Forest Insect Pests Research Articles

Respiration by unprocessed pine logs creates a severe hypoxic and hypercapnic atmosphere in enclosed spaces

Wood products, particularly whole, unprocessed logs, are a significant risk pathway for forest insect pests. Freshly harvested logs continue to respire, creating a high carbon dioxide (CO2), and low oxygen (O2) atmosphere in enclosed spaces. Such modified atmospheres may reduce the effectiveness of insect control treatments applied during the transit of logs, making it important to accurately quantify how the atmosphere is modified. We used gas chromatography to measure the amount of CO2 and O2 respired by radiata pine (Pinus radiata D.Don) logs under three temperatures (10, 15 and 20 °C) in airtight containers for 14 days to simulate real world conditions in a ship’s hold. We repeated the experiment across all seasons (i.e. spring, summer, autumn and winter). The atmosphere in the containers became severely hypoxic/hypercapnic (low O2/high CO2) by day five, and our study confirmed that temperature, time and season were significant factors influencing log respiration. Our results suggest that the atmosphere in a ship’s hold during the export of unprocessed wood products changes rapidly to hypoxic/hypercapnic conditions that are then maintained for weeks. This highlights a potential challenge for the effectiveness of insect control treatments during transit of logs, particularly treatments that require respiratory uptake of a toxin by insects.

Drought drives the pine caterpillars (Dendrolimus spp.) outbreaks and their prediction under different RCPs scenarios: A case study of Shandong Province, China

Drought is an important driver of forest pests, and reports of climate change are becoming more conspicuous as a result of enhanced drought. These projected changes have a positive impact on forest insect pests that result in substantial forest damage, adverse economic impacts, and losses of ecosystem resources. Therefore, we explored the impact of drought on the outbreak of pine caterpillars and predicted the future trend of pine caterpillar outbreaks under different emission scenarios by constructing a drought-pine caterpillar model (using a greenhouse gas emission scenario: Representative Concentration Pathways, RCP4.5 and RCP8.5 from 2016 to 2099). The results showed that: (1) Long-term or prolonged drought had a greater positive impact on pine caterpillar outbreaks than short-term drought; (2) The drought was more severe in the RCP 8.5 scenario than that in RCP 4.5; (3) The outbreaks of pine caterpillars in Shandong Province will gradually decrease approaching 2100 under the RCP4.5 and RCP8.5 scenarios. There is a trend of cyclical changes of approximately 30 years under the RCP4.5 scenario, while these changes primarily occurred before the 2050s and then decreased significantly and even became almost zero in the 2090s. (4) Under the two scenarios, light infestations comprised the largest area, followed by moderate and severe. Our study is important to promote the understanding of climate change and provide references and direction for forest managers.

Respiration, predatory behavior and prey consumption by Podisus nigrispinus (Heteroptera: Pentatomidae) nymphs exposed to some insecticides

Podisus nigrispinus Dallas (Heteroptera: Pentatomidae) preys on insect pests in eucalyptus plantations where it can be exposed to insecticides used in pest control. The effect of insecticides on non-target natural enemies requires further study. The objective of the present study was to evaluate the side-effects of Bacillus thuringiensis (Bt), permethrin, tebufenozide and thiamethoxam on third instar nymphs of the predator P. nigrispinus in the laboratory. The toxicity of insecticides for this insect was determined by estimating their lethal concentrations. Podisus nigrispinus behavior after exposure to insecticides was analyzed using a video tracking system and the respiratory rate with a respirometer. Prey/nymph consumption was assessed after 24 h of starvation. The preference of P. nigrispinus nymphs, for prey treated or not with the insecticides, was evaluated in free choice tests. The insecticides Bt [LC50 = 1.10(0.83–1.46) mg mL−1], permethrin [LC50 = 0.25(0.17–0.34) mg mL−1], tebufenozide [LC50 = 5.71(4.17–7.57) mg mL−1] and thiamethoxam [LC50 = 0.04(0.02–0.06) mg mL−1] are toxic to P. nigrispinus nymphs. Bt and the insecticides tebufenozide, permethrin and thiamethoxam reduced the respiratory rate of P. nigrispinus. The insecticides permethrin, tebufenozide and thiamethoxam affect the locomotion of this insect’s nymphs. Prey treated with Bt, permethrin and thiamethoxam are less preferred by P. nigrispinus. The survival of the nymphs of this predator was 93.3%, 66.7%, 56.6%, 0% and 0% in the control, tebufenozide, Bt, permethrin and thiamethoxam treatments, respectively. In addition, the reduction of prey consumption, treated with neurotoxic insecticides, reduces the predatory potential of this natural enemy. Bt and tefubenozide present low toxicity for P. nigrispinus, but the neurotoxic products have low compatibility with this natural enemy and, therefore, are not recommended, with this predator in the management of forest insect pests.

