Ken Raffa
Hilldale, Vilas Distinguished Achievement, and Sorenson Professor Emeritus
Please note: I am not accepting new graduate students or postdocs.
(608) 262-1125
345 Russell Labs
1630 Linden Drive
Madison, WI 53706
PhD Entomology – Washington State University-Pullman, 1980
M.S. Entomology – University of Delaware, 1976
B.S. Biology – Saint Joseph’s College, 1972
Research Interests:
Our program addresses mechanisms that drive the population dynamics of forest insects, with special emphasis on plant-insect interactions, predator-prey relationships, and insect-microbial-symbioses. We investigate each within the context of host plant properties that affected herbivore behavior, reproduction, and susceptibility to natural enemies, as well as herbivore counter-adaptations against multiple ecological constraints. We analyze biological thresholds and cross-scale interactions in insect outbreaks. Our study systems involve insects that pose challenges to natural resource management, so this information can improve our ability to address invasive species, sustainable production systems, biodiversity, and global change.
Our recent research highlights include: 1) How host selection behavior of individual bark beetles varies with beetle population density and thereby generates positive feedback during transitions from non-outbreak to outbreak conditions. These behaviors involve genetic, environmental responses to host compounds; 2) How attraction by predators to chemical signaling among herbivores can drive biochemical counter-adaptations that allow partial escape while allowing intraspecific functionality; 3) The critical role of thresholds in linking patterns with processes of insect outbreaks, specifically that tree defense is a crucial determinant of whether outbreaks occur, yet inconsequential after they do. 4) Beetles egest bacteria in oral secretions that inhibit opportunist fungi from exploiting host trees after their defenses are exhausted by beetle mass attacks; 5) Enteric gut bacteria are crucial to susceptibility of gypsy moth to the microbial pathogen Bt. Future research will expand our results on how microscale processes such as insect-symbiont-plant interactions can have landscape-scale outcomes.
All are collaborative projects, with interdisciplinary colleagues from UW depts. Forest & Wildlife Ecol, Plant Path, Microbio, and Zool, the US Forest Service, and various universities.
Research Category: Suborganismal, Organismal and Applied
Publications
Online Profiles
Highlighted Publications
- Howe M, Yanchuk A, Wallin KF & Raffa KF. 2024. Quantification of heritable variation in multiple lodgepole pine chemical and physical traits that contribute to defense against mountain pine beetle (Dendroctonus ponderosae). For. Ecol. & Manag. doi.org/10.1016/j.foreco.2023.121660.
- Schulz A Havill N, Marsico T, Ayres M, Gandhi K, Herms D Hoover A, Hufbauer, R, Liebhold A, Raffa, K, Thomas K, Tobin P, Uden D & Mech A. 2025. What is a specialist? Quantifying host breadth enables impact prediction for invasive herbivores. Ecol. Letters. doi.org/10.1111/ele.70083.
Recent Publications
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Ecology letters. pmid:39967421, doi:10.1111/ele.70083
Herbivores are commonly classified as host specialists or generalists for various purposes, yet the definitions of these terms, and their intermediates, are often imprecise and ambiguous. We quantified host breadth for 240 non-native, tree-feeding insects in North America using phylogenetic diversity. We demonstrated that a partitioning of host breadth: (1) causes 67% of non-native insects to shift from a generalist to specialist category, (2) displays a reduction in host breadth from the native…
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Journal of insect science (Online). pmid:38417130, pmc:PMC10901542, doi:10.1093/jisesa/ieae018
The parasitoid wasp, Ooencyrtus kuvanae (Howard) (Hymenoptera: Encyrtidae), is a natural enemy of the spongy moth, a significant forest pest in North America. We investigated the oviposition behavior of O. kuvanae females on spongy moth egg masses by (i) presenting female parasitoids with a single spongy moth egg mass that was replaced every day, 2nd day, 4th day, 8th day, or 16th day (which is the total length of the oviposition period) and (ii) presenting female parasitoids with 1, 2, 4, or 8…
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Annual review of phytopathology. pmid:37253697, doi:10.1146/annurev-phyto-021722-024626
Society is confronted by interconnected threats to ecological sustainability. Among these is the devastation of forests by destructive non-native pathogens and insects introduced through global trade, leading to the loss of critical ecosystem services and a global forest health crisis. We argue that the forest health crisis is a public-good social dilemma and propose a response framework that incorporates principles of collective action. This framework enables scientists to better engage…
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Ecological applications : a publication of the Ecological Society of America. pmid:36218183, doi:10.1002/eap.2761
Some introduced species cause severe damage, although the majority have little impact. Robust predictions of which species are most likely to cause substantial impacts could focus efforts to mitigate those impacts or prevent certain invasions entirely. Introduced herbivorous insects can reduce crop yield, fundamentally alter natural and managed forest ecosystems, and are unique among invasive species in that they require certain host plants to succeed. Recent studies have demonstrated that…
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BMC biology. pmid:36002826, pmc:PMC9400205, doi:10.1186/s12915-022-01388-y
CONCLUSIONS: Overall, our high-quality reference genome represents an important resource for genomics study of invasive bark beetles, which will facilitate the functional study and decipher mechanism underlying invasion success of RTB by integrating the Pinus tabuliformis genome.
