Dissertations / Theses on the topic 'Entomology|Forestry'

Fire is an important tool in the sustainable management of ecosystems at global and local scales. In addition to increasing biodiversity, fire has been shown to decrease exotic species invasion, promote growth of commercially and ecologically important trees, and reduce risk of wildfire. Missouri has a long history of anthropogenic and naturally induced fire aiding the establishment of oak and pine-dominated woodlands and savannas. Fire has been reintroduced through forest management in the region after a period of fire suppression to help retain oak-dominance in forests throughout Missouri. Research on the effects of fire is ample for many wildlife species and plants but virtually excludes insects including ants, especially in Missouri and most of the United States. Ants are considered ecosystem engineers for their contribution to soil turnover, aeration and chemical and structural modification and are important seed dispersers. The effects of prescribed burning on ant assemblage diversity, abundance, composition and function were examined in oak-hickory and oak-pine forests in the Missouri Ozark Highlands. Where fire was present annually for over sixty years, ant abundance, Generalized Myrmicinae, soil and litter nesters and small ants increased. Fire every four years for over sixty years resulted in higher Shannon diversity, Cryptic Species, litter nesters and small and medium ants. In addition, this treatment shared ants with both the control and annually burned plots. Control plots were dominated by Subordinate Camponotini, Cold Climate Specialists, wood nesters and medium sized ants. Ants were also assessed after just two fires over the course of ten years. Five and six years after fire ant assemblages were more affected by topographic position than by prescribed burning. Ant assemblages of burned and unburned sites were homogenous when compared using a Morisita Similiarity index. When comparing these treatments to those that have been burned for over sixty years using the Similarity index, both were more similar to the control. In summary, long term fire implementation results in more lasting changes in ant communities because habitat alteration is maintained over time. Habitat heterogeneity produces a more diverse assemblage of ants at the landscape scale and hence higher functional diversity. Finally, categorization of ant communities may simplify ant sampling so that the natural history of each species need not be known in order to assess ecological effects of ant assemblages associated with burn treatments.

Whitebark pine (Pinus albicaulis Engelm.) tree-ring chronologies of 700 to greater than 1,000 years in length were developed for four sites in the Sawtooth-Salmon River region, central Idaho. These ring-width chronologies are used to (1) assess the dendrochronological characteristics of this species, (2) detect annual mortality dates of whitebark pine attributed to a widespread mountain pine beetle (Dendroctonus ponderosae Hopk.) epidemic during the 1909 to 1940 period, and (3) establish the response of whitebark pine tree ring-width growth to climate variables. Crossdating of whitebark pine tree-ring width patterns was verified. Ring-width indices had low mean sensitivity (0.123-0.174) typical of high elevation conifers in western North America, and variable first order autocorrelation (0.206-0.551). Mortality of dominant whitebark pine caused by mountain pine beetle had a maxima at 1930 on all four sites. Response functions and correlation analyses with state divisional weather records indicate that above average radial growth is positively correlated with winter and spring precipitation and inversely correlated with April temperature. These correlations appear to be a response to seasonal snowpack. Whitebark pine is a promising species for dendroclimatic studies.

Tree-ring records were used to reconstruct the spatial and temporal patterns of western spruce budworm (Choristoneura occidentalis Freeman) outbreaks in the Rio Grande National Forest (RGNF) of southern Colorado. Reconstructions at 11 host stands showed a synchronous pattern of outbreaks with a peak in the number of trees recording outbreaks over the entire RGNF on average every 24 years. These synchronous periods of outbreaks coincided with periods of increased moisture as indicated by an independently reconstructed summer Palmer Drought Severity Index, while relatively few trees recorded outbreaks during dry periods. The reconstruction on the RGNF does not support the hypothesis that human land use has significantly altered outbreak patterns. Tree response to outbreaks in the RGNF was different from prior studies as reductions in growth were typically detectable only when growth was compared to that of nonhost tree species.

The goldspotted oak borer (GSOB), Agrilus auroguttatus Schaeffer, is an invasive wood-borer associated with tree mortality in San Diego County, California since 2008, and is believed to have been introduced via infested firewood from southeastern Arizona. From 2011-2013, I recorded GSOB emergence holes on Quercus agrifolia trees at eight locations within San Diego County. I evaluated the effectiveness of crown class and purple prism traps as tools to monitor GSOB populations. I also identified possible tree and site characteristics that could explain the variation in GSOB population densities. Crown class was useful in monitoring GSOB populations unlike purple prism traps. Larger trees (>50 cm diameter at breast height), trees located near a stand's edge, and trees previously infested had the greatest emergence hole densities. Sites closer to GSOB's putative original point of infestation and those with an intermediate Q. agrifolia density (30-50 trees per hectare) had greatest infestation levels.