Bacterial Communities Associated with the Pine Wilt Disease Insect Vector Monochamus alternatus (Coleoptera: Cerambycidae) during the Larvae and Pupae Stages.

Monochamus alternatus is an important insect pest in pine forests of southern China and the dispersing vector of the pine wood nematode, Bursaphelenchus xylophilus, which leads to pine wilt disease (PWD). Microbiome of M. alternatus may contribute to survival of larvae in the host pine trees. In order to investigate the intestinal bacterial structure of M. alternatus during the larvae and pupae stages in host trees, and infer the function of symbiotic bacteria, we used 16S rRNA gene Illumina sequencing to obtain and compare the bacterial community composition in the foregut, midgut, and hindgut of larvae, pupal intestines, larval galleries, and pupal chambers of M. alternatus. The diversity of the bacterial community in larval intestines and pupal intestines were similar, as well as was significantly greater in larval galleries and pupal chambers. Although there were differences in bacterial compositions in different samples, similar components were also found. Proteobacteria and Firmicutes were the two most dominant phyla in all samples, and genera Enterobacter, Raoultella, Serratia, Lactococcus, and Pseudomonas were dominant in both the intestinal samples and plant tissue samples. Enterobacter was the most abundant genus in larval intestines, and Serratia was dominant in pupal intestine. The functions of these dominant and specific bacteria were also predicted through metagenomic analyses. These bacteria may help M. alternatus degrade cellulose and pinene. The specific role of symbiotic bacteria in the infection cycle of PWD also warrants further study in the future.

Biology and feeding potential of Eocanthecona furcellata (Wolff) on its lesser known prey, Spilosoma obliqua (Walker)

Eocanthecona furcellata (Wolff) (Hemiptera: Pentatomidae) is an important polyphagous predator of several agricultural, horticultural and forest insect pests. The biology and feeding potential of E. furcellata were investigated on Bihar hairy caterpillar, Spilosoma obliqua (Walker), a lesser known prey under laboratory conditions. Gravid female laid on an average 203.6±12.56 eggs during its life time. Nymphs passed through five instars in 22.25 to 27.25 days and developed into adults. First instar nymphs had the shortest duration (2.5 to 3.25 days) while fourth instar took maximum days (5.5 to 6.5) to complete, while second, third and fifth instars completed in 5.07 ± 0.26, 5.20 ± 0.71 and 5.24 ± 0.39 days, respectively. Female bugs were bigger in size and lived up to 28 days, while males survived up to 18 days when fed on second instar larvae of S. obliqua . Neonate nymphs devoured 1.6 larvae of S. obliqua while second, third, fourth and fifth instar nymphs consumed 7.73, 11.93, 12.13, 18.67 larvae of S. obliqua , respectively. Individual male and female in their adult stage consumed average 84.25 and 125.5 larvae, respectively, and total consumptions were 136.31 and 177.56 larvae during their life-cycle. From the study, it is evident that S. obliqua could be used as an alternative host to mass rear E. furcellata under laboratory conditions when the main host is scarce or not available.

