Nonhost Trees Research Articles

Spatial Pattern of Host Tree Size, Rather than of Host Tree Itself, Affects the Infection Likelihood of a Fungal Stem Disease.

The spatial pattern of diseased forest trees is a product of the spatial pattern of host trees and the disease itself. Previous studies have focused on describing the spatial pattern of diseased host trees, and it remains largely unknown whether an antecedent spatial pattern of host/nonhost trees affects the infection pattern of a disease and how large the effect sizes of the spatial pattern of host/nonhost trees and host size are. The results from trivariate random labeling showed that the antecedent pattern of the host ash tree, Fraxinus mandshurica, but not of nonhost tree species, impacted the infection pattern of a stem fungal disease caused by Inonotus hispidus. To investigate the effect size of the spatial pattern of ash trees, we employed the SADIE (Spatial Analysis by Distance IndicEs) aggregation index and clustering index as predictors in the GLMs. Globally, the spatial pattern (vi index) of ash trees did not affect the infection likelihood of the focal tree; however, the spatial pattern of DBH (diameter at breast height) of ash trees significantly affected the infection likelihood of the focal tree. We sampled a series of circular plots with different radii to investigate the spatial pattern effect of host size on the infection likelihood of the focal tree locally. The results showed that the location (patch/gap) of the DBH of the focal tree, rather than that of the focal tree itself, significantly affected its infection likelihood in most plots of the investigated sizes. A meta-analysis was employed to settle the discrepancy between plots of different sizes, which led to results consistent with those of global studies. The results from meta-regression showed that plot size had no significant effects.

Overwintering spruce budworm population density as predictor of following-year larval density and defoliation on balsam fir

The Early Intervention Strategy (EIS) was developed to control spruce budworm (SBW) populations before an outbreak develops. It uses an action threshold population density originally based on feeding fourth-instar larvae (L4) sampled in spring. But in practice, in all SBW management strategies, it is the density of overwintering second-instar larvae (L2) sampled in the previous fall that is used in decision making. Those densities serve to predict defoliation and plan control operations for the following summer. Therefore, there was a need to establish a relationship between L2 and L4 (apparent survival) by which to adequately express treatment thresholds in terms of L2 rather than L4. This was done with samples collected in each life stage in several sites in Quebec and New Brunswick and over three different periods between 1999 and 2022. We found that the distribution of L2 is more aggregated than that of L4, and thus that sample sizes needed for precise density estimation in that stage are larger than at the L4. We also found that apparent survival between L2 and L4 varies at low and high L2 densities for different reasons. For example, movement of larvae from the inner crown, bole, or non-host trees affect apparent survival at the lowest population densities. In contrast, at very high densities survival of populations during these early larval stages is reduced by crowding effects. At densities in the mid-range where control decisions need to be made, apparent survival is very close to 100% and varies little among years. The current threshold density is 3.5 L4 per 45-cm branch tip and was established as 7 L2 per 75-cm branch by assuming 50% mortality. Considering the results presented here, we recommend that the current EIS intervention threshold be set at 3.5 L2 per 75-cm branch. In this density, defoliation typically ranges between 15 and 30% in the following summer in the absence of treatment.

The attractive host volatiles can enhance oviposition of Anoplophora glabripennis on a non-host tree.

The Asian longhorned beetle (ALB), Anoplophora glabripennis, is a serious wood borer of hardwood trees. Populus deltoides 'Shalinyang' (PdS) is attractive to ALB adults for oviposition but highly resistant to their offspring. Investigation of the chemicals regulating ALB oviposition is scarce in previous studies until now. To determine which chemicals emitted by PdS were attractive and induced oviposition behavior by ALB on non-host poplar tree species, we first: collected and identified the bio-active volatiles produced by PdS using coupled gas chromatography-mass spectrometry (GC-MS) and coupled gas chromatography-electroantennographic detector (GC-EAD); then evaluated which chemicals were attractive in a Y-tube olfactometer bioassay; and finally screened key compounds affecting ALB oviposition using a 'chemical-stimulated oviposition on non-host tree' bioassay. (E)-2-Hexenal, hexyl acetate, (Z)-3-hexenol acetate, 1-hexanol, (Z)-3-hexenol, β-caryophyllene, and salicylaldehyde emitted from PdS were attractive to ALB. When (E)-2-hexenal, 1-hexanol, (Z)-3-hexenol acetate, and (Z)-3-hexenol were applied to the non-host tree Populus tomentosa, oviposition by ALB females was significantly increased. Furthermore, the mean number of oviposition pits increased as the (Z)-3-hexenol concentrations increased. Further tests on synergy between pairs of chemicals showed that (Z)-3-hexenol stimulated production of the most oviposition pits, but that the percentage of effective oviposition pits (those containing an egg and larva and not empty) decreased. (Z)-3-Hexenol is the main chemical component inducing ALB oviposition. These results increase understanding about the oviposition behavior of ALB and could help improve management strategies that regulate ALB behavior by planting mixed-species forests resistant to ALB. © 2023 Society of Chemical Industry.

