Winter starch reserves of white oak as a predictor of attack by the twolined chestnut borer,Agrilus bilineatus (Weber) (Coleoptera: Buprestidae)

Summary The twolined chestnut borer, Agrilus bilineatus (Weber) (Coleoptera: Buprestidae), attacks oaks (Quercus spp.) and is associated with extensive mortality of trees in the eastern deciduous forests of North America. We tested the hypothesis that winter starch reserves of oak roots are an indicator of tree vigor and that only trees low in stored starch would be attacked by A. bilineatus. We measured the levels of stored starch in the roots of 200 non-infested healthy white oaks during the dormant season and determined their correlation with A. bilineatus attacks the following spring. There was a significant increase in A. bilineatus captures on sticky traps with a decrease in winter starch reserves. Trees low in stored starch that were also stressed by phloem-girdling attracted 3.7 times as many beetles as did non-girdled trees that were low in starch. However, non-girdled trees that had low winter starch reserves were also attacked. Only oaks that had had extremely low winter root starch reserves (<5mg/g dry weight of root sapwood tissue) were heavily attacked by A. bilineatus and subsequently died. One third of non-girdled low starch trees and 67% of phloem-girdled low starch trees died, whereas none of the trees with root starch >5 mg/g dry wt died. These results indicate that winter starch reserves are a good predictor of A. bilineatus attack.The investigation reported in this paper (No. 87-7-8-118) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

Attraction of ambrosia and bark beetles to coast live oaks infected by Phytophthora ramorum

1 Sudden oak death is caused by the apparently introduced oomycete, Phytophthora ramorum. We investigated the role of bark and ambrosia beetles in disease progression in coast live oaks Quercus agrifolia. 2 In two Marin County, California sites, 80 trees were inoculated in July 2002 with P. ramorum and 40 were wounded without inoculation. Half of the trees in each group were sprayed with the insecticide permethrin [cyclopropanecarboxylic acid, 3‐(2,2‐dichloroethenyl)‐2,2‐dimethyl‐(3‐phenoxyphenyl) methyl ester] to prevent ambrosia and bark beetle attacks, and then were sprayed twice per year thereafter. After each treatment, sticky traps were placed on only the permethrin‐treated trees. Beetles were collected periodically in 2003. 3 Inoculated trees accounted for 95% of all beetles trapped. The ambrosia beetles Monarthrum scutellare and Xyleborinus saxeseni and the western oak bark beetle Pseudopityophthorus pubipennis were the most abundant of the seven species trapped. 4 Permethrin treatment delayed initiation of beetle attacks and significantly reduced the mean number of attacks per tree. Beetles did not attack any wounded or noncankered inoculated trees. 5 Trees with larger cankers trapped more beetles early in the disease. Once permethrin lost effectiveness, the number of beetle entrance tunnels was a more reliable predictor of subsequent trap catch than was canker size. 6 Beetles were initially attracted to P. ramorum cankers in response to kairomones generated in the host‐pathogen interaction. After beetles attacked the permethrin‐treated trees, aggregation pheromones most probably were the principal factor in beetle colonization behaviour.     

Ambrosia beetle response to ethanol concentration and host tree species

Ethanol emitted by stressed trees is an olfactory cue used by ambrosia beetles (Coleoptera; Curculionidae; Scolytinae) to locate susceptible hosts to colonize. In addition, ethanol enhances the growth of ambrosia beetle fungal symbionts, improving colonization. Whether host selection and colonization are affected also by the amount of ethanol produced by stressed trees and by tree species is unclear. To investigate these mechanisms, we induced attacks by ambrosia beetles in bolts of eight tree species by coring and filling them with either 5% or 90% ethanol solutions in water. For each ethanol concentration, bolts of the eight different tree species were replicated six times in a randomized complete block design. Entry holes were used as a proxy for host selection whereas gallery development stage was used as a proxy for colonization. Ethanol concentration differentially affected host selection of the three ambrosia beetles that were active during this study. Anisandrus dispar Fabricius preferentially attacked bolts with 90% ethanol concentration, Xylosandrus crassiusculus (Motschulsky) preferentially attacked bolts with 5% ethanol concentration, and Xyleborinus saxesenii (Ratzeburg) attacked bolts irrespective of ethanol concentration. Colonization of X. crassiusculus reflected the same pattern observed for entry holes. The effect of host tree species on host selection was most prominent for X. saxesenii, while X. crassiusculus established a higher number of developed galleries in Ostrya carpinifolia Scopoli bolts than on five of the other tested tree species. Our results suggest that ethanol concentration and host tree species may influence ecological niche partitioning among ambrosia beetle species.     

