Frass Size as an Indicator of Spruce Budworm Larval Instars

Frass width, but not its length or volume, shows correlation with the various larval instars. The mean width, and the standard deviation, for each instar are tabulated. Frass, collected in cone-shaped cloth traps in the field, can be used as an index of the percent of larvae in each instar present when the collection is made.