Outbreaks of pine shoot beetles (Tomicus spp.) have caused widespread tree mortality in Southwest China. However, the understanding of the role of climatic drivers in pine shoot beetle outbreaks is ...limited. This study aimed to characterize the relationships between climate variables and pine shoot beetle outbreaks in the forests of Yunnan pine (Pinus yunnanensis Franch) in Southwest China. The pine shoot beetle-infested total area from 2000 to 2017 was extracted from multi-data Landsat images and obtained from field survey plots. A temporal prediction model was developed by partial least squares regression. The results indicated that multi consecutive year droughts was the strongest predictor, as such a condition greatly reduced the tree resistance to the beetles. The beetle-infested total area increased with spring temperature, associated with a higher success rate of trunk colonization and accelerated larval development. Warmer temperatures and longer solar radiation duration promoted flight activity during the trunk transfer to the shoot period and allowed the completion of sister broods. Multi consecutive year droughts combined with the warmer temperatures and higher solar radiation duration could provide favorable conditions for shoot beetle outbreaks. Generally, identifying the climate variables that drive pine shoot beetle outbreaks could help improve current strategies for outbreak control.
(Hartig) and
Kirkendall and Faccoli are two sympatric species that infest
(Franchet) in southwest China, contributing to growth losses. Accurate sampling plans are needed to make informed control ...decisions for these species. We investigated three pine forests within experimental sites in Yuxi, Yunnan province, China from 2016 to 2018. The spatial distribution patterns of two pine shoot beetles during the shoot-feeding phase were determined using Taylor's power law. The optimum sample sizes and stop lines for precision levels of 0.25 and 0.10 were calculated. The model was validated using an additional 15 and 17 independent field datasets ranging in density from 0.06 to 1.90 beetles per tree.
and
adults showed aggregated spatial distributions. For
, sample sizes of 41 and 259 trees were adequate for a
of 0.25 and 0.10, respectively, while for
a mean density of one individual per tree required sample sizes of 33 plants (
= 0.25) and 208 plants (
= 0.10). The software simulations of this sampling plan showed precision levels close to the desired levels. At a fixed-precision level of 0.25, sampling is easily achievable. This sampling program is useful for the integrated pest management (IPM) of two sympatric
species.
The pine shoot beetles Tomicus minor and Tomicus yunnanensis are important stem borers of Pinus yunnanensis in southwestern China. To determine strategies for cold resistance and changes in major ...cold-resistant substances in adults of two Tomicus species during two critical transferring periods, “shoot-to-trunk” and “trunk-to-shoot”, the insects’ supercooling point (SCP), freezing point (FP), and antifreeze protective substances were determined. The SCP and FP did not differ between female and male adults in the shoot-to-trunk phase, but were significantly lower in females in the trunk-to-shoot period. Although there was no difference in the SCP and FP between the two Tomicus species adults, both indexes were significantly lower in the shoot-to-trunk period than in the trunk-to-shoot period. The trehalose content in females of two Tomicus species was significantly lower than that in males in the trunk-to-shoot period, and the protein, glycerol, glycogen, fat, and sorbitol contents were different between the species in the same period. The protein and water content in adults of both species were significantly lower in the shoot-to-trunk period than in the trunk-to-shoot period, but the content of glycerol, trehalose, water, sorbitol, glycogen, and fat content were significantly higher in the shoot-to-trunk. Different types of cold-resistant substances regulating sex, species, and developmental stages were found, and the most abundant were cold-resistant substances regulating developmental stages.
Bark beetles infest several pine tree species, often creating major economic losses. Biotic interactions between Scolytinae populations inhabiting Pinus sylvestris were analyzed using a new sampling ...method involving a two dimensional division of tree space resources into units and sections. The goal was to evaluate the effects of the type of available reproduction material on insect infestation. The P. sylvestris stands in this study included an analysis of bark beetles colonizing dead trees and uninfested living trees (trap trees). Analyzed trees were harvested and their stems divided into ten equal units; each unit was halved into two sections (half of the stem circumference). The colonization of dead trees by insects was evaluated immediately after cutting for infested trees and 2 months after cutting for trap trees. The type of breeding material significantly affected the species composition of bark beetles infesting P. sylvestris. The dead trees were colonized mostly by Trypodendron lineatum and Tomicus minor, and to a lesser extent by Tomicus piniperda, which dominated in trap trees. Tomicus piniperda and T. lineatum preferred thicker stems; however, T. minor, Hylurgops palliatus and Pityogenes bidentatus preferred thinner ones. The application of the new sampling method helped to increase the accuracy of niche segregation among insect species. The results of niche segregation indicate bark beetles exhibited spatial specialization in the use of resources, mainly related to the moisture content of breeding material and the availability of food resources which is the main factor determining the coexistence of bark beetles in the same environment.
