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Canada United States Spruce Budworms Program Larval Densities and Trends of Insect Species Associated With Spruce Budworms in Buds and Shoots in Oregon and Washington V.M. Carolin V. M. CAROLIN is consulting entomologist for the Pacific Northwest Forest and Range Experiment Station, Portland,, Oregon. Larval Densities and Trends of Insect Species Associated With Spruce Budworms in Buds and Shoots in Oregon and Washington by V. M. Carolin Reference Abstract Research Summary Research Paper PNW-273 Carolin, V. M. 1980. Larval densities and trends of insect species 1980 associated with spruce budworms in buds and shoots in Oregon and Washington. USD A For. Serv. Res. Densities and trends of insect species feeding in Pap. PNW-273, 18 p. Pac. Northwest For. and Range opening buds with the western spruce budworm, Exp. Station, Portland, Oregon. Choristoneura occidentalis Freeman, in Oregon and Washington, were analyzed for the period 1951 Sampling studies on western spruce budworm through 1962. During sampling at fixed plots for and Modoc budworm disclosed a substantial C. occidentalis in both sprayed and unsprayed number of associated insect species at the time areas, larvae of associated insect species were iden- larvae were in opening buds. About 20 species tified and quantified as numbers per one hundred occur with sufficient regularity to justify identi- 15-inch twigs. A similar but lesser effort was made fication by field crews. in 1960-62 in unsprayed infestations of the Modoc budworm, C. viridis Freeman, in southern Oregon. Keywords: Insect populations, reproductive behavior (insect), western spruce budworm, iden- The various associated insect species and their tification (insect), Choristoneura occidentalis, frequencies on Douglas-fir, grand fir, and white fir Modoc budworm, Choristoneura viridis. are tabulated. Trends of six major associates at Douglas-fir and subalpine fir plots are shown graph- ically by study area; periods covered are 1951-59 for sprayed areas and 1955-58 for unsprayed areas. Major associates were: Acleris gloverana (Walsing- ham), Argyrotaenia dorsalana (Dyar), Coleotech- nites sp., near piceaella (Kearfott), Dioryctria reniculelloides Mutuura and Munroe, Griselda radicana (Heinrich), and Zeiraphera hesperiana Mutuura and Freeman. Approximate trends in an infestation in the eastern Washington Cascades during 1960-62 and before spraying were deduced. Indications as to preference of associated insect species for Douglas-fir and grand fir were obtained from two paired tree studies, one in northeast Oregon and one in the eastern Washington Cas- cades. Preference for Douglas-fir was shown by two associated species, and preference for grand fir by three associated species. About 20 associated species occurred with suf- ficient frequency to justify their recognition as a routine part of sampling studies. Major peaks for most associates occurred in 1957 or 1958, along with the western spruce budworm. Contents Page INTRODUCTION ........................................................................................................................................... 1 METHODS ......................................................................................................................................................... 2 Data Collection .......................................................................................................................................... 2 Occurrence of Associated Defoliators by Tree Species .............................................................................. 2 Trends of Associated Species..................................................................................................................... 3 Sprayed Areas ................................................................................................................................. 3 Unsprayed Areas ............................................................................................................................. 3 Host Preference ........................................................................................................................................ 4 RESULTS ........................................................................................................................................................ 5 Occurrence of Associated Defoliators by Tree Species .............................................................................. 5 Common and Occasional Associates .................................................................................................. 5 Rare and Sporadically-occurring Associates ...................................................................................... 5 Trends of Associated Species ..................................................................................................................... 5 Sprayed Areas ................................................................................................................................. 5 Unsprayed Areas ............................................................................................................................. 11 Host Preference ....................................................................................................................................... 13 Northeast Oregon............................................................................................................................... 13 Eastern Washington Cascades............................................................................................................. 14 DISCUSSION ..................................................................................................................................................... 14 CONCLUSIONS ................................................................................................................................................. 15 LITERATURE CITED...................................................................................................................................... 16 APPENDIX ...................................................................................................................................................... 17 Introduction A new series of outbreaks by the western spruce bud- Biological studies starting in 1950 gradually disclosed worm, Choristoneura occidentalis Freeman, have been the identity of the principal associated defoliators; underway in parts of the West. In 1973, infestations subsequently, information on recognition of principal appeared to be increasing in Oregon, Washington, Ari- associated defoliators was made available to survey zona, New Mexico, and Colorado, although decreasing and control personnel in the form of hand-colored in the northern Rocky Mountains (Chansler and Toko larval diagrams.1 A publication on the effects of DDT 1975). As of 1973, the eastern counterpart — the spraying on the western spruce budworm (Carolin spruce bud worm, C. fumiferana (Clemens) — had and Coulter 1971) included evidence of differential infested large areas in the State of Maine, eastern survival between the budworm and its associates. Canada, and the Lake States; and aerial control proj- ects were underway. Concern over the prospects of Untapped data on associated defoliators in the files of widespread damage by these budworms led to the the Pacific Northwest Forest and Range Experiment initiation in 1977 of a 6-year cooperative program Station have recently been synthesized and analyzed. between the United States and Canada, with a mission Comparisons were made between the frequency of of developing management strategies for controlling occurrence of various associates on three different these budworms, or learning to manage budworm- tree species, between trends of common associates susceptible forests. in sprayed and unsprayed areas, including relationship to budworm trends, and between various associates One of the program objectives is to develop and as to host preference. improve methods for assessing and predicting bud- worm population levels. Such determination requires that associated defoliators be recognized and that any 1 peculiar relationships between spruce budworms and Unpublished report by V. M. Carolin and W. H. these associates be defined. Evaluation of control Klein, 1958, Pacific Northwest Forest and Range effectiveness also demands that associated defoliators Experiment Station, Portland, Oregon. be identified in both pre-control and post-control sampling. To this end, information on these associ- ates needs to be made available to workers in the ongoing program. One source of information is biological data obtained during a previous budworm outbreak in Oregon and Washington. The major outbreak, mostly in the Blue Mountains and Cascade Range, began in 1947 and ended in 1959, after 4.7 million acres were sprayed with DDT. A subsequent flare-up in the eastern Wash- ington Cascades in 1959 was terminated in 1962 by aerial spraying. Also in 1959, the Modoc budworm, C.viridis Freeman, was found to be in epidemic status over a large area in southern Oregon and northern California. It reached a peak in 1960, then declined from natural causes. 1 Methods Data Collection During the examination of twig samples, larvae of unknown or uncertain identity were examined under Numbers of associated defoliators were recorded on a hand lens and given a temporary name, often a nick- foliage samples at spruce budworm study plots during name, under which numbers were recorded.

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