Tree canopy patterns in a temperate forest in Oaxaca, Mexico after bark beetle outbreaks: Implications for ecological resistance and resilience

Bark beetles (BB) are an insect that can become a forest pest and that principally affects temperate regions globally, massively killing tree hosts, mainly coniferous species. When tree hosts are the dominant species in the canopy, BB outbreaks may impose important changes in the structure, composition and diversity of forests, from the stand to the regional scale. In Mexico, during the current century, BB pests have become the main biotic threat in forests where Pinus species are dominant. Questions addressed in this study are: What is the structure, composition and diversity of the forest canopy after BB disturbances? and “What are the implications for ecological resistance and resilience of the forest”? The study site was located in the Sierra Norte region in Oaxaca, Mexico, where more a decade ago BB outbreaks affected the forest. In ninety plots of 500 m2 (4.5 ha) all live trees with ≥ 5 cm diameter at breast height (DBH) were located, their DBH was measured, and the species was identified. As well, all stumps resulting from previous sanitation logging and timber extraction (TE) were located and for each condition, basal diameter was estimated and the genera identified. For the post-disturbance canopy, density basal area, species composition and diversity (alpha and beta) were estimated. This data plus the analysis of the stumps was used to estimate the tree canopy structure before the BB outbreaks. Statistical comparisons among BB, TE disturbances and condition without disturbance were conducted. Based on interviews with local experts, a rank of risk to BB among Pinus species was established. A total of 4,053 live trees and 547 stumps were found. The live trees corresponded to 24 species from 8 genera. Pinus genus and, particularly P. patula predominated. Seventy-five percent of the individuals had < 20 cm DBH and a J-inverted diametric distribution resulted. Individuals with DBH ≥ 100 cm were found only in the condition without disturbance. Three of the nine Pinus species, were BB main-host species, and the least preferred host was P. ayacahuite. The three BB main-host species dominated the post-disturbance canopy (including regeneration). In contrast, P. ayacahuite and other non-host tree species dominated in the conditions without disturbance, and the three main-host species showed low density. As well, high species richness occurred in areas affected by BB. Since climate change will likely continue to exacerbate BB outbreaks, it is proposed that to increase ecological resistance and resilience forest management practices should focus on reducing density, promoting a mix of host and non-host species, increasing tree diversity and avoiding stands with monodominance of main-host species.

When tree diversity does not work: The interacting effects of tree diversity, altitude and amount of spruce on European spruce bark beetle outbreaks

The frequency of large-scale insect outbreaks is expected to increase with climate change, and the European spruce bark beetle (Ips typographus) is a major forest pest in Europe that has caused more extensive and widespread outbreaks in recent years. It is therefore important to evaluate forest management strategies for controlling bark beetle populations. While tree species diversity is often promoted as a way to improve forest resistance to specialist insects, the relationship between tree species diversity and bark beetle outbreaks is not well understood, partly due to the complex interactions with other factors. The aim of this study was to assess the impact of tree species diversity on European spruce bark beetle outbreaks, while controlling for host availability across different altitudes. We analysed data from a systematic 1 × 1 km grid in Slovenia. For each grid cell, we extracted data on the sanitary felling of Norway spruce that followed bark beetle outbreaks from a national data base covering the period 1996–2017. Additionally, we extracted data on resource availability (i.e., the percentage of Norway spruce in the grid cell), non-host tree species diversity and average altitude. We analysed the effect of altitude, forest cover, percentage of spruce and non-host tree species diversity during outbreak and non-outbreak periods on the probability of sanitary felling and on the amount of sanitary felling, separately. The probability of sanitary felling was higher at low altitudes and increased with an increasing proportion of spruce in the growing stock in the grid cell, but it was not affected by non-host tree species diversity. In contrast, the amount of sanitary felling decreased with increasing non-host tree species diversity, particularly at low altitudes. However, the effect of non-host tree species diversity on the amount of sanitary felling diminished as the percentage of Norway spruce increased. Thus, non-host tree species diversity per se is not the main driver of outbreak risk but strengthens biotic resistance with lower host availability at low altitudes where abiotic conditions are the least favourable to Norway spruce.

