PENDUGAAN INSTAR LARVA ULAT KANTONG (Pteroma plagiophleps Hampson) PADA SENGON BERDASARKAN LEBAR KAPSUL KEPALA DAN UKURAN KANTONG (Instar Larvae Estimation of Bagworm Pteroma plagiophleps Hampson in Albizia Based on Head Capsule Width and Bag Size)

ABSTRACT  Pteroma plagiophleps bagworm is an important insect pest of albizia. It is necessary to understand the development stages of the larvae as the basis for its control. The research aims to determine the number of instars and the rate of increase in larval size based on the width of the head capsule. Furthermore, larval bag size as an easily observable variable was used to estimate the instar stage. Instar number and the size range were determined by non linear regression, while the instar stage was estimated by the regression equation using bag diameter and length. We concluded that the larvae experienced four instars. The head capsule of larvae grew regularly following Dyar’s pattern, with the value approximately 1.42. The bag size of instar 1, instar 2, instar 3, and instar 4 were estimated as a range from 0-2.19 mm; 2.19-3.55 mm; 3.55-6.10 mm; and more than 6.10 mm in length respectively. The bag length was reasonable to be used as a reliable predictor of the instar stage. ABSTRAK Ulat kantong Pteroma plagiophleps merupakan serangga hama penting pada tanaman sengon. Perkembangan larvanya perlu diketahui sebagai dasar pengendaliannya. Penelitian ini bertujuan untuk menentukan jumlah instar dan laju pertambahan ukuran larva berdasarkan lebar kapsul kepalanya. Selain itu, juga untuk menduga instarnya dengan menggunakan ukuran kantong larva. Jumlah instar dan kisaran ukurannya ditentukan menggunakan persamaan regresi non linear, sedangkan tingkat instar diturunkan dari persamaan regresi linear menggunakan peubah ukuran diameter dan panjang kantong. Hasil penelitian menunjukkan bahwa larva ulat kantong diduga mengalami empat instar. Pertumbuhan larva mengikuti pola yang relatif konstan dengan nilai “koefisien Dyar” rata-rata 1,42. Dugaan ukuran panjang kantong larva instar 1, instar 2, instar 3, dan instar 4 masing-masing memiliki kisaran antara 0-2,19 mm 2,19-3,55 mm, 3,55-6,10 mm, dan lebih dari 6,10 mm. Peubah panjang kantong larva cukup baik untuk digunakan sebagai penduga instar larva.