COMPLEXITIES IN THE NUMBER OF LARVAL INSTARS OF THE BIRCH CASEBEARER IN NEWFOUNDLAND (LEPIDOPTERA: COLEOPHORIDAE)

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Abstract
The birch casebearer, Coleophora fuscedinella Zeller, has five larval instars in northeastern North America, but commonly only four in insular Newfoundland. The occurrence of four larval instars in Newfoundland represents the omission of either the third or the fourth instar. Local Newfoundland populations may have five larval instars, but the late-developing larvae of these populations have only four larval instars. Head capsule width can be used to identify instars but case characteristics are recommended because the bimodality of third instar head widths can cause confusion.