Abstract:

The number of larval instars and stage duration of each instar of the Emerald Ash Borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae) were determined by sampling periodically in forests. Six variables including the body length, body width, width of the prothoracic plate, width of the peristoma, length of the urogomphus, and anteriormost width of the urogomphus were examined under binocular microscope with an eyepiece micrometer for choosing the optimal morphological characters or index for the separation of larval instars. Results showed that the larvae of EAB have 4 instars. The urogomphus and its length were the best characteristic and variable for the separation of larval instars, and the width of peristoma was the second best according to the overlapping degree of variable. Body length, body width, width of the prothoracic plate, and anteriormost width of the urogomphus were not reliable due to high variation. Morphological characters on the inner side of larval urogomphus are also helped to separate the instars tersely and conveniently. The average stadia based on the median value of samples was as follows: 18.1d for the 1^st instar, 11.2d for the 2^nd instar, 10.7d for the 3^rd instar, and 261.2d for the 4^th instar. The total larval stage duration was 301.3d naturally.

Key words: Agrilus planipennis, larval instars, variables for instar separation, stadia