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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]

We investigated the effect of water potential (WP) on the growth of, and interaction between, two ophiostomatoid fungi, Grosmannia clavigera and Ophiostoma montium, associated with the mountain pine beetle (Dendroctonus ponderosae). The WP of malt extract agar was amended by adding potassium chloride (KCl) or sucrose. Growth of both fungi decreased with WP on KCl-amended media. Growth of G. clavigera also decreased with WP on sucrose-amended media, although growth was stimulated on these media compared to unamended treatments. Growth of O. montium remained relatively constant on sucrose-amended media, confounding the effect of WP on this species. Both fungi were able to colonize media occupied by the other species, but at a slower rate than on unoccupied media, indicating competition. In most treatments, G. clavigera grew faster than O. montium and colonized a greater area when the two fungi were inoculated concurrently but distant to one another on a Petri dish. However, when each fungus was inoculated adjacent to a 10-d-old well-established colony of the other species, O. montium colonized occupied media more effectively than G. clavigera considering the growth rate of each species alone. Thus, G. clavigera dominated primary (uncolonized) resources on most media, whereas O. montium was more effective in colonizing secondary (occupied) resources. The differential response of the two fungi to sucrose indicates that they may use different carbon sources, or use different carbon sources at different rates, in the tree. Fine-scale resource partitioning, differences in primary and secondary resource capture abilities, and the non-equilibrium dynamics in an attacked tree over time, could all act to promote the co-existence of two unit-restricted dispersers on a discontinuous resource.