Field determination of larval instar for the lantana leaf‐mining beetles Octotoma scabripennis Guérin‐Méneville and Uroplata girardi Pic (Coleoptera: Chrysomelidae: Hispinae)

A method of identifying larval instars based on the width of the central chamber of their mines in lantana leaves was developed for two hispine beetles, Octotoma scabripennis Guérin‐Méneville and Uroplata girardi Pic. Head‐capsule widths and the width of the widest part of the larval mine were measured to the nearest 0.001 mm and 1 mm, respectively. Analyses confirmed that head‐capsule measurements followed the Brooks‐Dyar rule. Both species have three larval instars with mean head‐capsule widths of 0.4, 0.57 and 0.80 mm for O. scabripennis, and mean widths of 0.35, 0.50 and 0.80 mm for U. girardi. The width of the larval mine similarly increases with instar. I found that first‐instar larvae of both species occupy mines 1 mm wide; third‐instar larvae were found in mines greater than 8 mm wide for O. scabripennis and 5 mm for U. girardi. For mine widths between these sizes, a fixed percentage of larvae were instar 2 or 3. This method of measuring instar is proposed as an alternative to destructive sampling.