Host records ex. Choristoneura conflictana: Prentice 1955 (SK, MB); † Arnaud 1978 (SK, MB); † Huber et al. 1996 (America north of Mexico).
Host records ex. Choristoneura fumiferana: Dowden et al. 1951, ex. Archips fumiferana (NY); Miller 1955 (NB); Blais 1960 (QC); † Miller 1963 (NB); Blais 1965 (QC); Huber et al. 1996 (NB).
Host records ex. Choristoneura fumiferana and/or Choristoneura occidentalis: Dowden et al. 1948, ex. Archips fumiferana (North America); † Arnaud 1978, ex. C. fumiferana (BC, OR, QC, NB, NY); † Zwolfer 1961, as Phryxe saundersii ex. C. fumiferana (North America)
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 occidentalis: McKnight 1974 (CO); Harris & Dawson 1979 (BC); Schmid 1981 (NM); Torgersen et al., 1984 (WA, OR, ID, MT); † Torgersen 1985 (WA, OR, ID, MT).
Host records probably ex. Choristoneura occidentalis: Bedard 1938, ex. Cacoecia fumiferana on Douglas fir (“northern Rocky Mountain region”); Wilkes et al. 1949, ex. C. fumiferana (BC); Coppel 1953, ex. C. fumiferana (BC); Carolin & Coulter 1959, ex. C. fumiferana (OR); † Coppel 1960, ex. C. fumiferana (BC).
Host records ex. Choristoneura occidentalis and/or Choristoneura retiniana: Schaupp et al. 1991 (OR).
Host records ex. Choristoneura parallela: Johnson 1925, ex. Cacoecia parallela (MA); Franklin 1950, ex. Archips parallela (MA); † Arnaud 1978 (MA); † Huber et al. 1996 (America north of Mexico).
Host records ex. Choristoneura pinus: Kulman & Hodson 1961 (MN); Dixon & Benjamin 1963 (WI); Allen et al. 1969 (MI); † Arnaud 1978 (MN, WI, MI); † Huber et al. 1996 (America north of Mexico).
Madremyia saundersii is a common and widespread species ranging from the Yukon and British Columbia to Newfoundland, and south to Mexico in the West and Virginia in the East (O’Hara & Wood 2004). Adults are generally 4.0–7.5mm long and mostly dark coloured with faint silvery bands on the abdomen. Madremyia saundersii 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). The egg, larval instars, and puparium were described by Coppel and Maw (1954 b).
Madremyia belongs to the tribe Eryciini (in the Exoristinae) and is closely related to Phryxe, a species of which is treated below. The biology of M. saundersii was studied by Coppel and Maw (1954 b). They observed that females deposit fully incubated eggs directly on the integument of a host. Soon after oviposition, the first instar exits from the end of the egg through the underside of the chorion and burrows into the host. Females generally lay 75– 100 eggs during a lifetime of 20–60 days. Usually only one parasitoid emerges per host but multiparasitism also occurs. Madremyia saundersii attacks late instar larvae of Choristoneura species and emerges from the sixth instar or pupa (Dowden et al. 1948; Coppel & Maw 1954 b; Carolin & Coulter 1959; Allen et al. 1969). The fully mature maggot falls to the ground and pupariates in the soil (Coppel & Maw 1954 b). A second generation is passed in an alternate host, and perhaps a third generation as well (Schaffner & Griswold 1934; Coppel & Maw 1954 b). Coppel and Maw (1954 b) speculated that M. saundersii passes the winter as a first or second instar in an alternate host.
Parasitism of coniferfeeding Choristoneura species by M. saundersii has been reported as higher in western than eastern North America. Dowden et al. (1948) recorded emergence of M. saundersii from up to 6 % of larvae and up to 14 % of pupae in Colorado. Coppel and Maw (1954 b) reported up to 7.5% parasitism in British Columbia. In Oregon, Carolin and Coulter (1959) reported parasitism approaching 10 % and Schaupp et al. (1991) recorded parasitism as high as 13 %; in both these studies there was an increase in parasitism as budworm outbreaks progressed. Wilkes et al. (1949) ranked M. saundersii as the twelfth most important parasitoid, and sixth most important dipterous parasitoid, of C. occidentalis (as C. fumiferana) in British Columbia. Dowden et al. (1951) and Blais (1960) reported very low parasitism of C. fumiferana in New York and Québec, respectively. In northwestern Ontario, McGugan and Blais (1959) did not rear M. saundersii from C. fumiferana and Nealis (1991) did not rear it from C. pinus. Tilles and Woodley (1984) excluded M. saundersii from their treatment of spruce budworm parasitoids in Maine, presumably because of its rarity as a parasitoid of C. fumiferana in that state.
Madremyia saundersii has a broad host range of over 30 known species, including members of the Danaidae, Geometridae, Lasiocampidae, Lymantriidae, Noctuidae, Nymphalidae, Pieridae, Pyralidae, and Tortricidae (Arnaud 1978).