BackgroundRelatively little is known about the genomic basis and evolution of wood-feeding in beetles. We undertook genome sequencing and annotation, gene expression assays, studies of plant cell wall degrading enzymes, and other functional and comparative studies of the Asian longhorned beetle, Anoplophora glabripennis, a globally significant invasive species capable of inflicting severe feeding damage on many important tree species. Complementary studies of genes encoding enzymes involved in digestion of woody plant tissues or detoxification of plant allelochemicals were undertaken with the genomes of 14 additional insects, including the newly sequenced emerald ash borer and bull-headed dung beetle.ResultsThe Asian longhorned beetle genome encodes a uniquely diverse arsenal of enzymes that can degrade the main polysaccharide networks in plant cell walls, detoxify plant allelochemicals, and otherwise facilitate feeding on woody plants. It has the metabolic plasticity needed to feed on diverse plant species, contributing to its highly invasive nature. Large expansions of chemosensory genes involved in the reception of pheromones and plant kairomones are consistent with the complexity of chemical cues it uses to find host plants and mates.ConclusionsAmplification and functional divergence of genes associated with specialized feeding on plants, including genes originally obtained via horizontal gene transfer from fungi and bacteria, contributed to the addition, expansion, and enhancement of the metabolic repertoire of the Asian longhorned beetle, certain other phytophagous beetles, and to a lesser degree, other phytophagous insects. Our results thus begin to establish a genomic basis for the evolutionary success of beetles on plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-1088-8) contains supplementary material, which is available to authorized users.

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Retinal sensitivity of Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) was examined with an aim to improve trap efficacy for the beetle. Electroretinogram (ERG) recordings from dark-adapted compound eyes of male and female were measured at different wavelengths across the spectrum ranging from 300 to 700 nm. The spectral sensitivity curves revealed peaks in the UV (340 nm), the violet/purple (420-430 nm), blue (460 nm), and green (540-560 nm) regions of the spectrum. Females were sensitive to red regions of the spectrum (640-670 nm), whereas males were not. A spectrophotometer was used to measure the wavelength and reflectance for ash foliage, purple corrugated plastic traps, as well as the elytra and abdomen of adult A. planipennis. Traps were painted using colors based on ERG and spectrophotometer measurements and compared with purple corrugated plastic traps currently used by the USDA-APHIS-PPQ-EAB National Survey. In a field assay conducted along the edges of several A. planipennis-infested ash stands, there were no significant differences in trap catch among green, red, or purple treatments. Dark blue traps caught significantly fewer A. planipennis than red, light green, or dark purple traps. In a second assay where purple and green treatments were placed in the mid canopy of ash trees (approximately 13 m in height), trap catch was significantly higher on green treatments. We hypothesize that when placed in the mid-canopy, green traps constitute a foliage-type stimulus that elicits food-seeking and/or host seeking behavior by A. planipennis.

Characterizing the current population structure of potentially invasive species provides a critical context for identifying source populations and for understanding why invasions are successful. Non-native populations inevitably lose genetic diversity during initial colonization events, but subsequent admixture among independently introduced lineages may increase both genetic variation and adaptive potential. Here we characterize the population structure of the gypsy moth (Lymantria dispar Linnaeus), one of the world's most destructive forest pests. Native to Eurasia and recently introduced to North America, the current distribution of gypsy moth includes forests throughout the temperate region of the northern hemisphere. Analyses of microsatellite loci and mitochondrial DNA sequences for 1738 individuals identified four genetic clusters within L. dispar. Three of these clusters correspond to the three named subspecies; North American populations represent a distinct fourth cluster, presumably a consequence of the population bottleneck and allele frequency change that accompanied introduction. We find no evidence that admixture has been an important catalyst of the successful invasion and range expansion in North America. However, we do find evidence of ongoing hybridization between subspecies and increased genetic variation in gypsy moth populations from Eastern Asia, populations that now pose a threat of further human-mediated introductions. Finally, we show that current patterns of variation can be explained in terms of climate and habitat changes during the Pleistocene, a time when temperate forests expanded and contracted. Deeply diverged matrilines in Europe imply that gypsy moths have been there for a long time and are not recent arrivals from Asia.

Summary 1.Understanding why invading populations sometimes fail to establish is of considerable relevance to the development of strategies for managing biological invasions. 2. Newly arriving populations tend to be sparse and are often influenced by Allee effects. Mating failure is a typical cause of Allee effects in low-density insect populations, and dispersion of individuals in space and time can exacerbate mate-location failure in invading populations. 3. Here we evaluate the relative importance of dispersal and sexual asynchrony as contributors to Allee effects in invading populations by adopting as a case study the gypsy moth ( Lymantria dispar L.), an important insect defoliator for which considerable demographic information is available. 4. We used release-recapture experiments to parameterize a model that describes probabilities that males locate females along various spatial and temporal offsets between male and female adult emergence. 5. Based on these experimental results, we developed a generalized model of mating success that demonstrates the existence of an Allee threshold, below which introduced gypsy moth populations are likely to go extinct without any management intervention.

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