Darrell W. Ross

Competition thresholds for the survival and growth of ponderosa pine seedlings associated with woody and herbaceous vegetation

Patterns of survival and stem-volume growth for planted seedlings of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) competing with various levels of woody and herbaceous vegetation were derived from three previous studies—one in Oregon and two in Montana. Negative hyperbolic curves of opposite concavity describe the relation between the abundance of woody or herbaceous vegetation and (1) the survival and (2) the stem volume of the pine seedlings. From these curves, two types of competition thresholds for managing forest vegetation are identified: (1) maximum-response threshold—a level of vegetation abundance where additional control measures will not yield an appreciable increase in tree performance; and (2) minimum-response threshold—a level of vegetation abundance that must be reached before additional control measures will yield an appreciable increase in tree performance. The maximum- and minimum-response thresholds for pine stem volume occurred at lower levels of vegetation abundance than those for pine survival. Thus, forest managers may need to consider ponderosa pine survival and stemvolume growth as separate objectives when managing woody and herbaceous vegetation in young plantations. Knowledge of maximum- and minimum-response thresholds also can be used to improve herbicide prescriptions.

Predators associated with the hemlock woolly adelgid (Hemiptera: Adelgidae) in the Pacific Northwest.

Abstract The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is causing widespread mortality of eastern hemlock, Tsuga canadensis L. Carrière, in the eastern United States. In western North America, feeding by A. tsugae results in negligible damage to western hemlock, Tsuga heterophylla (Raf.) Sargent. Host tolerance and presence of endemic predators may be contributing to the relatively low levels of injury to T. heterophylla caused by A. tsugae. Field surveys of the predator community associated with A. tsugae infestations on 116 T. heterophylla at 16 sites in Oregon and Washington were conducted every 4–6 wk from March 2005 through November 2006. Fourteen uninfested T. heterophylla were also surveyed across 5 of the 16 sites. Each sample tree was assigned an A. tsugae population score ranging from 0 to 3. Predators collected from A. tsugae–infested T. heterophylla represent 55 species in 14 families, listed in order of abundance: Derodontidae, Chamaemyiidae, Hemerobiidae, Coccinellidae, Cantharidae, Reduviidae, Miridae, Syrphidae, Chrysopidae, Coniopterygidae, Staphylinidae, Anthocoridae, Nabidae, and Raphidiidae. Laricobius nigrinus Fender (Coleoptera: Derodontidae), Leucopis argenticollis Zetterstedt (Diptera: Chamaemyiidae), and Leucopis atrifacies (Aldrich) (Chamaemyiidae) were the most abundant predators; together comprising 59% of predator specimens recovered. Relationships among predators and A. tsugae were determined through community structure analysis. The abundances of Laricobius spp. larvae, L. nigrinus adults, Leucopis spp. larvae, and L. argenticollis adults were found to be positively correlated to A. tsugae population score. Predators were most abundant when the two generations of A. tsugae eggs were present. L. argenticollis and L. atrifacies were reared on A. tsugae in the laboratory, and host records show them to feed exclusively on Adelgidae.

Kairomonal response of Thanasimus undatulus, Enoclerus sphegeus (Coleoptera: Cleridae), and Temnochila chlorodia (Coleoptera: Trogositidae) to bark beetle semiochemicals in Eastern Oregon

Abstract The kairomonal responses of Thanasimus undatulus (Say), Enoclerus sphegeus F., and Temnochila chlorodia (Mannerheim) to semiochemicals used by Dendroctonus pseudotsugae Hopkins, D. rufipennis Kirby, D. brevicomis LeConte, D. ponderosae Hopkins, and Ips pini (Say) to locate hosts were quantified in the field during the period of D. pseudotsugae dispersal in the spring and early summer. Traps baited with frontalin plus seudenol caught significantly more T. undatulus than traps baited with any other lure. Only a few E. sphegeus were collected during the study, suggesting that it might use semiochemicals other than those tested in this study to locate its prey. All of the traps baited with lures containing exo-brevicomin caught significantly more T. chlorodia than traps baited with other lures. These results suggest that T. undatulus uses seudenol primarily to locate its prey habitat, and T. chlorodia uses exo-brevicomin for the same purpose. These predators likely feed upon bark beetles that produce these compounds or other bark beetles that are found in the same habitats. A secondary pest of ponderosa pine, Pityogenes carinulatus (LeConte), was attracted in significant numbers to the traps baited with I. pini pheromone components. Traps baited with ipsdienol and lanierone caught significantly more P. carinulatus than traps baited with ipsdienol alone.