Ponderosa pine delayed mortality, and bark beetle attacks and emergence were monitored on 459 trees for 3 years following one prescribed fire in Idaho and one wildland fire in Montana. Resin flow volume (ml) was measured on 145 fire-injured ponderosa pine 2 and 3 years post-fire. Logistic regression was used to construct two predictive ponderosa pine mortality models, and two predictive bark beetle-attack models. Post-fire delayed tree mortality was greater with the presence of primary bark beetles independent of diameter at breast height (DBH) (cm), and was greater in smaller diameter trees most likely due to direct effects of fire-caused injuries; mortality was lower in trees with less percent bud kill (PBK). The frequency of bark beetle attack was greater in trees with less percent bud kill and greater bole char height proportion (CHIP). Attack frequency was also greater on trees with higher percent bud kill and greater diameter at breast height. Classification tables for all predictive models were presented for application in post-fire management development. Multivariate ANOVA analyses were used to describe the effects of morphological and fire-injury variables on ponderosa pine resin production, and bark beetle attack preference and emergence. Resin production (ml) was significantly greater on burned than unburned trees. Resin flow increased significantly between June and July 1 year following fire and from June to August 2 years following fire. Resin flow was lower on the north bole aspect than the south and west aspects of unburned trees. Resin flow of burned trees significantly increased through the summer and was greatest in trees with high pre-fire live crown length (m) (LCL). Resin flow of unburned trees differed significantly by year, month, bole aspect, and live crown length. Resin increased by month and live crown length, decreased from 2005 to 2006, and was less on the northern bole aspect than all other aspects. Bark beetles preferred to attack fire-injured trees, especially within bole-scorched areas. No significant differences in bark beetle emergence were found between fire-injured and non fire-injured trees. On burned sites, beetle emergence was greatest from larger diameter trees with less severe fire injury. Western pine beetle (Dendroctonus brevicomis LeConte) had the greatest emergence from fire-injured ponderosa pine, and Ips pini (Say) had significantly greater emergence from non fire-injured ponderosa pine.

Hybrid poplars are a short rotation woody crop grown for a variety of target markets including paper pulp, saw timber, and biofuels in the Pacific Northwest. Development of pest control strategies within hybrid poplar plantations over the last several decades has focused on controlling foliar feeding herbivores and wood boring pests, and has overlooked the epigeal arthropod community. Understanding this unstudied suite of organisms would allow pest managers to better evaluate the impact their management strategies have on the poplar agroecosystem. Qualitative surveys of the arthropod communities in hybrid poplar plantations and nearby native habitats demonstrated that a greater arthropod diversity persists in the surrounding native areas. Additionally, the poplar plantation's epigeal arthropod community was composed of species found within sampled native areas.

Historically poplar research focused on protecting trees in the years following establishment through harvest from emerging pests while discounting cutting mortality by replanting areas of failure. Describing unrooted cutting transplant morality and distribution within newly established planting block could provide a risk assessment tool that growers could utilize to evaluate their potential crop loss. It was determined through the examination of damaged cuttings that several pests were responsible for diminishing establishment success. Identification of these risks led to the development of a management strategy to reduce mortality in newly planted areas. Soaking cuttings in imidacloprid for 48 hrs provided superior herbivore protection for unrooted cuttings until root formation allowed for uptake from chemigation treatments.

An additional study was motivated by the increased concern in growing `clear wood' as poplar has migrated from pulp to saw timber. The accompanying renewed interest in reducing insect galleries in mature trees led to the exploration of deploying a mass trapping, or trap out, effort to reduce populations of Prionoxystus robiniae (Lepidoptera Cossidae) in specific areas of a hybrid poplar plantation. We show that a trap out effort of roughly 5 pheromone-baited traps/ha decimated P. robiniae populations in treated areas throughout the trap out effort and three years post application.