Linoleic Acid Promotes Emission of Bark Beetle Semiochemicals by Fungal Symbionts

Tree-killing bark beetles in conifer forests vector symbiotic fungi that are thought to help the beetles kill trees. Fungal symbionts emit diverse volatile blends that include bark beetle semiochemicals involved in mating and host localization. In this study, all 12 tested fungal isolates emitted beetle semiochemicals when growing in medium amended with linoleic acid. These semiochemicals included the spiroacetals chalcogran, trans-conophthorin and exo-brevicomin, as well as 2-methyl-3-buten-1-ol, the main aggregation pheromone component of the spruce bark beetle Ips typographus. The emission of these compounds was affected by the type of fatty acid present (linoleic vs. oleic acid). Accumulating evidence shows that the fatty acid composition in conifer bark can facilitate colonization by bark beetles and symbiotic fungi, whereas the fatty acid composition of non-host trees can be detrimental for beetle larvae or fungi. We hypothesize that beetles probe the fatty acid composition of potential host trees to test their suitability for beetle development and release of semiochemicals by symbiotic fungi.

Factors affecting pine processionary moth (Thaumetopoea pityocampa) incidence in Mediterranean pine stands: A multiscale approach

The occurrence of the pine processionary moth (Thaumetopoea pityocampa, hereafter PPM) in Mediterranean pine forests and plantations is of increasing concern as processes such as global warming and forest cover expansion have amplified the frequency and virulence of outbreaks. This study attempts to provide as complete an overview as possible of the different factors involved in pine forest susceptibility to PPM in 98 pine stands in Central Spain. A large study area (∼3,000 km2) was considered, including three different spatial scales (<1 ha, 1 ha, 10 ha) and four different pine tree species (Pinus pinaster, P. nigra, P. sylvestris, P. pinea), monitored over a 4-year period. Models were fitted for each of the three spatial scales, as well as for a combination of them (multiscale model). Pine species had a strong influence on vulnerability to PPM, with higher incidences in stands dominated by P. pinaster and P. nigra and lower for those dominated by P. sylvestris and P. pinea. Grazing pressure, a factor thus far disregarded, was also determining, with a prominent role at both the multiscale and the stand-scale levels. Other variables were highly influential at some of the spatial scales, showing a greater resistance in pine forests or plantations with a higher diversity of pine sizes, greater tree density, and a larger cover of non-host tree species. Open habitats also played a role in PPM incidence: we detected that, both at the locality and the plot scale, the presence of clearings occupied by bushes or rocky outcrops reduced vulnerability to PPM, while the clearings with a more simplified structure produced the opposite effect. We conclude that PPM incidence is greater in structurally simple pine forests, with strong grazing pressure and abundant open spaces without woody vegetation that may favour PPM pupation. To reduce damage by PPM, pine forest and plantations should be managed to avoid oversimplified forest structures. Patches of non-host tree species should be promoted, as well as some presence of shrubs in open areas. This implies avoiding overgrazing and other management models leading to an excessive increase in bare soil. Nevertheless, it should be noted that the implementation of these recommendations should consider the remaining challenges that need to be addressed in the current context of global change, such as the increased risk of wildfires and the emergence of other pests and diseases.

Climate affects the outbreaks of a forest defoliator indirectly through its tree hosts.

Although spatial variation in climate can directly affect the survival and reproduction of forest insects and the tree species compositions of forests, little is known about the indirect effects of climate on outbreaks of forest insects through its effects on forest composition. In this study, we use structural equation modeling to examine the direct and indirect effects of climate, water capacity of the soil, host tree density, and non-host density on the spatial extent of Lymantria dispar outbreaks in the Eastern USA over a period of 44years (1975-2018). Host species were subdivided into four taxonomic and ecologically distinct groups: red oaks (Lobatae), white oaks (Lepidobalanus), other preferred hosts, and intermediate (less preferred) hosts. We found that mean annual temperature had stronger effects than mean annual precipitation on the spatial extent of outbreaks, and that indirect effects of temperature (via its effects on oak density) on defoliation were stronger than direct effects. The density of non-host trees increased with increasing precipitation and, consistent with the 'associational resistance hypothesis', defoliation decreased with increasing density of non-host trees. This study offers quantitative evidence that geographic variation in climate can indirectly affect outbreaks of a forest insect through its effects on tree species composition.

