Determination of Larval Instars of the Bronze Birch Borer, Agrilus anxius (Coleoptera: Buprestidae)1

The bronze birch borer, Agrilus anxius Gory (Coleoptera: Buprestidae), has four larval instars in young European white birch, Betula pendula Roth, planted in Pennsylvania for surface mine reforestation. Of seven morphological variables measured, the width of the peristoma, an exposed sclerotized portion of the head capsule, provides the clearest separation of instars. Although any of three variables measured in the caudal region of the larva is satisfactory, the anteriormost width of the urogomphi is the most reliable caudal variable.