PARASITOIDS OF ENDEMIC AND EPIDEMIC POPULATIONS OF CHORISTONEURA OCCIDENTALIS FREEMAN AND CHORISTONEURA RETINIANA (WALSINGHAM) (LEPIDOPTERA: TORTRICIDAE) IN SOUTHERN OREGON

Abstract

Parasitoid species attacking sparse, endemic populations of Choristoneura occidentalis Freeman and C. retiniana (Walsingham) are reported from 2 years of host collections at seven sites across southern Oregon. Results are compared with rearings from epidemic populations either from the same region or the same plot. Collections were designed to allow quantitative estimation of host density. Most of the parasitoid species present during epidemics across North America were recovered from the endemic and epidemic populations studied. The major difference is that at endemic host densities Glypta fumiferanae (Viereck) (Ichneumonidae) is rare to absent, whereas ichneumonids of the tribe Campoplegini, especially Tranosema (= Diadegma) interruptum (Ashmead), are common. This is the reverse of the situation at epidemic densities and consistent with results reported from eastern North America. It is suggested that the observed shift in the parasite complex with budworm density has the potential for predicting population trends.

A review of the tachinid parasitoids (Diptera: Tachinidae) of Nearctic Choristoneura species (Lepidoptera: Tortricidae), with keys to adults and puparia

“…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). (Aldrich, 1916) Eumea caesar is a common tachinid found throughout temperate and boreal Canada, and south to California and Texas in the West and Virginia in the East (O'Hara & Wood 2004).…”

“…The rate of parasitism of C. auricaudata in conifer-feeding Choristoneura is negligible in the East but significant in the West, with parasitism of up to 13% reported by Wilkes et al (1949) and up to 16% reported by in British Columbia, and up to 13% reported by Schaupp et al (1991) in Oregon. Wilkes et al (1949) ranked C. auricaudata as the fourth most important parasitoid, and second most important dipterous parasitoid, of C. occidentalis (as C. fumiferana) in British Columbia.…”

“…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.…”

“…in southern Oregon. Schaupp et al (1991) noted that A. interrupta is usually rare in epidemic populations of conifer-feeding 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.…”

Abundance of Different Tortricid Species and Their Parasitoid Antagonists in Ecological Apple Orchards in Southern Germany

“…However, considering only parasitization rate, the incidence of host feeding by parasitoids on host mortality, although it might be of considerable importance, is completely neglected. However, observations of Galli (1984) and Schaupp et al ( 1991) of a lower parasitization rate in epidemic populations of A. orana and C. retiniana than in endemic populations, could be confirmed to a certain extent. Whether the lower parasitization rate is reason for, or consequence of, the population outbreak of A. orana cannot be decided by these data.…”