Elution rate and spacing of antiaggregation pheromone dispensers for protecting live trees from Dendroctonus pseudotsugae (Coleoptera: Scolytidae)

Abstract The antiaggregation pheromone 3-methylcyclohex-2-en-1-one (MCH) is highly effective in preventing the infestation of high-risk trees by Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins. A large portion of the cost of an MCH treatment is related to the time applicators spend walking through an area dispersing the formulated pheromone. Application of fewer MCH dispensers eluting at a higher rate than those currently registered for operational use could potentially reduce treatment costs. Two higher elution rates, 6 and 18 mg/d per dispenser, were compared with the current standard of 2 mg/d per dispenser and an untreated control on 1-ha circular plots. Dispensers were spaced 5, 15, and 44 m apart around the plot perimeters eluting 2, 6, and 18 mg/d, respectively. The nominal dose of MCH was 144 mg/ha/d on all plots. Percentages of Douglas-fir trees ≥20 cm diameter at breast height mass attacked by Douglas-fir beetle were significantly lower on plots treated with dispensers eluting 2 and 6 mg/d and spaced 5 and 15 m apart, respectively, compared with the untreated control. Infestation rate on plots treated with dispensers eluting 18 mg/d and spaced 44 m apart was not significantly different from the control. Douglas-fir beetle abundance and host tree availability were similar on all plots. These results indicate that MCH dispensers eluting 6 mg/d (three times the current standard rate) and spaced 15 m apart (three times existing standard distance) can effectively prevent Douglas-fir beetle infestations.

Prey Suitability and Phenology of Leucopis spp. (Diptera: Chamaemyiidae) Associated With Hemlock Woolly Adelgid (Hemiptera: Adelgidae) in the Pacific Northwest

ABSTRACT Leucopis spp. (Diptera: Chamaemyiidae) from the Pacific Northwest previously were identified as potential biological control agents for the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), in the eastern United States. We collected Leucopis spp. larvae from A. tsugae infested western hemlocks in Oregon and Washington and reared them on an unidentified Pineus spp., Pineus strobi (Hartig), Adelges cooleyi (Gillette), Adelges piceae (Ratzeburg), and A. tsugae in three no-choice tests. Leucopis spp. survival on A. tsugae was significantly higher than on A. piceae during the 2010 progrediens generation test and significantly higher than on P. strobi and A. cooleyi during the 2010 sistens generation test. However, across all three tests, some larvae completed development to adult on all four of the alternative adelgid species. Larvae that survived to the adult stage were identified as Leucopis argenticollis Zetterstedt and Leucopis piniperda Malloch. These results suggest that populations of L. argenticollis and L. piniperda in the Pacific Northwest may not be specific to A. tsugae. We also studied the phenology of Leucopis spp. on fourteen A. tsugae infested western hemlock trees in Oregon and Washington over a period of 14 mo. Leucopis spp. larvae were collected year-round, but highest densities coincided with the presence of progrediens and sistens eggs and adults of A. tsugae. There was a positive correlation between Leucopis spp. and A. tsugae abundance.

Orientation Behavior of the Predator Laricobius nigrinus (Coleoptera: Derodontidae) to Hemlock Woolly Adelgid and Host Tree Odors in a Multi-Chambered Olfactometer

ABSTRACT We studied the adult ambulatory response of the predator, Laricobius nigrinus Fender (Coleoptera: Derodontidae), to odors from its prey, Adelges tsugae Annand, the hemlock woolly adelgid, and foliage of hemlock woolly adelgid, host hemlocks (Tsuga spp.), and other conifers. Both the predator and hemlock woolly adelgid are apparently native to western North America, but the predator is being released in the eastern United States, which has different hemlock species, for biological control of a lineage of hemlock woolly adelgid inadvertently introduced from Japan. L. nigrinus responded to odors from hemlock woolly adelgid host trees, but not to odors from hemlock woolly adelgid. L. nigrinus collected from hemlock woolly adelgid-infested western hemlock were more strongly attracted to odors from western hemlock [Tsuga heterophylla (Rafinesque) Sargent] than eastern hemlock [Tsuga canadensis (L.) Carrière] in most trials. Odors from western white pine (Pinus monticola Douglas ex D. Don) and white spruce [Picea glauca (Moench) Voss] were as attractive as western hemlock odors whereas odors from Douglas-fir [Pseudotsuga menziesii variety menziesii (Mirbel)] and ponderosa pine (Pinus ponderosa Douglas ex Lawson) were avoided. L. nigrinus reared on hemlock woolly adelgid-infested eastern hemlock in the laboratory were lethargic and were not attracted to either eastern or western hemlock odors. Predators collected in the field and tested monthly from December to March responded similarly each month, except February, when they flew rather than walked in the olfactometer, suggesting a period of dispersal or mate finding at that time of year. The implications of these results for programs to release L. nigrinus in the eastern United States for control of hemlock woolly adelgid are discussed.

High release rate 3-methylcyclohex-2-en-1-one dispensers prevent Douglas-fir beetle (Coleoptera: Curculionidae) infestation of live Douglas-fir.

