LIFE HISTORY AND SEASONAL DEVELOPMENT OF THE WESTERN WINTER MOTH, OPEROPHTERA OCCIDENTALIS (LEPIDOPTERA: GEOMETRIDAE), IN WESTERN OREGON' JEFFREYC. MILLERand JANE. CRONHARDT Department of Entomology, Oregon State University, Corvallis, Oregon 97331 Abstract Can. Ent. 114: 62%636 (1982) In western Oregon, Operophtera occidentalis (Hulst) has four larval instars, is univoltine, and polyphagous. Adult activity peaked in early December, eggs overwintered, larvae were present from March to June, and pupae from May to December. Temperature thresholds for egg and larval development were estimated to be 2°C. Few species of natural enemies were observed and rates of parasitism averaged 2%. Resume Dans l'ouest de I'Oregon, Operophtera occidentalis (Hulst) passe par 4 stades larvaires, est univoltine et polyphage. L'activitk des adultes est passke par un sommet t6t en dicembre, les oeufs ont hivernk, les larves ont it6 observkes de mars a juin et les chrysalides de mai a dicembre. Les seuils themiques pour le dCveloppement de l'oeuf et le dCveloppement larvaire ont it6 estimis 2 2OC. Peu d'espkces d'ennemis naturels ont Ctk observies et les incidences de parasitisme Ctaient de 2% en moyenne Introduction The genus Operophtera has four species in northwestern North America, three of which are native to North America. The western winter moth, 0. occidentalis (Hulst), and Danby's winter moth, 0. danbyi (Hulst), appear to be endemic to the Pacific Northwest while the Bruce spanworm, 0. bruceata (Hulst), has a northern distribution throughout the Nearctic region. The European winter moth, 0. brurnata (L.), is presumed to have been introduced from Europe into Nova Scotia prior to 1949 (Smith 1950) and is presumed to have occurred in British Columbia before 1972 (Gillespie et al. 1978) and in Oregon as early as 1958 (Ferguson 1978). Studies on 0. bruceata and 0. brumata have been conducted in North America by Brown (1962), Cuming (1961), Eidt and Embree (1968), Eidt et al. (1966), Embree (1966, 1967, 1970, 1971), Gillespie and Finlayson (1981), MacPhee (1967), and Sanford and Herbert (1966). These studies document a general life history as follows: mated, brachypterous females are active in the winter and deposit eggs which overwinter on the trunk and branches of deciduous trees; larvae emerge in the spring and feed on blossoms and foliage through four (0. bruceata) or five (0. brumata) instars; pupae occur in the soil through summer and early fall and adults emerge in late fall and early winter. Few native natural enemies of Operophtera have been found in North America. The biology of 0. occidentalis has not been documented as well as its congeners. A review of the literature on the biology of 0. occidentalis indicated only that adults occur in the late fall and early winter, and that larvae feed on leaves of various deciduous trees and shrubs (McFarland 1963; Sugden 1966; Tietz 1972; Furniss and Carolin 1977). A reference to 0. occidentalis larvae occurring on conifers and adults occurring in April does not conform to the general ecological characteristics of other Nearctic Operophtera (see Prentice 1963). These data suggest that additional research is needed and that the native 0. occidentalis and the exotic 0. brumata (which are presently sympatric in parts of Oregon) may be similar in 'Technical paper No. 5978. the Oregon Agricultural Experiment Station. 630 THE CANADIAN ENTOMOLOGIST July 1982 the ecology of their development. The degree of similarity in the ecology of Operophtera species is of importance as it affects the feasibility of biological control of 0. brumata in Oregon. This paper reports the life history and seasonal devel- opment of 0.occidentalis in western Oregon. Methods Field. The life history of 0. occidentalis was investigated in western Oregon from the fall of 1979 through the spring of 1981. Principal field sites were in MacDonald Forest, 9.6 km northwest of Corvallis, Benton County, and in West Salem, 59 km distant in Polk County. The MacDonald Forest site (ca. 17,000 ha) was a mixed coniferous forest dominated by Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, with a mixture of deciduous trees, primarily oak, Quercus garryana Dougl.; maple, Acer macrophyllum Pursh; ash, Fraxinus latifolia Benth.; alder, Alnus rubra Bong.; hazel, Corylus cornuta Marsh var. californica (A.DC.) Sharp; and cherry, Prunus emarginata (Doug.) Walp. The Salem site was a commercial sweet cherry orchard (ca. 10 ha) with an adjacent stand (ca. 3 ha) of mixed deciduous trees primarily maple, oak, and hazel. Adults were collected with nets, beating sheets, emergence net traps (see Briggs 1957), and sticky band traps. Eggs and larvae were collected by clipping selected foliage and twigs in the field for evaluation in the laboratory. Also, a beating sheet and sweep net were used to collect larvae. Pupae were collected by sifting