Abstract:

The citrus borer, Agrilus auriventris Saunders, burst to attack citrus trees in recent years in some areas of Zhejiang Province, China. The larval instar numbers should be determined before further studying on its life history, biology and IMP. In this study, larval samples of different instars were collected from both the field and the laboratory, and four variables were measured, including the width of peristoma, the width of urogomphi, the length of urogomphi and the left lateral length of urogomphi. Based on frequency histograms and Dyar's law, the larvae of citrus borer were divided into 5 instars. Of the four variables measured, the width of peristoma provided the best division of instars. The average width of peristoma of the 1st instar larvae was 0.1196±0.0013 mm, the 2nd instar 0.2008±0.0030 mm, the 3rd instar 0.3304±0.0041 mm, the 4th instar 0.5150±0.0049 mm and the 5th instar 0.7844±0.0040 mm. The best linear regression equation of the width of peristoma against the instar numbers was: y=-0.0766+exp (-1.9883+(0.3675)×x)(R²＝0.9876）.

Key words: Agrilus auriventris, larval instar, peristoma, urogomphi, Dyar's law, regression equation