by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
RNA interference (RNAi) is a highly specific gene-silencing mechanism that can cause rapid insect mortality when essential genes are targeted. RNAi is being developed as a tool for integrated pest management of some crop pests. Here we focus on an aggressive forest pest that kills extensive tracts of pine forests, the southern pine beetle (SPB), Dendroctonus frontalis. We sought to identify reference genes for quantitative real-time PCR (qPCR) and validate RNAi responses in SPB by mortality and gene silencing analysis. Using an adult beetle feeding bioassay for oral ingestion of dsRNA, we measured the expression and demonstrated knockdown of target genes as well as insect mortality after ingestion of target genes. Our study validates reference genes for expression analyses and demonstrates highly effective RNAi responses in SPB, with RNAi response to some target dsRNAs causing 100% beetle mortality after ingestion.
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Kyre, Bethany R., Thais B. Rodrigues, and Lynne K. Rieske. 2019. “RNA Interference and Validation of Reference Genes for Gene Expression Analyses Using QPCR in Southern Pine Beetle, Dendroctonus Frontalis.” Scientific Reports 9 (April): 5640. https://doi.org/10.1038/s41598-019-42072-6.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Future anthropogenic-induced changes to the earth’s climate will likely include increases in temperature and changes in precipitation that will increase the frequency and severity of droughts. Insects and fungal diseases are important disturbances in forests, yet understanding of the role of drought in outbreaks of these agents is limited. Current knowledge concerning the effects of drought on herbivorous insect and pathogen outbreaks in U.S. forests is reviewed, and compared between the relatively mesic and structurally diverse forests of the eastern U.S. and the more xeric forests of the western U.S. Theory and limited evidence suggests a non-linear relationship between drought intensity and outbreaks of aggressive bark beetle species (i.e., those capable of causing extensive levels of tree mortality), where moderate droughts reduce bark beetle population performance and subsequent tree mortality, whereas intense droughts, which frequently occur in the western U.S., increase bark beetle performance and tree mortality. There is little evidence for a role of drought in outbreaks of the southern pine beetle (Dendroctonus frontalis), the only bark beetle species that causes large amounts of tree mortality in the eastern U.S. Defoliators do not show consistent responses to drought. The response of sapfeeders to drought appears non-linear, with the greatest performance and impacts at intermediate drought intensity or when drought is alleviated by wetter periods. Interactions between tree pathogens and drought are poorly understood, but available evidence suggests reduced pathogen performance and host impacts in response to drought for primary pathogens and pathogens whose lifecycle depends directly on moisture (humidity). In these cases, rates of reproduction, spread, and infection tend to be greater when conditions are moist. In contrast, secondary fungal pathogens (i.e., those that depend on stressed hosts for colonization) are anticipated to respond to drought with greater performance and host impacts. In the western U.S., drought increases stress on trees severely infected by mistletoes thereby predisposing mistletoe-infected trees to attack by insects, particularly bark beetles and wood borers. Research needed to advance understanding of drought impacts on forest insects and diseases, and the role of forest management in mitigation of infestations during drought are discussed.
Keywords
Climate change, Drought, Forest pathogens, Forest health, Forest insects, Herbivory
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Kolb, Thomas E., Christopher J. Fettig, Matthew P. Ayres, Barbara J. Bentz, Jeffrey A. Hicke, Robert Mathiasen, Jane E. Stewart, and Aaron S. Weed. 2016. “Observed and Anticipated Impacts of Drought on Forest Insects and Diseases in the United States.” Forest Ecology and Management 380 (November): 321–34. https://doi.org/10.1016/j.foreco.2016.04.051.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Conifer bark beetles attack and kill mature spruce and pine trees, especially during hot and dry conditions. These beetles are closely associated with ophiostomatoid fungi of the Ascomycetes, including the genera Ophiostoma, Grosmannia, and Endoconidiophora, which enhance beetle success by improving nutrition and modifying their substrate, but also have negative impacts on beetles by attracting predators and parasites. A survey of the literature and our own data revealed that ophiostomatoid fungi emit a variety of volatile organic compounds under laboratory conditions including fusel alcohols, terpenoids, aromatic compounds, and aliphatic alcohols. Many of these compounds already have been shown to elicit behavioral responses from bark beetles, functioning as attractants or repellents, often as synergists to compounds currently used in bark beetle control. Thus, these compounds could serve as valuable new agents for bark beetle management. However, bark beetle associations with fungi are very complex. Beetle behavior varies with the species of fungus, the stage of the beetle life cycle, the host tree quality, and probably with changes in the emission rate of fungal volatiles. Additional research on bark beetles and their symbiotic associates is necessary before the basic significance of ophiostomatoid fungal volatiles can be understood and their applied potential realized.