Pandora moth (Coloradia pandora Blake) is a phytophagous insect, defoliating ponderosa pine trees in the western United States. However, long-term studies of this insect and its effects on the forest ecosystem have not been conducted. Using dendrochronological techniques, I examined past timing and intensity of defoliation through its effects on radial growth of trees in the forests of south central Oregon. Pandora moth leaves a distinctive ring-width "signature" that was easily identifiable in the wood. The growth for the first year of the signature was half the normal ring-width with narrow latewood. The following two years produced extremely narrow rings, with the entire suppression lasting from 4 to 18 years. Twenty-two individual outbreaks were reconstructed from this 620 year chronology. I found that pandora moth outbreaks were episodic on individual sites, with a return interval of 9 to 156 years. Conversely, on the regional scale of south central Oregon, outbreaks demonstrated a 37-year periodicity. On average, pandora moth defoliation caused a 29% mean periodic growth reduction in defoliated ponderosa pine trees. Spread maps of the first year that sites demonstrated suppression were plotted revealing an apparent annual spread of the outbreaks. Examination of a fire history on one pandora moth outbreak site suggested that pandora moth outbreaks delay fire by interrupting the needle fall needed for fire spread. Superposed epoch analysis showed that the year that the outbreak was first recorded was significantly dry and the fourth year prior was significantly wet. Therefore, climate may be a triggering factor in pandora moth outbreaks. The stem analysis demonstrated that the percent volume reduction was greatest at the base of the tree and declined further up the bole. The percent volume reduction in the canopy of the trees was variable with outlying high and low values. The mean volume reduction per outbreak was .053 m³ per tree. Although this insect is considered a forest pest and causes inconvenience for people living nearby, pandora moth is not as widespread and damaging as some other phytophagous insects. However, its very distinctive ring-width signature and the length of the ponderosa pine record enables reconstruction of very long outbreak histories, which may deepen our understanding of the interaction between defoliating insects and their ecosystem.

The western corn rootworm, or WCR, (Diabrotica virgifera virgifera LeConte) is the most significant pest of field corn (Zea mays) in the United States, and has recently expanded its range into Europe. Since 2004, hybrid corn containing Bt toxins targeting the corn rootworm complex have been heavily adopted and are now the primary control measure for this pest in North American corn production.

The evolution of resistance is an ongoing concern, and to ensure Bt products will retain their usefulness, insect resistance management (IRM) tactics using various refuge structures have been adopted. One of the key tenets of the refuge strategy is that males and females emerging from Bt and refuge plantings mate randomly. A violation of this largely untested assumption would lead to acceleration of resistance development.

To generate empirical field data on mating rates between beetles emerging from Bt and refuge plants, field cage studies using field populations of WCR in Indiana were utilized. Various refuge configurations were tested; all refuge plants were labeled using the stable isotope N15. This mark persists in the adult beetles after eclosion, allowing for collection and analysis of isotopic ratios of beetles in mating pairs. This approach was used to test the random mating assumption in Bt and refuge beetles collected from field cages. Other data collected include emergence rates, timing and sex ratios for each of the treatments.

Results indicate that mating based on natal host may not be as important of a factor as initially thought. Mixed mating occurs at a high rate when there are higher numbers of susceptible rootworms even though the measured fitness parameters between Cry3Bb1 and refuge adults were significantly different (p< 0.05). The main indication from this study is that not enough susceptible individuals are produced from a 5% refuge-in-a-bag strategy which is the dominant form of refuge planting in the United States.

High-dose verbenone, verbenone plus nonhost volatiles (NHVs), and both semiochemicals in combination with aggregant-baited funnel traps were tested for stand- level protection against mountain pine beetle attack for two consecutive years (2004-2005) at three seral high elevation whitebark pine sites in the Greater Yellowstone Ecosystem. In 2004, two 0.25-hectare treatments comprised of 25 high-dose verbenone pouches or verbenone pouches combined with single baited funnel traps were tested in a push-pull strategy. In 2005, 25 high-dose verbenone and 25 NHV pouches, or verbenone and NHV in combination with baited funnel trap clusters were tested. In both years, treatments were compared to 0.25-hectare control plots with no semiochemicals or funnel traps. The proportion of trees attacked by mountain pine beetle in treated plots was significantly reduced, when compared to control plots, at only one site treated with verbenone in 2004, and at only one site in 2005. High-dose verbenone alone, verbenone and NHVs, and both semiochemicals combined with baited funnel traps in a push-pull strategy did not consistently reduce the proportion of mountain pine beetle attacked trees relative to control plots. No covariates tested, including stand density, beetle population size, or tree size were consistently significant in explaining proportion of trees attacked.

