BackgroundThe mountain pine beetle, Dendroctonus ponderosae Hopkins, is the most serious insect pest of western North American pine forests. A recent outbreak destroyed more than 15 million hectares of pine forests, with major environmental effects on forest health, and economic effects on the forest industry. The outbreak has in part been driven by climate change, and will contribute to increased carbon emissions through decaying forests.ResultsWe developed a genome sequence resource for the mountain pine beetle to better understand the unique aspects of this insect's biology. A draft de novo genome sequence was assembled from paired-end, short-read sequences from an individual field-collected male pupa, and scaffolded using mate-paired, short-read genomic sequences from pooled field-collected pupae, paired-end short-insert whole-transcriptome shotgun sequencing reads of mRNA from adult beetle tissues, and paired-end Sanger EST sequences from various life stages. We describe the cytochrome P450, glutathione S-transferase, and plant cell wall-degrading enzyme gene families important to the survival of the mountain pine beetle in its harsh and nutrient-poor host environment, and examine genome-wide single-nucleotide polymorphism variation. A horizontally transferred bacterial sucrose-6-phosphate hydrolase was evident in the genome, and its tissue-specific transcription suggests a functional role for this beetle.ConclusionsDespite Coleoptera being the largest insect order with over 400,000 described species, including many agricultural and forest pest species, this is only the second genome sequence reported in Coleoptera, and will provide an important resource for the Curculionoidea and other insects.

Pine-feeding bark beetles (Coleoptera: Scolytidae) interact chemically with their host pines (Coniferales: Pinaceae) via the behavioral, physiological, and biochemical effects of one class of isoprenoids, the monoterpenes and their derivatives. Pine monoterpenes occur in the oleoresin and function as behaviorally active kairomones for pine bark beetles and their predators, presenting a classic example of tritrophic chemical communication. The monoterpenes are also essential co-attractants for pine bark beetle aggregation pheromones. Ironically, pine monoterpenes are also toxic physiologically to bark beetles at high vapor concentrations and are considered an important component of the defense of pines. Research over the last 30 years has demonstrated that some bark beetle aggregation pheromones arise through oxygenation of monoterpenes, linking pheromone biosynthesis to the host pines. Over the last 10 years, however, several frequently occurring oxygenated monoterpene pheromone components (e.g., ipsenol, ipsdienol and frontalin) have also been shown to arise through highly regulated de novo pathways in the beetles (reviewed in Seybold and Tittiger, 2003). The most interesting nexus between these insects and their plant hosts involves the latestage reactions in the monoterpenoid biosynthetic pathway, during which isomeric dimethylallyl diphosphate and isopentenyl diphosphate are ultimately elaborated to stereospecific monoterpenes in the trees and to hydroxylated monoterpenes or bicyclic acetals in the insects. There is signal stereospecificity in both production of and response to the monoterpenoid aggregation pheromones of bark beetles and in response to the monoterpenes of the pines. In the California fivespined ips, Ips paraconfusus, we Dedicated to Professor David L. Wood on the occasion of his 75th birthdayÓ Springer Science+Business Media B.V. 2006have discovered a number of cytochome P450 genes that have expression patterns indicating that they may be involved in detoxifying monoterpene secondary metabolites and/or biosynthesizing pheromone components. Both processes result in the production of oxygenated monoterpenes, likely with varying degrees of stereospecificity. A behavioral analysis of the stereospecific response of I. paraconfusus to its pheromone is providing new insights into the development of an efficacious bait for the detection of this polyphagous insect in areas outside the western United States. In contrast, a Eurasian species that has arrived in California, the Mediterranean pine engraver, Orthotomicus (Ips) erosus, utilizes both a monoterpenoid (ipsdienol) and a hemiterpenoid (2-methyl-3-buten-2-ol) in its pheromone blend. The stereospecificity of the response of O. erosus to the monoterpenoid appears to be the key factor to the improved potency of the attractant bait for this invasive species.

These authors contributed equally to this work. SummaryFeeding forest tent caterpillars (FTCs) induced local and systemic diurnal emissions of (À)-germacrene D, along with (E )-b-ocimene, linalool, (E )-4,8-dimethyl-1,3,7-nonatriene (DMNT), benzene cyanide, and (E,E )-a-farnesene, from leaves of hybrid poplar. FTC feeding induced substantially higher levels of volatiles in local and systemic leaves than did mechanical wounding. A full-length poplar sesquiterpene synthase cDNA (PtdTPS1) was isolated and functionally identi®ed as (À)-germacrene D synthase. Expression of PtdTPS1, expression of genes of early, intermediate and late steps in terpenoid biosynthesis, and expression of a lipoxygenase gene (PtdLOX1) were analyzed in local FTC-infested and systemic leaves. Transcript levels of PtdTPS1 and PtdLOX1 were strongly increased in response to herbivory. PtdTPS1 was also induced by mechanical wounding or by methyl jasmonate (MeJA) treatment. FTC feeding did not affect transcript levels of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), and isoprene synthase (IPS). Two other TPS genes, PtdTPS2 and PtTPS3, and farnesyl diphosphate synthase were only very transiently induced. These results illustrate differential expression of terpenoid pathway genes in response to insect feeding and a key function of (À)-germacrene D synthase PtdTPS1 for herbivore-induced local and systemic volatile emissions in hybrid poplar. FTC-induced transcripts of PtdTPS1 followed diurnal rhythm. Spatial patterns of FTC-induced PtdTPS1 transcript accumulation revealed acropetal but not basipetal direction of the systemic response. Implications for tritrophic poplar-FTCpredator/parasitoid interactions are discussed.