Parasitoids of Siricidae are not very diverse, but they are striking for their large size. Not all parasitoid species have large specimens, but most have specimens ranging from small to very large depending on size of the host specimen. They are all easily recognized at family and generic level, and in many instances at species level. The North American parasitoids of Siricidae are keyed for Megarhyssa, Pseudorhyssa, and Rhyssa (Ichneumonidae) (Townes and Townes 1960), for Ibalia (Ibaliidae) (Liu and Nordlander 1992, 1994), and for Schlettererius (Stephanidae) (Townes 1949, Aguiar and Johnson 2003). Adults of most species fly before the main flight period of their siricid host. Even when the host adults are flying commonly, some parasitoids can still be found. Oviposition may easily be observed when it occurs on the lower portion of a tree trunk. We observed a female of Megarhyssa macrura (Linnaeus) ovipositing for 15 minutes (Fig. A4.1). Miller and Clark (1935: 155) observed and illustrated the oviposition stages in Rhyssa persuasoria (Linnaeus). For more information on the biology of parasitoids and their host trees see Champlain (1922), Chrystal and Myers (1928a, 1928b), Chrystal (1930), Hanson (1939), Cameron (1965), Taylor (1977) and Kirk (1974, 1975). An unusual behaviour of Megarhyssa is described by Fattig (1949). Males were observed inserting their abdomen for some time into the emergence hole of a female. Then, they waited for the female to emerge, and mated several times. A female parasitoid may visit the same tree several times in search of hosts.
New World species of parasitoids associated with Siricidae are listed below. Because it is often difficult to associate a parasitoid with a siricid host we also provide a list of named tree species as a clue. The flight period and range for each parasitoid species is then given.
| Parasitoid Species | Siricid Species | Tree Name & Note |
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| IBALIIDAE | ||
| Ibalia anceps Say (Fig. A4.2) | Tremex columba (Linnaeus) | See host trees under T. columba |
| Ibalia arizonica Liu & Nordlander | Conifer Siricidae | |
| Ibalia kirki Liu & Nordlander | Perhaps Sirex nitidus (T. W. Harris) | Picea engelmannii |
| Ibalia leucospoides (Hochenwarth) (Fig. A4.3) | Sirex sp., S. behrensii (Cresson), Sirex noctilio Fabricius, S. cyaneus Fabricius, S. areolatus (Cresson), S. nigricornis Fabricius, Urocerus sp., U. albicornis (Fabricius), Xeris sp. | Various conifers genera; common in Pinus resinosa |
| Ibalia montana Cresson | Probably conifer Siricidae | |
| Ibalia ruficollis Cameron | Probably conifer Siricidae | |
| Ibalia rufipes Cresson | Sirex cyaneus Fabricius or S. nitidus (T. W. Harris) | Various conifers genera |
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| ICHNEUMONIDAE | ||
| Megarhyssa atrata (Fabricius) (Fig. A4.4) | Tremex columba (Linnaeus) | See host trees under T. columba |
| Urocerus sp. (unlikely host) | ||
| Megarhyssa greeni Viereck | Tremex columba (Linnaeus) | See host trees under T. columba |
| Megarhyssa macrura (Linnaeus) (Fig. A4.5) | Tremex columba (Linnaeus) | See host trees under T. columba |
| Megarhyssa nortoni (Cresson) | Sirex noctilio Fabricius, Urocerus albicornis (Fabricius), Xeris morrisoni (Cresson) | Abies concolor, A. grandis, A. lasiocarpa, A. magnifica, Picea sitchensis, Pinus contorta, P. jeffreyi, Pseudotsuga menziesii, Tsuga canadensis |
| Rhyssa alaskensis Ashmead | Siricidae on conifers | Abies lasiocarpa, Picea englemannii, P. sitchensis, Pinus contorta, Tsuga heterophylla |
| Rhyssa crevieri (Provancher) | Sirex noctilio Fabricius | Abies balsamea |
| Urocerus albicornis (Fabricius) | ||
| Rhyssa hoferi Rohwer | Siricidae on conifers | Juniperus sp., Pinus edulis, P. ponderosa |
| Rhyssa howdenorum Townes & Townes | Sirex cyaneus Fabricius, S. nigricornis Fabricius | Pinus virginiana |
| Rhyssa lineola (Kirby) (Fig. A4.6) | Sirex sp., Sirex nigricornis Fabricius, S. cyaneus Fabricius or S. nitidus (T. W. Harris), S. noctilio Fabricius, Urocerus albicornis (Fabricius), U. flavicornis (Fabricius) | Abies balsamea, A. fraseri, A. lasiocarpa, Picea sitchensis, Pinus radiata, P. rigida, Tsuga canadensis |
| Rhyssa persuasoria (Linnaeus) (Fig. A4.7) | Sirex areolatus (Cresson), S. cyaneus Fabricius, S. noctilio Fabricius, Xeris sp. | Abies balsamea, A. concolor, A. lasiocarpa, Juniperus scopulorum, Larix decidua, Picea engelmannii, Pinus edulis, P. ponderosa, P. virginiana |
| Rhyssa ponderosae Townes & Townes | Sirex areolatus (Cresson) | Pinus ponderosa |
| Pseudorhyssa nigricornis (Ratzeburg) (Fig. A4.8) | Cleptoparasite on Rhyssa spp. | Abies balsamea, A. concolor, Larix laricina; Picea engelmannii, P. mariana, Pinus ponderosa, |
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| STEPHANIDAE | ||
| Schlettererius cinctipes (Cresson) (Fig. A4.9) | Sirex sp., Sirex noctilio (in Tasmania), Urocerus sp., Xeris sp. | Abies concolor, Picea engelmannii, Pinus ponderosa, Pseudotsuga menziesii |
To read a summary about the range and flight period of each species of parasitoids, please click on the family name in the above table.
