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Insects respond to environmental conditions with a variety of developmental responses which include changing developmental rates, or suppressing development altogether in quiescence or diapause. Such responses have important implications for survival and voltinism. The spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), has long been assumed to have an obligatory adult diapause based on field observations that adults always overwinter prior to dispersing and reproducing; however, it has never been experimentally demonstrated and recent evidence suggests that adults in some populations may exhibit facultative tendencies. We examined the emergence of adults at a constant 22°C after exposure to 2°C for 0 (no cold), 25, 50, and 75 d. Our observations of a delayed and extremely protracted emergence period in the absence of a substantive cold period, which could last several months, in combination with rapid, synchronous mass emergence after a substantive cold period, are most consistent with an obligate diapause. Approximately 50% of individuals could complete diapause in 55 d at 2°C, and 75 d of cold was adequate for almost all individuals to complete diapause. Beetles that emerged slowly over time may still have been in diapause; however, additional research would be required to test this hypothesis. Conditions throughout the beetle's range in Canada should facilitate successful completion of diapause. An obligate adult diapause for spruce beetle populations in western Canada would limit the shortest possible life cycle to 1 yr, but would also serve to maintain an adaptive 1-yr life cycle, especially under a changing climate. [ABSTRACT FROM AUTHOR]

Determining the cold tolerance of mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is critical for assessing its long-term persistence and eruptive potential in its new habitat, as well as the risk of continued range expansion across Canada's boreal forest. We used supercooling points (SCPs) and mortality assessments with exposure to different temperatures to determine the cold tolerance of pupae. Mountain pine beetle pupae cold tolerance did not increase with chilling and there was little change in the lethal temperature regardless of treatment or sample time. SCPs were reflective of expected mortality due to freezing: the lethal temperature for 50% mortality was –19.3°C and the mean SCP was –18.7°C. However, significant mortality occurred over time at much warmer temperatures (0 and –9°C), indicating that this life stage suffers significant prefreeze mortality. On the basis of our results, it is unlikely that pupae would be able to successfully overwinter in most regions in Canada. This study is part of a larger project aimed at producing a comprehensive assessment of the cold tolerance of all life stages of the mountain pine beetle to feed population models, climatic suitability indices, and spread assessments. [ABSTRACT FROM AUTHOR]

Dendroctonus rufipennis (Kirby, Coleoptera: Curculionidae) uses pheromone blends containing aggregative components (frontalin, verbenene, 1-methyl-2-cyclohexen-1-ol [MCOL], and seudenol) and an anti-aggregative component (3-methyl-2-cyclohexen-1-one [MCH]) to coordinate attacks against host trees, but little is known about the influence of external stimuli on pheromone production. We conducted feeding experiments followed by pheromone extractions to determine if feeding duration and mate presence affected pheromone production in D. rufipennis. Unfed beetles of both sexes produced very little of any pheromone component. Females fed for 48 h produced significantly more MCH and MCOL compared to those which fed for 24 h. Males fed for 48 h produced significantly less seudenol than those which fed for 24 h. Male presence did not significantly affect female pheromone production. We propose that the pheromone blend produced by beetles transitions from aggregative to anti-aggregative shortly after colonizing a host, regardless of mate presence. [ABSTRACT FROM AUTHOR]

Winter mortality is expected to be a key factor determining the ability of mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), to expand its range in Canada. We determined the mortality rate and supercooling points of eggs from the beetle's historic range in southern British Columbia as well as the recently expanded range in north-central Alberta and tested if eggs require an extended period of chilling to reach their maximum cold tolerance. We found no effect of population source or acclimation time on egg cold tolerance. Although 50% of eggs can survive brief exposure to°20.5° C (LT50), storage at 0.3 °C and -7.5 °C for 59 d resulted in 50% and 100% mortality, respectively. Our results indicate that eggs suffer significant prefreeze mortality and are not well-adapted to overwintering: eggs are unlikely to survive winter throughout much of the beetle's range. Our results provide information that can be used to help model the climatic suitability of mountain pine beetle, including how changes in seasonality associated with new or changing climates may affect winter survival. In addition to lower lethal temperatures, it is critical that the duration of exposure to sublethal cold temperatures are considered in a comprehensive index of cold tolerance and incorporated into survival and population models. [ABSTRACT FROM AUTHOR]

