Relative impacts of gypsy moth outbreaks and insecticide treatments on forest resources and ecosystems: An experimental approach

1. Gypsy moth outbreaks cause severe defoliation in Holarctic forests, both North America where it is invasive, and its native range Eurasia. Defoliation can hamper timber production impact ecological communities processes. Aerial insecticide applications are regularly performed outbreak areas to mitigate economic losses. These operations be financially costly harmful non-target species may disrupt interaction networks. However, replicated studies of the relative impacts gypsy application on forest growth animal rare have yet carried out species' indigenous range. 2. Here, we review pathways which chemical control these affect ecosystems. We then present an experimental design established South Central Germany early 2019, aiming study consequences eruptions oak forests. The study's full factorial comprises stands at high low risk, either treated with tebufenozide or left unsprayed, within 12 blocks. Measurements structure, tree mortality, density, composition lepidopteran, bird, bat, ground beetle, canopy arthropod will conducted for several years. 3. One-year intensive monitoring populations damage across selected sites showed substantial differences population density between plots risk efficacy suppressing plots. In first year experiment, predicted differed strongly, confirming importance using many replicates blocking spatial heterogeneity. experiment running continuously during coming years produce short- medium-term data improve our understanding management outbreaks. Massenvermehrungen des Schwammspinners verursachen schwere Entlaubungen holarktischen Wäldern, sowohl Nordamerika als invasive Art auch ihrem natürlichen Verbreitungsgebiet Eurasien. Eine Entlaubung kann die Holzproduktion beeinträchtigen und sich auf ökologische Gemeinschaften Prozesse auswirken. Um ökonomische Schäden zu mindern, werden Massenvermehrungsgebieten regelmäßig Insektizide mittels Luftfahrzeugen ausgebracht. Diese Einsätze können teuer sein schädlich Nichtzielorganismen Interaktionsnetzwerke von Arten Allerdings gibt es nur wenige replizierte Studien, Einflüsse Schwammspinnerausbrüchen der damit verbundenen Insektizidbehandlung Waldwachstum Tiergemeinschaften untersuchen. Auch im stehen entsprechende Untersuchungen noch aus. Wir geben hier einen Überblick, welchen Wegen Massenvermehrung dessen chemische Bekämpfung Waldökosysteme beeinflusst. Anschließend stellen wir experimentellen Versuchsaufbau vor, Anfang 2019 Süd- Mitteldeutschland etabliert wurde darauf abzielt, ökologischen ökonomischen Konsequenzen Schwammspinnerausbrüche Eichenwäldern Das vollfaktorielle Design Studie umfasst experimentelle Versuchsflächen aus Waldbeständen mit hohem niedrigem Entlaubungsrisiko, entweder Tebufenozid behandelt wurden oder unbehandelt blieben. –struktur, Baumsterblichkeit, Schwammspinnerdichte sowie Gemeinschaftsstruktur Schmetterlingen, Vögeln, Fledermäusen, Laufkäfern Arthropoden Baumkronen über mehrere Jahre aufgenommen. Ein Jahr intensives Monitoring Schwammspinnerpopulation den ausgewählten zeigten substanziellen Unterschied Populationsdichte zwischen Flächen Entlaubungsrisiko eine hohe Wirksamkeit beim Unterdrücken behandelten Flächen. Im ersten Untersuchungsjahr unterschieden prognostizierten Ausbruchsflächen stark, was Wichtigkeit vielen Replikaten Blöcken bestätigt, um räumliche Heterogenität auszugleichen. Experiment wird kontinuierlich während kommenden durchgeführt, kurzfristige mittelfristige Daten generieren, zur Verbesserung unseres Verständnisses Managements beitragen werden. Lymantria dispar L. (Lepidoptera: Erebidae), a tussock Europe Asia, widely acknowledged as one most critical defoliators region. It exhibits cyclical dynamics that often periodic spatially synchronous over large distances (Haynes, Liebhold, & Johnson, 2009) believed driven by more trophic interactions (Johnson, Bjørnstad, McManus, 2005). larvae voracious folivores feed up 10 