Cyzenis incrassata ( Smith, 1912 )

O’Hara, James E., 2005, A review of the tachinid parasitoids (Diptera: Tachinidae) of Nearctic Choristoneura species (Lepidoptera: Tortricidae), with keys to adults and puparia, Zootaxa 938, pp. 1-46 : 21-22

Cyzenis incrassata ( Smith, 1912) , Fig. 41

Host records ex. Choristoneura occidentalis: Torgersen, et al. 1984, as Phorocera incrassata (WA, OR, ID, MT); † Torgersen 1985, as P. incrassata (WA, OR, ID, MT); O’Hara & Cooper 1992 (BC, OR, NM); † Huber et al. 1996 ( America north of Mexico).

Host records probably ex. Choristoneura occidentalis: Wilkes 1946 , as Phorocera incrassata ex. Archips fumiferana (BC); Coppel 1947, as P. incrassata ex. A. fumiferana (BC); † Dowden et al. 1948, as P. in cra ss at a ex. A. fumiferana (western North America); †Wilkes 1949, as P. incrassata ex. A. fumiferana (BC); Wilkes et al. 1949, as P. in cra ss at a ex. C. fumiferana (BC); † Ross 1952, as P. incrassata ex. spruce and/or jack pine budworm ( Canada); Coppel 1958, as P. i n c r a s s a t a ex. C. fumiferana (BC); Carolin & Coulter 1959, as P. incrassata ex. C. fumiferana (OR); † Coppel 1960, as P. incrassata ex. C. fumiferana (BC); † Zwolfer 1961, as Clemelis incrassata ex. C. fumiferana (BC); † Graham & Jones 1962, as P. incrassata ex. C. fumiferana (BC); † McGugan & Coppel 1962, as P. incrassata ex. C. fumiferana (BC); † Arnaud 1978, as P. incrassata ex. C. fumiferana (BC, OR); † Clausen 1978, as P. incrassata ex. C. fumiferana (BC); † Huber et al. 1996, ex. C. fumiferana ( America north of Mexico).

Host records ex. Choristoneura occidentalis and/or C. retiniana: Schaupp et al. 1991, as Phorocera incrassata (OR); † O’Hara & Cooper 1992 (OR).

Cyzenis incrassata is a grayish black tachinid about 5–7.5mm long with a known range comprising British Columbia, Washington, Idaho, Oregon, and New Mexico ( O’Hara & Cooper 1992; O’Hara & Wood 2004). Attempts to establish C. incrassata in eastern Canada were unsuccessful ( McGugan & Coppel 1962; O’Hara & Cooper 1992). The Nearctic species of Cyzenis were revised, and C. incrassata redescribed, by O’Hara and Cooper (1992). Cyzenis incrassata (as Phorocera incrassata ) 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 of Cyzenis incrassata were described and illustrated by Coppel (1958). Records of Cyzenis incrassata parasitizing C. fumiferana in western North America are likely erroneous and based on misidentifications of C. occidentalis .

Cyzenis belongs to the Goniini (Exoristinae) , a tribe characterized by the production of huge numbers of microtype eggs in the female reproductive system ( Herting 1984; Wood 1987). These eggs are deposited on foliage, sometimes in response to feeding damage ( Roland et al. 1989), and contain fully developed first instars. The eggs are ingested by a feeding host and pass unharmed into the gut, where they soon hatch under the influence of digestive enzymes and perhaps physical trauma ( Mellini 1990). First instars burrow through the gut wall and move to specific locations within the host ( Mellini 1990). In the case of Cyzenis incrassata , the first instar delays development until the host begins to pupate, then rapidly completes larval development and forms a puparium within the host’s pupal case ( Coppel 1958). Adults emerge from their puparia after 12–14 days ( Coppel 1958).

Adults of Cyzenis incrassata appear in June in British Columbia and attack maturing C. occidentalis larvae ( Coppel 1958). Adults of the next generation appear in July and early August when C. occidentalis larvae are unavailable. Cyzenis incrassata must therefore overwinter in an alternate host, but its identity has not been determined ( Coppel 1958). Choristoneura species remain almost exclusively the only known hosts of this species ( Arnaud 1978; O’Hara & Cooper 1992).

Wilkes et al. (1949) ranked Cyzenis incrassata (as Phorocera incrassata ) as the eighth most important parasitoid, and fifth most important dipterous parasitoid, of C. occidentalis (as C. fumiferana ) in British Columbia, with an average parasitism rate of 1.1% during 1943–1947. Other studies have reported similarly low levels of parasitism, e.g., 0.008– 0.500% in British Columbia ( Coppel 1958) and 0.0–2.5% in Oregon ( Schaupp et al. 1991, with higher rates found in epidemic than endemic populations).

Figures

FIGURES 37 – 42. Habitus images. 37. Actia diffidens. 38. Actia interrupta. 39. Ceromasia auricaudata. 40. Compsilura concinnata. 41. Cyzenis incrassata. 42. Eumea caesar.