Genetic evidence of broad spreading of Lymantria dispar in the West Siberian Plain

Integration of satellite remote sensing and MaxEnt modeling for improved detection and management of forest pests

Forest pests pose a major threat to ecosystem services worldwide, requiring effective monitoring and management strategies. Recently, satellite remote sensing has emerged as a valuable tool to detect defoliation caused by these pests. Lymantria dispar, a major forest pest native to Japan, Siberia, and Europe, as well as introduced regions in North America, is of particular concern. In this study, we used Sentinel-2 satellite imagery to estimate the defoliation area and predict the distribution of L. dispar in Toyama Prefecture, central Japan. The primary aim was to understand the spatial distribution of L. dispar. The normalized difference vegetation index (NDVI) difference analysis estimated a defoliation area of 7.89 km2 in Toyama Prefecture for the year 2022. MaxEnt modeling, using defoliation map as occurrence data, identified the deciduous forests between approximately 35° and 50° at elevations of 400 m and 700 m as highly suitable for L. dispar. This predicted suitability was also high for larval locations but low for egg mass locations, likely due to differences in larval habitats and ovipositing sites. This study is the first attempt to utilize NDVI-based estimates as a proxy for MaxEnt. Our results showed higher prediction accuracy than a previous study based on the occurrence records including larvae, adults, and egg masses, indicating better discrimination of the distribution of L. dispar defoliation. Therefore, our approach to integrating satellite data and species distribution models can potentially enhance the assessment of areas affected by pests for effective forest management.

Exploring and validating observations of non-local species in eDNA samples

The development of DNA-based methods in recent decades has opened the door to numerous new lines of research in the biological sciences. While the speed and accuracy of DNA methodologies are clearly beneficial, the sensitivity of these methods has the adverse effect of increased susceptibility to false positives resulting from contamination in field or lab. Here, we present findings from a metabarcoding study on the diet of and food availability for five insectivorous birds, in which multiple lepidopteran species not known to occur locally were discovered. After describing the pattern of occurrences of these non-local species in the samples, we discuss various potential origins of these sequences. First, we assessed that the taxonomic assignments appeared reliable, and local occurrences of many of the species could be plausibly ruled out. Then, we looked into the possibilities of natural environmental contamination, judging it to be unlikely, albeit impossible to fully falsify. Finally, while dissimilar combinations of non-local species' occurrences across the samples did not initially suggest lab contamination, we found overlap with taxa and sequences handled in the same lab, which was undoubtedly not coincidental. Even so, not all exact sequences were accounted for in these locally conducted studies, nor was it clear if these and other sequences could remain detectable years later. Although the full explanation for the observations of non-local species remains inconclusive, these findings highlight the importance of critical examination of metabarcoding results, and showcase how species-level taxonomic assignments utilizing comprehensive reference libraries may be a tool in detecting potential contamination events, and false positives in general.

Phenological Features of the Spongy Moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), in the Northernmost Portions of Its Eurasian Range

The spongy moth, Lymatria dispar, is a classic example of an invasive pest accidentally introduced from Europe to North America, where it has become one of the most serious forest defoliators, as in its native range. The present study was aimed at (i) identifying the current northern limit of L. dispar's Eurasian range and exploring its northward expansion in Canada using pheromone trap data, and (ii) comparing northern Eurasian populations with those from central and southern regions with respect to male flight phenology, the sums of effective temperatures (SETs) above the 7 °C threshold necessary for development to the adult stage, and heat availability. We show that the range of L. dispar in Eurasia now reaches the 61st parallel, and comparisons with historical data identify the average speed of spread as 50 km/year. We also document the northern progression of L. dispar in southern Canada, where the actual northern boundary of its range remains to be identified. We show that the median date of male flight does not vary greatly between northern and southern regions of the spongy moth range in Eurasia despite climate differences. Synchronization of flight at different latitudes of the range is associated with an acceleration of larval development in northern Eurasian populations. Similar changes in developmental rate along a latitudinal gradient have not been documented for North American populations. Thus, we argue that this feature of spongy moths from northern Eurasia poses a significant invasive threat to North America in terms of enhanced risks for rapid northward range expansion.