Plant-insect communication in urban forests: Similarities of plant volatile compositions among tree species (host vs. non-host trees) for alder leaf beetle Agelastica coerulea

Behavior of insects, such as pollination and grazing, is usually determined by biogenic volatile organic compounds (BVOCs). However, particularly in O3-polluted urban forests, the BVOCs-based plant-insect communication can be disrupted by the reaction of O3 with leaf-emitted BVOCs, such as between Japanese white birch (Betula platyphylla var. japonica) and a leaf beetle (Agelastica coerulea). To understand plant-insect communication in O3-polluted environments, it is necessary to identify chemical species of BVOCs that contribute to attractiveness toward insects but are diminished by elevated O3. In this study, we conducted olfactory response tests and gas chromatography mass spectrometry (GC-MS) analyses to clarify whether there is a similarity of BVOC components among Betulaceae host trees that can explain the attraction of the stenophagous insect A. coerulea. The olfactory response tests indicated that Betulaceae host trees attract A. coerulea via leaf-emitted BVOCs, while there was no preference of the leaf beetles to non-host trees (Sorbus commixta and Morus bombycis). However, GC-MS analyses indicated that the composition of BVOC blends considerably differed among Betulaceae host trees, although alders (Alnus hirsuta and A. japonica) had a similar composition of BVOC blend in each season (June and September) during which the adult leaf beetle is active. A distinct characteristic of the emission from B. platyphylla was that 2-carene and limonene, which are O3-reactive species, were emitted with a high monoterpene ratio irrespective of the season. Thus, these volatiles and the blend could be expected to lead the disrupted communication found between B. platyphylla and A. coerulea under elevated O3 in previous field studies. In addition, our results indicated that A. coerulea is attracted to more than one blend within Betulaceae host trees, suggesting that grazing damages can be affected by different host preferences and O3 reactivity with specific BVOCs in the field. BVOCs-based plant-insect interactions should be further studied in multi-species communities to better understand plant-insect communication in O3-polluted environments.

Electroantennographic Responses of Cerambyx welensii Küster to Host-Related Volatiles

Wood-boring insects, such as Cerambyx welensii Küster, are involved in oak decline in Mediterranean areas. To advance our understanding of the olfactory perception of C. welensii, we recorded electroantennographic (EAG) responses from male and female antennae to 32 tree volatile organic compounds typical of emissions from its main Quercus L. hosts, and also analysed the dose-dependent response. Cerambyx welensii antennae responded to 24 chemicals. Eight odorants elicited the highest EAG responses (normalized values of over 98%): 1,8-cineole, limonene-type blend, β-pinene, pinene-type blend, sabinene, α-pinene, turpentine and (E)-2-hexenal. Cerambyx welensii exhibits a broad sensitivity to common tree volatiles. The high EAG responses to both limonene- and pinene-type blends suggest the detection of specific blends of the main foliar monoterpenes emitted by Q. suber L. and Q. ilex L. (limonene, α- and β-pinene, sabinene and myrcene), which could influence the intraspecific host choice by C. welensii, and in particular, females may be able to detect oak trees with a limonene-type chemotype. In addition, C. welensii showed high antennal activity to some odorants that characterize emissions from non-host tree species (1,8-cineole, β-pinene, α-pinene, turpentine, δ3-carene and camphene). The results obtained may be applicable to optimize monitoring and mass-trapping programmes in an integrated pest management context.

Functional Evolution of a Bark Beetle Odorant Receptor Clade Detecting Monoterpenoids of Different Ecological Origins.