Abstract The Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (Coleoptera: Curculionidae), antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), has been used by natural resource managers and landowners to protect high-value, high-risk trees from Douglas-fir beetle infestation throughout the western United States since 2000. Labor is a major portion of the cost of MCH treatments. MCH is applied by walking through treatment areas and stapling the formulated pheromone in bubble capsules to trees and other objects on a regular grid pattern. Reducing the number of MCH release points and increasing the distance between them could significantly reduce labor costs, particularly in areas with steep terrain or large volumes of woody debris that could impede the movement of applicators. This study compared the standard MCH application method with a method releasing MCH at a 3 times higher rate and placed at three times fewer release points per unit area. Treatments were applied to 2-ha plots simulating an operational application. Aggregation pheromone-baited traps were placed at plot centers to ensure that dispersing adult beetles would be present on all plots. Both MCH treatments were equally effective at preventing the infestation of live Douglas-fir, Pseudotsugae menziesii (Mirbel) Franco, trees (≥30 cm diameter at breast height). These results confirm that MCH formulated to release at three times the current standard rate and placed at 3 times fewer points per unit area can effectively prevent the infestation of live Douglas-fir. The new treatment will significantly reduce the labor cost of MCH applications making them feasible for areas that may have previously been marginal economically.

Parasitoids Reared From Predators of Hemlock Woolly Adelgid (Hemiptera: Adelgidae), and the Hymenopterous Parasitoid Community on Western Hemlock in the Pacific Northwest

Abstract In western North America, infestations of the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), are common on orchard, ornamental, and roadside western hemlock, Tsuga heterophylla (Raf.) Sargent. However, these infestations rarely cause T. heterophylla mortality. Host tolerance and presence of endemic predators may be contributing to the relatively low levels of injury to T. heterophylla caused by A. tsugae. Field surveys of the arthropod community associated with A. tsugae infestations on 116 T. heterophylla at 16 sites in Oregon and Washington were conducted every 4–6 wk from January 2005 through November 2006. Fourteen uninfested T. heterophylla were also surveyed across 5 of the 16 sites. Immature A. tsugae predators collected in the field were brought to the laboratory for rearing. Eight species of hymenopterous parasitoids were reared from pupae of predators of A. tsugae in the laboratory. Two Pachyneuron spp. (Pteromalidae) and a Melanips sp. (Figitidae) were reared from Leucopis spp. (Diptera: Chamaemyiidae) puparia. Syrphoctonus pallipes (Gravenhorst) (Ichneumonidae), Woldstedtius flavolineatus (Gravenhorst) (Ichneumonidae), Syrphophagus sp. (Encyrtidae), and Pachyneuron albutius Walker were reared from Syrphidae (Diptera) puparia. A Helorus sp. (Heloridae) was reared from a Chrysoperla sp. (Neuroptera: Chrysopidae) cocoon. Laboratory rearing did not show any direct association between parasitoids and A. tsugae. In the field survey, a total of 509 adult parasitic Hymenoptera representing 19 families and at least 57 genera were collected from T. heterophylla. Nonparametric analysis of community structure showed Pachyneuron spp. were strongly correlated to abundance of their Leucopis spp. hosts and to A. tsugae population score in the field. The possible impact of parasitism on Leucopis spp., potential A. tsugae biological control candidates for the eastern United States, is discussed.

Pathogenicity to western larch (Larix occidentalis) of two fungi, Ophiostoma pseudotsugae and Leptographium abietinum, associated with the Douglas fir beetle (Coleoptera: Scolytidae)

1 Pole‐sized, live western larch Larix occidentalis Nutt. were mass‐inoculated with Ophiostoma pseudotsugae (Romb.) von Arx or Leptographium abietinum (Peck) Wingf., two blue‐stain fungi associated with the Douglas fir beetle Dendroctonus pseudotsugae Hopkins, to assess their pathogenicity.

Predicting Dendroctonus pseudotsugae (Coleoptera: Curculionidae) Antiaggregation Pheromone Concentrations using an Instantaneous Puff Dispersion Model

ABSTRACT An instantaneous puff dispersion model was used to assess concentration fields of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), within a 1-ha circular plot. Several combinations of MCH release rate and releaser spacing were modeled to theoretically analyze optimal deployment strategies. The combinations of MCH release rate and releaser spacing used in the modeling exercise were based on results of previous field studies of treatment efficacy. Analyses of model results suggest that a release rate up to six times the initial standard, at a correspondingly wider spacing to keep the total amount of pheromone dispersed per unit area constant, may be effective at preventing Douglas-fir beetle infestation. The model outputs also provide a visual representation of pheromone dispersion patterns that can occur after deployment of release devices in the field. These results will help researchers and practitioners design more effective deployment strategies.