Changes in streamside riparian forest canopy and leaf litter nutrient flux to soils during an emerald ash borer infestation in an agricultural landscape

The invasive forest insect pest, emerald ash borer (EAB), is causing rapid, widespread ash tree mortality across eastern North America. Riparian (streamside) forests in agricultural landscapes often represent residual patches of high quality forest habitat that, owing to their strong land/water ecological linkages, can be critical for maintaining stream water quality and aquatic and terrestrial biodiversity. When riparian forests contain high numbers of ash trees, EAB can pose a risk of disrupting some of those land/water linkages thereby reducing riparian and aquatic habitat quality. We tracked ash tree mortality, streamside forest canopy cover, leaf litter deposition rates, and nutrient flux to soils in 18 riparian forest plots with an average of 24% ash by stem density over a 5 year period from early to late stages of an EAB invasion (2010–2015). Ash tree mortality increased from an average of 10–98% over 5 years in most plots, but when blue ash were dominant, final ash mortality was about 34%. Despite the nearly complete mortality of ash trees in almost all plots by 2015, the average canopy openness measured at 1.5 m above ground only increased to about 9%, which was significantly higher than the 2010 average of 6% open. Final canopy openness was significantly but weakly (r2 = 0.24) associated with the proportion of ash in riparian plots, indicating highly patchy openness resulting from ash mortality. Ash leaf litter deposition to streamside traps declined by 84% and elm declined by 20%, whereas leaf deposition from the other four most common contributors to riparian leaf litter increased by up to 37% over the same period. The large reductions in ash litter deposition were sufficient to reduce macro-nutrient flux to the streamside forest floor and therefore likely to streams. Amounts of N, C, P, K, and Ca delivered to the streamside soils via leaf litter fall were all consistently, some of them significantly, lower by 2014 than in the baseline year of 2010. Although total leaf litter mass returned to near pre-infestation levels by 2014, the altered composition of leaf litter caused a persistent reduction in nutrient flux to riparian soils. We also measured stem density of regenerating ash saplings ( 0.5 m height) at the end of the study period and found them to be abundant with an average of 2084 stems/ha. Our results provide an empirical demonstration of EAB-induced disruptions to ecological linkages and processes in riparian forests, at least over the short term.

Improving trapping methods for buprestid beetles to enhance monitoring of native and invasive species

AbstractMost of the current understanding of the orientation and communication of jewel beetles arose from research on the Asian emerald ash borer (EAB), Agrilus planipennis, which has become one of the most destructive invasive forest insect pests in history following its introduction to North America and European Russia. From a European perspective, a number of jewel beetles have a high invasive risk similar to that of the emerald ash borer, including the potential threat of the bronze birch borer Agrilus anxius, the goldspotted oak borer Agrilus auroguttatus, and the twolined chestnut borer Agrilus bilineatus. Native jewel beetles expanding their geographic range include the cypress jewel beetle Ovalisia festiva and the black-banded oak borer Coraebus florentinus. Other native species are increasing in their importance, including the flathead oak borer Coraebus undatus, the two-spotted oak borer Agrilus biguttatus, the flatheaded beech borer Agrilus viridis and Agrilus cuprescens. Commonly used prism and multi-funnel trap designs and other promising experimental trap designs have been tested and compared in the US and in Europe. One factor considered has been colouration, typically purple and green. Another is olfactory attraction, both to plant volatiles and extracts such as (Z)-3-hexenol, Manuka oil, Phoebe oil and Cubeb oil, and also to pheromones such as (Z)-3-lactone, for emerald ash borer. Field observations have been made of mating and host-finding behaviours of oak buprestids based upon visual stimuli in North America and Europe. By using pinned dead EAB models, visual mating approaches have been observed by males of Agrilus biguttatus, Agrilus sulcicollis and Agrilus angustulus, which is a behaviour similar to that previously observed in EAB. Green plastic-covered branch-traps significantly out-performed other trap designs and caught more Agrilus jewel beetles if an artificial visual decoy that copies a beetle body was included. A higher fidelity decoy offered the same distinctive light-scattering pattern as real resting EAB females and elicited the full sequence of stereotypical male mating flight behaviour of EAB and A. biguttatus from up to 1 m away. An optimization of visual, olfactory and other possible stimuli has likely not yet been achieved. More sophisticated trap designs could lead to more sensitive detection capabilities with increased selectivity.

