Sequencing, Assembly and Annotation of the Whole-Insect Genome of Lymantria dispar dispar, the European Gypsy Moth

The European gypsy moth, Lymantria dispar dispar (LDD), is an invasive insect and a threat to urban trees, forests and forest-related industries in North America. For use as a comparator with a previously published genome based on the LD652 pupal ovary-derived cell line, as well as whole-insect genome sequences obtained from the Asian gypsy moth subspecies L. dispar asiatica and L. dispar japonica, the whole-insect LDD genome was sequenced, assembled and annotated. The resulting assembly was 998 Mb in size, with a contig N50 of 662 Kb and GC content of 38.8%. Long interspersed nuclear elements (LINEs) constitute 25.4% of the whole-insect genome, and a total of 11,901 genes predicted by automated gene finding encoded proteins exhibiting homology with reference sequences in the NCBI NR and/or UniProtKB databases at the most stringent similarity cutoff level (i.e., the gold tier). These results will be especially useful in developing a better understanding of the biology and population genetics of L. dispar and the genetic features underlying Lepidoptera in general.

Effects of Rearing Density on Developmental Traits of Two Different Biotypes of the Gypsy Moth, Lymantria Dispar L., from China and the USA

The life-history traits of the gypsy moth, Lymantria dispar L. (Lepidoptera: Erebidae), have been observed to vary with larval population density, which can increase significantly during an outbreak of this pest. Laboratory studies on density-dependent variation in gypsy moth development have focused on single populations and were limited to comparing solitary larvae with groups of larvae reared at a single density. To evaluate how density-dependent impacts on development vary with different populations and subspecies of L. dispar, we compared the effects of rearing larvae of a European gypsy moth (L. dispar dispar L.) population from Connecticut, USA; and larvae of two populations of the Asian gypsy moth (L. dispar asiatica Vnukovskij) from Guizhou and Hebei provinces in China. Larvae were reared on an artificial diet at densities of one, three, five, seven, and nine larvae per 115 mL container, and the duration of larval development, percentage of surviving larvae, and the rates of pupation and emergence were measured at each density. A two-tailed response to density variation with values falling away on both sides from a peak or climbing from a base was observed for all three populations tested, with the most rapid larval development and the highest values of survival, pupation, and emergence observed at a density of five larvae/container. Although differences in larval development time, survival, pupation and emergence were observed among the different populations under the conditions of our study, our findings indicate that density-dependent effects on the development of different gypsy moth subspecies and populations follow the same trends.

Potential Differences and Methods of Determining Gypsy Moth Female Flight Capabilities: Implications for the Establishment and Spread in Novel Habitats

The introduction of the Asian gypsy moth into novel environments continues with frequent interceptions in North America. There is a concern that these subspecies will pose a greater threat to the forests and urban environments of North America than the established gypsy moths (Lymantria dispardispar L.), due to their greater capacity for female flight. Asian gypsy moth populations vary in many key traits, including female flight capabilities. The potential impacts of female flight, in combination with the other key traits, on the ecology and spread of this insect are first discussed in this communication. This also provides the first review of most of the current literature on the variations in flight capability and flight distance of gypsy moth populations, as well as variation in other traits of concern and the potential methods of identification, with special attention paid to the Asian subspecies Lymantria dispar japonica Motschulsky and Lymantria dispar asiatica Vinkovskij. There are currently good tools for identifying the general origin of introduced gypsy moth populations, but these do not provide enough information to effectively manage introductions. Gypsy moth key traits differ among populations, even within each subspecies of the gypsy moth, so introduction of gypsy moths from other world areas into locations where the gypsy moth is already present could result in unwanted changes in gypsy moth biology. It also appears that the introduction of flight-capable females could enhance a population’s dispersal capability and require modifications to management protocols used for flightless females. Therefore, rapid tools to assess key traits in introduced populations are needed to adequately plan for, or deal with, new introductions into novel habitats.

Transcriptomic and Metabolomic Analyses to Unravel Responses of Populus Simonii × P. Nigra to attack by Asian Gypsy moth Lymantria Dispar (Lepidoptera: Lymantriidae)

Background: Poplar is frequently attacked by herbivorous insects, including the Asian gypsy moth, Lymantria dispar. Here, we combined metabolomic and transcriptomic analysis to identify key genes and metabolites involved into the molecular mechanism of defensive enhancement against L. dispar herbivory on poplar. Results: The 3666 differentially expressed genes (DEGs, 1,799 up-regulated and 1,867 down-regulated) and 1,171 DEGs (695 up-regulated and 476 down-regulated) were specific in L. dispar herbivory and mechanical wounding, respectively. Moreover, the 9,108 and 7,656 ions were detected while 636 and 531 different ions were obtained using positive (pos) mode and negative (neg) mode, respectively. Among these ions, the 33 and 7 different ions were specific in L. dispar herbivory and mechanical wounding in pos mode while 46 and 4 different ions in L. dispar herbivory and mechanical wounding in neg mode, respectively. The 3,666 specific DEGs in L. dispar herbivory group were classified into phenylpropanoid and flavonoid secondary metabolism pathways by comprehensive networks between transcriptomes and metabolomes. Conclusions: The current findings greatly improve our understanding of the induced defensive response in poplar plants against L. dispar infestation, and will contribute to develop insect-resistance poplar varieties.