Range‐wide population genomics of the spongy moth, Lymantria dispar (Erebidae): Implications for biosurveillance, subspecies classification and phylogeography of a destructive moth

The spongy moth, Lymantria dispar, is an irruptive forest pest native to Eurasia where its range extends from coast to coast and overspills into northern Africa. Accidentally introduced from Europe in Massachusetts in 1868-1869, it is now established in North America where it is considered a highly destructive invasive pest. A fine-scale characterization of its population genetic structure would facilitate identification of source populations for specimens intercepted during ship inspections in North America and would enable mapping of introduction pathways to help prevent future incursions into novel environments. In addition, detailed knowledge of L. dispar's global population structure would provide new insight into the adequacy of its current subspecies classification system and its phylogeographic history. To address these issues, we generated >2000 genotyping-by-sequencing-derived SNPs from 1445 contemporary specimens sampled at 65 locations in 25 countries/3 continents. Using multiple analytical approaches, we identified eight subpopulations that could be further partitioned into 28 groups, achieving unprecedented resolution for this species' population structure. Although reconciliation between these groupings and the three currently recognized subspecies proved to be challenging, our genetic data confirmed circumscription of the japonica subspecies to Japan. However, the genetic cline observed across continental Eurasia, from L. dispar asiatica in East Asia to L. d. dispar in Western Europe, points to the absence of a sharp geographical boundary (e.g., the Ural Mountains) between these two subspecies, as suggested earlier. Importantly, moths from North America and the Caucasus/Middle East displayed high enough genetic distances from other populations to warrant their consideration as separate subspecies of L. dispar. Finally, in contrast with earlier mtDNA-based investigations that identified the Caucasus as L. dispar's place of origin, our analyses suggest continental East Asia as its evolutionary cradle, from where it spread to Central Asia and Europe, and to Japan through Korea.

Economics of a Feeding Budget: A Case of Diversity of Host Plants for Lymantria dispar L. (Lepidoptera) Feeding on Leaves and Needles

Relationships were analyzed among the energy-related characteristics of feed consumption by caterpillars of the spongy moth (also known as gypsy moth) Lymantria dispar L., survival of individuals, and fecundity of females depending on the species of a host plant. An optimization model of feed consumption was used for the calculations. In this model, efficiency of consumption depends on two parameters: efficiency of metabolic degradation of feed and efficiency of caterpillar biomass synthesis. Experiments were conducted regarding the feeding of caterpillars on the leaves of silver birch Betula pendula Roth. and needles of Siberian larch Larix sibirica Ldb. and Scotch pine Pinus sylvestris L. On the basis of the results of experiments, “costs” of the feed for females and males were calculated, the consumption efficiency of different types of feed was found, and the relationship between efficiency of feed consumption and female fecundity was determined. The proposed approach can be employed to assess feeding efficiency of insects in various habitats.

Asian gypsy moth (Lymantria dispar L.) populations: Tolerance of eggs to extreme winter temperatures

Gypsy moth Lymantria dispar (GM) is a polyphagous insect and one of the most significant pests in the forests of Eurasia and North America (U.S. and Canada). Accurate information on GM cold-hardiness is needed to improve methods for the prediction of population outbreaks, as well as for forecasting possible GM range displacements due to climate change. As a result of laboratory and field studies, we found that the lower lethal temperature (at which all eggs die) range from -29.0 °C to -29.9 °C for three studied populations of L. dispar asiatica, and no egg survived cooling to -29.9 °C. These limits agree, to within one degree, with the previously established cold-hardiness limits of the European subspecies L. dispar, which is also found in North America. This coincidence indicates that the lower lethal temperature of L. dispar is conservative. Thus, we found that the Siberian populations of GM inhabit an area where winter temperatures go beyond the limits of egg physiological tolerance, because temperatures often fall below -30 °C. Apparently, it is due to the flexibility of ovipositional behavior that L. dispar asiatica survives in Siberia: the lack of physiological tolerance of eggs is compensated by choosing warm biotopes for oviposition. One of the most important factors contributing to the survival of GM eggs in Siberia is the stability of the snow cover.

