DINAMIKA POPULASI Scirpophaga incertulas (Walker) (LEPIDOPTERA: CRAMBIDAE) DI KECAMATAN MARDINGDING, KABUPATEN KARO, SUMATRA UTARA

Abstract

Scirpophaga incertulas (Walker) merupakan hama utama pada pertanaman padi yang menyebabkan gejala sundep pada fase vegetatif dan beluk pada fase generatif. Di Kecamatan Mardingding, Kabupaten Karo, hama ini menjadi permasalahan penting karena pertanaman padi berlangsung hampir sepanjang tahun, sehingga ketersediaan inang bagi S. incertulas relatif terus-menerus dan memungkinkan populasi hama bertahan dari satu musim tanam ke musim berikutnya. Penelitian ini bertujuan untuk menganalisis dinamika populasi dan tingkat serangan S. incertulas pada pola tanam monokultur dan polikultur, mengevaluasi keanekaragaman serta komposisi artropoda pada agroekosistem padi dan mengkaji biologi S. incertulas pada tiga varietas padi, yaitu Ciherang, Hibrida dan Condong. Dengan demikian, penelitian ini tidak hanya menilai keberadaan hama dari aspek populasi dan kerusakan tanaman, tetapi juga menghubungkannya dengan struktur komunitas artropoda, keseimbangan musuh alami dan kesesuaian varietas padi sebagai inang. Penelitian ini dilaksanakan dengan tiga tahapan yang saling terintegrasi. Tahap I, dilakukan melalui pengamatan dinamika populasi dan tingkat serangan S. incertulas pada lahan padi monokultur dan polikultur di Kecamatan Mardingding, dengan pengamatan populasi imago menggunakan perangkap cahaya serta pengukuran luas serangan dan intensitas serangan setiap minggu sejak 1 sampai 12 minggu setelah tanam (MST). Tahap II, pengamatan keanekaragaman dan komposisi artropoda pada pertanaman padi, dengan pengambilan sampel menggunakan alat hisap yang dimodifikasi, kemudian spesimen diidentifikasi berdasarkan ordo, famili dan morfospesies, serta dikelompokkan menurut peran ekologisnya sebagai herbivora, predator, parasitoid dan kelompok artropoda lainnya. Tahap III, pengujian biologi S. incertulas pada tiga varietas padi, yaitu Ciherang, Hibrida dan Condong, dengan mengamati lebar kapsul kepala larva, masa inkubasi telur, durasi pergantian instar larva, periode pupa, lama hidup imago, total siklus hidup dan parameter reproduksi. Data yang diperoleh dianalisis secara deskriptif dan statistik untuk melihat pengaruh pola tanam, musim tanam dan varietas padi terhadap populasi, serangan, komunitas artropoda dan perkembangan S. incertulas. Hasil penelitian menunjukkan bahwa pola tanam monokultur cenderung mendukung populasi dan tingkat serangan S. incertulas yang lebih tinggi dibandingkan polikultur. Populasi imago pada monokultur mencapai puncak pada 2 MST sebesar 75 individu dengan estimasi model 74,5, sedangkan pada polikultur puncaknya lebih rendah, yaitu 22 individu pada 3 MST dan 21 individu pada 8 MST. Rata-rata populasi imago, luas serangan dan intensitas serangan juga lebih tinggi pada pola tanam monokultur dibandingkan polikultur pada kedua musim tanam dan pola tanam berpengaruh nyata terhadap ketiga parameter tersebut. Serangan mulai meningkat pada 2–3 MST dan mencapai puncak utama sekitar 4 MST, sehingga fase awal pertumbuhan padi menjadi periode penting untuk pemantauan dan penentuan teknik pengendalian hama. Berdasarkan hasil komunitas artropoda, pada musim tanam pertama menunjukkan jumlah spesies pada pola tanam monokultur berkisar 34–52 spesies dengan H’ 1,71–1,85 sedangkan pada polikultur berkisar 56–78 spesies dengan H’ 1,96–2,21. Pada musim tanam kedua, rata-rata jumlah spesies menurun menjadi 24–29 spesies pada monokultur dan 42–72 spesies pada polikultur. Nilai Shannon–Wiener pada polikultur mencapai H’ 1,63–2,27 dan monokultur H’ 1,67–1,88. Pola tanam berpengaruh terhadap keanekaragaman artropoda, sedangkan kemerataan Pielou berbeda nyata antarmusim tanam dan dominansi Simpson tidak berbeda nyata antarpola tanam maupun musim tanam. Secara fungsional, polikultur mendukung rasio musuh alami terhadap hama lebih tinggi, yaitu 1,90 dan 1,82, dibandingkan monokultur sebesar 1,17 dan 1,28. Perkembangan larva S. incertulas paling singkat terdapat pada varietas Hibrida, dengan total periode larva 28,60 hari. Sedangkan pada varietas Ciherang dan Condong periode perkembangan larva lebih panjang. Secara keseluruhan hasil penelitian ini menunjukkan bahwa pengelolaan S. incertulas perlu diarahkan melalui pemantauan dimulai dari persemaian, penerapan polikultur, konservasi musuh alami, rotasi tanaman untuk memutus ketersediaan inang dan pemilihan varietas padi yang tidak mendukung perkembangan larva, sehingga pengendalian hama dapat dilakukan secara lebih ekologis dan berkelanjutan.

