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

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.

EFFECTS OF ATTRACTANT COMPOSITION AND RELEASE RATE ON ATTRACTION OF MALE CHORISTONEURA RETINIANA, C. OCCIDENTALS, AND C. CARNANA (LEPIDOPTERA : TORTRICIDAE)

Attraction of male Choristoneura spp. to various mixtures of the pheromone components of C. occidentalis Freeman and C. retiniana (Walsingham) released at various rates was evaluated at several sites in western North America. At all but 1 location, male trap capture increased with progressively greater release rates of a 92:8 mixture of (E)- and (Z)-11-tetradecenals (TDALs), previously identified as active components of the attractant pheromone of C. occidentalis. Similarly, trap catch was positively correlated with release rate of an 84:7:8:1 mixture of (E)- and (Z)-11-tetradecenyl acetates and (E)- and (Z)-11-tetradecenols (1:0.1 TDACs:TDOLs), previously identified as active components of the attractant pheromone of C. retiniana. All release rates of TDALs attracted only C. carnana (C. occidentalis and C. carnana probably are subspecies of the same species) in the central Sierra Nevada, but in the southern Cascades all but the lowest release rate of TDALs attracted significant numbers of males classified as C. retiniana in addition to those classified as C. occidentalis. At all locations, 1:0.1 TDACs: TDOLs exhibited complete species specificity, attracting only C. retiniana at all release rates tested. The 1:0.1 ratio of TDACs: TDOLs was the most attractive mixture of these components to C. retiniana. Addition of 1:0.1 TDACs: TDOLs did not significantly affect attraction of C. carnana to TDALs. However addition of TDALs significantly decreased attraction of C. retiniana to 1:0.1 TDACs:TDOLs.