Thomas Davis

Colorado State University | CSU · Department of Forest, Rangeland and Watershed Stewardship

We provide a synthesis of the literature describing biochemical interactions between microorganisms and insects by way of microbial volatile organic compound (MVOC) production. We evaluated the functionality and ecological context of MVOC signals, and explored important metabolic pathways involved in MVOC production. The cosmopolitan distribution o...

The transmission of insect-borne plant pathogens, including viruses, bacteria, phytoplasmas, and fungi depends upon the abundance and behavior of their vectors. These pathogens should therefore be selected to influence their vectors to enhance their transmission, either indirectly, through the infected host plant, or directly, after acquisition of...

Wild bee community assemblages were surveyed in a high-elevation mixed conifer forest in central Colorado at multiple points during the growing season (April-August) and across a range of forest stand densities using blue vane traps. Understory forb communities were also characterized and related to bee species abundance and diversity. Overall γ-di...

1. Pine wilt disease, caused by pinewood nematode (Bursaphelenchus xylophilus; abbreviated ‘PWN’), is a damaging and globally distributed insect‐vectored forest pathogen. Native forest tree mortality associated with PWN is newly reported from the Front Range of Colorado, but there is no regional information on PWN frequency or biology of local inse...

In North American conifer forests, a variety of federally initiated thinning programs are implemented to restore pre‐European settlement forest structures, but these changes may impact ecosystem function via impacts on sensitive biotic communities. Across the wildland–urban interface of the Front Range region of Colorado, agencies associated with t...

Here, we describe patterns of reproduction and flight phenology of putative Phloeosinus punctatus in giant sequoia groves and compare morphology and genotypes of beetles from sympatric giant sequoia (Sequoiadendron giganteum) and California incense-cedar (Calocedrus decurrens). Surveys conducted in 2022 revealed that numerous branches fall from gia...

We test whether tissue moisture content affects settling and feeding behaviours of Monochamus galloprovincialis , a forest insect that feeds on multiple pine species and is a vector of tree disease. In a watering experiment using potted Aleppo pine trees, Pinus halepensis Miller (Pinaceae), water deprivation reduced mid-day shoot water potentials a...

The genus Dendroctonus is a Holarctic taxon composed of 21 nominal species; some of these species are well known in the world as disturbance agents of forest ecosystems. Under the bark of the host tree, these insects are involved in complex and dynamic associations with phoretic ectosymbiotic and endosymbiotic communities. Unlike filamentous fungi...

On publicly managed lands of western North America, canopy removal is practiced as a habitat improvement for sage grouse (Centrocercus species), often with the goal of converting dominant vegetation cover from pinyon pine (Pinus edulis) and juniper (Juniperus spp.) to sagebrush (Artemisia spp.). However, it remains unclear whether habitat conversio...

1. Forest restoration projects that create canopy gaps can promote floral diversity and may provide reservoirs for bee-flower interactions. However, periods of bee activity must match availability of floral nutrition for bees to benefit from these effects. 2. We model variation in canopy gap size, floral density, pollen protein and bee and floral...

Managed low‐severity surface fires are frequently implemented in efforts to restore disturbance processes to forests of North America; although the effects of managed fire on forest structure are well‐studied, few studies investigate whether these disturbances cascade to impact pollinator communities. We analysed bee‐habitat relationships in fire‐t...

To better understand functional ecology of bark beetle-microbial symbioses, we characterized yeast associates of North American spruce beetle (Dendroctous rufipennis Kirby) across populations. Seven yeast species were detected; Wickerhamomyces canadensis (Wickerham) Kurtzman et al. (Sachharomycetales: Saccharomycetaceae) was the most common (74% of...

Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guid...

A changing climate is altering ecosystem carbon dynamics with consequences for natural systems and human economies, but there are few tools available for land managers to meaningfully incorporate carbon trajectories into planning efforts. To address uncertainties wrought by rapidly changing conditions, many practitioners adopt resistance and resili...

Pollinator community responses to changing conditions are a concern for ecosystem managers, but it remains poorly understood how shifts in forest structure impact pollinators across small scales. To address this, bee assemblages were sampled in arid woodland habitat in the southwestern United States (Colorado) to evaluate effects of canopy cover an...

Global temperatures are generally increasing, and this is leading to a well documented advancement and extension of seasonal activity of many pest insects. Effects of changing precipitation have received less attention, but might be complex because rain and snow are increasing in some places but decreasing in others. This raises the possibility tha...

A variety of habitat‐associated factors moderate effects of grazing on insect biodiversity. Here, we examine how aridity, evolutionary history of grazing and grazing intensity individually and interactively mediate the effect of livestock grazing on pollinator biodiversity (native bees and butterflies). Using a meta‐analysis of 59 studies published...