Keywords
Symbiosis, Pest management, Fusel alcohol, Aliphatic alcohol, Aromatic compound, Terpenoid, Ophiostoma, Grosmannia, Endoconidiophora, Ips, Dendroctonus
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Kandasamy, Dineshkumar, Jonathan Gershenzon, and Almuth Hammerbacher. 2016. “Volatile Organic Compounds Emitted by Fungal Associates of Conifer Bark Beetles and Their Potential in Bark Beetle Control.” Journal of Chemical Ecology 42 (9): 952–69. https://doi.org/10.1007/s10886-016-0768-x.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
The research field of animal and plant symbioses is advancing from studying interactions between two species to whole communities of associates. High-throughput sequencing of microbial communities supports multiplexed sampling for statistically robust tests of hypotheses about symbiotic associations. We focus on ambrosia beetles, the increasingly damaging insects primarily associated with fungal symbionts, which have also been reported to support bacteria. To analyze the diversity, composition, and specificity of the beetles’ prokaryotic associates, we combine global sampling, insect anatomy, 454 sequencing of bacterial rDNA, and multivariate statistics to analyze prokaryotic communities in ambrosia beetle mycangia, organs mostly known for transporting symbiotic fungi. We analyze six beetle species that represent three types of mycangia and include several globally distributed species, some with major economic importance (Dendroctonus frontalis, Xyleborus affinis, Xyleborus bispinatus–ferrugineus, Xyleborus glabratus, Xylosandrus crassiusculus, and Xylosandrus germanus). Ninety-six beetle mycangia yielded 1,546 bacterial phylotypes. Several phylotypes appear to form the core microbiome of the mycangium. Three Mycoplasma (originally thought restricted to vertebrates), two Burkholderiales, and two Pseudomonadales are repeatedly present worldwide in multiple beetle species. However, no bacterial phylotypes were universally present, suggesting that ambrosia beetles are not obligately dependent on bacterial symbionts. The composition of bacterial communities is structured by the host beetle species more than by the locality of origin, which suggests that more bacteria are vertically transmitted than acquired from the environment. The invasive X. glabratus and the globally distributed X. crassiusculus have unique sets of bacteria, different from species native to North America. We conclude that the mycangium hosts in multiple vertically transmitted bacteria such as Mycoplasma, most of which are likely facultative commensals or parasites.
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Hulcr, J., N. R. Rountree, S. E. Diamond, L. L. Stelinski, N. Fierer, and R. R. Dunn. 2012. “Mycangia of Ambrosia Beetles Host Communities of Bacteria.” Microbial Ecology 64 (3): 784–93. https://doi.org/10.1007/s00248-012-0055-5.
by Dr. Molly Darr | May 24, 2022 | 2011-2020 Publications, Southern Pine Beetle
Abstract
Recent studies have revealed several examples of intimate associations between insects and Actinobacteria, including the Southern Pine Beetle Dendroctonus frontalis and the Spruce Beetle Dendroctonus rufipennis. Here, we surveyed Streptomyces Actinobacteria co-occurring with 10 species of Dendroctonus bark beetles across the United States, using both phylogenetic and community ecology approaches. From these 10 species, and 19 other scolytine beetles that occur in the same trees, we obtained 154 Streptomyces-like isolates and generated 16S sequences from 134 of those. Confirmed 16S sequences of Streptomyces were binned into 36 distinct strains using a threshold of 0.2% sequence divergence. The 16S rDNA phylogeny of all isolates does not correlate with the distribution of strains among beetle species, localities, or parts of the beetles or their galleries. However, we identified three Streptomyces strains occurring repeatedly on Dendroctonus beetles and in their galleries. Identity of these isolates was corroborated using a house-keeping gene sequence (efTu). These strains are not confined to a certain species of beetle, locality, or part of the beetle or their galleries. However, their role as residents in the woodboring insect niche is supported by the repeated association of their 16S and efTu from across the continent, and also having been reported in studies of other subcortical insects.
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Hulcr, Jiri, Aaron S. Adams, Kenneth Raffa, Richard W. Hofstetter, Kier D. Klepzig, and Cameron R. Currie. 2011. “Presence and Diversity of Streptomyces in Dendroctonus and Sympatric Bark Beetle Galleries Across North America.” Microbial Ecology 61 (4): 759–68. https://doi.org/10.1007/s00248-010-9797-0.
