DINAMIKA POPULASI DAN PEMBIAKAN MASSAL Neochetina eichhorniae (COLEOPTERA: CURCULIONIDAE) SEBAGAI AGENS PENGENDALI HAYATI ECENG GONDOK (Pontederia crassipes) DI PT GUNUNG MADU PLANTATIONS (GMP) LAMPUNG

Abstract

Eceng gondok (Pontederia crassipes) merupakan tanaman invasif yang mengganggu perairan irigasi tebu GMP di Lampung Tengah. Pengendalian hayati dengan Neochetina eichhorniae (Coleoptera: Curculionidae) menjadi strategi berkelanjutan untuk mengatasinya. Pemahaman terhadap dinamika populasi N. eichhorniae di habitat tertentu sangat penting untuk menilai efektivitas strategi pengendalian hayati. Penelitian ini bertujuan menganalisis dinamika populasi N. eichhorniae dan mengembangkan teknologi pembiakan massal N. eichhorniae di areal perairan PT GMP. Metode pengambilan sampel populasi N. eichhorniae di lapangan dilakukan menggunakan purposive sampling dengan mengambil 30 rumpun eceng gondok per lokasi yang terdiri dari 4 Lokasi dengan 5 kali ulangan di perairan di Lampung Tengah. Parameter yang diukur adalah populasi N. eichhorniae per tanaman eceng gondok, perbedaan populasi N. eichhorniae tiap lokasi, perbedaan nisbah kelamin imago, distribusi N. eichhorniae pada bagian tanaman, serta beberapa faktor lingkungan. Data populasi yang diperoleh disajikan dalam bentuk grafik dan piramida populasi serta dianalisis menggunakan program R. Pengaruh faktor lingkungan terhadap populasi N. eichhorniae dianalisis menggunakan generalized linear mixed model (GLMM). Pembiakan massal N. eichhorniae dilakukan pada kolam berukuran 0,65 × 0,65 × 1 m³ dengan perlakuan variasi kerapatan imago (12, 24, dan 36 individu), rasio jenis kelamin (1:1, 1:2, dan 1:3), serta keberadaan peneduh kolam (dengan dan tanpa naungan). Penelitian menguji pengaruh kerapatan induk betina, rasio kelamin, dan naungan terhadap kelimpahan hasil pembiakan massal N. eichhorniae. Setelah memastikan asumsi kebebasan, distribusi, dan homogenitas terpenuhi, signifikansi variabel diuji dengan GLM Negative Binomial (ANOVA Tipe II). Perbedaan signifikan (p < 0,05) dilanjutkan dengan uji Tukey HSD. Hasil menunjukkan bahwa demografi populasi di lapangan didominasi stadia larva diikuti oleh stadia telur, imago, dan terendah adalah pupa. Kepadatan imago di lapang adalah < 2 individu per tanaman. Struktur populasi N. eichhorniae (berupa piramida umur) berbeda antar lokasi. Perbedaan ini mencerminkan dinamika kelangsungan hidup dari telur hingga imago. Faktor lokasi lebih berpengaruh signifikan terhadap kelimpahan populasi N. eichhorniae dibandingkan faktor abiotik yang dicatat selama pengamatan seperti suhu udara, kelembapan udara, pH air, suhu air, serta kadar oksigen terlarut (dissolved oxygen/DO) air. Distribusi tertinggi N. eichhorniae pada bagian tanaman secara berurutan yaitu pada bagian petiol (1.096 individu), bonggol (1.088 individu), akar (711 individu). Pada percobaan pembiakan massal, perlakuan tanpa naungan menghasilkan populasi N. eichhorniae yang jauh lebih tinggi dibandingkan perlakuan naungan. Pada kondisi tanpa naungan, perbedaan jumlah betina indukan tidak berpengaruh nyata terhadap hasil pembiakan massal, sedangkan pada kondisi naungan hanya beberapa perlakuan yang menunjukkan perbedaan nyata. Keberhasilan pembiakan massal N. eichhorniae lebih dipengaruhi oleh kondisi lingkungan, khususnya ketersediaan cahaya yang mendukung pertumbuhan eceng gondok, dibandingkan oleh jumlah betina indukan. Beberapa faktor teknis, seperti infestasi awal pada tanaman inang, migrasi imago antarperlakuan, dan ketidakseragaman umur indukan, diduga turut memengaruhi variasi populasi yang diamati selama penelitian.

Water hyacinth (Pontederia crassipes) is an invasive aquatic plant that disrupts the sugarcane irrigation waterways of PT Gunung Madu Plantations (GMP) in Central Lampung, Indonesia. Biological control using Neochetina eichhorniae (Coleoptera: Curculionidae) has been adopted as a sustainable management strategy. Understanding the population dynamics of N. eichhorniae within a specific habitat is essential for evaluating the effectiveness of this biological control approach. This study aimed to analyze the population dynamics of N. eichhorniae and develop a mass-rearing technique for the species in the aquatic environments of PT GMP. Field sampling of N. eichhorniae populations was conducted using a purposive sampling method by collecting 30 water hyacinth clumps per location from four locations, with five sampling periods in aquatic habitats in Central Lampung. The parameters measured included the population of N. eichhorniae per water hyacinth clump, population differences among locations, adult sex ratio, distribution of N. eichhorniae within plant parts, and several environmental variables. Population data were presented as graphs and population pyramids and analyzed using R software. The effects of environmental factors on N. eichhorniae populations were analyzed using a Generalized Linear Mixed Model (GLMM). Mass rearing of N. eichhorniae was conducted in ponds measuring 0.65 × 0.65 × 1 m³ using different adult densities (12, 24, and 36 individuals), sex ratios (1:1, 1:2, and 1:3), and shading treatments (with and without shade). The experiment evaluated the effects of female parent density, sex ratio, and shading on the abundance of N. eichhorniae produced through mass rearing. After confirming that assumptions of independence, distribution, and homogeneity were met, the significance of predictor variables was tested using a Negative Binomial Generalized Linear Model (GLM) with Type II ANOVA. Significant differences (p < 0.05) were further analyzed using Tukey’s HSD test. The results showed that field population demography was dominated by larval stages, followed by eggs and adults, while pupae were the least abundant stage. Adult density in the field was less than two individuals per plant. The population structure of N. eichhorniae (represented by age pyramids) differed among locations, reflecting variation in survival from the egg stage to adulthood. Location had a more significant effect on N. eichhorniae abundance than the abiotic factors recorded during the study, including air temperature, relative humidity, water pH, water temperature, and dissolved oxygen (DO). The highest distribution of N. eichhorniae within plant parts was found in the petiole (1,096 individuals), followed by the crown (1,088 individuals) and roots (711 individuals). In the mass-rearing experiment, the unshaded treatment produced substantially higher populations of N. eichhorniae than the shaded treatment. Under unshaded conditions, differences in the number of female parents did not significantly affect mass-rearing output, whereas under shaded conditions only a few treatments differed significantly. The success of mass rearing was influenced more strongly by environmental conditions, particularly light availability that promotes water hyacinth growth, than by the number of female parents used. Several technical factors, including initial infestation of host plants, adult migration among experimental units, and variation in the age structure of parent populations, were also suspected to contribute to the population variation observed during the study.