uttar Pradesh.
• The probable areas for the establishment of FAW based on climatic suitability and presence of major host, i.e., Maize are projected in the Indian map (Fig 3), while the State maps are projected in

III. DISCUSSION
The current FAW climate conditions projected for the model closely matches previous distributions, where FAW is listed as the major maize pest. In the present study, the reliability, accuracy and robustness of Climex model are reflected in high proportions from the validation area falling within the modelled area. The currently generated potential areas for fall army worm also include the recently infested areas in India thus validating the current prediction model. The maps generated based on Compare species 1 option appears to be more precise for the FAW species establishment. Hence, this option is recommended for better analysis subjected to the availability of the data on growth and stress parameters of the species.

IV. CONCLUSION AND WAY FORWARD
The FAW is polyphagous pest with many economically important hosts majorly attacking maize in India.
Predicting the climatically suitable areas in India is essential to protect the future production of both staple and non-staple crops, since FAW attacks both. With this information, farmer, policy makers and government could implement adaption measures, such as the new technology, new varieties and management practices to overcome the impacts of FAW on important economic crops.
Pest management in agriculture may be more challenging under future climate and variability. The risk maps generated has application for mainly three types of personnel: pest survey specialists, program managers, and risk analysts for implementing surveys, for allocation of resources and to assess the potential establishment for high-risk pathways, commodities, or pests, respectively. Risk maps may also be useful in delimiting surveys or for managing pest eradications.
The results can be used to help guide pest risk assessments by the National Plant Protection Organization (NPPO), effective monitoring and surveillance of the unintentional introductions of this pest via trade from currently infested countries, and, policy makers and trade negotiators in making science-based decisions. In addition, India which is dealing with a relatively recent introduction and spread of fall army worm, the generated maps can be used to identify areas most at risk of the expansion of this pest. Efforts can be coordinated and concentrated strategically across susceptible areas to stem the incursion. An additional potential application of these maps is for Regional Central Integrated Pest Management Centres (CIPMCs) in the identification of areas most suitable for area-wide pest suppression or eradication. Areas with established populations of pests which are on the extreme margins of climate suitability can be targeted as the most likely locations for these suppression and eradication efforts.
The current modelling approach was carried out using only the climate data, which ignore potential genetic changes in species and adaption to new climatic conditions (Bradshaw & Holzapfel 2006). Future studies at global and regional levels are essential for better understanding of the FAW risk.