Lymantria dispar (L.) (Lepidoptera: Erebidae): Current Status of Biology, Ecology, and Management in Europe with Notes from North America

Seasonality of forest insects: why diapause matters

Insects have major impacts on forest ecosystems, from herbivory and soil-nutrient cycling to killing trees at a large scale. Forest insects from temperate, tropical, and subtropical regions have evolved strategies to respond to seasonality; for example, by entering diapause, to mitigate adversity and to synchronize lifecycles with favorable periods. Here, we show that distinct functional groups of forest insects; that is, canopy dwellers, trunk-associated species, and soil/litter-inhabiting insects, express a variety of diapause strategies, but do not show systematic differences in diapause strategy depending on functional group. Due to the overall similarities in diapause strategies, we can better estimate the impacts of anthropogenic change on forest insect populations and, consequently, on key ecosystems.

Building a reference indicator model using co-kriging interpolation to determine the geographical origin of the flighted spongy moth complex in China

Using stable isotopes to detect and analyze the geographical origin of insects represents an important traceability technology, which requires a rich isotope database. In this study, we representatively sampled the Chinese provinces where flighted spongy moth complex (FSMC) has been reported and, for the first time, used co-kriging interpolation to predict the distribution patterns of FSMC δ13 C values in the main distribution areas. From 2020 to 2022, we set up 60 traps in 12 provinces and cities in China and collected 795 FSMCs. Then, 6 main climatic factors were obtained by multi-collinearity screening from 21 types of meteorological data collected at the sample plots, and a correlation analysis was carried out by combining longitude, latitude, and altitude data with the δ13 C values of FSMC. Next, we performed a co-kriging interpolation using the 2 climatic factors with the highest correlation (isothermality and altitude) and the δ13 C values of FSMC. A cross-validation was performed to systematically test 11 candidate models and select the best semi-variogram model ("Exponential"), which was then used to build a co-kriging interpolation model. The geographical distribution patterns of the FSMC δ13 C values obtained from the 2 interpolation models (i.e., interpolated with isothermality and altitude, respectively) were almost the same. Moreover, the δ13 C values varied significantly at the regional scale, showing regular changes in spatial distribution. Overall, the reference indicator map of the δ13 C values generated from stable isotopes can be used to greatly improve the efficiency of discrimination analyses on the geographical origin of FSMC.

The Diversity of Parasitoids and Their Role in the Control of the Siberian Moth, Dendrolimus sibiricus (Lepidoptera: Lasiocampidae), a Major Coniferous Pest in Northern Asia

The Siberian moth, Dendrolimus sibiricus Tschetv., 1908 (Lepidoptera: Lasiocampidae) is a conifer pest that causes unprecedented forest mortality in Northern Asia, leading to enormous ecological and economic losses. This is the first study summarizing data on the parasitoid diversity and parasitism of this pest over the last 118 years (1905-2022). Based on 860 specimens of freshly reared and archival parasitoids, 16 species from two orders (Hymenoptera and Diptera) were identified morphologically and/or with the use of DNA barcoding. For all of them, data on distribution and hosts and images of parasitoid adults are provided. Among them, the braconid species, Meteorus versicolor (Wesmael, 1835), was documented as a parasitoid of D. sibiricus for the first time. The eastern Palaearctic form, Aleiodes esenbeckii (Hartig, 1838) dendrolimi (Matsumura, 1926), status nov., was resurrected from synonymy as a valid subspecies, and a key for its differentiation from the western Palaearctic subspecies Aleiodes esenbeckii ssp. esenbecki is provided. DNA barcodes of 11 parasitoid species from Siberia, i.e., nine hymenopterans and two dipterans, represented novel records and can be used for accurate molecular genetic identification of species. An exhaustive checklist of parasitoids accounting for 93 species associated with D. sibirisus in northern Asia was compiled. Finally, the literature and original data on parasitism in D. sibiricus populations for the last 83 years (1940-2022) were analysed taking into account the pest population dynamics (i.e., growth, outbreak, decline, and depression phases). A gradual time-lagged increase in egg and pupal parasitism in D. sibiricus populations was detected, with a peak in the pest decline phase. According to long-term observations, the following species are able to cause significant mortality of D. sibiricus in Northern Asia: the hymenopteran egg parasitoids Telenomus tetratomus and Ooencyrtus pinicolus; the larval parasitoids Aleiodes esenbeckii sp. dendrolimi, Cotesia spp., and Glyptapanteles liparidis; and the dipteran pupal parasitoids Masicera sphingivora, Tachina sp., and Blepharipa sp. Their potential should be further explored in order to develop biocontrol programs for this important forest pest.