Insects detect odors using an array of odorant receptors (ORs), which may expand through gene duplication. How and which new functions may evolve among related ORs within a species remain poorly investigated. We addressed this question by functionally characterizing ORs from the Eurasian spruce bark beetle Ips typographus, in which physiological and behavioral responses to pheromones, volatiles from host and nonhost trees, and fungal symbionts are well described. In contrast, knowledge of OR function is restricted to two receptors detecting the pheromone compounds (S)-(–)-ipsenol (ItypOR46) and (R)-(–)-ipsdienol (ItypOR49). These receptors belong to an Ips-specific OR-lineage comprising seven ItypORs. To gain insight into the functional evolution of related ORs, we characterized the five remaining ORs in this clade using Xenopus oocytes. Two receptors responded primarily to the host tree monoterpenes (+)-3-carene (ItypOR25) and p-cymene (ItypOR27). Two receptors responded to oxygenated monoterpenoids produced in larger relative amounts by the beetle-associated fungi, with ItypOR23 specific for (+)-trans-(1R, 4S)-4-thujanol, and ItypOR29 responding to (+)-isopinocamphone and similar ketones. ItypOR28 responded to the pheromone E-myrcenol from the competitor Ips duplicatus. Overall, the OR responses match well with those of previously characterized olfactory sensory neuron classes except that neurons detecting E-myrcenol have not been identified. The characterized ORs are under strong purifying selection and demonstrate a shared functional property in that they all primarily respond to monoterpenoids. The variation in functional groups among OR ligands and their diverse ecological origins suggest that neofunctionalization has occurred early in the evolution of this OR-lineage following gene duplication.

Dendrochronological Indication of Phyllophages’ Outbreaks by Larch Radial Growth in the Forest-steppe Zone of the Republic of Tyva

One of the possible consequences of climate change is a change in the demographic dynamics of phyllophagous insects. For a retrospective analysis of this dynamics, tree rings are used, especially in regions with limited documentary data. Due to the complex nature of the factors determining tree growth, in order to more clearly identify pest-induced defoliation in tree-ring chronologies one suppress the climatic signal expressed directly or indirectly (through chronologies of non-host tree species). However, in South Siberia, the choice of non-host species is hampered by the wide distribution of polyphages, like the gypsy moth (Lymantria dispar Linnaeus) and the Siberian silk moth (Dendrolimus sibiricus Tsch.). Therefore, the analysis of pest outbreaks in larch forests of the Republic of Tuva low mountains was started by removing the climatic response based on instrumental data, identifying depressions in the residual time-series of individual tree radial growth at several sites, and comparing them with available actual data on forest damage by phyllofages. Dendroclimatic analysis showed that the model including the precipitation-to-maximum-temperature ratio for June-September of the previous season and June of the current year, i.e. the degree of aridity during the previous and current growing season, describes 43.7% of the regional variation in the growth of Siberian larch (Larix sibirica Ledeb.). After removal of this component, several periods of larch growth depression were revealed during confirmed outbreaks of the Siberian silk moth, gypsy moth, and larch tortrix (Zeiraphera diniana Gn.). The use of documented data over 1998–2016 allowed to clarify the threshold values of the portion of affected trees for intensities of the growth depression ranging 1–1.5 standard deviations, providing the required reliability of the outbreak reconstruction. The dependence of the spatio-temporal patterns of growth depression on the pest species was revealed, reflecting their migration in the affected area. It has been shown that growth depressions may be delayed compared with the actual damage by pests due to the long recovery after recurrent defoliation.

Wood ants prefer conifers to broadleaved trees in mixed temperate forests

Abstract Wood ants, species of the subgenus Formica s. str., are one of the most important groups of insects in forest ecosystems due to their high abundance and activity. We assessed the foraging pressure of Formica polyctena and Formica rufa, two dominant wood ant species in the Białowieża Forest. In addition, we compared coniferous and mixed stands in these respects. In mixed stands F. polyctena visited more trees per plot than F. rufa. F. polyctena might forage a larger area due to higher population sizes, which further confirms higher foraging pressure of F. polyctena in comparison with F. rufa. In our study area, host trees of the ant–aphid mutualism were larger in diameter than nonhost trees. The ants also preferred trees situated closer to their nests. In both mixed and coniferous stands, the most visited tree species was Norway spruce. Thus, we can conclude that Norway spruce seems to be preferred by the ant. The decline of living spruce in the Białowieża Forest may endanger their food source and impact the vitality of ant colonies.

Semiochemical-based Reproductive Isolation Among Sympatric Species of Trypodendron (Coleoptera: Curculionidae: Scolytinae).

