Key to puparia of tachinid parasitoids of Nearctic Choristoneura species

1. Posterior spiracular discs borne on a cylindrical projection that is about as long as wide (Fig. 36) ...................................................................................... Actia interrupta

– Posterior end of puparium without such a projection (Figs. 22–35) ............................ 2

2. Slits of posterior spiracular discs broadened considerably (Fig. 35) ...... Actia diffidens

– Slits narrow (Figs. 22–34) ............................................................................................ 3

3. Each posterior spiracular disc with three slits (Figs. 27–34) ....................................... 4

– Each posterior spiracular disc with four slits (Figs. 22–26) ....................................... 12

4. Prominent bulge present below posterior spiracular discs, much broader and higher than a single disc (Figs. 31, 33) .................................................................................... 5

– Bulge below posterior spiracular discs absent or small, not higher or broader than a single disc (Figs. 28–30, 32) ........................................................................................ 7

5. Posterior spiracular discs scarcely raised above surface of puparium, with shallow grooves between spiracular slits; bulge below spiracular discs rarely extended dorsally to region between discs (Fig. 33) ................................................... Smidtia fumiferanae

– Posterior spiracular discs protruding above surface of puparium, with deep grooves between spiracular slits; bulge below spiracular discs varied along dorsal edge (Figs. 28, 31) ......................................................................................................................... 6