weeks per than 300 broadleaf coniferous trees (Elkinton 1990). This combination dynamics, broad polyphagy long larval duration granted unmatched ability rapidly defoliate forested areas. Multiple been reported last decades throughout range, including (Alalouni, Schädler, Brandl, 2013; Lentini et al., 2020; Villemant, 2010; Wulf Graser, 1996), Africa (Villemant, 2010), Asia (Orozumbekov, Ponomarev, Tobin, Japan (Liebhold, Higashiura, Unno, 1998). owes infamous reputation mostly disastrous American Since introduction Massachusetts 1869, has colonized Eastern United States Southeastern Canada keeps expanding Halverson, Elmes, 1992; Régnière, Nealis, Porter, 2009; Tobin 2004). Recent cost estimates government expenditures losses, appraised overall financial toll invasion staggering US$3.2 billion (Bradshaw 2016). Europe, problem generally considered less (McManus Csóka, 2007) although comprehensive synthesis lacking. Estimates costs merely extrapolated from published reports extent insecticides (Alalouni 2013), while related market remain scarce scattered. Likewise, current knowledge their associated practices drawn species. Both measures synthetic biological adverse effects ecosystems (Herms, 2003). Experimental approaches integrating aspects would grant powerful tool environmental sustainability but rare. study, reviewed different through use used synthesized biologically sound hypotheses (Figure 1) baseline develop field aims address processes moth. univoltine life cycle Adult females lay egg masses indiscriminately bare surfaces vicinity host midsummer, each cluster typically containing 100 1200 eggs (Andresen 2001; Doane 1981). already fully developed inside 1 month after oviposition enter diapause winter months, eventually hatching spring bud-burst. young caterpillars hang branch tips silken threads, allowing them spread other forests via airborne dispersal. described spring-early summer defoliator. feeding starts late April continues weeks, until pupation June–early July. Pupation takes place various sheltered places, example bark ridges, lasts approximately 2 weeks. Adults wings July August live 6–10 days. Females pheromones attract males shortly mating close site emergence (Doane 1981; Wellenstein Schwenke, primarily health defoliation, turn significantly reduce production. primary include reduced (Muzika 1999; Naidoo Lechowicz, 2001), root biomass (Thomas, Blank, Hartmann, 2002) fruit (Gottschalk, also induce levels mortality (Campbell Sloan, 1977; Kegg, 1973; Lobinger, 1999), vary intensity depending frequency, magnitude vitality trees, well additive action biotic abiotic stresses (Davidson, Gottschalk, 1999). death community structure regeneration herbaceous vegetation competitive among sub-canopy released increased light availability gaps (Fajvan Wood, 1996). Damage caused vegetative reproductive parts can, turn, bottom-up communities. Increased proportion snags deadwood benefit cavities (Koenig, Walters, 2011). Strong reduction green leaf shown negatively herbivores sharing plants, especially specialist (Work McCullough, 2000), damage-induced changes chemistry impede survival competing (Nykanen Koricheva, 2004; Redman Scriber, 2000). Furthermore, secondary infestations pathogens inhibit later-season herbivory (Csóka, Pödör, Nagy, Hirka, 2015; Tack, Gripenberg, Roslin, 2012) mast failure rely acorns food source (Clotfelter 2007). Additionally, drive activity predators parasitoids, intensifying top-down pressures (Faeth, 1986; difficult quantify level, dramatically (Timms Smith, fact, analyses lepidopteran assemblages moth-infested only minor alterations compared non-outbreak situations, despite strong negative responses single (Sample, Butler, Zivkovich, Whitmore, Reardon, 1996; Timms 2011; Work generate resource pulses erupting caterpillar densities offer superabundance prey insectivorous predators, influencing behaviour dynamics. well-adapted moth, such cuckoos Coccyzus sp., hunter Calosoma sycophanta (Coleoptera: Carabidae), strongly correlated (Gale, DeCecco, Marshall, McClain, Cooper, Weseloh, 1985). Moreover, nitrogen-rich faeces, corpses prematurely abscised foliage spike nitrogen input soil (Lovett, Canham, Arthur, Weathers, Fitzhugh, 2006), lead leaching when (Lovett 2002). stimulated development subdominant increases habitat understory-nesting birds (Cooper, Dodge, 1993; Gale openness promotes nest predation (Thurber, 1994). States, combat since inception 19th century (Liebhold Even though hopes eradication were definitively abandoned 1960s, still measure contain expansion protect distribution area (Natural Resources Canada, USDA Forest Service, 2020). Insecticides frequently employed species’ differs countries moulting disruptor diflubenzuron 1980s 1999) applied some European recently (Schönfeld, 2009). Although not toxic vertebrates, concerns raised regard invertebrates (Durkin, 2004a) potential metabolite 4-chloroalinine human (European Food Safety Authority, 2012). microbial Bacillus thuringiensis var. kurstaki (BTK) hormone agonist later approved biorational alternatives due Lepidopteran-specific nowadays principal management. While BTK (USDA 2020), preferred option Germany, greater reliability effectively (Lemme, Müller-Kroehling, 2019). Toxic side-effects appear restricted Lepidoptera 2004b references therein; Durkin Klotzbach, 2004 therein), assessment involving comparatively (but see Kondo, Blue, 1997 Leroy spraying usually mid-spring soon start leaves. At this time, insect canopies dominated (Martinat, Coffman, 1988; Southwood, Wint, Kennedy, Greenwood, 2013). Therefore, about depressed abundances mainly fulfil energy requirements breeding season Martinat, Donahoe, no effect bird communities, foraging behaviour, success observed individual (Awkerman Durkin, 2004a, Holmes, 1998; Lih, Stephen, Wallis, Diet shifts relocation territories documented rodents (Bellocq, Bendell, Cadogan, Seidel 1995). Indirect predatory arthropods poorly known. Klenner (1996) Carabid beetles unable determine whether pattern direct toxicity availability. scarcity expected parasitoid populations, parasitism sub-lethally intoxicated hosts appears differ could influenced insecticide-specific physiological (Erb, Bourchier, van Frankenhuyzen, McCravy, Dalusky, Berisford, Weseloh 1983). Based respective Lepidoptera, Scriber (2004) suggested decision non-intervention damaging insecticides. hypothesis tested integrative approach numerous play 1). Such should consider fact variable. Due factors interactions, stands, potentially leading considerable variation (e.g. Sample Because must order effective, decisions based counts trunks previous winter. surveys cannot systematically predict instar larvae, initiation tailored treatment following conditions: (1) selection broadly differing mass densities, allow contrasting conditions; (2) sufficiently able realistic scale; (3) exclusion recent history so results confounded carry-over past treatments; (4) sufficient replication account unforeseeable sites; (5) randomized block closely located structurally comparable blocks, heterogeneity (6) blocks stand climatic conditions, generalization results. Here describe large-scale fulfils conditions. composed two densities. An randomly attributed plot class. three main objectives: fostering range; providing information indirect ecosystems; evaluating tebufenozide-based treatments help sustainable article, introduce process, variables measured experiment. discuss viability year. set region Franconia, north-western Bavaria, 2400 km2 delimited cities Würzburg West, Schweinfurt North, Bamberg East Bad Windsheim 2). landscape matrix agricultural land (arable land, vineyards grasslands) surrounding patches variable size Forests deciduous oaks (Quercus robur Quercus petraea Mattuschka) subjected 1990s (Lemme Local district foresters four administrative regions – Upper Middle Lower Franconia Swabia fall 2018, standardized protocol. number counted lowest m along transect comprising, cases, dominant social abundance underside lower branches