Trypodendron retusum (LeConte) (Coleoptera: Curculionidae: Scolytinae) females excised from newly attacked trembling aspen, Populus tremuloides Michaux (Salicaceae), were shown for the first time to produce the aggregation pheromone (+)-lineatin. Coupled gas chromatographic-electroantennographic detection analysis (GC-EAD) disclosed that the antennae of T. retusum, as well as the antennae of three sympatric species, native T. lineatum (Olivier) and T. rufitarsus (Kirby) and exotic T. domesticum (L.), respond to synthetic (+)-lineatin, but not the (-) enantiomer. In contrast, the antennae of T. betulae Swaine responded to SR- and RR-linalool oxide pyranoid and did not detect lineatin. GC-EAD analysis of volatiles from host and nonhost tree species revealed that conifer-produced α-pinene and angiosperm-produced conophthorin and salicylaldehyde were perceived by the antennae of all three native lineatin-perceiving species, suggesting behavioral activity. Field trapping experiments showed that salicylaldehyde synergized the response of coastal, but not interior, T. retusum to lineatin and inhibited the response of T. lineatum and T. rufitarsus. In the absence of salicylaldehyde, α-pinene appeared to inhibit the response of interior T. retusum to lineatin, while for T. lineatum and T. rufitarsus it had an apparent positive additive or synergistic effect. No behavioral response occurred to conophthorin. The results provide evidence for semiochemical-based reproductive isolation between T. retusum and T. betulae, and between these two angiosperm-infesting species and the two conifer-infesting species. They do not explain how isolation could be maintained between T. lineatum and T. rufitarsus.

Disruption of coniferophagous bark beetle (Coleoptera: Curculionidae: Scolytinae) mass attack using angiosperm nonhost volatiles: from concept to operational use

AbstractAlthough the use of nonhost plants intercropped among host crops has been a standard agricultural practice for reducing insect herbivory for millennia, the use of nonhost signals to deter forest pests is much more recent, having been developed over the past several decades. Early exploratory studies with synthetic nonhost volatile semiochemicals led to targeted electrophysiological and trapping experiments on a variety of bark and ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) across three continents. This work disclosed a suite of antennally and behaviourally active nonhost volatiles, which are detected in common across a range of coniferophagous bark beetles. It also established the fact that dispersing bark and ambrosia beetles detect nonhost signals while in flight and avoid nonhost trees without necessarily landing on them. Later work showed that groups of synthetic nonhost volatiles, sometimes combined with insect-derived antiaggregants, are effective in protecting individual trees and forest stands. Further work in this system may lead to the development of a variety of new and useful tactics for use in various integrated pest management strategies.

Effect of Logging on the Ficus Community at Batu Timbang Research Station, Imbak Canyon Conservation Area, Sabah

We investigated the effect of logging on Ficus species at a community level in the Imbak Canyon Conservation Area (ICCA) in Sabah, Malaysian Borneo. We made comparisons of species composition, density, fig size, and host-tree size (DBH) between heavily logged and relatively old forests, and assessed factors affecting the size of hemi-epiphytic species. There were no significant differences in species composition, density, and fig size between the two habitats. There were significant differences between the DBH of host and non-host trees in both young and old forests as well as between those of host trees in young and old forests. The DBH of hemi-epiphytic species was negatively affected by the DBH of host trees. The results obtained in this study indicate that Ficus species, particularly hemi-epiphytes, can survive in degraded habitats that have recently been logged as well as in undegraded forests, and that their growth is not greatly affected by prior logging activities. Thus, Ficus exhibits both flexibility and adaptability to habitat change. This indicates that Ficus species make ideal plants for the restoration of logged forests considering that figs are an important food resource for numerous animal species, and can promote seed dispersal of other plants by attracting these animals into degraded habitats.

Will Peri-Urban Cydia pomonella (Lepidoptera: Tortricidae) Challenge Local Eradication?

Codling moth, Cydia pomonella (Lepidoptera: Tortricidae), is a phytosanitary pest of New Zealand’s export apples. The sterile insect technique supplements other controls in an eradication attempt at an isolated group of orchards in Hawke’s Bay, New Zealand. There has been no attempt in New Zealand to characterize potential sources of uncontrolled peri-urban populations, which we predicted to be larger than in managed orchards. We installed 200 pheromone traps across Hastings city, which averaged 0.32 moths/trap/week. We also mapped host trees around the pilot eradication orchards and installed 28 traps in rural Ongaonga, which averaged 0.59 moths/trap/week. In Hastings, traps in host trees caught significantly more males than traps in non-host trees, and spatial interpolation showed evidence of spatial clustering. Traps in orchards operating the most stringent codling moth management averaged half the catch rate of Hastings peri-urban traps. Orchards with less rigorous moth control had a 5-fold higher trap catch rate. We conclude that peri-urban populations are significant and ubiquitous, and that special measures to reduce pest prevalence are needed to achieve area-wide suppression and reduce the risk of immigration into export orchards. Because the location of all host trees in Hastings is not known, it could be more cost-effectively assumed that hosts are ubiquitous across the city and the area treated accordingly.

