DOI: 10.5061/dryad.41ns1rnks
title: Data from: Forest defoliation by an invasive outbreak insect: Catastrophic consequences for a charismatic mega moth

description: Earth is now experiencing declines in insect abundance and diversity
 unparalleled in human history. The drivers underlying those declines are
 many, complex, and incompletely known. Here, using a natural experiment,
 we report the first test of the hypothesis that forest defoliation by an
 invasive outbreak insect compromises the fitness of a native insect via
 damage-induced increases in toxicity of the forest canopy. We demonstrate
 that defoliation by the invasive spongy moth (Lymantria dispar) elicits an
 average 8.4-fold increase in foliar defense expression among aspen
 (Populus tremuloides) genotypes. In turn, elevated defense dramatically
 reduces survivorship, feeding, and growth of a charismatic mega moth
 (Anthereae polyphemus). This work suggests that changes to the
 phytochemical landscape of forests, mediated by invasive outbreak insects,
 are likely to negatively impact native insects, with potential
 repercussions for community diversity and ecosystem function across
 expansive scales.
description: # Data from: Forest defoliation by an invasive outbreak insect:
 Catastrophic consequences for a charismatic mega moth ## General
 description data from invasive species defoliation study This file
 describes the data files associated with the manuscript Forest defoliation
 by an invasive outbreak insect: catastrophic consequences for a
 charismatic mega moth. This project investigated downstream effects of an
 invasive outbreak species (*L. dispar*) on chemical composition of a host
 plant (aspen) to a charismatic native species(*Anthereae polyphemus*). We
 analysed phytochemical defense compounds (salicinoid phenolic glycosides,
 SPGs) between undefoliated forest throughout the year in which the
 outbreak took place. We assessed polyphemus larval performance via
 targeted feeding bioassays, incorporating leaves from the previously
 undefoliated and defoliated aspen forests. ### Forest phytochemistry data
 The file entitled `forest_phytochemistry_data.csv` contains data on aspen
 SPG (salicinoid phenolic glycoside) levels collected over multiple years
 (2020-2021) from two experimental forests. Each row represents
 observations for a single tree. Variable (column) descriptions are as
 follows: * **year**: calendar year during which the tree was sampled *
 **forest**: the experimental forest in which the tree resides.
 "UND" indicates the forest that was not subject to the *L.
 dispar* outbreak (undefoliated) and "DFL" indicates the forest
 that was defoliated. * **source**: a data clustering identifier
 ("A", "B", "C", or "D") used to
 filter the data for some analysis. * **collection_period**: the calendar
 period during which leaves were collected from trees for chemical
 analysis. * **genet**: the unique identifier of the tree's genotype.
 * **tree_ID**: the unique identifier of the individual tree. *
 **Scort_pct**, **Tcin_pct**, **Scin_pct**, **Tdin_pct**, and **SPG_pct**:
 the measured concentration, as a percent of dry leaf mass, of the
 salicinoids salicortin, tremulacin, salicortin, tremuloidin, and their
 sum. * **outbreak**: indicates whether the trees were measured before
 ("pre") or after ("post") the outbreak of *L. dispar*.
 ### Polyphemus bioassay data The file entitled
 `polyphemus_bioassay_data.csv` contains data from the Polyphemus feeding
 trials, in tabular form. Each row represents observations taken from a
 single third instar (L3) larva. Missing data, caused by larval mortality
 are represented by 'NA'. The columns are grouped such that
 columns 1-3 provide tree information, 4-8 provide foliar chemistry
 (salicinoid) data, 9-10 provide larva information, and 11-17 provide
 larval performance data. More detailed variable (column) descriptions are
 as follows: * **forest**: the experimental forest from which bioassay
 leaves were collected. "UND" indicates the forest that was not
 subject to the *L. dispar* outbreak (undefoliated) and "DFL"
 indicates the forest that was defoliated. * **genet**: the unique genotype
 identifier of the tree from which bioassay leaves were collected. *
 **tree_ID**: the unique tree identifier from which bioassay leaves were
 collected. * **Scort_pct**, **Tcin_pct**, **Scin_pct**, **Tdin_pct**, and
 **SPG_pct**: the measured concentration, as a percentage dried leaf mass,
 of salicorin, tremulacin, salicin, tremuloidin, and total salicinoid
 phenolic glycocides (i.e., sum of preceding four SPGs). * **larval_ID**:
 the unique identifier for an individual bioassay larva. * **larval_rep**:
 larval replicate (1 or 2). For each tree within a genotype, two replicate
 larvae were included in the bioassays. * **consumption_mg**: the amount of
 dry biomass, in milligrams, consumed by a larva during the bioassay. *
 **biomass_gained_mg**: the amount of dry biomass, in milligrams, gained by
 a larva during the bioassay. * **RGR**: relative growth rate, in dry
 milligrams per milligram per day, of a larva during the bioassay. *
 **RCR**: relative consumption rate, in dry milligrams per milligram per
 day, of a larva during the bioassay. * **instar_duration_d**: total number
 of days that the larva remained in the third larval stadium. *
 **larva_survived**: indication of whether ("yes") or not
 ("no") the larva survived the bioassay. ### Analysis The
 documents `analysis.Rmd` and `analysis.R` contain R code needed to
 reproduce the statistical analyses conducted in the manuscript.