In fire-adapted ponderosa pine forests of western North America, fire suppression policies during much of the 19th century gradually resulted in high stem densities undesirable for fire risk management. To restore desirable forest structures, regional ecosystem management efforts often focus on reducing stand densities and re-introducing fire distu...

The climate of the southwestern United States of America (USA) is projected to become warmer and drier as atmospheric CO2 concentrations continue to increase, and these environmental shifts are likely to impact the ecology of plant-insect interactions in regional forest ecosystems. Increasing atmospheric CO2 concentrations can enhance tree growth r...

Understanding whether pollinator behaviors and species richness drive crop yields is a key area of investigation in pollination ecology. Using sunflower as a study species we describe variation in mean floral visitation times among bee taxa and test how interactions between bee richness and the proportion of bumblebees in localized communities impa...

Many animals change feeding habits as they progress through life stages, exploiting resources that vary in space and time. However, complex life histories may bring new risks if rapid environmental change disrupts the timing of these switches. Here, we use abundance times series for a diverse group of herbivorous insects, aphids, to search for trai...

There is considerable interest in applying entomopathogenic fungi as a biological control to limit insect populations due to their low environmental and human applicator impacts. However, despite many promising laboratory tests, there are few examples where these fungi were successfully applied to manage bark beetles. Here, we explore how environme...

In temperate coniferous forests, biotic disturbances such as bark beetle outbreaks can result in widespread tree mortality. The characteristics of individual trees and stands, such as tree diameter and stand density, often influence the probability of tree mortality during a bark beetle outbreak. However, it is unclear if these relationships are me...

Differences in defensive traits of tree species may predict why some conifers are susceptible to bark beetle-fungal complexes and others are not. A symbiotic fungus (Leptographium abietinum) associated with the tree-killing bark beetle (Dendroctonus rufipennis) is phytopathogenic to host trees and may hasten tree decline during colonization by beet...

Research interests in Invasive Alien Plant Species (IAPS) have expanded globally, and nationally in Nepal, over the last few decades. Here we provide a systematic compilation and analysis of the scientific literature to exploreresearch trends and identify research gaps in plant invasion biology in Nepal. We compiled and examined journal publication...

Livestock grazing and non-native plant species affect rangeland habitats globally. These factors may have important effects on ecosystem services including pollination, yet, interactions between pollinators, grazing, and invasive plants are poorly understood. To address this, we tested the hypothesis that cattle grazing and site colonization by che...

Landscape-scale bark beetle outbreaks alter forest structure with direct and indirect effects on plants and animals in forest ecosystems. Using alpine spruce forest and a native bee community as a study system, we tested how tree mortality from bark beetles impacts bee foraging habitats and populations. Bees were collected across the growing season...

Engelmann spruce, Picea engelmannii Parry ex Engelm. (Pinaceae), in the southern Rocky Mountains is composed of two distinct phloem monoterpene chemotypes that differ in relative abundances of multiple monoterpenes, particularly α-pinene and Δ 3-carene (hereafter, the "α-pinene chemotype" and the "Δ 3-carene chemotype"). Here, relative toxicity of...

Symbiotic fungi associated with tree-killing bark beetles can alter host-tree physiology with consequences for tree survival, and symbiont genetic variation and environmental variability may impact these interactions. Here, we test whether multiple genetically distinct isolates of a symbiotic fungus (Leptographium abietinum (Peck) M.J. Wingf.) asso...

Beauveria bassiana is a ubiquitous entomopathogen and widely used as a biological control agent for a variety of arthropod pests, including bark beetles. The North American spruce beetle (Dendroctonus rufipennis) is a major pest in forest landscapes and recent studies show that B. bassiana is pathogenic to beetles in the lab but successful field ap...

The cost of plant reproduction or defense at the expense of other fitness traits is a central component of life history theory. Yet the three central resource allocation pathways of growth, reproduction, and defense have rarely been assessed simultaneously nor across individual to landscape scales. This information is critical towards identifying t...

Forest inventory indicated recent decline in a P. coulteri population at its northern extent but live stems in sympatric P. sabiniana increased. Patterns of cone production, localized factors associated with regeneration, relations between wildfire and tree age distributions, and correlations between climate, seedling establishment, and tree growth...

Novel satellite measurements of solar‐induced chlorophyll fluorescence (SIF) can improve our understanding of global photosynthesis; however, little is known about how to interpret the controls on its spectral variability. To address this, we disentangle simultaneous drivers of fluorescence spectra by coupling active and passive fluorescence measur...

Spruce beetle, Dendroctonus rufipennis Kirby, is associated with forest mortality in Colorado and across western North America, yet it is not well understood how thermal variability affects basic population processes such as flight phenology. However, phenology–temperature relationships are important for understanding patterns of ecosystem disturba...