tree, vitality, age reported. calculate ‘defoliation index’ (DRI) identify (Supplementary Information, file S1). total, 26823 surveyed 2802 transects. searched oak-dominated (DRI>1) (DRI<0.5) excluding (i.e. average overstory <70 old) spray history, centrally stored records Bavaria. Candidate individually checked on-site visits stand-structural homogeneity, heterogeneous excluded. minimum (two DRI DRI) least five hectares each, random class fashion, consists plots: unsprayed (further referred ‘high-control’); sprayed (‘high treatment’); (‘low-control’); (‘low-treatment’) (Figures Overall, 142 778 transects (7534 trees) inspected, 22 candidate comprising 108 retained. Once suitable approval landowners sought nested into design. As aim attribution initially done drawing number. process challenged constraints. First, allowed defoliation. denomination (‘treatment setting’) Bavarian State Institute Forestry (LWF) legal basis Thus, all low-treatment plots, high-treatment falling outside setting, permission had authorities. Second, decide follow recommendation LWF not. Owners’ objections allocation led 18 S2-1 Supporting Information). Third, concurrent negotiations, compliance state guidelines nature protection. prohibit apply shortlist local conservation value impacted directly Euplagia quadripunctaria, Lepidoptera: Erebidae) indirectly Bubo bubo, Strigidae). obtained permissions under rule eight threat posed minimal available plot; Figure Information; Supplementary S3). A final 48-plot covering total 647 ha, 311 ha tebufenozide, outcome validation Around centre plot, 4.5-ha subplot investigations conducted. detailed description location, size, composition, type, date provided Table S4-1 Information. Tebufenozide Mimic® (Spiess-Urania Chemicals, Hamburg, Germany; 240 g L−1 active ingredient [a.i.]) maximal rate 750 mL diluted 50 L water 180 a.i. ha−1), 3 23 May 2019. length window extended procedures unfavourable weather Treatment Bell 208 helicopter equipped Simplex system (Simplex Aerospace, Portland, Oregon, USA) nozzle 5 according German regulations (German Federal Office Consumer Protection Safety, 2019) ranging 6.7 27.8 314 (Table S5-1 Application proceeded dry wind conditions speed below 2.5 s−1) block-wise applicable. During (2019), intensively sampled response components ecosystem (trees, fauna) hereby collection shall repeated post-treatment assess continuing recovery. Photographs survey methods, map list found S6. marked 20 44 × = 880 (11 blocks; T included time constraints). addition central six nearest neighbours diameter breast height higher 7 cm influences (Prodan, 1968). Starting ‘six-tree samples’ taken cardinal points 3(a)). circles positioned 25, 50, 75, 125 infested (origin coordinate 3(b)). sample served record characteristics basal area, standing stock). Within circle, medium sampling. Species, diameter, position crown transparency neighbour scored. investigate long-term additionally permanent girth tape. growing season, tapes read times (April, June, July, September November). 2020 additional future, reading checking annually autumn completion annual ring formation immediately before growth, eliminate artefacts swelling shrinkage, defects manipulation overstretching tension springs. January 2020, fences (5 m) installed 30 natural 3). fence analyse influence browsing. adjacent areas, individuals maximum m, separated species, intervals cm. browsing addressed individual. estimate regeneration, undamaged representative entire spectrum dried constant weight weighed separately shoot. recordings 2021 another if possible. With i representing focal point: peak, refoliation. TLS extra year, To taken: (a) sampling pyrethrum knockdown, (b) ground-dwelling pitfall traps, (c) adult (d) songbird recorders boxes, (e) bat call recorders. Canopy arthropods. Crown-dwelling knockdown SwingFog SN50 fogging machines (Swingtec GmbH, Isny, Germany). mature area. Fogging away response, prevent impacting populations. Four tarpaulin sheets (3 laid floor crowns neighbours, distance