The ability to predict key phenological events, such as the timing of flight periods, is useful for the monitoring and management of insect pests. We used empirical data to describe the flight period of mountain pine beetle, Dendroctonus ponderosae Hopkins, in its recently expanded range east of the Rocky Mountains in Canada and developed a degree-day model based on the number of trapped beetles. Data were collected over four degrees of latitude and six years. The main flight period, when the middle 70% of the total number of beetles were caught, started during the second or third week of July, lasted 26 d, and peaked within 2 wk of starting. The best model accounted for 89% of the variation in the data. Mountain pine beetle's flight tended to start later and be more contracted at higher latitudes. The synchrony of mountain pine beetle's flight period in the expanded range appears to be comparable to the limited reports from the historic range, although it may start earlier. This suggests that conditions in the new range are suitable for a coordinated dispersal flight, which is critical for the beetle's strategy of overwhelming tree defenses by attacking en masse. Forest managers can use the model to support operational decisions, e.g., when to impose hauling restrictions to reduce the risk of spread through the transport of infested material, or the time frame for control programs. Understanding the flight period may also improve our ability to assess the response of mountain pine beetle to novel and changing climates in the future. [ABSTRACT FROM AUTHOR]

We used the mountain pine beetle (Dendroctonus ponderosae Hopkins) and its two fungal associates, Grosmannia clavigera and Ophiostoma montiwn, to study potential nutritional benefits of fungi to bark beetles. We tested for potential effects of feeding on phloem colonized by fungi on beetle performance in field and laboratory studies. The fungi increased nitrogen levels in the phloem of attacked trees by 40%, indicating that it may be an important source of dietary nitrogen for mountain pine beetles. However, nitrogen levels of phloem inoculated with fungi in the laboratory were similar to uncolonized phloem, indicating that the fungi may redistribute nitrogen from the sapwood to the phloem rather than increase absolute levels of nitrogen. Beetles emerging from attacked trees carrying G. clavigera were larger than beetles carrying O. montiuns, which in turn were larger than beetles lacking fungi. Results of experimental laboratory studies varied, likely because of differences in the growth and sporulation of fungi under artificial conditions. Results indicate that the two fungi may offer complementary benefits to the mountain pine beetle because larvae preferentially fed on phloem colonized by both fungi together over phloem colonized by one fungus or uncolonized phloem. Teneral adults preemergence fed on spores in pupal chambers when they were produced and consumed little phloem before emerging. Teneral adults mined extensively in the phloem before emerging when spores were not produced in the pupal chamber. Our results provide evidence for a nutritional role of fungi in the diet of bark beetles and show that multiple associates may differentially affect beetle performance, which could have important implications for bark beetle population dynamics. [ABSTRACT FROM AUTHOR]

Summary: We tested the resistance and tolerance of 79 Douglas‐fir halfsibling seedling families to artificial inoculation with Ophiostoma pseudotsugae in a shade house experiment. The Douglas‐fir beetle vectors the fungus where it colonizes the phloem and sapwood, often leading to tree mortality. The 79 halfsibling seedling families originated from four seed planning zones in BC that span ecological gradients ranging from moist‐warm to cool‐wet. We tested resistance to the fungus by measuring lesion size and tolerance by measuring seedling height. We found variation in both resistance and tolerance within seed zones and halfsibling hierarchies. Trees from zones and families that were shortest before inoculation appeared to have the most tolerance after inoculation suggesting a cost for carrying tolerance traits. There was a cost in height growth for resistance after inoculation versus wounding alone. There was no trade‐off between family resistance and tolerance defence strategies indicating that both developed independently in the population. Higher resistance and lower tolerance to the fungus were the least commonly occurring trait combination in families. Douglas‐fir trees are moderately shade intolerant at the sapling stage, and as height increment is crucial for light capture, they probably avoid costly strategies such as resistance alone. This defence strategy may change in older stands. [ABSTRACT FROM AUTHOR]