Thesis (MSc)--University of Stellenbosch, 2011.
ENGLISH ABSTRACT: The current biodiversity crisis requires creative initiatives for mitigating further biodiversity loss. The use of ecological networks (ENs) is such an initiative. The South African forestry industry recognizes that there is loss of biodiversity at the smaller patch scale, while attempting to mitigate this loss at the landscape scale by implementing largescale ENs. The aim of this study was to determine how representative grassland biodiversity in ENs are of similar habitat in a nature reserves (NR). The study was conducted in the northeast of the KwaZulu-Natal Province, adjacent iSimangaliso Wetland Park, which is a natural World Heritage site. A systematic approach compared a wide range of taxa, namely plants, decomposition macrofungi, vertebrates (birds and large mammals) and faunal manifestations (e.g. molehills, dung and ant nests) between the EN and nature reserve, while controlling for differences in disturbance regime. Species richness was compared using Mann-Whitney U tests, while differences in species composition were determined using Correspondence Analyses, Multi-Dimensional Scaling and Analyses of Similarity. Grassland ENs had significantly less plant species. In addition, there were differences in plant and fungi species composition. Differences were probably caused by (1) degree of isolation i.e. proximity to source habitat patches in the surrounding matrix, and (2) habitat quality. Habitat quality was determined by local disturbance regimes (e.g. grazing and fire) and plantation-induced drought for plants, and size and amount of coarse woody debris for fungi. In addition, significant differences in abundances of mole hills (NR>EN) and small mammal burrows (EN>NR) might have had an effect on succession and regeneration of plant communities. There were differences in plant species composition between grassland EN and that at the adjacent nature reserve. However, differences between EN and NR were small when compared to differences between habitat types at the landscape spatial scale. It is concluded that grassland ENs among forestry plantations contribute to biodiversity conservation in the commercially-productive landscape. This approach to land use planning should be explored for other commercial land uses.
AFRIKAANSE OPSOMMING: Die huidige biodiversiteitskrisis vereis kreatiewe strategieë om ‘n verdere verlies in biodiversiteit te bekamp. Ekologiese Netwerke (EN’e) is een voorbeeld van sulke kreatiewe strategieë. Die Suid Afrikaanse bosbou-industrie erken die verlies in biodiversiteit wat kenmerkend in plantasies gevind word. Implementering van grootskaalse EN’e kan egter die verlies aan biodiversiteit, wat in plantasies ondervind word, temper. Die doel van hierdie studie was om vas te stel hoe goed biodiversiteit in grasveld EN’e soortgelyke habitat in ‘n nabygeleë natuurreservaat verteenwoordig. Die studie was uitgevoer in die noordooste van KwaZulu-Natal, langs iSimangaliso Wetland Park wat ‘n wêrelderfenisgebied is. Ons het ‘n stelselmatige benadering gevolg waartydens ‘n wye verskeidenheid taksa, naamlik plante, makro-fungi, vertebrate (groot soogdiere en voëls) en tekens van diere-aktiwiteit (bv. miersneste, dieremis en molshope), in die EN vergelyk is met die van ‘n natuurreservaat terwyl ons vir verskillende versteuringe gekontrolleer het. Spesiesrykheid is vergelyk met Mann-Whitney U toetse terwyl verskille in spesiessamestelling vasgestel is met Correspondence Analyses, Multi-Dimensional Scaling en Analyses of Similarity. Daar was ‘n statisties beduidende verskil in die hoeveelheid spesies tussen grasveld EN’e en die natuurreservaat. Grasveld EN’e het minder plant spesies gehad. Boonop was daar verskille in die samestelling van plant en fungi gemeenskappe. Verskille was waarskynlik veroorsaak deur (1) isolasie of die hoeveelheid nabygeleë habitatbronne in die omliggende omgewing, en (2) habitat kwaliteit. Habitat kwaliteit word bepaal deur versteuringe (bv. brand en beweiding) en die uitdrogingseffek van plantasies vir plante, en die hoeveelheid en grootte van growwe houtagtige puin vir fungi. Daar was ook beduidende verskille in die hoeveelheid molshope (NR>EN) en klein soogdier gate (EN>NR), wat moontlik ‘n effek kon hê op suksessie en herstel van plantgemeenskappe. Daar was verskille in plantspesiessamestelling tussen grasveld EN’e en die van die langsliggende natuurreservaat. Hierdie verskille was egter klein wanneer dit vergelyk word met die verskille tussen verskillende soorte habitatte in die landskap. Daarom kom ons tot die gevolgtrekking dat grasveld EN’e tussen bosbouplantasies bydra tot die bewaring van biodiversiteit in kommersiële landskappe. Hierdie benadering tot grondgebruik behoort verder verken te word vir ander kommersiële bosbou en boerderypraktyke.

