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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]

Laurel wilt disease (LWD) is a lethal vascular wilt caused by an exotic ambrosia beetle–fungal complex, the redbay ambrosia beetle, Xyleborus glabratus Eichhoff, and its nutritional symbiont, Harringtonia lauricola (Harr., Fraedrich & Aghayeva) de Beer & Procter. LWD is responsible for the widespread mortality of redbay, Persea borbonia (L.) Spreng., devastating coastal forests in the southeast United States. More recently, LWD is causing mortality of understory sassafras, Sassafras albidum (Nutt.) Nees, in deciduous forests in Kentucky, USA; the biology, epidemiology, and long-term impacts of LWD in deciduous forests are unclear. All North American lauraceous species evaluated have shown susceptibility, and numerous additional ambrosia beetles have demonstrated vector potential, but no studies to date have assessed the presence of H. lauricola in other insects associated with LWD-infected sassafras. We sampled infected sassafras from the leading edge of the LWD range and collected insect associates to evaluate phoretic and internal presence of H. lauricola. We recorded 118 individuals of 38 morphospecies emerging; most were Coleoptera. Of the 48 specimens evaluated for H. lauricola, none tested positive for phoretic presence, but internal presence was evident in the granulate ambrosia beetle, Xylosandrus crassiusculus Motschulsky, and in a hidden snout weevil, Apteromechus ferratus Say. This is the first report of H. lauricola associated with a non-ambrosia beetle and expands our understanding of the vector potential of additional insect species while confirming the role of the granulate ambrosia beetle. These findings contribute to our understanding of LWD epidemiology in sassafras hosts from more northerly latitudes. [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.

Environmental conditions associated with climate change are exacerbating pine mortality caused by the southern pine beetle (SPB) (Dendroctonus frontalis), prompting investigations into innovative management strategies.Triggering the RNA interference (RNAi) pathway using species‐specific double‐stranded RNA (dsRNA) to silence genes and cause mortality is effective in SPB and is an emerging technology for pest management, but specificity and safety must be demonstrated.We evaluated three pine‐associates (the scolytine six‐spined ips, Ips calligraphus, a foliage feeding pine sawfly, Neodiprion lecontei, and the detritivorous eastern subterranean termite, Reticulitermes flavipes), for transcriptome sequence overlap with the SPB dsRNA and performed bioassays to evaluate lethal and sublethal effects after dsRNA ingestion.Genetic analyses revealed little overlap between dsRNA sequences and target gene orthologs, with only two matches found in I. calligraphus, the most closely related phylogenetically.No lethal or sublethal effects were observed in any of the nontarget organisms evaluated, and changes in gene expression occurred only in I. calligraphus, but with no discernible effects on adult survival.Our findings build on previous nontarget evaluations for SPB‐specific dsRNA in model insects and demonstrate that the use of RNAi as a component of an IPM strategy would not directly compromise commonly occurring non‐congeneric pine associates. [ABSTRACT FROM AUTHOR]

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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]