Land managers face constant challenges when balancing multiple land use goals that include ensuring that keystone species are protected. As mindful stewards of our natural areas we aim to promote, secure, and enhance our natural landscapes and the species that make them their home. When we focus our efforts on protecting and promoting pollinators a...

Conifer secondary metabolites play a key role in mechanisms of resistance to biotic disturbance, especially by bark beetles and beetle-associated microorganisms. Here, we describe variation in constitutive monoterpenes isolated from Engelmann spruce, Picea engelmannii, phloem across fourteen high-elevation populations in the Rocky Mountains of Colo...

The ophiostomatoid fungus Leptographium abietinum is symbiotic with the North American spruce beetle Dendroctonus rufipennis; however, the ecology of these interactions are not understood. Multiple functional hypotheses regarding beetle-symbiont interactions pervade the literature, especially the view that symbionts may provide nutrition, competiti...

An isolate of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) was tested for its ability to reduce survival and reproduction of spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Scolytinae), under laboratory and field conditions. Conidial suspension applied directly to adults or to filter pape...

An isolate of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) was tested for its ability to reduce survival and reproduction of spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Scolytinae), under laboratory and field conditions. Conidial suspension applied directly to adults or to filter pape...

Spruce beetle populations (Dendroctonus rufipennis) (Coleoptera: Scolytinae) in Engelmann spruce (Picea engelmannii) stands were monitored at twelve sites for 6 years in northern Colorado using pheromone-baited Lindgren funnel traps. During the trapping period, over 30,000 beetles were captured, and beetle abundance data were used to construct empi...

Recent advances in the retrieval of Chl fluorescence from space using passive methods (solar‐induced Chl fluorescence, SIF) promise improved mapping of plant photosynthesis globally. However, unresolved issues related to the spatial, spectral, and temporal dynamics of vegetation fluorescence complicate our ability to interpret SIF measurements. We...

In cereal cropping systems of the Pacific Northwestern United States (PNW), climate change is projected to increase the frequency of drought during summer months, which could increase water stress for crop plants. Yet, it remains uncertain how interactions between herbivore species are affected by drought stress. Here, interactions between two cere...

Intraspecific specialization by insect herbivores on different host plant species contributes to the formation of genetically distinct " host races, " but the effects of plant virus infection on interactions between specialized herbivores and their host plants have barely been investigated. Using three genetically and phenotypically divergent pea a...

1.Although phytophagous insects can vary genetically in host use and exhibit long-range movements, the combined implications of these phenomena for pest management have received limited attention. 2.To address this, we surveyed the genetic diversity of pea aphid Acyrthosiphon pisum using twelve microsatellite loci and assessed host association pat...

Biological control of pests is a key feature of integrated pest management programmes in many agroecosystems. An assessment of the potential impacts of climate change on biological control is critical but challenging, because biological control depends on interspecific interactions, which are generally complex. This chapter considers the potential...

Infection with phytoviruses influences plant responses to environmental stress, but the biochemical mechanisms underlying these interactions are unknown. Infection of wheat (Triticum aestivum) with a cereal virus (Barley yellow dwarf virus, BYDV) has context-dependent effects on plant productivity and survival conditional to water stress, and we hy...

Acquisition of Pea enation mosaic virus (PEMV) by chickpea (Cicer arietinum) when fed on by viruliferous pea aphid (Acyrthosiphon pisum) was tested for combinations of two chickpea varieties ('Bronic', a kabuli type and 'Sierra', a desi type) and three plant ages (14, 28 and 42 days after germination). It was determined whether inoculation with PEM...

Agricultural cropping system models used as a decision support tools to predict crop growth and yield under different soil, climate and management scenarios, are most often limited by a lack of incorporated constraints from insects, pathogens and weeds. Coupling crop models with pest modules can help explain the gap between potential and actual yie...

Symbiotic interactions are prevalent in all bark beetle communities. For many species, the ability to associate with multiple partners enables species to persist through fluctuations in climate, resources, predation, and partner availability. Symbionts, particularly mutualistic species associated with bark beetles, can increase bark beetle fitness...

The cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae) is an introduced, widespread pest of small grains causing economic losses to wheat, oats, and barley throughout North America. Climate models indicate environmental suitability for this insect could increase by mid-21st century, but these models do not consider the indirect effect...

We compared the settling preferences and reproductive potential of an oligophagous herbivore, the pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), in response to pea plants, Pisum sati-vum L. cv. 'Aragorn' (Fabaceae), infected with two persistently transmitted viruses, Pea enation mosaic virus (PEMV) and Bean leaf roll virus (BLRV), th...

Yeasts are extremely common associates of scolytine bark beetles, yet the basic ecology of yeasts in the bark beetle holobiont remains poorly understood. Yeasts are present in all beetle life stages and consistently isolated from adult, larval, and pupal integuments and mycangial structures, but yeasts are also found in oviposition galleries, pupal...