It remains challenging to control Tomicus spp., a pest with fast spreading capability, leading to the death of large numbers of Pinus yunnanensis (Franch.) and posing a severe threat to ecological ...security in southwest China. Therefore, it is crucial to effectively and accurately monitor the damage degree for Pinus yunnanensis attacked by Tomicus spp. at large geographical scales. Airborne hyperspectral remote sensing is an effective, accurate means to detect forest pests and diseases. In this study, we propose an innovative and precise classification framework to monitor the damage degree of Pinus yunnanensis infected by Tomicus spp. using hyperspectral UAV (unmanned aerial vehicle) imagery with machine learning algorithms. First, we revealed the hyperspectral characteristics of Pinus yunnanensis from a UAV-based hyperspectral platform. We obtained 22 vegetation indices (VIs), 4 principal components, and 16 continuous wavelet transform (CWT) features as the damage degree sensitive features. We classified the damage degree of Pinus yunnanensis canopies infected by Tomicus spp. via three methods, i.e., discriminant analysis (DA), support vector machine (SVM), and backpropagation (BP) neural network. The results showed that the damage degree detected from the BP neural network, combined with 16 CWT features, achieved the best performance (training accuracy: 94.05%; validation accuracy: 94.44%).
Two pine shoot beetles,
Tomicus yunnanensis
and
Tomicus minor
, are the most destructive pests of
Pinus yunnanensis
in southwestern China. We investigated behavioral responses within and between ...these two species during the shoot-feeding phase using walking bioassays. We also identified the pheromonal aspects of beetles by static solid phase microextraction (SPME) and hindgut extraction following interactive communication by gas chromatography-mass spectroscopy (GC-MS). Both species were significantly attracted by their own species and the same sex, and attraction was inhibited by exposure to additional beetles or to the hindgut extracts of beetles which had shown interaction. Female and male
T. minor
and
T. yunnanensis
hindguts contained 0.19, 0.09, 0.22, and 0.05 ng/individual of (−)
-trans
-verbenol, respectively; following interaction with additional beetles, this increased to 16.74–292.71 ng/individual in
T. minor
females. Mean concentration of verbenone detected in the hindguts of female/male individuals of
T. minor
and
T. yunnanensis
under natural conditions were 0.16, 0.06, 0.03, and 0.05 ng/individual, respectively, but these correspondingly increased to 5.90, 2.43, 0.06, and 0.19 ng/individual after exposure to additional insects. In
T. yunnanensis
, the amounts of detectable (−)
-trans
-verbenol and verbenone extracted from hindguts were lower than those from
T. minor
. The levels of
cis
-verbenol and (−)
-trans
-verbenol most attractive to walking
T. yunnanensis
and
T. minor
were 0.1 and 1.0 ng/μl, respectively. Verbenone was not attractive at any of the concentrations tested. The addition of verbenone to
cis
-verbenol or (−)
-trans
-verbenol reduced the attraction responses. We conclude that the (−)
-trans
-verbenol produced by these two pine shoot beetles is attractive at low concentrations and repellant at high concentrations, thereby fostering intraspecific competition. Verbenone is produced to prevent overcrowding via interspecific inhibition, and to expel beetles during shoot-feeding.