Feasting on the ordinary or starving for the exceptional in a warming climate: Phenological synchrony between spongy moth (Lymantria dispar) and budburst of six European tree species

Global warming is affecting the phenological cycles of plants and animals, altering the complex synchronization that has co-evolved over thousands of years between interacting species and trophic levels. Here, we examined how warmer winter conditions affect the timing of budburst in six common European trees and the hatching of a generalist leaf-feeding insect, the spongy moth Lymantria dispar, whose fitness depends on the synchrony between egg hatch and leaf emergence of the host tree. We applied four different temperature treatments to L. dispar eggs and twig cuttings, that mimicked warmer winters and reduced chilling temperatures that are necessary for insect diapause and bud dormancy release, using heated open-top chambers (ambient or +3.5°C), and heated greenhouses (maintained at >6°C or >10°C). In addition, we conducted preference and performance tests to determine which tree species the larvae prefer and benefit from the most. Budburst success and twig survival were highest for all tree species at ambient temperature conditions, whereas it declined under elevated winter temperature for Tilia cordata and Acer pseudoplatanus, likely due to a lack of chilling. While L. dispar egg hatch coincided with budburst in most tree species within 10 days under ambient conditions, it coincided with budburst only in Quercus robur, Carpinus betulus, and, to a lesser extent, Ulmus glabra under warmer conditions. With further warming, we, therefore, expect an increasing mismatch in trees with high chilling requirements, such as Fagus sylvatica and A. pseudoplatanus, but still good synchronization with trees having low chilling requirements, such as Q. robur and C. betulus. Surprisingly, first instar larvae preferred and gained weight faster when fed with leaves of F. sylvatica, while Q. robur ranked second. Our results suggest that spongy moth outbreaks are likely to persist in oak and hornbeam forests in western and central Europe.

Chromosome-level genome assembly of the Asian spongy moths Lymantria dispar asiatica

The Asian spongy moth, Lymantria dispar asiatica, is one of the most devastating forestry defoliators. The absence of a high-quality genome limited the understanding of its adaptive evolution. Here, we conducted the first chromosome-level genome assembly of L. dispar asiatica using PacBio HIFI long reads, Hi-C sequencing reads and transcriptomic data. The total assembly size is 997.59 Mb, containing 32 chromosomes with a GC content of 38.91% and a scaffold N50 length of 35.42 Mb. The BUSCO assessment indicated a completeness estimate of 99.4% for this assembly. A total of 19,532 protein-coding genes was predicted. Our study provides a valuable genomics resource for studying the mechanisms of adaptive evolution and facilitate an efficient control of L. dispar asiatica.

The Impact of a Cypovirus on Parental and Filial Generations of Lymantria dispar L

Recently, we found that the spongy moth Lymantria dispar L. is susceptible to infection by a Dendrolimus sibiricus cytoplasmic polyhedrosis virus (DsCPV-1). In the present study, we evaluated the pathogenicity of DsCPV-1 against L. dispar larvae and its impact on surviving insects after the infection. Offspring of virally challenged insects were tested for susceptibility to a stress factor (starvation). In addition, we used light microscopy and quantitative polymerase chain reaction (qPCR) to test the ability of DsCPV-1 to be transmitted vertically. We found insect mortality of the L. dispar parents following the infection was positively associated with DsCPV-1 dose. DsCPV-1 was lethal to second-instar L. dispar larvae with a 50% lethal dose (LD50) of 1687 occlusion bodies per larva. No vertical transmission of DsCPV-1 to offspring larvae was detected, while the majority of insect deaths among offspring larvae were caused by microsporidia (Vairimorpha lymantriae), which was harbored by the parents. The offspring of virally challenged parents exhibited a higher number of detected microsporidia compared to the control. Our findings suggest that the application of DsCPV-1 is effective in controlling pests in terms of transgenerational impact following virus exposure.

Digestive enzyme activity and macromolecule content in the hemolymph of differentially adapted Lymantria dispar L. populations after short-term increases in ambient temperature

Global, unpredictable temperature increases have strong effects on all organisms, especially insects. Elucidating the effects of short-term temperature increases on midgut digestive enzymes (α-glucosidase, lipase, trypsin, and leucine aminopeptidase - LAP) and metabolic macromolecules in the hemolymph (proteins, lipids, and trehalose) of phytophagous pest larvae of Lymantria dispar is important for general considerations of insect adaptation to a warming climate and potential pest control options. We also wanted to determine whether the different adaptations of L. dispar populations to environmental pollution might affect their ability to cope with heat stress using larvae from the undisturbed, Kosmaj forest and disturbed, Lipovica forest. Heat treatments at 28 °C increased α-glucosidase activity in both larval populations, inhibited LAP activity in larvae from the polluted forest, and had no significant effect on trypsin and lipase activities, regardless of larval origin. The concentration of proteins, lipids, and trehalose in the hemolymph of larvae from the disturbed forest increased, whereas the population from the undisturbed forest showed only an increase in proteins and lipids after the heat treatments. Larval mass was also increased in larvae from the undisturbed forest. Our results suggest a higher sensitivity of digestive enzymes and metabolism to short-term heat stress in L. dispar populations adapted to pollution in their forest habitat, although climate warming is not beneficial even for populations from unpolluted forests. The digestive and metabolic processes of L. dispar larvae are substantially affected by sublethal short-term increases in ambient temperature.

