DOI: 10.5061/dryad.15dv41p0w
title: Tracking Global Invasion Pathways of the Spongy Moth (Lepidoptera: Erebidae) to the U.S. using Stable Isotopes as Endogenous Biomarkers

description: The spread of invasive insect species causes enormous ecological damage
 and economic losses worldwide. A reliable method that tracks back an
 invaded insect’s origin would be of great use to entomologists,
 phytopathologists and pest managers. The spongy moth (Lymantria dispar
 (L.d.), Linnaeus 1758) is a persistent invasive pest in the north-eastern
 United States (U.S.) and periodically causes major defoliations in
 temperate forests. We analysed field-captured (Europe, Asia, U.S.) and
 lab-reared L.d. specimens for their natal isotopic hydrogen and nitrogen
 signatures imprinted in their biological tissues (δ2H and δ15N) and
 compared these values to the long-term mean δ2H of regional precipitation
 (Global Network of Isotopes in Precipitation) and δ15N of regional plants
 at the capture site. We established the percentage of hydrogen-deuterium
 exchange for L.d. tissue (Pex=8.2%) using the comparative equilibration
 method and two-source-mixing-models, which allowed the extraction of the
 moth’s natal δ2H value. We confirmed that the natal δ2H and δ15N values of
 our specimens are related to the environmental signatures at their
 geographic origins. With our regression models, we were able to isolate
 potentially invasive individuals and give estimations of their geographic
 origin. To enable the application of these methods on eggs, we established
 an egg-to-adult fraction factor for L.d. (Δegg-adult = 16.3‰ ± 4.3‰). Our
 models suggested that around 25% of the field-captured spongy moths
 worldwide were not native in the investigated capture sites. East Asia was
 the most frequently identified location of probable origin. Furthermore,
 our data suggested that eggs found on cargo ships in U.S. harbors in
 Alaska, California and Louisiana most probably originated from Asian L.d.
 in East Russia. These findings show that stable isotope biomarkers give a
 unique insight into invasive insect species pathways and thus, can be an
 effective tool to monitor the spread of insect pest epidemics.
description: MEASUREMENTS<br>The data was obtained at the University of Natural Resources and Life
 Sciences isotope laboratory (Tulln, Austria) between 2017 and 2019
 by analysing tissue of spongy moths (Lymantira dispar,
 Lepidoptera: Erebidae, formally known as "gypsy moth") for
 their hydrogen stable isotope ratio (2H/1H
 = δ2H) using a TC/EA system (Thermo Fisher), a ConFlo III open
 split interface (Thermo Fisher) and a DeltaPLUS XP isotope-ratio mass spectrometer
 (IRMS, Thermo Fisher) nitrogen stable
 isotope ratio (15N/14N = δ15N) using a
 EA (Flash 2000) and IRMS
 Delta V system (Thermo Fisher) 
 For δ2Hanalysis, quadruplet
 samples of 0.2±0.025 mg
 each of the moths’ tarsus (lowest part of the leg, dominantly consisting
 of chitin) were weighed into silver capsules for solids (3.3x5 mm, IVA
 Analysentechnik). Eggs were sampled as a whole. A full complement of
 in-house water reference materials (measured against VSMOW and VSLAP) and
 the international standards IAEA CH7 PEF1 (δ2H = -100.3‰), USGS 43 Indian
 hair (δ2H = -44.4‰), IVA Casein 139443 (δ2H = -113.0‰) and IVA NBS22 (δ2H
 = -116.9‰) were used. The H3+ contribution (“H3-factor”) was determined
 before every measurement. For the δ15N analysis, 2±0.3 mg of moth tissue were sampled into tin capsules for solids (5x8 mm, IVA Analysentechnik). Due to a lack of samples, multiple specimens were combined into one sample for the δ15N analysis. This introduced additional variance to the δ15N results. We used IVA Urea (δ15N = -0.36‰), IAEA 600 Caffeine (δ15N = 0.9‰) and IVA Casein 165389 (δ15N = 5.9‰) as reference materials.
description: Microsoft Excel, 64-bit