Comparing Asian Gypsy Moth [Lymantria dispar asiatica (Lepidoptera: Erebidae) and L. dispar japonica] Trap Data From East Asian Ports With Lab Parameterized Phenology Models: New Tools and Questions

Management of the European gypsy moth [Lymantria dispar dispar (Linnaeus)] in North America has benefited from more than a century of research. The East Asian strains of the gypsy moth, however, bring new challenges including multiple subspecies (Lymantria dispar asiatica Vnukovskij and Lymantria dispar japonica Motschulsky), broad distributions across heterogeneous habitats, and a lack of data on the variation in the phenology of source populations, which may affect risk. To address these issues, published phenology parameters for eight populations of Asian gypsy moth were used to develop eight strain-specific agent-based phenological models. These models were applied to 47 ports in East Asia where the Asian gypsy moth is native, and output was compared with available trap data to assess the role of interpopulation variation in phenological parameters in predicting moth flight among varied locations, assess variation in the performance of models among years, and assess the importance of modeling phenology using parameters from a ‘local’ moth population. Variation in phenological parameters among the eight populations yielded variation in predicted flight times among the 47 ports analyzed, and the use of ‘local’ populations did not generally improve model fit. Model accuracy varied substantially among ports and among years within some ports. The larva-to-adult agent-based models described here have utility in estimating flight periods for some ports in their current form, but variation in model quality across the landscape suggests that there is potential for unsampled and unparameterized moth populations and factors that remain to be quantified.

Assessing the Potential Distribution of Asian Gypsy Moth in Canada: A Comparison of Two Methodological Approaches

Gypsy moth (Lymantria dispar L.) is one of the world’s worst hardwood defoliating invasive alien species. It is currently spreading across North America, damaging forest ecosystems and posing a significant economic threat. Two subspecies L. d. asiatica and L. d. japonica, collectively referred to as Asian gypsy moth (AGM) are of special concern as they have traits that make them better invaders than their European counterpart (e.g. flight capability of females). We assessed the potential distribution of AGM in Canada using two presence-only species distribution models, Maximum Entropy (MaxEnt) and Genetic Algorithm for Rule-set Prediction (GARP). In addition, we mapped AGM potential future distribution under two climate change scenarios (A1B and A2) while implementing dispersal constraints using the cellular automation model MigClim. MaxEnt had higher AUC, pAUC and sensitivity scores (0.82/1.40/1.00) when compared to GARP (0.70/1.26/0.9), indicating better discrimination of suitable versus unsuitable areas for AGM. The models indicated that suitable conditions for AGM were present in the provinces of British Columbia, Ontario, Quebec, Nova Scotia and New Brunswick. The human influence index was the variable found to contribute the most in predicting the distribution of AGM. These model results can be used to identify areas at risk for this pest, to inform strategic and tactical pest management decisions.

Microsatellite and Morphological Analyses Reveal Unexpected Diversity in Lymantria dispar in China

The gyspy moth Lymantria dispar Linnaeus, a widely distributed leaf-eating pest, is considered geographically isolated in the world, with two Asian gypsy moth subspecies, Lymantria dispar asiatica and Lymantria dispar japonica. In China, only one subspecies, L. d. asiatica, has been observed. In this study, we characterized gypsy moth diversity and divergence using 427 samples covering a wide range of the species distribution, with a focus on sampling along a latitudinal gradient in China. We combine the quantitative analysis of male genitalia and the genetic diversity analysis of nine microsatellite loci of nuclear genes nuclear genes to study the structure of gypsy moth individuals in 23 locations in the world and the male genitalia of gypsy moths in some areas. In mixed ancestry model-based clustering analyses based on nuclear simple sequence repeats, gypsy moths were divided into three well-known subspecies, a unique North American cluster, and a southern Chinese cluster with differentiation between the Asian gypsy moth and European gypsy moth. We also found individuals identified as European gypsy moths in two distant regions in China. The results of a quantitative analysis of male genitalia characteristics were consistent with an analysis of genetic structure and revealed the differentiation of gypsy moths in southern China and of hybrids suspected to be associated with L. d. japonica in the Russian Far East. Admixture in gypsy moths can be explained by many factors such as human transport. In China, we detected European gypsy moths, and found unexpectedly high genetic diversity within populations across a wide range of latitudes.