Description of damage and loss of corn production caused by Spodoptera frugiperda (Lepidoptera Noctuidae) in West Sumatera, Indonesia

Corn is the second-largest agricultural product after rice in Indonesia. The main problem faced in corn production is pests. This study aims to identify and learn the percentage of damage and lost production by the new invasive pest attack on maize in West Sumatera, Indonesia. The location took place in Padang Pariaman and Solok Districts. A survey was used in this research. The results exposed a severe attack of a new invasive pest, S. frugiperda. This pest was found in Padang Pariaman and Solok Districts. The percentage of damage by S. frugiperda in Padang Pariaman (0.71 larvae population per stem) was higher than in Solok District (0.52 larvae population per stem). Then, the population fluctuation of S. frugiperda in Padang Pariaman District was higher than in Solok district. The correlation between the population of S. frugiperda and the production of maize was carried out by regression analysis. The regression model is logarithmic, with a formula y= 380.87 ln(x) + 28 and a value R2= 1 for Batang Anai Subdistrict, and y = 213.52 ln(x) + 35 and a value R2= 1 for Kampung Dalam Subdistrict, Padang Pariaman. Then a formula y= 474.65ln(x) + 11 with a value R2= 1 for Tanah Garam Subdistrict, Solok, and y= 367.89ln(x) + 12 with a value R2= 1 for Tikalak Subdistrict, Solok. S. frugiperda is a new invasive pest, and the vegetative phase is susceptible to S. frugiperda on maize. This pest can cause lost production. If this pest is controlled too late, it can reduce the production of maize. Therefore, farmers must know the right time to control this pest.


Introduction
Maize (Zea mays) is Indonesia's subsequent staple food after rice.Data from the Central Statistics Agency (BPS) shows that Padang Pariaman and Solok are maize production centers in West Sumatra.Maize production in Padang Pariaman district was 60,524 tons from the planted area of 9,400 hectares, and Solok district was 3,919 tons from 397 Hectares [1].
One of the main problems in maize production is pests.The fall armyworm, Spodoptera frugiperda (J.E.Smith) (Lepidoptera: Noctuidae), originates from tropical and subtropical regions of the Americas.The appearance of this species was first reported in Nigeria (part of the West African region) and also the island of São Tomé and Principe in 2016 [2], and subsequently in almost all sub-Saharan African countries [3,4,5,6,7,8].The distribution of the pest in conjunction with a recently published climate suitability model has shown that the environmental requirements for this pest to settle permanently are present in most of Africa, Asia, and parts of Europe.[9,10].
In the development of this pest, its spread has reached the southern outskirts of the Sahara, and several states in India [11,12] and also distributed to Yemen, Myanmar, Thailand, and Sri Lanka [2,10,13,14].Indeed, it is likely that this armyworm will spread further into northern Europe and other countries in Asia.
In early 2019, this pest was found on corn plants in the Sumatra region [15].In early July 2019, Sari et al. that maize in several districts in West Sumatra was attacked by S. frugiperda [16] and several Districts in West Sumatra [17].This species has also been found in Bandung (West Java) [18], Bengkulu [19], Lampung [14], and West Pasaman (West Sumatra) [17].However, scientific reports on S. frugiperda in West Sumatra are still limited.Therefore, research about new invasive pests on maize in West Sumatra is urgently needed.Furthermore, information about the intensity of attacks on S. frugiperda is urgently required to prevent the blast of S. frugiperda.

Experimental Areas and Materials
This research was conducted in two districts of maize production centers in West Sumatra from April 2019 to August 2019.The two sub-districts of maize production centers in Padang Pariaman are Batang Anai and Kampung Dalam, while another two sub-districts in Solok are Lubuk Sikarah and Junjung Sirih.The identification process was carried out in the Bioecology Laboratory, Faculty of Agriculture, Universitas Andalas, Indonesia.The material used in this research was alcohol 96%.Meanwhile, the equipment used includes a microscope, tube microcentrifuge, plastic clip, pipette dropper, petri dish, container box, insect tweezers, cap, field shoes, label paper, digital camera Sony HX-300®, tissue, face shield, mask, and other tools.