An established host-parasitoid-hyperparasitoid system was used to investigate how the physiological and behavioural characteristics of parasitoids influence the outcomes of laboratory-based host specificity tests. The characteristics of the two pteromalid egg parasitoids, Enoggera nassaui (Girault) and Neopolycystus insectifurax Girault, were assessed and interpreted in regard to the particular host specificity testing methods used and the control of the eucalypt defoliating beetle Paropsis charybdis Stål (Chrysomelidae) in New Zealand. The physiology of N. insectifurax was examined to determine how to increase production of female parasitoids that were physiologically capable and motivated to parasitise P. charybdis eggs in laboratory trials. Neopolycystus insectifurax were found to be more synovigenic than E. nassaui. Provisioning them with honey and host stimuli for three days, and allowing females to parasitise hosts in isolation (i.e. in the absence of competition) was an effective means of achieving these goals. No-choice tests were conducted in Petri dish arenas with the four paropsine beetles established in New Zealand. All four were found to be within the physiological host ranges of E. nassaui and N. insectifurax, but their quality as hosts, as indicated by the percent parasitised and offspring sex ratios, varied. The results of paired choice tests between three of the four species agreed with those of no-choice tests in most instances. However, the host Trachymela catenata (Chapuis), which was parasitised at very low levels by E. nassaui in no-choice tests, was not accepted by that species in paired choice tests. A much stronger preference by N. insectifurax for P. charybdis over T. catenata was recorded in the paired choice test than expected considering the latter was parasitised at a high level in the no-choice test. The presence of the target host in paired choice tests reduced acceptance of lower ranked hosts. Both no-choice and choice tests failed to predict that eggs of the acacia feeding beetle Dicranosterna semipunctata (Chapuis) would not be within the ecological host range of E. nassaui and N. insectifurax. Behavioural observations were made of interspecific competition between E. nassaui and N. insectifurax for access to P. charybdis eggs. Two very different oviposition strategies were identified. Neopolycystus insectifurax were characterised by taking possession of, and aggressively guarding host eggs during and after oviposition. They also appeared to selectively oviposit into host eggs already parasitised by E. nassaui, but did not emerge from significantly more multi-parasitised hosts than E. nassaui. Enoggera nassaui did not engage in contests and fled when approached by N. insectifurax. Although often prohibited from ovipositing by N. insectifurax, E. nassaui were able to locate and begin ovipositing more quickly, and did not remain to guard eggs after oviposition. It is hypothesised that although N. insectifurax have a competitive advantage in a Petri dish arena, E. nassaui may be able to locate and parasitise more host eggs in the field in New Zealand, where competition for hosts in is relatively low. The biology of the newly established encyrtid Baeoanusia albifunicle Girault was assessed. It was confirmed to be a direct obligate hyperparasitoid able to exploit E. nassaui but not N. insectifurax. Field and database surveys found that all three parasitoids have become established in many climatically different parts of New Zealand. Physiological characteristics were identified that may allow B. albifunicle to reduced effective parasitism of P. charybdis by E. nassaui to below 10%. However, the fact that hyperparasitism still prevents P. charybdis larvae from emerging, and that B. albifunicle does not attack N. insectifurax, may preclude any significant impact on the biological control of P. charybdis. Overall, parasitoid ovigeny and behavioural interactions with other parasitoids were recognised as key characteristics having the potential to influence host acceptance in the laboratory and the successful biological control of P. charybdis in the field. It is recommended that such characteristics be considered in the design and implementation of host specificity tests and might best be assessed by conducting behavioural observations during parasitoid colony maintenance and the earliest stages of host specificity testing.

The ambermarked birch leafminer (AMBLM) (Profenusa thomsoni) is an invasive leafminer native to the Palearctic from the United Kingdom to Turkey to Japan. It was introduced to the eastern United States in 1921 and has since spread to the mid-western U.S. states and Canadian provinces. This leafminer was introduced to Alaska in 1996, where it has since spread over 140,000 acres, from Haines to Fairbanks. The most severe damage is found throughout the Anchorage bowl, which extends south to Girdwood and North to Wasilla. The damage caused by P. thomsoni can be severe, defoliating entire trees. In 2006, it was noted that urban areas in Alaska experienced higher densities of AMBLM leafminer than adjacent forested areas. To examine the effects of habitat on leafminer densities, twenty permanent plots were established in Anchorage, Alaska in 2006 and were classified as urban and forest (ten each). Temperature records for the twenty permanent sites showed that average daily temperatures and average accumulated degree-days differed significantly between urban and forest sites. In 2007 and 2008, leafminer abundance in each habitat was examined weekly at six plots (three urban and three forest) within the city of Anchorage. Asynchronous emergence, flight, and oviposition times were observed between leafminers in forests versus urban areas, with peaks of these parameters in forests being about three weeks later than in urban areas. To control the spread and effects of P. thomsoni, a cooperative biological control project was launched in 2003 and the parasitoid wasp Lathrolestes thomsoni (Hymenoptera: Tenthredinidae) was selected for release. Parasitized leafminer larvae were collected from the provinces of Northwest Territories and Alberta, in Canada and transferred in soil tubs as pre-pupae to Alaska. From 2004-2008, 3636 adult L. thomsoni adults were released in birch tree stands in Anchorage, Soldotna, and Fairbanks, Alaska. Parasitoids have been recovered at all release sites in Alaska and have established populations at most release sites. Currently, AMBLM densities have declined by over 40% in the Anchorage area and the spread of the leafminer throughout the state appears to have slowed. Throughout the course of the biological control program two additional parasitoids were discovered attacking P. thomsoni in Alaska. The first, Lathrolestes soperi, an endoparasitoid with similar biology to the released parasitoid L. thomsoni, was found to attack early instar larvae within the leaf. The second species, Aptesis segnis, is an ecotoparasitoid that attacks pupae and prepupae in their earthen cells in soil. Lathrolestes soperi was found to contribute a significant proportion of mortality against the leafminer. The presence of A. segnis in the parasitoid guild raised mortality of P. thomsoni to 40.3%, showing that the percent parasitism by A. segnis was 26%, double that provided by L. soperi. This suggests that A. segnis is the dominant parasitoid in the guild. It is unknown what effect that the introduced wasp L. thomsoni will have on the presumably native L. soperi and if one species will outcompete the other over time, or both will coexist. Future work on this system is recommended in five to ten years to see if L. thomsoni and L. soperi populations remain stable or to see if one parasitoid outcompetes the other and if A. segnis maintains its dominant place in the system.

