Developmental Parameters of a Southern Mountain Pine Beetle (Coleoptera: Curculionidae) Population Reveal Potential Source of Latitudinal Differences in Generation Time

Mountain pine beetle (Dendroctonus ponderosae, Hopkins) is a major disturbance agent in pine ecosystems of western North America. Adaptation to local climates has resulted in primarily univoltine generation time across a thermally diverse latitudinal gradient. We hypothesized that voltinism patterns have been shaped by selection for slower developmental rates in southern populations inhabiting warmer climates. To investigate traits responsible for latitudinal differences we measured lifestage-specific development of southern mountain pine beetle eggs, larvae and pupae across a range of temperatures. Developmental rate curves were fit using maximum posterior likelihood estimation with a Bayesian prior to improve fit stability. When compared to previously published data for a northern population (Régnière et al. 2012), optimal development of southern individuals occurred at higher temperatures, with higher development thresholds, as compared with northern individuals. Observed developmental rates of the southern and northern populations were similar across studied lifestages at 20 °C, and southern lifestages were generally faster at temperature extremes (10, 27 °C). At 25 °C southern fourth instars were significantly slower than northern fourth instars. Our results suggest that evolved traits in the fourth instar and remaining unstudied lifestage, teneral (i.e., pre-emergent) adult, likely influence latitudinal differences in mountain pine beetle generation time

Individual-Based Modeling: Mountain Pine Beetle Seasonal Biology in Response to Climate

Over the past decades, as significant advances were made in the availability and accessibility of computing power, individual-based models (IBM) have become increasingly appealing to ecologists (Grimm 1999). The individual-based modeling approachprovides a convenient framework to incorporate detailed knowledge of individuals and of their interactions within populations (Lomnicki 1999). Variability among individuals is essential to the success of populations that are exposed to changing environments, and because natural selection acts on this variability, it is an essential component of population performance. © Springer International Publishing Switzerland 2015

The Fire and Tree Mortality Database, for Empirical Modeling of Individual Tree Mortality After Fire

Wildland fires have a multitude of ecological effects in forests, woodlands, and savannas across the globe. A major focus of past research has been on tree mortality from fire, as trees provide a vast range of biological services. We assembled a database of individual-tree records from prescribed fires and wildfires in the United States. The Fire and Tree Mortality (FTM) database includes records from 164,293 individual trees with records of fire injury (crown scorch, bole char, etc.), tree diameter, and either mortality or top-kill up to ten years post-fire. Data span 142 species and 62 genera, from 409 fires occurring from 1981-2016. Additional variables such as insect attack are included when available. The FTM database can be used to evaluate individual fire-caused mortality models for pre-fire planning and post-fire decision support, to develop improved models, and to explore general patterns of individual fire-induced tree death. The database can also be used to identify knowledge gaps that could be addressed in future research

Climate change and forest disturbance: The case of the mountain pine beetle

Forecasts of climate change raise concerns about future modifications to forest ecosystem composition, structure and dynamics. Distributions of some tree species are also predicted to change with alterations in abiotic conditions and possible repercussions to biotic interactions. Native bark beetles in the genus Dendroctonus have historically played important roles in forest ecosystem dynamics through their influence on patterns of tree mortality. Climate change is predicted to influence Dendroctonus populations, thereby affecting community dynamics and succession pathways of forest ecosystems. In susceptible forests, climatic changes influence bark beetle populations directly through effects on beetle physiology, and indirectly through effects on host trees. The direct and indirect influences of temperature and precipitation on population outbreak dynamics is complex, however, and can result in both positive and negative feedbacks to beetle population success. To predict spatial and temporal patterns of future tree mortality, and evaluate future forest resiliency capacity, it is necessary to understand the climate-driven processes that influence beetle population success. I will discuss field, laboratory, and model-derived data that describe physiological processes driving potential response of Dendroctonus ponderosae, the mountain pine beetle, in a changing climate. Connecting models of thermally-driven bark beetle population dynamics and forest ecosystems will also be discussed

Temperature-Dependent Development of the Mountain Pine Beetle (Coleoptera : Scolytidae) and Simulation of its Phenology