,
, and
are the most economically significant pests of
in Southwestern China. Chemical and physical factors play critical roles in diverse biological activities. Here, we describe the fine structure ...of the adult mouthparts of these three
species using scanning and transmission electron microscopy. We identified three types of mandibular shapes, which determine their biomechanical properties, their ability to process food, and their preferred foraging locations on tree trunks. Eleven types of sensilla were discernible, including sensilla basiconica (Sb.1-2), sensilla twig basiconica (Stb.1-3), sensilla coeloconica (Sco), sensilla chaetica (Sch.1-2), sensilla trichoidea (Str.1-2), and sensilla digitiformia (Sdi). Each basiconic sensillum occurs on the palpal tips and is innervated by 2-6 dendrites. Sb.1 are gustatory receptors, Sb.2 are olfactory receptors, and the three other sensilla have dual taste and mechanical functions. Sco, Sch, and Str are mechanoreceptors. Sdi are mechanical vibration receptions, given that they are innervated by one dendrite with numerous dendritic branches into the nonporous cuticle. No significant differences among the sexes or species were identified; however, intraspecific variability in the number of Stb.3 and Sdi sensilla was evident. These results will aid future studies of
beetle behaviors.
The association between insects and fungi has evolved over millions of years and is ubiquitous in nature. This symbiotic relationship holds critical implications for both partners, the insects and ...the associated microbes. Numerous fungi are externally allied with bark beetles and form a close symbiosis, but the community structures of these fungi are largely unknown. In Yunnan Province in southwestern China, the beetles
,
.
, and
.
are major forest pests that cause large losses of two indigenous pines,
and
.
. In this study, we used the Illumina MiSeq PE300 platform to process 48 samples of epibiotic fungal communities pooled from 1348 beetles; the beetles were collected during both the branch- and trunk-infection sections from five locations across Yunnan Province. Considerably greater species richness was detected using high-throughput sequencing of amplified internal transcribed spacer 1 (ITS1) ribosomal DNA (rDNA) libraries than previously documented by using culture-dependent methods. In total, 1,413,600 reads were generated, and a 97% sequence-similarity cutoff produced eight phyla, 31 classes, 83 orders, 181 families, 331 genera, 471 species, and 1157 operational taxonomic units (OTUs), with 659, 621, and 609 OTUs being confined to
.
,
.
, and
.
, respectively.
,
.
, and
.
had the similar OTUs richness and evenness of fungal communities in Yunnan Province; nevertheless, the two fungal community compositions associated with
.
and
.
were structurally similar to each other but distinct from that associated with
.
. Lastly, the results of principal co-ordinates analysis suggested that epibiotic fungal community structures of the three
spp. were conditioned strongly by the locations and pine hosts but weakly by beetle species and infection sections. Our findings provide baseline knowledge regarding the epibiotic fungal communities of three major
spp. in southwestern China.
•Aleppo pine mortality increases after severe droughts.•Droughts and bark beetle infestation trigger tree death.•Beetle-infested trees produce less resin ducts two years prior to death.•Beetle ...infestation does not depend on tree growth and water-use efficiency.•Beetle-infested trees showed reduced growth sensitivity to climate.
Drought and bark-beetle infestation are major and often interconnected drivers of forest dieback and tree death. These two stressors may interact and accelerate forest mortality, since warmer and drier conditions boost beetle attacks and reduce tree growth. However, the way in which drought and bark-beetle infestation interact and affect declining or dying trees is still poorly understood. To disentangle the long-term interaction between the two stressors, we quantified radial growth (basal area increment), resin production, mortality and intrinsic water-use efficiency (iWUE) inferred from wood-carbon isotope discrimination. We compared trees infested and recently killed by two abundant bark beetle species (Orthotomicus erosus and Tomicus piniperda) with non-infested living trees in a drought-prone Aleppo pine plantation. Growth and iWUE showed similar values in infested and non-infested trees. Since bark-beetle-infested trees did not grow less than non-infested trees, our results did not support the hypothesis of higher costs of resin production at the expense of stem-wood formation. Radial growth was enhanced by cool and wet winter conditions prior to the growing season. However, infested trees showed lower growth responsiveness than did non-infested trees with respect to this climatic driver of growth. Infested trees also showed a lower resin-duct production two years prior to death than non-infested trees. The growth responsiveness to climate should be characterized in bark-beetle-infested trees, since a weak correlation between climate and growth can be regarded as a predisposing factor of infestation-induced tree death. Such reduced responsiveness to climate stress could be linked to the tree vulnerability to beetle attacks in drought-prone forests.
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