North American gypsy moth disperse as larvae on the wind in a behavior called ballooning prior to feeding for the first time. Resources used in dispersal are therefore limited to those carried over from the egg. I measured levels of two yolk storage proteins, vitellin (Vt) and glycine-rich protein (GRP), using quantitative immunoelectrophoresis, I determined the tendency of larvae to balloon in a wind tunnel. I estimated the length of the window for dispersal from the longevity of unfed neonates. Pre-hatch levels of Vt and GRP had no influence on the tendency of neonates to balloon. Levels of these proteins were positively associated with and accounted for 40-50% of the variation in longevity of neonates from the first-laid and center thirds of egg masses. Longevity was greatest for neonates from the first-laid third which also had the highest pre-hatch levels of Vt and GRP. Nutritionally stressed females compensated to maintain levels of Vt and GRP by reducing the number of eggs produced. This compensation was reflected in similar longevities of offspring of stressed and unstressed females. The tendency of larvae to balloon, however, was greater in offspring of unstressed females. It is possible that traits selected for in nutritionally stressed females may be expressed in offspring as a reduced tendency to disperse. Temperature during the six weeks prior to eclosion had a significant effect on pre-hatch levels of Vt and GRP and on neonate longevity. Eggs held at 7$\sp\circ$C or less had similar pre-hatch levels of both proteins. Eggs held at 10$\sp\circ$C for six weeks, however, were depleted of Vt and GRP suggesting a threshold between 7 and 10$\sp\circ$C for stimulation of protein utilization. Eggs held for alternating weeks at 4 and 10$\sp\circ$C had protein levels similar to eggs held at 4$\sp\circ$C indicating eggs must be exposed to temperatures above the threshold for a period greater than a week before utilization of proteins is increased.

Lymantria mathura Moore is a polyphagous defoliator of hardwood trees in the Russian Far East, Japan, India, and China. Its egg masses were intercepted on ships arriving to Pacific Northwest. If introduced and established in North America, L. mathura is likely to cause serious economic consequences. As a part of a program for development of monitoring and control measures, possible host range, larval air-borne dispersal, mating behavior, and pheromone communication of L. mathura were studied. Survival and development of first instars of L. mathura were examined on 24 hardwood and conifer tree species from North America, Europe, and Asia. Lymantria mathura performed well on hosts in the family Fagaceae. Survival and growth rate was high in the genus Fagus (beech) and Quercus (oak), particularly white oak group. Performance was intermediate on species of red oak group and species from Juglandaceae, Betulaceae, and Oleaceae. Survival was poor on Pinaceae. Dispersal rates, settling velocities, and diel periodicity of dispersal for both L. mathura and Asian L. dispar were studied to predict probable extent of neonate dispersal. Dispersal rates for L. mathura exceeded those of Asian and North American gypsy moths. Neonates of L. mathura weighed less and had slower settling velocities than Asian or North American gypsy moths. Pheromone-baited traps would be important for detecting introductions of L. mathura, but a sex pheromone has not yet been identified. I studied the olfactory reaction of males to females and to odor compounds in the wind tunnel. Number of males performing searching flight in a pheromone plume was lower than moths performing non-pheromone mediated flight. There was no difference in male performance when stimulated with preparations of female abdominal tip extracts or synthetic compounds derived from females. Studies of courtship showed that females initiated calling shortly after start of scotophase, and courtship occurred several hours later. Mating occurred after a calling female starts wing fanning, initiating a fanning response and flight in a nearby male. A receptive female lifts the wings and allows a male underneath. During behavioral studies, low frequency atonal sound associated with wing fanning was recorded in both sexes of L. mathura, and several other lymantriids tested for comparison. There were differences in wing beat frequencies between sexes and species.