Scirpophaga incertulas (Walker) is a major insect pest of rice, causing deadheart symptoms during the vegetative stage and whitehead symptoms during the generative stage. In Mardingding District, Karo Regency, this pest represents an important constraint to rice production because rice is cultivated almost throughout the year. Consequently, host plants are continuously available, allowing S. incertulas populations to persist from one growing season to the next. This study aimed to analyze the population dynamics and infestation levels of S. incertulas under monoculture and polyculture cropping systems, evaluate the diversity and composition of arthropod communities in rice agroecosystems, and investigate the biology of S. incertulas on three rice varieties, namely Ciherang, Hybrid and Condong. This study not only assessed the pest in terms of its population and crop damage, but also integrated these aspects with arthropod community structure, the balance between natural enemies and pests and the suitability of rice varieties as host plants. The study was conducted in three integrated stages. Stage I involved observations of the population dynamics and infestation levels of S. incertulas in monoculture and polyculture rice fields in Mardingding District. Adult populations were monitored using light traps, while the extent and intensity of infestation were recorded weekly from 1 to 12 weeks after planting (WAP). Stage II focused on the diversity and composition of arthropod communities in rice fields. Arthropods were sampled using a modified suction device, after which the specimens were identified to order, family and morphospecies levels and classified according to their ecological functions as herbivores, predators, parasitoids and other arthropod groups. Stage III examined the biology of S. incertulas on three rice varieties Ciherang, Hybrid and Condong by observing larval head capsule width, egg incubation period, duration of each larval instar, pupal period, adult longevity, total life cycle, and reproductive parameters. The data were analyzed descriptively and statistically to determine the effects of cropping system, growing season, and rice variety on S. incertulas population dynamics, infestation, arthropod communities, and development. The results showed that monoculture cropping tended to support higher S. incertulas populations and infestation levels than polyculture. In monoculture fields, the adult population reached its peak at 2 WAP, with 75 individuals observed and a model estimate of 74.5 individuals. In polyculture fields, lower population peaks were recorded, with 22 individuals at 3 WAP and 21 individuals at 8 WAP. The mean adult population, infestation extent, and infestation intensity were also higher under monoculture than under polyculture during both growing seasons, and the cropping system had a significant effect on all three parameters. Infestation began to increase at 2–3 WAP and reached its main peak at approximately 4 WAP, indicating that the early growth stage of rice is a critical period for pest monitoring and for determining appropriate control measures. Arthropod community analysis showed that polyculture supported greater species richness and diversity than monoculture. During the first growing season, monoculture fields contained 34–52 species with Shannon–Wiener diversity index (H’) values of 1.71–1.85, whereas polyculture fields contained 56–78 species with H’ values of 1.96–2.21. During the second growing season, species richness declined to 24–29 species in monoculture and 42–72 species in polyculture, nevertheless, polyculture consistently maintained greater species richness. The Shannon–Wiener diversity index in polyculture ranged from H’ 1.63–2.27, whereas in monoculture it ranged from H’ 1.67–1.88. The cropping system had a significant effect on arthropod diversity, whereas Pielou’s evenness differed significantly between growing seasons. Simpson’s dominance index did not differ significantly between cropping systems or growing seasons. From a functional perspective, polyculture supported higher natural enemy-to-pest ratios, with values of 1.90 and 1.82, compared with 1.17 and 1.28 under monoculture. The shortest larval development period of S. incertulas was observed on the hybrid rice variety, with a total larval period of 28.60 days. In contrast, larval development was longer on the Ciherang and Condong varieties. Overall, the results of this study indicate that the management of S. incertulas should be directed toward early monitoring beginning at the nursery stage, the implementation of polyculture systems, the conservation of natural enemies, crop rotation to disrupt host availability, and the selection of rice varieties that are less suitable for larval development. These approaches are expected to support more ecologically based and sustainable pest management.