soil from 0.5 d trays which were placed in the field. Adult development was monitored between October and January with 30 sticky band traps twice a week in 1979 and 81 traps once a week in 1980. Larval development was monitored by collecting (at the Salem site) 80 leaf clusters twice a week from the same set of 10 trees through the spring of 1980. Also, 80 leaf clusters were collected twice a week from a single tree chosen at random. Through the spring of 1981, 175 leaf clusters were collected once a week from the same set of five trees. Larval development was also observed outside of the Salem site. Leaf clusters from a variety of plant species were collected for in field and laboratory evaluation. Laboratory. A culture of 0. occidentalis was started in the fall of 1979 and maintained for three generations. Field-collected adults were observed and reared under conditions of 4-6"C, 12L:12D photoperiod. Field-collected eggs and larvae were reared separately at 16"C, 14L: 10D photoperiod, and 70-85% relative humidity. Parasitoids reared from these larvae were preserved and moths were added to the laboratory culture. Adults used for laboratory observations on longevity and fecundity were obtained from larvae collected in the field during the previous generation, or from adults collected directly from the field. The developmental requirements of the eggs and larvae of 0. occidentalis were investigated under constant temperatures of 4", lo0, 16", 22", 28", and 34°C. Relative humidity ranged between 70% and 85% and the photoperiod was 14L:lOD. Eggs and larvae used in this study were F, progeny of field-collected adults. A total of 231 eggs were held at 4"-6'C for 3 months and then placed individually in one of the six constant temperature cabinets. At least 3 1 eggs were used in each temperature treatment. Eggs were observed at 12 h intervals until hatch or death due to desic- cation, which was indicated by collapse. A total of 192 larvae were placed indi- vidually in one of the six temperature cabinets. At least 29 larvae were placed in each cabinet except the 34°C cabinet which had only 19. The larvae were fed fresh, Volume 114 THE CANADIAN ENTOMOLOGIST 63 1 young cherry leaves as a standard diet and observed at 12 h intervals until death or pupation. Climatological data for field studies were obtained for the Salem airport from the National Oceanic and Atmospheric Administration. Results and Discussion Sampling techniques. The technique most productive for collecting both male and female moths was sticky bands around tree trunks about m from the ground. However, specimens were damaged and not suitable for behavioral studies. Males for behavioral studies were captured with an aerial net just after dusk and females by beating tree branches over drop cloths. The stationary net trap described by Briggs (1957) did not capture as many females as did the other techniques. Eggs and larvae of all age classes were most easily collected by clipping branches from trees and inspecting blossom/leaf clusters in the laboratory. Middle and late instar larvae could be located easily by searching for foldedltied leaves. The technique of beating branches was more satisfactory for collecting late instar than early instar larvae. Pupae were difficult to locate in the field. The sifting of "native" soil and the placement/analysis of soil filled trays were too time-consuming and the recovery of specimens negligible. Life history. In western Oregon, 0.occidentalis is univoltine (Fig. 1). A major portion of the development time, 9 of 12 months, was spent either in the overwin- tering egg or oversummering pupal stage. Larval stages and active adults each occurred over a period of 8 weeks during the spring and late fall - early winter, respectively. Adults were most active between dusk and midnight. Prior to darkness, adults were found at the soil surface beneath leaf litter. Approximately '12-1 h after sunset, males would begin to fly and would remain active for a 6-h period. When temper- atures were below freezing, males would not fly but did ascend trees and could locate females. Also, the brachypterous females would ascend trees at dusk and presumably return to the ground litter. No females were collected from the tree canopy during daylight hours. Males and females in copulo were observed on tree trunks and branches from ground level to 2 m above ground between dusk and midnight. I -Adults Eggs Larvae I Larvae II: P -Larvae JK -Larvae IP Pupae 1'~~1~~.1,~b1~1,1,~,1,~#1*#11I~~+- Oct. Dec. Feb. April June-Sept. FIG. 1. The seasonal distribution of Operophtera occidenzalis. Salem, Oregon, 1979-1981. 632 THE CANADIAN ENTOMOI.OGIS7 July 1982 Field-collected adults and adults from laboratory cultures were observed to document longevity and reproductive potential. Males from laboratory cultures were kept alive for an average of 9.4 days (n = 9, S.D.