Temperature-dependent development of the egg, larval, and pupal life-stages of the mountain pine beetle (Dendroctonus ponderosae Hopkins) was described using data from constant-temperature laboratory experiments. A phenology model describing the effect of temperature on the temporal distribution of the life-stages was developed using these data. Phloem temperatures recorded in a beetle-infested lodgepole pine (Pinus contorta Douglas) were used as input to run the model. Results from model simulations suggest that inherent temperature thresholds in each life-stage help to synchronize population dynamics with seasonal climatic changes. This basic phenological information and the developed model will facilitate both research and management endeavors aimed at reducing losses in lodgepole pine stands caused by mountain pine beetle infestations

2003): Comparison of reproductive capacity among univoltine, semivoltine, and re-emerged parent spruce beetles (Coeloptera: Scolytidae). The Canadian Entomologist 135

Abstract-New spruce beetle, Dendroctonus rufipennis (Kirby), adults of univoltine and semivoltine life cycles, as well as re-emerged parent beetles, were laboratory-tested for differences in reproductive capacity and brood characteristics. Parameters measured from the three groups include dry weight, lipid content, and egg production. Brood characteristics measured include egg length, development rates, and survival densities. Although there were some differences in dry weight and lipid content, females from the univoltine, semivoltine, and re-emerged parent groups did not greatly differ in egg production. Egg length was slightly smaller for eggs from univoltine parents, but other measured brood characteristics did not differ among the three parent groups, including the density of the surviving brood. In a field study, re-emerged parent beetles were determined to be flight capable. These findings imply that populations with univoltine broods will have higher growth rates than semivoltine populations. Consequently, the presence of univoltine broods, which is weather dependent, increases the risk of a beetle outbreak or can accelerate the rate of spruce mortality in an established outbreak. These results also indicate that re-emerged parent beetles can contribute substantially to brood production. Suppression strategies can be more effective if managers consider the ecological consequences of brood production from the three parent groups. résultats laissent croire aussi que les parents émergés pour une seconde fois peuvent contribuer substantiellement à la production de la progéniture. Les stratégies de suppression seront plus efficaces si les gestionnaires tiennent compte des conséquences écologiques de la reproduction des trois groupes de parents. [Traduit par la Rédaction

Fungi associated with the North American spruce beetle, Dendroctonus rufipennis

Abstract: Fungi were isolated from individual Dendroctonus rufipennis (Kirby) collected from six populations in Alaska, Colorado, Utah, and Minnesota, U.S.A. In all populations, Leptographium abietinum (Peck) Wingfield was the most commonly isolated mycelial fungus (91-100% of beetles). All beetles in all populations were associated with yeasts and some with only yeasts (0-5%). In one population, Ophiostoma ips (Rumbold) Nannf. was also present on 5% of the beetles but always in combination with L. abietinum and yeasts. Ophiostoma piceae (Munch) H. & P. Sydow was found on 2% of beetles in another population. Ceratocystis rufipenni Wingfield, Harrington & Solheim, previously reported as an associate of D. rufipennis, was not isolated from beetles in this study. Ceratocystis rufipenni is a virulent pathogen of host Picea, which has led to speculation that C. rufipenni aids the beetle in overcoming tree defenses and therefore contributes positively to the overall success of the beetle during colonization. However, our results, considered along with those of others, indicate that C. rufipenni may be absent from many populations of D. rufipennis and may be relatively rare in those populations in which it is found. If this is true, C. rufipenni may be only a minor or incidental associate of D. rufipennis and, as such, not likely to have significant impacts on beetle success or population dynamics. Alternatively, the rarity of C. rufipenni in our and others isolations may be due to difficulties in isolating this fungus in the presence of other faster growing fungi such as L. abietinum. Résumé : Des champignons ont été isolés sur des dendroctones (Dendroctonus rufipennis Kirby) capturés dans six populations provenant de l'Alaska, du Colorado, de l'Utah et du Minnesota aux États-Unis. Dans toutes les populations, Leptographium abietinum (Peck) Wingfield était le champignon le plus communément isolé (91-100 % des dendroctones). Tous les dendroctones dans toutes les populations étaient associés à des levures et certains seulement à des levures (0-5 %). Dans une population, Ophiostoma ips (Rumbold) Nannf. était également présent sur 5 % des dendroctones mais toujours en association avec L. abietinum et des levures. Ophiostoma piceae (Munch) H. & P. Sydow a été isolé sur 2 % des dendroctones dans une autre population. Ceratocystis rufipenni Wingfield, Harrington & Solheim, déjà mentionné comme étant associé à D. rufipennis, n'a pas été isolé des dendroctones dans cette étude. Ceratocystis rufipenni est un pathogène virulent du genre Picea, ce qui a donné naissance à l'idée que C. rufipenni pouvait aider le dendroctone à vaincre les défenses de l'arbre et par conséquent contribuer positivement au succès global du dendroctone lors de la colonisation. Cependant, nos résultats considérés avec ceux d'autres chercheurs indiquent que C. rufipenni est probablement absent dans plusieurs populations de D. rufipennis et relativement rare dans les populations où il est retrouvé. Si cela est vrai, C. rufipenni pourrait être associé à D. rufipennis de façon marginale et accessoire et comme tel n'aurait vraisemblablement pas d'impact majeur sur la dynamique de population et le succès du dendroctone. Par contre, la rareté de C. rufipenni dans nos isolations et les isolations d'autres chercheurs pourrait être due à la difficulté d'isoler ce champignon en présence d'autres champignons qui croissent rapidement comme L. abietinum