Trap Designs, Colors, and Lures for Emerald Ash Borer Detection

The emerald ash borer, Agrilus planipennis, is the most damaging invasive forest insect pest ever to have invaded North America. It is native to Asia and is established in the United States, Canada, European Russia and Ukraine where it threatens native ash across North America and Europe. We evaluated trap designs, colors, and lures for A. planipennis detection at sites with varying infestation levels. Sticky prism traps and multiple funnel traps (purple and green) hung in the canopy of ash trees and double-decker traps had high capture rates even at sites with very low infestation levels. At a low infestation site, females were more attracted to dark purple sticky prism traps hung in the canopy and to Manuka oil and Phoebe oil lures than to light green sticky prism traps or cis-3-hexenol lures; whereas, males were more attracted to light green sticky prism traps in the canopy and cis-3-hexenol lures than to dark purple sticky prism traps or Manuka and Phoebe oil lures. More males and females were captured in double-decker traps with dark green upper prisms and light purple lower prisms, baited with cis-3-hexenol, than in double-decker traps with dark purple upper and lower prisms. Dark green funnel traps and double-decker traps with dark green upper and light purple lower prisms baited with cis-3-hexenol lures captured more females than dark green sticky prism traps hung in the canopy at sites with very low infestation levels. Detection rates were similar among trap types and ranged from 75-80% for dark green sticky prism traps, 82.5-100% for dark green funnel traps, and 100% for double-decker traps with dark green upper and light purple lower prisms at sites with very low population densities. Each trap type has different advantages and disadvantages in terms of costs, ability to reuse the traps, and ease of deployment. These and other factors including trap placement, host density and condition should be considered in selecting traps for operational surveys. Future research is needed to determine effective trapping radius, relationship of trap catches to population density, cost benefit of different trap types, and optimal deployment strategy.

Identification and field verification of aggregation-sex pheromone from the predaceous bug, Arma chinensis

Arma chinensis is a predaceous insect species that can effectively suppress a wide range of agricultural and forest insect pests in the orders Lepidoptera, Coleoptera, Hymenoptera and Hemiptera in Northeast Asia. Adult A. chinensis males produce an aggregation-sex pheromone from dorsal abdominal glands and artificial aggregation-sex pheromone can attract adults of both sexes. The aggregation-sex pheromone consists of (E)-2-hexenal, (E)-2-hexen-1-ol, benzaldehyde and benzyl alcohol. Both antennae and proboscises of A. chinensis females and males responded to components from male dorsal abdominal gland extracts. (E)-2-hexenal and benzaldehyde elicited significantly higher EAG responses than those with (E)-2-hexen-1-ol and benzyl alcohol. Benzyl alcohol elicited the weakest EAG responses, although benzyl alcohol was the most abundant of the four major components in male dorsal abdominal gland extracts. A field bioassay using trap catches demonstrated that (E)-2-hexenal and benzyl alcohol were key components of the pheromone for catching conspecific adults. Single pheromone components were the least attractive to A. chinensis in the field.

Modeling of the Regional Forest Sector to Improve Economic and Legal Relations in Forest Management

The diversity of the problems of forestry in Russia requires a new common approach to solving them. One option is to conduct a comprehensive study of the factors influencing the development of the forest sector from different perspectives including climate change problem. The general logic of the analysis is based on the premise that the forest economy is in a mutual relationship with the climate change process. One of the major challenges for the future development of the Russian forestry are the insect pests’ outbreaks, which cause forest fires and tree losses on vast territories, especially in Siberia. Economic and legal research on this aspect of forest sector development is still lacking. We suggest to design a new Integrated Assessment Model of the Russian forest sector with a special focus on the regions of Siberia, which will include key components reflecting microeconomic linkages within the sector, the macroeconomic environment, resource base dynamics, climate change trends and international trade. Forecasts made using this model will allow policy-makers to understand in depth both the possible effects of different measures and the effects of exogenous factors, such as forest fires and insect pests

Monitoring, Assessment and Management of Forest Insect Pests and Diseases

Forest pests are one of the most important factors disturbing forest ecosystems, by impacting forestry economy, ecosystem services, biodiversity, and sustainable ecosystem management. Monitoring the occurrence of forest pests offers clues to understand their impacts on the forest ecosystem and develop a sustainable ecosystem management strategy. This special issue is designed to create a better understanding of the changes and impacts of forest pests according to forest changes, caused by natural or anthropogenic causes. There are 13 papers published in this special issue, covering several issues concerning forest pests. Two of the papers reviewed the changes in forest pests in Korea or Poland. The remaining twelve papers covered issues concerning the monitoring, assessment, and management of forest pests. Through this special issue, we expect to contribute towards the improvement of our knowledge of the structures and processes in forest ecosystems relating to forest pests and fundamental information for the effective management of forest pests.

