DOI: 10.5061/dryad.9s4mw6mns
title: Data from: Winter-moth populations are isolated on co-occurring tree species with contrasting budburst-phenology

description: Differences between neighbouring tree species in phenology could isolate
 populations of host-plant generalists that depend on matching the
 phenology of their host. We studied the relationship between the
 budburst phenology of two co-occurring tree species with early (hornbeams)
 and late (oaks) budburst, and the egg-hatching date of associated winter
 moths (Operophtera brumata) during two seasons (autumns starting in 2020
 and 2021). A previous study in spring 2019 had found no winter
 moth larvae on the focal oaks, while we found them mainly on oaks with
 hornbeam neighbours in 2022. Congruently, adult winter moths were rarely
 encountered during the autumns of 2018 and 2019 and sparsely in 2020 and
 2021, and then mainly near hornbeams.The vast majority of winter moths had
 early-hatching eggs when both hornbeams and oaks were present, matching
 the hornbeams rather than the oaks. Where hornbeam was absent in the
 neighbourhood, the few winter moths had late-hatching eggs.These results
 suggest that winter moth populations on hornbeam and oak are to some
 degree isolated from each other despite spatial proximity, so that
 recolonization of oaks by populations synchronized with budburst of
 hornbeam is slow. Therefore, trees would benefit from differing from their
 neighbours in budburst phenology with respect to herbivore damage.
description: <em>Study system:</em> We selected 35 individual
 mature sessile oaks and recorded the species identity of neighboring trees
 (trees with which the crown is in touch) in the Puszcza Zielonka forest in
 Western Poland [52°33′12″N 17°06′48″E; 17]. This forest consists mainly of
 sessile oaks and pines (<em>Pinus sylvestris </em>L., not
 suitable for winter-moth larvae), with a sub-canopy of common hornbeam in
 some areas [18]. The selected oaks were located in two clusters near the
 villages Kamińsko and Zielonka. The neighbourhoods of focal oak trees near
 Kamińsko often included hornbeams (4 out of 7 sites), but hornbeams were
 absent in sites near Zielonka village (6 sites). In this region, hornbeams
 typically are among the first trees to burst buds, and oaks the
 last. Winter-moth larvae are generalist feeders,
 attacking leaves and flowers of most woody angiosperms in temperate
 regions, including oaks and hornbeam. They can cause extensive defoliation
 in forest stands during cyclic outbreaks, leading to reduction in radial
 growth of trees. The wingless females eclose from the leaf litter during
 evenings of autumn of early winter, orient towards tree trunks where they
 mate with winged males, and then climb up to deposit eggs in the canopy.
 The egg-hatching phenology is highly heritable. When larvae hatch from
 eggs in spring, they can wait for several days for buds to burst, and they
 may also disperse by ballooning to avoid starvation. In case eggs hatch
 when leaves have already developed, their food quality is low and this
 results in lower fitness. Overall, host-plant choice is limited to larvae
 making the risky decision to leave a tree. Larvae finally pupate in the
 leaflitter below the tree. <em>Abundance of
 larvae</em>: We used a slingshot and ropes to obtain canopy branches
 from ten focal oaks [sampled before in 2019; 17] on May
 11<sup>th</sup> and 16<sup>th</sup> 2022. From
 each tree, we collected two to three branches on a sheet and counted the
 number of winter-moth larvae. Three of these trees were in neighbourhoods
 with hornbeams, while the others were far from hornbeams.
 <em> </em><em>Budburst phenology</em>: We
 determined the budburst date of focal oak trees, their neighbouring oaks
 (in total 126 individual oaks) and hornbeams (24 individuals) in 2022. To
 estimate the day of 50% budburst for each tree, we visited trees every
 three to four days during the period of budburst. On each observation day,
 one observer scored the per cent budburst of each tree crown on branches
 from four cardinal directions using binoculars. We then interpolated or
 extrapolated the day of 50 per cent budburst.
 <em>Egg-hatching phenology</em>: Our attempts to
 collect adult winter moths in 2018 and 2019 were largely unsuccessful. We
 collected mating pairs of winter moths in October and November 2020 and
 2021 (between 5 pm and 8 pm) from the trunks of focal oak trees and their
 neighbours into plastic vials with foam stoppers. That same evening, we
 transferred mated females to vials with rolled tissue paper for egg-laying
 and kept the vials with eggs outdoors in the shade. We then determined the
 date-of-first-egg-hatching during the following spring for the eggs of
 each female.
description: These are Excel files with raw data, plus the R code for the
 eg-hatching data.
description: # Data from: Winter-moth populations are isolated on co-occurring tree
 species with contrasting budburst-phenology One file shows the data on
 collection of winter moths at the trunk of trees, and subsequent egg
 hatching date. There is a separate sheet for each year. The file also
 gives information about the neighborhood of the focal trees (trees with
 which the crown is in contact). The other file shows the budburst
 phenology of the trees. Each file has a sheet with explanations of column
 names. Moths were collected into vials in the field and females were then
 transferred to a vial with tissue paper on which she could lay eggs in
 autumn. Vials with eggs were stored outdoors. In spring, we daily checked
 all the vials for hatchling caterpillars.  Egg hatching data column names.
 | Date | Date moth was collected | | :------- |
 :----------------------------------------------------------------------------------------- | | Vial | Vial number | | tree | Tree on which the moth was collected | | Remarks | Comments | | EggHatch | Date of hatching of first eggs | | Oak | Percentage of oaks | | Pine | Percentage of pines | | Beech | Percentage of beech | | Hornbeam | Percentage of hornbeams | | HBpres | Pressence of hornbeams in the neighborhood, including small trees not counted as neighbors | Budburst data. We estimated the percentage budburst of up to 4 cardinal directions of a tree and then averaged these foe a date. We then plotted percent budburst over time and interpolated the date of 50% budburst. | Entry | data entry code | | :------- | :------------------------------------------------------------------------------------ | | Tree | Tree individual. Focal trees are numbered with neighboring trees denoted with letters | | Species | Hornbeam or oak. | | 50%Date | Estimated date of 50% budburst | | Date | Date of observation | | meanBuds | Mean of the 4 branches observed | | N | North | | W | West | | S | South | | E | East | | comment | comments |