Host records ex. Choristoneura conflictana: Prentice 1955 (SK, MB); O’Hara 1991 (†MB, SK); † Arnaud 1978 (SK, MB); † Huber et al. 1996 (America north of Mexico).
Host records ex. Choristoneura fumiferana: Daviault 1946, ex. Archips fumiferana (QC); Reeks et al. 1948 (Maritime provinces and NF); Daviault 1950 (QC); Dowden et al. 1951, ex. Archips fumiferana (NY); Miller 1955, as Gymnophthalma interrupta (NB); McGugan & Blais 1959 (ON); Blais 1960 (QC); MacDonald & Webb 1963 (NB); † Miller 1963 (NB); Blais 1965 (QC); † Tilles & Woodley 1984 (ME); Huber et al. 1996 (NB); Cappuccino et al. 1998 (QC); Cappuccino et al. 1999 (QC); Schoenmaker et al. 2001 (QC); † Smith et al. 2002 (eastern Canada); Cusson et al. 2002 (QC).
Host records ex. Choristoneura fumiferana and/or Choristoneura occidentalis: Brown 1941 ex. Cacoecia fumiferana (Canada); Dowden et al. 1948, ex. Archips fumiferana (North America); † Zwolfer 1961, ex. C. fumiferana (North America); † Arnaud 1978, ex. C. fumiferana (BC, OR, ON, QC, NB, NF, NY); O’Hara 1991, ex. C. fumiferana (BC, ID, †OR, CO, AB, MB, ON, QC, NB, NF, NY, VT).
Host records ex. Choristoneura fumiferana, Choristoneura occidentalis and/or Choristoneura pinus: † Ross 1952, ex. spruce and/or jack pine budworm (Canada).
Host records ex. Choristoneura lambertiana: O’Hara 1991 (MT); † Huber et al. 1996 (America north of Mexico).
Host records ex. Choristoneura occidentalis: McKnight 1974 (CO); Harris & Dawson 1979 (BC); O’Hara 1991 (BC, ID, MT); † Huber et al. 1996 (America north of Mexico).
Host records probably ex. Choristoneura occidentalis: Bedard 1938, as Actia pilipennis ex. Cacoecia fumiferana on Douglas fir (“northern Rocky Mountain region”); Wilkes et al. 1949, as Gymnophthalma interrupta ex. C. fumiferana (BC); Carolin & Coulter 1959, ex. C. fumiferana (OR); † Coppel 1960, as Gymnophthalma interrupta ex. C. fumiferana (BC).
Host records ex. Choristoneura occidentalis and/or Choristoneura retiniana: Schaupp et al. 1991 (OR).
Host records ex. Choristoneura pinus: Benjamin & Drooz 1954 (MI); Dixon & Benjamin 1963 (WI); Allen et al. 1969 (MI); † Arnaud 1978 (WI, MI); O’Hara 1991 (MB, ON, †WI, MI); † Huber et al. 1996 (America north of Mexico).
Host records ex. Choristoneura rosaceana: Schuh & Mote 1948, ex. Archips rosaceana (OR); Neunzig & Gyrisco 1955 (NY); † Arnaud 1978 (OR, NY); Hagley & Barber 1991 (ON); O’Hara 1991 (†OR, ON, NS, NY); † Huber et al. 1996 (America north of Mexico); Wilkinson et al. 2004 (MI).
Actia interrupta is a very small tachinid, generally 4–5mm long, that is easily recognized among the species treated here by the dorsally haired wing veins R 1, R 4 + 5 and CuA 1 (Fig. 13). It is a common and widespread species found mostly in wooded areas from Alaska and British Columbia to Newfoundland, and south to California in the West and Virginia and Tennessee in the East (O’Hara 1991). Actia interrupta was included in a key to the puparia of dipterous parasitoids of Choristoneura species by Ross (1952) and in a key to the adults of dipterous parasitoids of C. occidentalis (as C. fumiferana) in British Columbia by Coppel (1960, as Gymnophthalma interrupta). Tilles and Woodley (1984) included A. interrupta among the five tachinids treated in their manual of spruce budworm parasitoids in Maine. O’Hara (1991) redescribed A. interrupta and figured portions of its puparium in his revision of the Nearctic species of Actia.
Eggs laid by Actia females contain fully developed first instars that hatch soon after oviposition. It is likely that the eggs are laid in the vicinity of a host and the first instar actively searches for the host.
Actia interrupta attacks coniferfeeding Choristoneura species as late instar larvae, usually attacking the fifth or sixth instar but occasionally the fourth, and emerges from the sixth instar (Dowden et al. 1948; Miller 1955; Carolin & Coulter 1959; Cusson et al. 2002). Choristoneura rosaceana is apparently attacked earlier, from the third instar onwards, with emergence from the third to sixth instar (Bostanian, pers. comm.; Westbrook, pers. comm.). There are two or more generations per year (Schaffner 1959, Westbrook, pers. comm.), with a variety of alternate hosts. Fully developed maggots pupariate away from the host and the species overwinters in the pupal stage (Tilles & Woodley 1984).
Actia interrupta is frequently recorded from Choristoneura species, but parasitism rates are generally low. However, Blais (1965) recorded up to 32 % parasitism in a residual C. fumiferana outbreak in Québec, and Schaupp et al. (1991) reported 40 % parasitism in an endemic population of Choristoneura sp. in southern Oregon. Schaupp et al. (1991) noted that A. interrupta is usually rare in epidemic populations of coniferfeeding Choristoneura species. The relatively low fecundity of A. interrupta (probably not more than a hundred or so eggs, compared to thousands in goniine tachinids that produce microtype eggs) may limit its ability to respond quickly to outbreaks.
Hosts of A. interrupta include about 25 species of Tortricidae and a species each of Geometridae and Notodontidae (Arnaud 1978; O’Hara 1991).