Judul: Spodoptera frugiperda (J. E. Smith) (Lepidoptera:  Noctuidae): Attacks and Their Natural Enemies on Corn in Munte Village, Munte Sub district, Karo District, North S
Abstrak: Spodoptera frugiperda (Lepidoptera: Noctuidae) is a relatively new pest in Indonesia and an essential pest of the corn. Corn cultivation is dominant in Munte village. This study aimed to estimate the damage caused by S. frugiperda, inventory natural enemies, estimate parasitization level of parasitoids and population of predator and observe entomopathogen fungi in Munte Village, Karo District, North Sumatera. Observations were conducted on an area of ± 2500 m2 . Damage level were observed on five plots, each consist of 20 plants with an interval of one plant. Larvae and eggs were collected and reared in the laboratory, as well as suspected predatory insects. The level of damage from each observation for 8 weeks after planting (WAP) reached > 30% or was classified as heavy. Natural enemies found were parasitoids, predators, and entomopathogenic fungi groups. The parasitoids belong to Hymenoptera and Diptera, the proportion of population were 29.71% Telenomus sp. (Hym.: Scelionidae), 3.40% Trichogramma sp. (Hym.: Trichogrammatidae), 1.65% Microplitis sp. (Hym.: Braconidae), 0.41% Charops sp. (Hym.: Ichneumonidae), 1.23% Anomaloninae (Hym.: Ichneumonidae), 0.41% Megaselia sp. (Dipt.: Phoridae), and 0.41% of Tachinidae (Diptera). The other natural enemies found were predators Doru sp. (Der.: Forficulidae) and Oxyopes sp. (Ara.: Oxyopidae), entomopathogenic fungi was Metarhizium sp. Telenomus sp. wasthe most found in the field and had potentially reduced the eggs of S. frugiperda.
Keyword: damage level, parasitoid, parasitization level, predator

Judul: Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) Attacks and Its Parasitoids on Corn Cultivation in Situ Gede Village, West Bogor District, Bogor, West Java
Abstrak: Jagung merupakan tanaman pangan dan bahan baku industri yang penting di Indonesia. Produksi jagung sangat terpengaruh dengan adanya serangan hama invasif baru di Indonesia yaitu ulat grayak jagung (UGJ) atau fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Pemanfaatan musuh alami merupakan salah satu metode pengendalian yang dapat digunakan. Penelitian ini bertujuan mengetahui tingkat serangan dan parasitoid S. frugiperda yang ditemukan pada pertanaman jagung di Kelurahan Situ Gede, Kecamatan Bogor Barat, Bogor, Jawa Barat. Pengamatan dilakukan sejak tanaman berumur dua minggu setelah tanam (MST) hingga 10 MST dengan interval dua minggu pada 100 tanaman sampel. Larva S. frugiperda dikumpulkan dari plot sampel lalu dipelihara dan diamati, kemudian parasitoid yang muncul dihitung tingkat parasitisasi dan diidentifikasi. Tingkat serangan UGJ meningkat sejak tanaman jagung berumur dua MST hingga delapan MST dan serangannya konstan hingga 10 MST. Intensitas serangan S. frugiperda tertinggi sebesar 64,40% yang termasuk kategori sangat berat. Parasitoid yang ditemukan yaitu Cotesia sp., Microplitis sp. (Hymenoptera: Braconidae), Charops sp. (Hymenoptera: Ichneumonidae), dan Phoridae (Diptera). Tingkat parasitisasi tertinggi oleh Microplitis sp. sebesar 6,72%., Corn is an important food crop and industrial raw material in Indonesia. Corn productivity is greatly affected by the attack of a new invasive pest in Indonesia, fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Using natural enemies is one of the methods to control this pest. This study aimed to determine the plant damages caused by FAW and its natural enemies on corn cultivation at Situ Gede Village, West Bogor District, Bogor, West Java. Observations have been done from two weeks after planting (WAP) to ten WAP with two-week intervals. The plant damage of S. frugiperda was observed on 100 plant samples. The larvae of S. frugiperda were collected from other plant samples and reared in the laboratory until the parasitoids emerged. The parasitoids were then identified. The plant damages increased until the corn cultivation was eight WAP, and the plant damages were constant until harvest. The most severe plant damage of S. frugiperda reached 64.40% and was included in the very heavy category. The parasitoids found during the study were Cotesia sp., Microplitis sp. (Hymenoptera: Braconidae), Charops sp. (Hymenoptera: Ichneumonidae), and Phoridae (Diptera). The highest level of parasitization was Microplitis sp., with 6.72%.
Keyword: fall armyworm, natural enemies, plant damages

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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