The tachinid fly Compsilura concinnata (Meigen) was introduced to North America in 1906 for the biocontrol of the forest defoliators Lymantria dispar (L.) and Euproctis chrysorrhea (L.) when these caterpillars were defoliating large areas of eastern Massachusetts. Most of the flies released, however, were the progeny of adults emerging from E. chrysorrhea caterpiliars collected in Eastern Europe. Although this tachinid is a generalist parasitoid, in Europe it is considered an important specialist of pestiferous species based on the level of its recovery there. Also, as one of the first insects established against forest defoliators in the Northeast, C. concinnata is in a premier position of providing information about colonization that increases the understanding in population genetics of how founder effects and dispersal influence the establishment of exotic insect populations. Initially in this study, a historical analysis was conducted to prepare a chronology of release of C. concinnata into North America and delimit its distribution. The introduction and release of C. concinnata was relatively restricted as they were primarily reared from one host E. chrysorrhea collected in Eastern Europe. More importantly, the extent to which this fly moved ahead of successive releases suggested there may be a historical basis to expect little differentiation among their nearctic populations. The literature on population genetics and use of electrophoretic analyses were surveyed to establish their use with C. concinnata in North America. Enzyme electrophoresis has been widely used for delimiting populations of non-native parasitoids and tracking their movement into new hosts and localities. To determine the suitability of enzyme electrophoresis for a population genetic analysis of C. concinnata, selected isozymes were identified and cataloged in an established laboratory strain. The analysis of isoenzyme patterns for measuring the relatedness among and between individuals, is useful in molecular studies of population genetics provided these patterns are heritable. To determine the heritablility of isozymes in C. concinnata, an electrophoretic analysis was conducted using both the parents and adult progeny of observed matings. The genetics of some C. concinnata isoenzymes followed simple patterns of Mendlian inheritance and were allozymic. The population genetic structure of C. concinnata in North America was examined with trap-hosts placed throughout the Northeast. The flies reared out were sampled with protein electrophoresis. There were slight differences in the allozymes and allele frequencies of C. concinnata and in comparison with other Diptera, the variation among Northeastern populations was relatively low. The variability among Northeastern populations of this parasitoid reflect limited genotypes in the founding populations. Over time new differences in protein loci between geographically separated populations probably arise through selection or drift than through non-lethal mutations. The time needed for protein coding loci between distantly spaced populations of introduced insects to diverge sufficiently for them to be detectable has not been determined. Estimating the time needed for allozymes of introduced insects to reject such differentiation is useful in understanding the evolution of biotypes, but is not a trivial process. Historical research in combination with analyses of the variability in allele frequencies among populations can be useful in determining the extent of divergence in non-native species that may lead toward new biologically adapted forms.

We used the nuclear polyhedrosis virus (LdNPV) of the gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae), to test a basic assumption of most models of disease dynamics; that the rate of horizontal transmission is directly proportional to the product of the densities of healthy larvae and virus. We made measurements of virus transmission, using small-scale experiments in bags on red oak (Quercus rubra) and black oak (Q. velutina) and observed a decline in the transmission constant as the densities of both healthy larvae and pathogen increased. We hypothesized two possibilities for the non-linearity observed in this system: (1) pathogen inhibition via the effects of induced foliage chemistry and (2) the effect of spatial heterogeneity of LdNPV (pathogen clumping effects). Previous work has linked larval damage on oak foliage to subsequently higher levels of tannins in damaged leaves; and laboratory bioassays have linked higher levels of tannins to a decrease in mortality caused by LdNPV. We damaged LdNPV-contaminated oak foliage using larvae, then bioassayed foliage with test larvae and measured tannins in damaged leaves. None of the experiments showed significant effects of foliage damage on mortality of test larvae or tannin content of damaged leaves, and we concluded that induced foliage responses cannot explain non-linearity of transmission in our previous work, or transmission dynamics in the field. To evaluate the role of pathogen clumping in transmission dynamics, we redefined parameters of the host-parasitoid model of Nicholson and Bailey (1935) for use in the gypsy moth-LdNPV system: a relationship between the assumptions of this model and the continuous time Anderson-May model was described. Using a version of this discrete-time model incorporating spatial heterogeneity, we observed transmission dynamics similar to those in field experiments. To evaluate safety issues in use of genetically altered baculoviruses as insecticides, we field-tested LdNPV that had been genetically-engineered for non- persistence. The EV was released in a forest setting, and did not persist or spread past the first year of release. Concerns regarding movement of baculoviruses were also addressed in experiments exploring the action of rainfall on the translocation of LdNPV.