The Impact of Moth Migration on Apparent Fecundity Overwhelms Mating Disruption as a Method to Manage Spruce Budworm Populations

Aerial applications of a registered formulation of synthetic spruce budworm female sex pheromone were made in 2008, 2013 and 2014 to disrupt mating in populations of this forest insect pest in Quebec, Canada. Each year, the applications resulted in a 90% reduction in captures of male spruce budworm moths in pheromone-baited traps. A commensurate reduction in mating success among virgin females held in individual cages at mid-crown of host trees was also obtained. However, there was no reduction in the populations of eggs or overwintering larvae in the following generation (late summer and fall). The failure of this approach as a viable tactic for spruce budworm population reduction could have resulted from considerable immigration of mated females, as evidenced by high rates of immigration and emigration that caused steep negative relationships between apparent fecundity and the density of locally emerged adults.

Dealing with growing forest insect pests: The role of top‐down regulation

Abstract Forest insect pests are becoming increasingly common in Europe. A recent paper published in this journal dealt with a particular case of pest spreading in Portuguese coniferous forests. The authors discussed the effect that mass trapping and clear‐cut belts had on slowing down the invasion and suggested that likely causes of pest spreading are stress due to global warming and the introduction of exotic species. Inspired by that paper, we defend here the point that forest communities are not only regulated by bottom‐up mechanisms, such as water stress, but also by top‐down mechanisms, such as predation. We provide information from European metadata showing that forest biomass grew by 38% (1991–2015) whereas forest insectivorous passerine trends were stable (1980–2016). Synthesis and applications. We suggest that rebounding European forests are too young to support large communities of insectivorous birds and that an effective way to solve pest problems could be to promote the use of nest boxes for them (and for other insect predators), as it was done in the past in large reforestations implemented in Spain. Additionally, the presence of large mammalian herbivores is needed to reduce the density of trees in forests. Priority should be given to this ecological management in comparison with massive trapping and clear‐cut belt construction or at least it should be used together with those engineering practices.

The predicted effect of the polar vortex of 2019 on winter survival of emerald ash borer and mountain pine beetle

We use simulation models of the winter biology of two forest insects — emerald ash borer (Agrilus planipennis Fairmaire, 1888) and mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) — to illustrate the anticipated effect of the polar vortex of the winter of 2019 on overwintering survival. Cold spells in late January and early and mid-February were cool enough that relatively high levels of mortality of both species may be expected in many parts of northern Canada. However, the high mortality response is not ubiquitous, and neither is it particularly severe compared with winter weather patterns from earlier decades. Forest insect pest managers will be required to carry on their usual work of population assessment and response. As Earth’s climate continues to warm, overwintering survival should, on average, increase in both species. However, the common occurrence of a split polar vortex associated with increasingly meridional jet stream flows should bring the odd winter of heavy mortality.

Climate change alters elevational phenology patterns of the European spruce bark beetle (Ips typographus).

The European spruce bark beetle Ips typographus is the most important insect pest in Central European forests. Under climate change, its phenology is presumed to be changing and mass infestations becoming more likely. While several studies have investigated climate effects across a latitudinal gradient, it remains an open question how phenology will change depending on elevation and topology. Knowing how an altered climate is likely to affect bark beetle populations, particularly across diverse topographies and elevations, is essential for adaptive management. We developed a time-varying distributed delay model to predict the phenology of I. typographus. This approach has the particular advantage of capturing the variability within populations and thus representing its stage structure at any time. The model is applied for three regional climate change scenarios, A1B, A2 and RCP3PD, to the diverse topography of Switzerland, covering a large range of elevations, aspects and slopes. We found a strong negative relationship between voltinism and elevation. Under climate change, the model predicts an increasing number of generations over the whole elevational gradient, which will be more pronounced at low elevations. In contrast, the pre-shift in spring swarming is expected to be greater at higher elevations. In comparison, the general trend of faster beetle development on steep southern slopes is only of minor importance. Overall, the maximum elevation allowing a complete yearly generation will move upwards. Generally, the predicted increase in number of generations, earlier spring swarming, more aggregated swarming, together with a projected increase in drought and storm events, will result in a higher risk of mass infestations. This will increase the pressure on spruce stands particularly in the lowlands and require intensified management efforts. It calls for adapted long-term silvicultural strategies to mitigate the loss of ecosystem services such as timber production protection against rockfall and avalanches and carbon storage.