1. Although both endogenous and exogenous processes regulate populations, the current understanding of the contributions from density dependence and climate to the population dynamics of eruptive herbivores remains limited. 2. Using a 17‐year time series of three cereal aphid species [ Rhopalosiphum padi L., Metopolophium dirhodum (Walker), and Diu...

The cereal aphid Metopolophium festucae subsp. cerealium (Stroyan) is a recent addition to North America, but little is known about this species in its exotic habitat. We surveyed aphid populations for 3 years (2011-2013) to investigate changes in aphid density in the Pacific Northwest United States. We tested aphid host settling preference and fec...

Orange mint moths, Pyrausta orphisalis (Walker) (Crambidae), were initially trapped in a study of noctuid moth attraction to floral volatiles. A subsequent series of trapping experiments in commercial mint fields determined that phenylacetaldehyde and 4-oxoisophorone were attractive to P. orphisalis, whereas benzyl acetate, eugenol, cis-jasmone, li...

Research to discover and develop attractants for the codling moth, Cydia pomonella L., has involved identification of the chemicals eliciting moth orientation to conspecific female moths, host fruits, fermented baits, and species of microbes. Pear ester, acetic acid, and N-butyl sulfide are among those chemicals reported to attract or enhance attra...

The cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae) is an introduced, widespread pest of small grains causing economic losses to wheat, oats, and barley throughout North America. Climate models indicate environmental suitability for this insect could increase by the mid-21st century, but these models do not consider the indirect ef...

Although bacterial endosymbioses are common among phloeophagous herbivores, little is known regarding the effects of symbionts on herbivore host selection and population dynamics. We tested the hypothesis that plant selection and reproductive performance by a phloem-feeding herbivore (potato psyllid, Bactericera cockerelli) is mediated by infection...

We measured traits of 470 Pinus ponderosa in northern Arizona and constructed equations scaling phloem thickness and resin flow to tree size. We tested the hypothesis that these traits were related to tree monoterpene chemotype. The monoterpene composition of resin was analyzed for a subset of trees (n = 146). Correlation analyses revealed that all...

The rate of entry by neonate larvae of the frugivorous codling moth, Cydia pomonella (L.) (Lepido-ptera: Tortricidae), into fruit material was investigated. We used no-choice bioassays in climate-controlled rooms to assay larval entry across four host plant species (apple, pear, quince, walnut) and three varieties within a single fruit species (app...

We report here a first survey of insect orientation to fungal cultures and fungal volatiles from a community ecology perspective. We tested whether volatiles from a ubiquitous yeast-like fungus (Aureobasidium pullulans) are broadly attractive to insects in an agricultural landscape. We evaluated insect attraction to fungal cultures and synthetic co...

Although bacterial endosymbioses are common among phloeophagous herbivores, little is known regarding the effects of symbionts on herbivore host selection and population dynamics. We tested the hypothesis that plant selection and reproductive performance by a phloem-feeding herbivore (potato psyllid, Bactericera cockerelli) is mediated by infection...

Background / Purpose: The purpose of these studies was to determine whether eusocial wasps were orienting to volatiles produced by a ubiquitous microbial species. We also wanted to determine whether wasps vectored the microbes they were attracted to. Main conclusion: Wasps were attracted to fungal isolates in the field, and to synthetic chemic...

Field trapping experiments evaluated wine and vinegar baits for spotted wing drosophila flies, Drosophila suzukii (Matsumura), and assessed variance in bait attractiveness with wine type, vinegar type, and bait age. A mixture of apple cider vinegar and a Merlot wine attracted more flies than a mixture of acetic acid and ethanol. The vinegar/wine mi...

Ant–acacia mutualisms are conspicuous biotic associations in Savannah and neotropical ecosystems; however, the effects of tree size and forest structure on ant behaviour and tree traits are rarely examined. We tested two hypotheses related to these effects: (1) ant responses to disturbance are influenced by tree size and forest basal area; and (2)...

Microbes are ubiquitous on plant surfaces. However, interactions between epiphytic microbes and arthropods are rarely considered as a factor that affects arthropod behaviors. Here, volatile emissions from an epiphytic fungus were investigated as semiochemical attractants for two eusocial wasps. The fungus Aureobasidium pullulans was isolated from a...

The inheritance and functional roles of quantitative traits are central concerns of evolutionary ecology. We report two sets of experiments that investigated the heritability and reproductive consequences of body size phenotypes in a globally distributed lepidopteran frugivore, Cydia pomonella (L.). In our first set of experiments, we tested the hy...

Many herbivores consume microbial food sources in addition to plant tissues for nutrition. Despite the ubiquity of herbivore-microbe feeding associations, few studies examine how host plant phenotypes affect microbial symbionts of herbivores. We tested the hypothesis that chemical polymorphism in a plant population mediates the performance of nutri...