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Oecologia. pmid:35226183, doi:10.1007/s00442-022-05129-4
Irruptive forest insects such as bark beetles undergo intermittent outbreaks that cause landscape-scale tree mortality. Despite their enormous economic and ecological impacts, we still have only limited understanding of the dynamics by which populations transition from normally stable endemic to irruptive densities. We investigated density-dependent changes in mountain pine beetle reliance on stressed hosts, host selection, spatial configuration of attacks, and the interaction of host selection…
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Plant, cell & environment. pmid:34612515, doi:10.1111/pce.14197
How carbohydrate reserves in conifers respond to drought and bark beetle attacks are poorly understood. We investigated changes in carbohydrate reserves and carbon-dependent diterpene defences in ponderosa pine trees that were experimentally subjected to two levels of drought stress (via root trenching) and two types of biotic challenge treatments (pheromone-induced bark beetle attacks or inoculations with crushed beetles that include beetle-associated fungi) for two consecutive years. Our…
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Global change biology. pmid:34428326, doi:10.1111/gcb.15861
Warming temperatures are allowing native insect herbivores to expand into regions that previously exceeded their thermal tolerance, encounter new host species, and pose significant threats to native communities. However, the dynamics of these expansions remain poorly understood, particularly in the extent to which outbreaks remain reliant on emigration from historical hosts or are driven by local reproduction within novel hosts in the expanded range. We tested these non-mutually exclusive…
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Journal of chemical ecology. pmid:33683546, doi:10.1007/s10886-021-01259-w
Climate warming can influence interactions between plants and associated organisms by altering levels of plant secondary metabolites. In contrast to studies of elevated temperature on aboveground phytochemistry, the consequences of warming on root chemistry have received little attention. Herein, we investigated the effects of elevated temperature, defoliation, and genotype on root biomass and phenolic compounds in trembling aspen (Populus tremuloides). We grew saplings of three aspen genotypes…
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The Fire and Tree Mortality Database, for empirical modeling of individual tree mortality after fire
Scientific data. pmid:32572035, pmc:PMC7308274, doi:10.1038/s41597-020-0522-7
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…
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Ecology and evolution. pmid:31832155, pmc:PMC6854116, doi:10.1002/ece3.5709
A long-standing goal of invasion biology is to identify factors driving highly variable impacts of non-native species. Although hypotheses exist that emphasize the role of evolutionary history (e.g., enemy release hypothesis & defense-free space hypothesis), predicting the impact of non-native herbivorous insects has eluded scientists for over a century.Using a census of all 58 non-native conifer-specialist insects in North America, we quantified the contribution of over 25 factors that could…
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The New phytologist. pmid:31494947, doi:10.1111/nph.16181
Plant interactions with herbivores and pathogens are among the most widespread ecological relationships, and show many congruent properties. Despite these similarities, general models describing how plant defenses function in ecosystems, and the prioritization of responses to emerging challenges such as climate change, invasive species and habitat alteration, often differ markedly between entomologists and plant pathologists. We posit that some fundamental distinctions between how insects and…
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The New phytologist. pmid:31494935, doi:10.1111/nph.16173
Drought has promoted large-scale, insect-induced tree mortality in recent years, with severe consequences for ecosystem function, atmospheric processes, sustainable resources and global biogeochemical cycles. However, the physiological linkages among drought, tree defences, and insect outbreaks are still uncertain, hindering our ability to accurately predict tree mortality under on-going climate change. Here we propose an interdisciplinary research agenda for addressing these crucial knowledge…
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Journal of chemical ecology. pmid:31493165, doi:10.1007/s10886-019-01105-0
Interactions between water stress and induced defenses and their role in tree mortality due to bark beetles are poorly understood. We performed a factorial experiment on 48 mature ponderosa pines (Pinus ponderosa) in northern Arizona over three years that manipulated a) tree water stress by cutting roots and removing snow; b) bark beetle attacks by using pheromone lures; and c) phloem exposure to biota vectored by bark beetles by inoculating with dead beetles. Tree responses included resin flow…
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Insect science. pmid:31407465, doi:10.1111/1744-7917.12715
The behavioral strategies and mechanisms by which some insects maintain monogamous mating systems are not well understood. We investigated the mating system of the bark beetle Dendroctonus valens, and identified several contributing mechanisms. Field and laboratory observations suggest the adults commonly form permanent bonds during host colonization. Moreover, it showed mated females that remained paired with males produced more offspring than mated females that were alone in galleries. In…
Selected Honors and Awards
- 2020 Western Forest Insect Work Conference Founders Award
- 2018 Entomological Society of America Plant-Insects Ecosystems Lifetime Achievement Award
- 2017 Hilldale Award in the Biological Sciences, Univ. Wisconsin
- 2015 University of Delaware CANR Distinguished Alumnus Award
- 2015 Vilas Distinguished Achievement / Douglas D Sorenson Professor, UW-Madison
- 2012 Fellow, Entomological Society of America
- 2011 Silverstein-Simeone Lecture Award, International Society of Chemical Ecology
- 2010 Entomological Society of America Founders Award
- 2010 Beers-Bascom Professorship in Conservation, UW-Madison
- 2008 Kellett MidCareer Research Award, UW-Madison
- 2000 Vilas Associate, UW-Madison
- 1999 Robert G.F. and Hazel T. Spitze Land Grant Faculty Award for Excellence
- 1995 USDA Forest Service “Bridging Ideas and Partnerships” Award
- 1991 Glenn Pound Outstanding Researcher Award, CALS, University of Wisconsin