Temporal variation in spatial genetic structure during population outbreaks: Distinguishing among different potential drivers of spatial synchrony.

Spatial synchrony is a common characteristic of spatio‐temporal population dynamics across many taxa. While it is known that both dispersal and spatially autocorrelated environmental variation (i.e., the Moran effect) can synchronize populations, the relative contributions of each, and how they interact, are generally unknown. Distinguishing these mechanisms and their effects on synchrony can help us to better understand spatial population dynamics, design conservation and management strategies, and predict climate change impacts. Population genetic data can be used to tease apart these two processes as the spatio‐temporal genetic patterns they create are expected to be different. A challenge, however, is that genetic data are often collected at a single point in time, which may introduce context‐specific bias. Spatio‐temporal sampling strategies can be used to reduce bias and to improve our characterization of the drivers of spatial synchrony. Using spatio‐temporal analyses of genotypic data, our objective was to identify the relative support for these two mechanisms to the spatial synchrony in population dynamics of the irruptive forest insect pest, the spruce budworm (Choristoneura fumiferana), in Quebec (Canada). AMOVA, cluster analysis, isolation by distance, and sPCA were used to characterize spatio‐temporal genomic variation using 1,370 SBW larvae sampled over four years (2012–2015) and genotyped at 3,562 SNP loci. We found evidence of overall weak spatial genetic structure that decreased from 2012 to 2015 and a genetic diversity homogenization among the sites. We also found genetic evidence of a long‐distance dispersal event over >140 km. These results indicate that dispersal is the key mechanism involved in driving population synchrony of the outbreak. Early intervention management strategies that aim to control source populations have the potential to be effective through limiting dispersal. However, the timing of such interventions relative to outbreak progression is likely to influence their probability of success.

Northern forest winters have lost cold, snowy conditions that are important for ecosystems and human communities.

Winter is an understudied but key period for the socioecological systems of northeastern North American forests. A growing awareness of the importance of the winter season to forest ecosystems and surrounding communities has inspired several decades of research, both across the northern forest and at other mid‐ and high‐latitude ecosystems around the globe. Despite these efforts, we lack a synthetic understanding of how winter climate change may impact hydrological and biogeochemical processes and the social and economic activities they support. Here, we take advantage of 100 years of meteorological observations across the northern forest region of the northeastern United States and eastern Canada to develop a suite of indicators that enable a cross‐cutting understanding of (1) how winter temperatures and snow cover have been changing and (2) how these shifts may impact both ecosystems and surrounding human communities. We show that cold and snow covered conditions have generally decreased over the past 100 years. These trends suggest positive outcomes for tree health as related to reduced fine root mortality and nutrient loss associated with winter frost but negative outcomes as related to the northward advancement and proliferation of forest insect pests. In addition to effects on vegetation, reductions in cold temperatures and snow cover are likely to have negative impacts on the ecology of the northern forest through impacts on water, soils, and wildlife. The overall loss of coldness and snow cover may also have negative consequences for logging and forest products, vector‐borne diseases, and human health, recreation, and tourism, and cultural practices, which together represent important social and economic dimensions for the northern forest region. These findings advance our understanding of how our changing winters may transform the socioecological system of a region that has been defined by the contrasting rhythm of the seasons. Our research also identifies a trajectory of change that informs our expectations for the future as the climate continues to warm.

Responses of forest insect pests to climate change: not so simple

Climate change is a multi-faceted phenomenon, including elevated CO2, warmer temperatures, more severe droughts and more frequent storms. All these components can affect forest pests directly, or indirectly through interactions with host trees and natural enemies. Most of the responses of forest insect herbivores to climate change are expected to be positive, with shorter generation time, higher fecundity and survival, leading to increased range expansion and outbreaks. Forest insect pest can also benefit from synergistic effects of several climate change pressures, such as hotter droughts or warmer storms. However, lesser known negative effects are also likely, such as lethal effects of heat waves or thermal shocks, less palatable host tissues or more abundant parasitoids and predators. The complex interplay between abiotic stressors, host trees, insect herbivores and their natural enemies makes it very difficult to predict overall consequences of climate change on forest health. This calls for the development of process-based models to simulate pest population dynamics under climate change scenarios.