Research Methods
This study used a survey located in the corn/maize field.Sampling was carried out four times in each location and done at 20, 40, 60, and 80 days after planting (DAP).The sample collection of S. frugiperda was carried out by direct observation of all plant samples.It is taking the larvae using tweezers.The sample obtained was put into a 1.5 ml microcentrifuge tube that already contained alcohol 96% of, then the microcentrifuge tube was labeled.The samples were taken to the Insect Bioecology laboratory, Faculty of Agriculture, Andalas University, to be identified.Identification of S. frugiperda that attacks maize in Padang Pariaman and Solok district, West Sumatra, was carried out by observing the morphology characteristic of the larvae and imago under the light microscope.The identification process expressed the morphological form of S. frugiperda [10,11,12,13,17,20,21,22,23,24,25,26,27,28,29,30,31,32,33].

Data analysis
The attack intensity of S. frugiperda was analyzed using Microsoft Excel, Minitab 16®, followed by a specific maize/corn disease description.Data processing aimed to determine and obtain an overview of S. frugiperda attack intensity to corn plantations in Padang Pariaman and Solok District, West Sumatra, Indonesia.

Results and Discussion
The results showed a severe attack from Spodoptera frugiperda on maize in Padang Pariaman and Solok District.S. frugiperda (Lepidoptera: Noctuidae) or Fall armyworm (FAW) is a new invasive pest in West Sumatra, Indonesia.The percentage of damage from S. frugiperda in Padang Pariaman District is higher than in Solok District.It reached 0.71 larvae per stem in Padang Pariaman District and 0.52 per stem in Solok District (Figure 1). Figure 1 shows that the damage ratio caused by S. frugiperda in the vegetative phase was higher than in the generative phase at all locations.The maize was severely damaged at the age of 20 and 40 DAP.The age of maize at that time indicated the vegetative stage of maize.It means that the vegetative phase has been the growth phase most susceptible to maize in the field.It was assumed that the early-age maize has a soft leaf structure, so S. frugiperda larvae highly favor it.
On the other hand, the percentage of damage from S. frugiperda decreased with the increasing age of maize (60 DAP dan 80 DAP), which has 0.00 to 0.14 larvae population per stem in Padang Pariaman District.On the other hand, there were 0.00 to 0.05 population larvae per stem in Solok District.It means that maize has a morphological structure of leaves and stems that are harder and stronger at 60 and 80 days after planting (generative phase).
The identification of S. frugiperda in Padang Pariaman and Solok districts was based on the morphological characteristics of the larvae and the symptoms of damage to maize plants in the field.S. frugiperda larvae attacked shoots and steam of maize, which are visible like the letter Y on the head of larvae, and there were larvae dropping feces such as sawdust (Figure 2).In Figure 2, it can be seen that the specific symptom of S. frugiperda that caused by the larvae.This new invasive pest, S. frugiperda, feeds on the growing point of maize production so that maize buds look cut and leave their feces like sawdust.Additional damage due to S. frugiperda in the generative phase can be seen at the end of maize cobs, even sometimes, the larvae can also be found there.If control efforts are delayed, there is a risk of maize failure.The losses incurred due to S. frugiperda in African and European countries are between 8.3 and 20.6 million tons per year.The results of this study are the same as those stated by [13], that S. frugiperda attacked plant growth points which can fails shoot formation.
In general, the population fluctuation of S. frugiperda in Padang Pariaman District was higher than in Solok District.For example, the population fluctuation of S. frugiperda was from 0.00 to 1.31 larvae per stem in Padang Pariaman and from 0.00 to 0.52 larvae per stem in Solok District (Figure 3).However, the population fluctuation of S. frugiperda decreased at 60 and 80 DAP.It was thought to be due to the control technique performed by farmers.Farmers in all locations used chemical pesticides when the pest population was high.Therefore, it means that the population of S. frugiperda will be smaller if farmers' timing and control techniques have been proper.
The correlation between the population of S. frugiperda and the production of maize was carried out using regression analysis (Figure 4).  Figure 4 describes several regression models between population larvae the maize production.Of the four regression models, the most depicting form of the models is logarithmic, with a formula y = 380.87ln(x) + 28 with a value R 2 = 1 for Batang Anai Subdistrict, and y = 213.52ln(x) + 35 with a value R 2 = 1 for Kampung Dalam Subdistrict, Padang Pariaman District.The regression analysis between the population of S. frugiperda and the production of maize in Solok District can be seen in Figure 5. Figure 5 shows the most depicting form of the regression model is logarithmic, with a formula y = 474.65ln(x)+ 11 with a value R 2 = 1 for Tanah Garam subdistrict, and y = 367.89ln(x)+ 12 with a value R 2 = 1 for Tikalak subdistrict, Solok District.
Padang Pariaman district is lowland (400 meters above sea level).The altitude ranges from 9 -30 meters above sea level.The landscape site is close to the sea level of Padang Pariaman District, allowing the spread of FAW, which is very likely to occur from one region to another.A report released news about S. frugiperda attacking maize since the beginning of 2019 [15].It is an alleged thing due to the change in extreme climate.Climate change can be helped the disappearance of S. frugiperda.The regions that were initially not changed to be converted into regional the spread of these new pest attacks.
S. frugiperda has been recorded as a polyphagous insect of pests attacking more than 80 crops [25].Some of the leading food crops host a group of Gramineae, like rice, wheat, sorghum, corn, and sugar cane.In Africa and Europe, S. frugiperda can cause 8.3 -20.6 million tons yield loss per year, with an economic loss between US 2.5 -6.2 billion per year [26].Then in Brazil and the United, S. frugiperda can cause a 34 to 38% yield loss [34].
Furthermore, the Food and Agriculture Organization (FAO) and CABI [25] imago of S. frugiperda is a strong flier with a high cruising range.Furthermore, the variety of maize in Padang Pariaman (NK 212) was liked by S. frugiperda compared with JH 27 in Solok District.A report showed that maize damage rates significantly differed in West Pasaman, Indonesia [17].The attack rate ranged from 6.0 to 96.0%, which the lowest attack percentage being on variety Bisi 18, and the highest on variety NK 212.
On the other hand, the types of plants around the maize also affect the percentage of S. frugiperda in Padang Pariaman and Solok District.On the other hand, the types of plants around maize also affected the rate of S. frugiperda in Padang Pariaman and Solok District.It is assumed to be an alternative host of S. frugiperda [25,26] that imago S. frugiperda was an aviator robust and had a high range.Tribun-Medan (May 1, 2019) reported thousands of land registered in east Lampung [14].
Moreover, Maharani et al. [18] said that S. frugiperda had been attacked on maize in Bandung, Garut, and Sumedang District, West Java.Nelly et al. [17] showed all varieties of maize in West Pasaman shot by S. frugiperda, which had the lowest attack rate on Bisi 18 variety and the highest was on NK 212 variety.The attack rate is between 6.0 and 96.0%, with an average of 0.70 larvae per stem.