Clearcut harvesting can create conditions unfavourable to forest regeneration. In response, variable retention harvest methods are being investigated in montane forests on Vancouver Island, Canada. The effect of this overstory removal is unknown for canopy microarthropods, especially oribatid mites. As mites contribute significantly to nutrient cycling and decomposition processes in the canopy, changes in community structure and abundance may have dramatic effects on forest productivity. I studied the effects of two variable retention treatments, patch-cut and shelterwood systems, on arthropod communities associated with Abies amabilis (amabilis fir) branches and lichens. Changes in community structure were evident among the treatments and an old-growth control site. I also investigated the use of lichen abundance as a surrogate for oribatid mite abundance because it is time consuming and laborious to collect, count and identify microarthropods. Lichen abundance was a good predictor of mites in the old-growth and shelterwood, but not in the patch-cuts. Lichen abundance estimates should not replace biotic inventories, but can he used as an indicator when rapid biodiversity assessments are required.

Ce projet de recherche évalue la réponse à court terme de coléoptères phloeophages et xylophages (Cerambycidae et Scolytinae) à différentes intensités de coupes partielles (0, 25 et 40% de la surface terrière prélevée) afin de déterminer la viabilité de cette méthode sylvicole en forêt boréale. Disposant de 12 parcelles expérimentales (4 répétitions pour chaque intensité de coupe) dans une sapinière à bouleau blanc située au sud de la forêt boréale (Québec, Canada), nous avons évalué l’abondance, la diversité ainsi que l’établissement (taux d’attaque) de ces deux groupes d’insectes, et ce dès la première année suivant la coupe. L’échantillonnage a été réalisé à l’aide de pièges à interception multidirectionnelle et de l’écorçage de sections de 3 espèces d’arbres exposées dans l’ensemble des parcelles. Nos résultats montrent une plus grande activité/abondance des deux taxons (abondance 5 à 6 fois plus élevée) ainsi qu’une composition en espèces différente et plus diversifiée dans les peuplements partiellement coupés (25 et 40%). De plus, la présence et la distribution d’espèces colonisant habituellement des hôtes affaiblis (e.g., Trypodendron lineatum, Rhagium inquisitor) – et pouvant donc réduire la valeur économique d’arbres résiduels – a été recensée et semble être favorisée entres autres par l’ouverture de la canopée et des blessures physiques faites aux arbres pendant les opérations sylvicoles. Par ailleurs, l’approche combinant différentes techniques d’échantillonnage a permis une meilleure compréhension des mécanismes de localisation/sélection d’hôte (variant en fonction de l’espèce), un aspect important de la dynamique des insectes pour l’évaluation des risques suite aux coupes forestières. Sur la base de cette étude à court terme, il ne semblerait pas y avoir de différence significative sur les risques pour le milieu quant à l’augmentation d’activité des Cerambycidae et Scolytinae entre les deux traitements de coupe appliqués. Il reste cependant indispensable de vérifier la validité de ces résultats sur une plus longue période afin d’établir des plans d’aménagement forestier durables pour la forêt boréale.
To evaluate the viability of partial cuts, short-term responses of phloeophagous and xylophagous beetles (Cerambycidae and Scolytinae) following different partial cut treatments (0, 25 and 40% of basal area cut) were determined in a balsam fir–white birch boreal forest in Quebec, Canada. Each treatment was replicated 4 times totaling 12 experimental stands. The summer following treatments, abundance and diversity of targeted beetle groups along with their establishment (attack rates) in partially cut stands were assessed with passive flight- interception traps and bark dissection of exposed, freshly cut boles from three tree species. Greater activity/abundance from both taxa were detected (abundance 5 to 6 times larger) along with a different and more diversified species composition in partially cut stands (25 and 40%). The presence and distribution of species that usually colonize weakened host trees (e.g., Trypodendron lineatum, Rhagium inquisitor) – and can thus reduce stands economic value for future harvest operations – were influenced by canopy openness and injuries on residual trees made during silvicultural operations. Furthermore, combining diverse sampling techniques allowed us to observe different host-selection patterns (random landing vs. primary attraction) given our multi-scale experimental approach, which we found to vary between insect species. Understanding these mechanisms for such beetle groups are important to evaluate stand vulnerability following partial cuts and predict impacts and risks in a given environment. While the 40% partial cuts remove additional wood volume, we found no significant increase in beetle activity between the 25 and 40% treatment. Though partial cuts render treated stands more vulnerable to greater Cerambycidae and Scolytinae attacks, further studies must be done to confirm this trend in longer term if proper boreal forest management plans are to be drawn.