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RNA interference (RNAi) is a sequence-specific gene silencing mechanism triggered by double-stranded RNA (dsRNA). Exploiting the RNAi mechanism to silence essential genes in insects has emerged as a promising new pest control strategy, and RNAi-based products are being developed for plant protection. RNAi has proven effective in silencing genes and causing mortality in the highly invasive emerald ash borer (EAB) (Agrilus planipennis) (Coleoptera: Buprestidae); however, a practical delivery method remains a barrier to its deployment. In this study, we evaluate the systemic distribution and retention of exogenously applied dsRNA in green ash (Fraxinus pennsylvanica) tissues to investigate the feasibility of dsRNA delivery through the host plant. To evaluate the distribution and persistence of dsRNA, seedings are exposed to EAB-specific dsRNA as a root soak, sampled 3, 7, 14, 21, and 30 d after exposure, and sectioned into root, woody-stem, soft-stem, and leaf tissues. Total RNA is extracted and evaluated by RT-PCR. Gel images and Sanger sequencing confirm the presence of exogenously applied dsRNAs, demonstrating successful uptake and translocation of dsRNAs throughout plant tissues. Our findings demonstrate that root application represents a viable delivery method for dsRNA in ash seedlings, supporting the potential of this technology in providing ash protection against EAB. [ABSTRACT FROM AUTHOR]

Considerable research has focused on gene silencing in tree-feeding insects, but how trees recognize and process double-stranded RNA (dsRNA) engineered to target plant pests is unknown. We performed transcriptomic assembly, preliminary differential expression analysis, and in silico annotation on loblolly pine (Pinus taeda, L.) seedlings exposed to southern pine beetle-specific dsRNA. This pilot study sought to elucidate the baseline response of seedlings challenged with insect-specific dsRNA. Treated and untreated seedlings were sequenced and following transcriptome assembly 20 RNAi-related proteins (RRPs) were annotated. Differential gene expression analysis conducted using DESeq2 followed by pathway enrichment revealed 7131 differentially expressed transcripts, of which 33% were upregulated and 67% were downregulated. Only two RRPs selected for analysis were upregulated in treated seedlings, showing a lack of detectable RNAi response with our methodology. Beyond RNAi-related proteins, pathway enrichment mapped to immune response systems and genetic and cellular processing. Upregulated transcripts included autophagy, amino sugar and nucleotide sugar metabolism, and plant hormone signal transduction. Downregulated transcripts included RNA degradation and fatty acid metabolism pathways. Multiple DICER-LIKE and ARGONAUTE proteins were also annotated in five other North American pines, revealing diversity among these crucial proteins. Understanding host plant response to RNAi-mediated pest control is essential to further develop this technology against tree pests. [ABSTRACT FROM AUTHOR]

The invasive emerald ash borer (Agrilus planipennis - EAB) is causing rapid and widespread ash (Fraxinus spp.) mortality in eastern North America, has established populations near Moscow, Russia, and is threatening ash resources in Europe. Given the prevalence of susceptible hosts these post-invasion forests will clearly differ from their pre-invasion counterparts. Understanding these changes is key to mitigating the impacts of invasion and developing sound management strategies. We evaluated short term changes in a forest stand invaded by EAB, and examined if the southern variant of the Forest Vegetation Simulator (FVS) could accurately predict those changes. Through simulation, managers can gain a clearer understanding of how pest invasions impact and alter future forest dynamics. However, many simulators are designed to achieve long-term predictions and thus do not align with the short term changes associated with rapid EAB-induced ash mortality. Woody vegetation was surveyed in 2010 and used to project impacts of EAB invasion into 2012 by simulating a 50% ash mortality rate. The same plots were then re-surveyed in 2012, allowing us to evaluate: (1) changes in actual forest composition and structure; and (2) simulation accuracy. Within our forest stand, FVS accurately estimated short term changes in stem density and basal area parameters, thus demonstrating its value as a short-term simulator for EAB-induced changes within the southern region of the United States. EAB-induced ash mortality is quickly changing these forests and will ultimately alter how stakeholders manage their lands. We discuss the potential usefulness of FVS as a tool for aiding management decisions in response to EAB invasion.

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Extensive ash mortality caused by the non-native emerald ash borer alters canopy structure and creates inputs of coarse woody debris as dead and dying ash fall to the forest floor; this affects habitat heterogeneity; resource availability; and exposure to predation and parasitism. As EAB-induced (emerald ash borer-induced) disturbance progresses the native arthropod associates of these forests may be irreversibly altered through loss of habitat; changing abiotic conditions and altered trophic interactions. We documented coleopteran communities associated with EAB-disturbed forests in a one-year study to evaluate the nature of these changes. Arthropods were collected via ethanol-baited traps on five sites with varying levels of EAB-induced ash mortality from May to September; captured beetles were identified to the family level and assigned to feeding guilds (herbivore; fungivore; xylophage; saprophage; predator; or parasite). Over 11,700 Coleoptera were identified in 57 families. In spite of their abundance; herbivores comprised a relatively small portion of coleopteran family richness (8 of 57 families). Conversely, coleopteran fungivore richness was high (23 families), and fungivore abundance was low. Herbivores and fungivores were more abundant at sites where ash decline was most evident. The predatory Trogossitidae and Cleridae were positively correlated with ash decline, suggesting a positive numerical response to the increased prey base associated with EAB invasion. Ash forests are changing, and a deeper understanding of arthropod community responses will facilitate restoration. [ABSTRACT FROM AUTHOR]