Associational resistance to a pest insect fades with time

Tree diversity is one of the drivers of forest resistance to herbivores. Most of the current understanding of the diversity resistance relationship comes primarily from short-term studies. Knowing whether tree diversity effects on herbivores are maintained over time is important for perennial ecosystems like forests. We addressed the temporal dynamics of the diversity resistance relationship by conducting a 6-year survey of pine attacks by the pine processionary moth Thaumetopoea pityocampa (PPM) in a tree diversity experiment where we could disentangle tree composition from host density effects. During the first years after planting the trees, PPM attacks on maritime pine Pinus pinaster were reduced in the presence of birch Betula pendula, a fast-growing non-host tree (i.e. associational resistance). This effect was maintained but faded with time as the pines eventually grew taller than neighbouring birches. The number of repeated attacks on individual pine trees also decreased in mixed pine–birch stands. Pine density had a positive effect on stand colonisation by PPM and a negative effect on the proportion of trees that were attacked. Pines were less likely to be repeatedly attacked as pine density increased, with attacks being spread over a larger number of host trees. Collectively, these results unravel the independent contribution of tree species composition and host density to tree resistance to herbivores. Both processes had directional changes over time. These results indicate that the resistance of planted forests to herbivores can be improved by carefully choosing the composition of mixed forests and the timing of species planting.

Tree-ring-based reconstruction of larch budmoth outbreaks in the Central Italian Alps since 1774 CE

The larch budmoth (Zeiraphera diniana Gn. - LBM) offers a unique example of cyclic fluctuations in insect populations. During regular LBM mass outbreaks, defoliation of European larch (Larix decidua Mill.) subalpine trees results in distinct ring-width reductions in the host trees. Although several observations, reconstructions and models suggest that LBM outbreaks travel from the southwest to the northeast along the Alpine arc, gaps in the underlying data still hamper our mechanistic understanding of the spatio-temporal system dynamics. Evidence of historical LBM outbreaks before 1964 is generally associated with uncertainty and is particularly scarce for the Central Italian Alps. Here, we introduce four new larch ring-width chronologies from Val di Sole in the Central Italian Alps and use time-series analyses and comparisons with non-host trees (Picea abies Karst.) to reconstruct LBM mass outbreaks. We identify distinct fingerprints of 15 spatially-synchronized LBM events that occurred between 1774 and 1964 CE. Our results are important for improving qualitative space-time models to simulate travelling wave dynamics of insect populations, and for correcting ring-width-based summer temperature reconstructions from this part of the Alpine arc.

Progression of seasonal activities of adults of the spotted lanternfly, Lycorma delicatula, during the 2017 season of mass flight dispersal behavior in eastern Pennsylvania

Abstract During the summer and fall of 2017 in northeastern Pennsylvania we studied the progression of adult behaviors of the spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae) when there was an upsurge in adult flight behavior that was not known to have occurred in 2015 or 2016, the first years following its initial detection in Pennsylvania in late 2014. Sex ratios on A. altissima trunks and branches were routinely ca. 50:50 male:female throughout the 2017 season except in two instances in two of the earliest samplings in which >60% were males. Within the first week after adult eclosion in 2017, in conjunction with extensive feeding-related behaviors on Ailanthus altissima tree trunks, short flights occurred indiscriminately from the foliage of one tree to another or between bushes, trees and vines. One week later these flights became more prevalent and lengthier. Adults of both sexes launched themselves into the wind from non-host trees or from porches, posts and other human-made structures to engage in level or gradually descending straight-line flight trajectories that allowed them to traverse only usually 10 to 40 m of ground in one episode. After the peak of flight dispersal had occurred, the first mating pairs were observed on September 25. All of the 21 pairs of adults we observed in copula exhibited swollen, yellow abdomens in contrast to the thinner, predominantly black abdomens of the adults we had sampled during the earlier feeding and flight phases. Copulating pairs were observed to remain coupled for 2 to 4 h.