The potential of dual-wavelength terrestrial lidar in early detection of Ips typographus (L.) infestation – Leaf water content as a proxy

Climate change is causing novel forest stress around the world due to changes in environmental conditions. Forest pest insects, such as Ips typographus (L.), are spreading toward the northern latitudes and are now able to produce more generations in their current range; this has increased forest disturbances. Timely information on tree decline is critical in allowing forest managers to plan effective countermeasures and to forecast potential infestation areas. Field-based infestation surveys of bark beetles have traditionally involved visual estimates of entrance holes, resin flow, and maternal-gallery densities; such estimates are prone to error and bias. Thus, objective and automated methods for estimating tree infestation status are required.In this study, we investigated the feasibility of dual-wavelength terrestrial lidar in the estimation and detection of I. typographus infestation symptoms. In addition, we examined the relationship between leaf water content (measured as gravimetric water content and equivalent water thickness) and infestation severity. Using two terrestrial lidar systems (operating at 905 nm and 1550 nm), we measured 29 mature Norway spruce (Picea abies [L.] Karst.) trees that exhibited low or moderate infestation symptoms. We calculated single and dual-wavelength lidar intensity metrics from stem and crown points to test these metrics' ability to discriminate I. typographus infestation levels using regressions and linear discriminant analyses.Across the various I. typographus infestation levels, we found significant differences (p < 0.05) in gravimetric water content, but not in equivalent water thickness due to the latter statistic's high correlation with leaf density. The results show correlations between the lidar intensity metrics and several infestation symptoms: defoliation, discoloration and resin flow. The intensity metrics explain 50% of the variation in the infestation severity (as determined in the field based on canopy and stem symptoms). The overall accuracy with three infestation classes (no, low, or moderate) was 66%, but the overall accuracy with two infestation classes (not infested, or infested) was 90%. The classifiers combine lidar intensity metrics from the stem and the canopy to allow for the detection of bark-beetle infestations in the early, so called green-attack stage. The intensity metrics explain part of the variations in tree-level gravimetric water content and equivalent water thickness, with adjusted R2 values of 0.48 and 0.68, respectively. Terrestrial dual-wavelength lidar shows potential for providing objective tree-decline measurements at tree level: this method can be further used to enhance forest inventories and automate tree-vigor data collection, which has traditionally required expert knowledge.

Phylogeography of Dendrolimus punctatus (Lepidoptera: Lasiocampidae): Population differentiation and last glacial maximum survival.

Although the Masson pine moth, Dendrolimus punctatus, is one of the most destructive forest pest insects and is an endemic condition in China, we still do not fully understand the patterns of how its distribution range varies in response to Quaternary climatic oscillations. Here, we sequenced one maternally inherited mitochondrial gene (COI) and biparentally inherited nuclear data (ITS1 and ITS2) among 23 natural populations across the entire range of the species in China. A total of 51 mitotypes and 38 ribotypes were separately obtained using mtDNA and ITS1 data. Furthermore, significant phylogeographical structure (N ST > G ST, p < 0.01) were detected. The spatial distribution of mitotypes implied that two distinct groups existed in the species: one in the southwest distribution, including 10 locations, and the other located in the northeast region of China. It is suggested, therefore, that each group was derived from ancestors that occupied different isolated refugia during previous periods, possibly last glacial maximum. Mismatch distribution and Bayesian population dynamics analysis suggested the population size underwent sudden expansion, which is consistent with the results of ecological niche modeling. As a typical phytophagous insect, the history of population expansion was in accordance with the host plants, providing abundant food resources and habitat. Intraspecific success rate of barcoding identification was lower than interspecific ones, indicating a level of difficulty in barcoding individuals from different populations. However, it still provides an early insight into the pattern of genetic diversity within a species.OPEN RESEARCH BADGES This article has been awarded an Open Data and Open Materials. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5061/dryad.2df87g2. Learn more about the Open Practices badges from the Center for Open Science: https://osf.io/tvyxz/wiki.