The microsporidium Nosema pyrausta as a potent microbial control agent of the beet webworm Loxostege sticticalis

The microsporidium Nosema pyrausta is an important mortality factor of the European corn borer, Ostrinia nubilalis. The present study was aimed at N. pyrausta virulence testing to the beet webworm (BW), Loxostege sticticalis. This agricultural pest, L. sticticalis, was highly vulnerable to N. pyrausta. The parasite's spores were located in salivary glands, adipose tissue, and Malpighian tubules of the infected specimens. Infection was transmitted transovarially through at least 3 laboratory generations, in which BW fitness indices were lower than in the control, and moth emergence and fertility decreased prominently. Transovarial infection was most detrimental to female egg-laying ability, resulting in zero fertility in F3. When propagated in BW, the microsporidium tended to increase its virulence to L. sticticalis, as compared to the Ostrinia isolates. The parasite's ability to infect this host at low dosages and transmit vertically should guarantee its effective establishment and spread within BW populations. In conclusion, N. pyrausta is a promising agent against BW, which is a notorious polyphagous pest in Eurasia.

Susceptibility of the Gypsy Moth Lymantria dispar (Lepidoptera: Erebidae) to Nosema pyrausta (Microsporidia: Nosematidae)

Simple Summary

Microsporidia are widespread insect pathogens and a single species may infect different hosts. Nosema pyrausta from the corn borer was tested against the gypsy moth. Thirty days after larvae were fed with spores, infection was established in the salivary glands and fat body of pupae and prepupae. Up to 10% of insects became infected. The gypsy moth can be referred to as a resistant host of N. pyrausta.

Abstract

The gypsy moth, Lymantria dispar, is a notorious forest defoliator, and various pathogens are known to act as natural regulators of its population density. As a widespread herbivore with a broad range of inhabited areas and host plants, it is potentially exposed to parasitic microorganisms from other insect hosts. In the present paper, we determined the susceptibility of gypsy moth larvae to the microsporidium Nosema pyrausta from the European corn borer, Ostrinia nubilalis. Gypsy moth samples from two localities of Western Siberia were used. N. pyrausta developed infections in the salivary gland and adipose tissue of gypsy moth prepupae and pupae, forming spore masses after 30 days of alimentary exposure to the second instar larvae. Among the experimental groups, the infection levels ranged from 0 to 9.5%. Effects of a covert baculovirus infection, phenylthiourea pretreatment and feeding insects on an artificial diet versus natural foliage were not significant in terms of microsporidia prevalence levels. Thus, L. dispar showed a low level of susceptibility to a non-specific microsporidium. It can be referred to as a resistant model host and not an appropriate substitute host for laboratory propagation of the microsporidium.

Tracking invasions of a destructive defoliator, the gypsy moth (Erebidae: Lymantria dispar): Population structure, origin of intercepted specimens, and Asian introgression into North America

Genetic data can help elucidate the dynamics of biological invasions, which are fueled by the constant expansion of international trade. The introduction of European gypsy moth (Lymantria dispar dispar) into North America is a classic example of human-aided invasion that has caused tremendous damage to North American temperate forests. Recently, the even more destructive Asian gypsy moth (mainly L. d. asiatica and L. d. japonica) has been intercepted in North America, mostly transported by cargo ships. To track invasion pathways, we developed a diagnostic panel of 60 DNA loci (55 nuclear and 5 mitochondrial) to characterize worldwide genetic differentiation within L. dispar and its sister species L. umbrosa. Hierarchical analyses supported strong differentiation and recovered five geographic groups that correspond to (1) North America, (2) Europe plus North Africa and Middle East, (3) the Urals, Central Asia, and Russian Siberia, (4) continental East Asia, and (5) the Japanese islands. Interestingly, L. umbrosa was grouped with L. d. japonica, and the introduced North American population exhibits remarkable distinctiveness from contemporary European counterparts. Each geographic group, except for North America, shows additional lower-level structures when analyzed individually, which provided the basis for inference of the origin of invasive specimens. Two assignment approaches consistently identified a coastal area of continental East Asia as the major source for Asian invasion during 2014-2015, with Japan being another source. By analyzing simulation and laboratory crosses, we further provided evidence for the occurrence of natural Asian-North American hybrids in the Pacific Northwest, raising concerns for introgression of Asian alleles that may accelerate range expansion of gypsy moth in North America. Our study demonstrates how genetic data contribute to bio-surveillance of invasive species with results that can inform regulatory management and reduce the frequency of trade-associated invasions.