Conclusions
A severe attack of a new invasive pest, S. frugiperda, on maize recently happened in Padang Pariaman and Solok District, West Sumatra, Indonesia.The percentage of damage from S. frugiperda in Padang Pariaman is higher than in Solok District.It reached 0.71 larvae per stem in Padang Pariaman District and 0.52 per stem in Solok District.The population fluctuation of S. frugiperda in Padang Pariaman was higher than in Solok District, with from 0.00 to 1.31 larvae per stem in Padang Pariaman and 0.00 to 0.52 larvae per stem in Solok District.The regression model between population and production of maize is logarithmic, with the formula y = 380.87ln(x) + 28 and a value R 2 = 1 for Batang Anai Subdistrict, and y = 213.52ln(x) + 35 and a value R 2 = 1 for Kampung Dalam Subdistrict, Padang Pariaman District, y = 474.65ln(x)+ 11 with a value R 2 = 1 for Tanah Garam Subdistrict, Solok District, and y = 367.89ln(x)+ 12 with a value R 2 = 1 for Tikalak Subdistrict, Solok District.

Figure 1 .
Figure 1.The percentage of damage by S. frugiperda in different maize ages in Padang Pariaman and Solok District, Indonesia.

Figure 2 .
Figure 2. S. frugiperda larva attacked steam of maize (a), and feces of S. frugiperda like sawdust (b)

Figure 3 .
Figure 3.The Population Fluctuation of S. frugiperda in Padang Pariaman and Solok District, West Sumatra, Indonesia.

Figure 3
Figure 3 describes the highest population of S. frugiperda at the age of 40 Day After Planting (DAP) at all locations, with 1.31 larvae per stem in Padang Pariaman and 0.52 larvae per stem in Solok district.However, the population fluctuation of S. frugiperda decreased at 60 and 80 DAP.It was thought to be due to the control technique performed by farmers.Farmers in all locations used chemical pesticides when the pest population was high.Therefore, it means that the population of S. frugiperda will be smaller if farmers' timing and control techniques have been proper.The correlation between the population of S. frugiperda and the production of maize was carried out using regression analysis (Figure4).

Figure 4 .
Figure 4. Regression Model for the Relationship between Production and Population of S. frugiperda in Padang Pariaman District, Indonesia.

Figure 5 .
Figure 5. Regression Model for the Relationship between Production of maize and Population of S. frugiperda in Solok Districts, West Sumatra, Indonesia.