Model Analysis of Mountain Pine Beetle (Coleoptera : Scolytidae) Seasonality

The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a natural disturbance agent of considerable consequence in western pine forests. This economically and ecologically important insect has a strong requisite for maintaining a strict seasonality. Given this ecological requirement, it is somewhat surprising that no evidence for diapause or other physiological timing mechanism has been found. Seasonality and phenological timing for this species are apparently under direct temperature control. The consequences of direct temperature control were investigated by first constructing a computationally efficient phenology model based on previously published temperature dependent developmental data. The dynamic properties of this model were explored when subjected to observed microhabitat temperatures representing a range of thermal habitats from one region of the mountain pine beetle distribution (Idaho, USA). The consequences of global climate change on phenology and seasonality were also investigated. The results indicate that an adaptive seasonality is a natural consequence of the interaction between developmental parameters and seasonal temperatures. Although this adaptive phenology appears to be resilient to temperature fluctuations, changes in climate within the magnitude of predicted climate change under a CO2 doubling scenario are capable of shifting a thermally hostile environment to a thermally benign environment. Similarly, increasing temperature by the same amount resulted in phenological disruption of a previously favorable thermal habitat. The implications of these results for restricting the current distribution of mountain pine beetle, and the potential for shifting distribution caused by global climate change are discussed

Data from: Mountain pine beetle seasonal timing and constraints to bivoltinism: a comment on Mitton and Ferrenberg (2012)

Mountain pine beetle tree colonization typically occurs in July and August, with completion of a generation one (univoltinism) or two (semivoltinism) years later. In a 2012 publication, Mitton and Ferrenberg suggested that climate change resulted in an unprecedented generation between June and September (a summer generation), with a concomitant shift to two generations in one year (bivoltinism). Although summer generations are not uncommon in this species, completion of a second generation across winter, between September and June, would be required for bivoltinism, a phenomenon not previously observed. Mitton and Ferrenberg showed that a summer generation can occur, but they failed to adequately track cohorts and provided no compelling evidence for bivoltinism. We demonstrate that a winter generation—and hence bivoltinism—would have been physiologically impossible at the high-elevation site used in Mitton and Ferrenberg due to lower thermal developmental thresholds. The mountain pine beetle is indeed being influenced by climate change. To address the challenges of future population outbreaks of this significant tree mortality agent, however, it is imperative to consider evolved, thermally dependent traits that serve to maintain seasonality

An Individual Based Model of Mountain Pine Beetle Responses to Climate and Host Resistance

We have developed a model describing the responses of mountain pine beetle to daily fluctuations of temperature, in terms of development, survival and reproduction. The model also describes the aggregation, attack, and competition of beetles in pine stands. Built in an individual based framework, using an object-oriented approach, this model can predict the response of beetle populations to climatic conditions and host plant resistance and distribution, at the stand level. We are using this model to better understand the interaction between climate and host plant resistance that determine population growth rates in various environments. We will focus on the contrasting population performance of MPB on whitebark pine compared to lodgepole pine