Pre-egg hatch efficacy of dormant applications against Lymantria dispar (Lepidoptera: Erebidae)

Lymantria dispar L. is an invasive, non-native defoliating Lepidopteran established in North America that feeds on forest and urban trees. While many products are available to manage L. dispar post-emergence, few exist to prevent egg hatch when applied to egg masses. Here, we present the results of 3 separate experiments aimed at determining the efficacy of pre-emergent insecticides against L. dispar egg hatch. We found that the labeled rate (1:1) of Golden Pest Spray Oil (GPSO; AI: 93% soybean oil) can prevent L. dispar larvae from emerging in both field and lab assays. In large public spaces, we found that this treatment was ineffective at preventing L. dispar emergence or defoliation. Acelepryn (AI: 18.4% chlorantraniliprole) resulted in some suppression of egg hatch at a very low rate (.06 ml/ 3.8 liter) in both lab and field settings and the efficacy of higher rates should be further investigated. We also tested GPSO against Lepitect (97.4% acephate) in a public area that also received a Foray 48B (12.65% Bacillus thuringiensis, subsp. kurstaki) aerial application. On large oak trees in public areas, GPSO and Lepitect were not effective at reducing defoliation. Dormant pesticide applications generally reduce the risk of affecting negatively predator and parasitoid communities and are therefore desirable. Lymantria dispar pre-egg hatch applications will not work in every situation but should be considered as part of an integrated pest management (IPM) strategy for individual homeowner trees where thorough coverage can be obtained.

SAFARIS: a spatial analytic framework for pest forecast systems

Non-native pests and diseases pose a risk of economic and environmental damage to managed and natural U.S. forests and agriculture. The U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine (PPQ) protects the health of U.S. agriculture and natural resources against invasive pests and diseases through efforts to prevent the entry, establishment, and spread of non-native pests and diseases. Because each pest or disease has its own idiosyncratic characteristics, analyzing risk is highly complex. To help PPQ better respond to pest and disease threats, we developed the Spatial Analytic Framework for Advanced Risk Information Systems (SAFARIS), an integrated system designed to provide a seamless environment for producing predictive models. SAFARIS integrates pest biology information, climate and non-climate data drivers, and predictive models to provide users with readily accessible and easily customizable tools to analyze pest and disease risks. The phenology prediction models, spread forecasting models, and other climate-based analytical tools in SAFARIS help users understand which areas are suitable for establishment, when surveys would be most fruitful, and aid in other analyses that inform decision-making, operational efforts, and rapid response. Here we introduce the components of SAFARIS and provide two use cases demonstrating how pest-specific models developed with SAFARIS tools support PPQ in its mission. Although SAFARIS is designed to address the needs of PPQ, the flexible, web-based framework is publicly available, allowing any user to leverage the available data and tools to model pest and disease risks.

Temperature- and Diet-Induced Plasticity of Growth and Digestive Enzymes Activity in Spongy Moth Larvae

Temperature and food quality are the most important environmental factors determining the performance of herbivorous insects. The objective of our study was to evaluate the responses of the spongy moth (formerly known as the gypsy moth) [Lymantria dispar L. (Lepidoptera: Erebidae)] to simultaneous variation in these two factors. From hatching to the fourth instar, larvae were exposed to three temperatures (19 °C, 23 °C, and 28 °C) and fed four artificial diets that differed in protein (P) and carbohydrate (C) content. Within each temperature regime, the effects of the nutrient content (P+C) and ratio (P:C) on development duration, larval mass, growth rate, and activities of digestive proteases, carbohydrases, and lipase were examined. It was found that temperature and food quality had a significant effect on the fitness-related traits and digestive physiology of the larvae. The greatest mass and highest growth rate were obtained at 28 °C on a high-protein low-carbohydrate diet. A homeostatic increase in activity was observed for total protease, trypsin, and amylase in response to low substrate levels in the diet. A significant modulation of overall enzyme activities in response to 28 °C was detected only with a low diet quality. A decrease in the nutrient content and P:C ratio only affected the coordination of enzyme activities at 28 °C, as indicated by the significantly altered correlation matrices. Multiple linear regression analysis showed that variation in fitness traits in response to different rearing conditions could be explained by variation in digestion. Our results contribute to the understanding of the role of digestive enzymes in post-ingestive nutrient balancing.