Eastern hemlock (Tsuga canadensis (L.) is a foundation species in eastern North America where it is under threat from the highly invasive, exotic hemlock woolly adelgid (Adelges tsugae). Eastern hemlock is especially important in riparian areas of Central and Southern Appalachia, so we compared the spatial and temporal composition of benthic collector-gatherers, collector-filterers, and grazers in headwater streams with hemlock-dominated riparian vegetation to those with deciduous tree-dominated riparian vegetation to evaluate the extent to which adelgid-induced hemlock loss could influence composition and abundance of these two functional feeding groups. We found differences in benthic invertebrate abundance and family-level diversity based on riparian vegetation and sampling approach, and, often, riparian vegetation significantly interacted with location or season. Collector-gatherers and grazers were more abundant in eastern hemlock streams in the summer, when hemlock litter is readily available and deciduous litter is relatively sparse. Riparian eastern hemlock appears to exert considerable influence on benthic invertebrate functional feeding group composition in headwater stream communities, as expected with a foundation species. With the loss of eastern hemlock due to adelgid-induced mortality, we should expect to see alterations in spatial and temporal patterns of benthic invertebrate abundance and diversity, with potential consequences to both benthic and terrestrial ecosystem function. [ABSTRACT FROM AUTHOR]

Micromechanical properties that help mediate herbivore access may be particularly important when considering herbivorous insects that feed with piercing-sucking stylets. We used microindentation to quantify the micromechanical properties of hemlock, Tsuga spp., to quantify the hardness of the feeding site of the invasive hemlock woolly adelgid, Adelges tsugae. We measured hardness of the hemlock leaf cushion, the stylet insertion point of the adelgid, across four seasons in a 1 y period for four hemlock species growing in a common garden, including eastern, western, mountain, and northern Japanese hemlocks. Leaf cushion hardness was highest in the fall and winter and lowest in summer for all species. Northern Japanese hemlock had relatively greater hardness than the remaining species. Our data contributes an additional perspective to the existing framework within which greater susceptibility and subsequent mortality of eastern hemlocks is observed. The potential application of microindentation to understanding the nature and relevance of plant mechanical defenses in plant-herbivore interactions is also demonstrated and highlighted. [ABSTRACT FROM AUTHOR]

Remote sensing and spatial analysis represent useful tools for modeling species' dispersal, characterizing the spread of invasions and the invasability of a region, and thus allowing more accurate predictions for developing mitigation strategies. American chestnut, Castanea dentata, was historically a dominant forest species in North America, but occurs only sporadically today after its functional elimination by an exotic fungal pathogen in the early 1900's. In recent decades Castanea resources have increased due to restoration efforts, commercial chestnut plantations, and horticultural uses. This resurgence is threatened by an additional exotic species, the globally invasive Asian chestnut gall wasp, Dryocosmus kuriphilus. The gall wasp was first discovered in Lexington, Kentucky (USA) in 2010. We used remotely sensed data and Geographic Information Systems to describe the local distribution of the Castanea hosts, and the occurrence and dispersal of the gall wasp. We tested the hypotheses that geomorphology, Castanea occurrence, and prevailing winds influence local proliferation. We found that gall wasp spread may be attributable to host plant distribution and to the effects of prevailing winds occurring during a brief period of adult insect emergence, and is influenced by topography. Our results suggest that weather data and topographic features can be used to delineate currently infested areas and predict future gall wasp infestations. [ABSTRACT FROM AUTHOR]

The article focuses on a research conducted in order to identify the effects of jasmonic acid (JA) and a JA-inhibitor, diethyldithiocarbamic acid on the growth and defense of the Asian chestnut gall wasp, Dryocosmus kuriphilus galls formed on American chestnut, Castanea dentata. It discusses the importance of JA in defenses against insects and pathogens as well as the regulation of nutrient partitioning. The study revealed the importance of JA treatments on gall wasps.

Dendroctonus frontalis also known as southern pine beetle (SPB), is the most damaging insect forest pest in the southeastern United States. Genomic data are important to provide information on pest biology and to identify molecular targets to develop improved pest management approaches. Here, we produced a chromosome-level genome assembly of SPB using long-read sequencing data. Synteny analyses confirmed the conservation of the core Coleopteran Stevens elements and validated the bona fide SPB X chromosome. Transcriptomic data were used to obtain 39 588 transcripts corresponding to 13 354 putative protein-coding loci. Comparative analyses of gene content across 14 beetles and three other insects revealed several losses of conserved genes in the Dendroctonus clade and gene gains in SPB and Dendroctonus that were enriched for loci encoding membrane proteins and extracellular matrix proteins. While lineage-specific gene losses contributed to the gene content reduction observed in Dendroctonus , we also showed that widespread misannotation of transposable elements represents an important cause of the apparent gene expansion in several non- Dendroctonus species. Our findings uncovered distinctive features of the SPB gene complement and disentangled the role of biological and annotation-related factors contributing to gene content variation across beetles., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)