Role of stressed mango host conditions in attraction of and colonization by the mango bark beetle Hypocryphalus mangiferae Stebbing (Coleoptera: Curculionidae: Scolytinae) and in the symptom development of quick decline of mango trees in Pakistan

The mango sudden death syndrome has become a serious threat to the mango industry and caused significant decline in mango production worldwide. The bark beetle Hypocryphalus mangiferae (Stebbing) (Coleoptera: Curculionidae: Scolytinae) has been suggested as a potential vector of the disease based primarily on field observations with little or no supporting empirical data. In this study, we investigated the role of infected mango trees in host attraction and colonization by H. mangiferae to determine if beetle attack and colonization contributes to the disease progression on mango trees. Initially, the role of various stress factors on beetle attraction and disease progression was assessed under lathe house conditions from 2008 to 2009. Results suggest that symptomatic or recently inoculated mango trees (without any obvious symptoms) are preferentially colonized by H. mangiferae. Although not significant, high numbers of beetles attacked stressed or wounded mango trees, compared to healthy or dead mango trees. Disease symptoms after beetle colonization, such as bark splitting, wilting and oozing, were further evaluated. These symptoms showed positive correlation with the degree of disease severity and host plant condition. Furthermore, two fungi, Ceratocystis fimbriata and Lasiodiplodia theobromae, were frequently isolated from the beetle and beetle-colonized trees. Based on these findings, they suggests that H. mangiferae can vector multiple fungi associated with mango sudden decline disease and play a significant role in outbreaks of this disease.     

Early responses of bark and wood boring beetles to an outbreak of the hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) in a boreal balsam fir forest of North America

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Boxes mimicking tree hollows can help conservation of saproxylic beetles

Old hollow trees have declined in Europe and many saproxylic (i.e. wood-dwelling) invertebrates living on them are threatened. The aim of this study was to investigate to what extent artificial habitats can be exploited by saproxylic beetles. To mimic the conditions in tree hollows, we constructed wooden boxes filled with different combinations of substrates like oak saw dust, oak leaves, a dead hen (Gallus domesticus), chicken dung, lucerne flour or potatoes and placed them on tree trunks. To investigate the importance of distance from dispersal sources, we placed boxes at different distances (0–1,800 m) from three species-rich sites with high densities of hollow oaks. Over 3 years, 3,423 specimens of 105 saproxylic beetle species were caught in 47 boxes. Among beetles found in hollow oaks that were either tree-hollow species, bird nest species, or wood rot species, 70% were also found in the boxes. A dead hen added to the artificial wood mould gave a higher number of beetle specimens. The number of species associated with tree hollows in oak decreased with distance from sites with hollow oaks. In conclusion, the prospects for using artificial environments for boosting substrate availability, or to fill spatial and temporal gaps therein, for saproxylic beetles are good.     

Hollow oaks and beetle conservation: the significance of the surroundings

In this study we investigated hollow oaks (Quercus robur, Q. petrea) situated in open landscapes and in forests in Norway in northern Europe, and compared their importance for rare and threatened beetles (Coleoptera). Old, hollow oak trees, both in parks and in forests, were extremely rich in red-listed beetles, and hosted a high proportion of threatened species. The proportion of oak associated species and the mean number of red-listed beetle species per tree was similar in the two site types, but rarefaction showed that for a certain number of individuals, oaks in forests had more threatened and near-threatened species than oaks in parks. The species composition also differed between site types: Park oaks had a higher proportion of species associated with hollows and animal nests, whereas in forests, there was a higher proportion of species depending on dead oak wood in general. Four factors were significant in explaining the richness of red-listed beetles in our study: Tree circumference, cavity decay stage, proportion of oak in the surroundings, and coarse woody debris (CWD) in the surroundings. Forest oaks were smaller, but they still trapped a species richness comparable to that of the larger park oaks—probably a result of high amounts of CWD in the surroundings. We show that oaks in open landscapes and oaks in forest have only partly overlapping beetle assemblages and, thus, cannot be substituted in conservation. Planning for conservation of red-listed beetles associated with this key habitat demands a large scale perspective, both in space and time, as the surroundings have important effects on associated threatened and near threatened species.     

Past levels of canopy closure affect the occurrence of veteran trees and flagship saproxylic beetles

Aim

Open woodlands are biologically highly diverse habitats, and veteran (i.e., old, senescent) trees are key structures supporting their biodiversity. Open canopy structure had been maintained by both natural‐ and human‐induced disturbances. In the past two centuries, suppression of such disturbances, together with forestry intensification, has turned most lowland woodlands into closed‐canopy forests. We investigated the effect of increased canopy closure on veteran trees and several threatened beetles associated with them.

Location

Floodplain woodlands along the lower Dyje and Morava rivers, Czech Republic.

Methods

We used an approach combining the study of aerial photographs with on‐ground survey of veteran trees and associated endangered beetles. The aerial images were used to obtain the information on historical (1938) and recent (2009) canopy closure in the area of 146 km², where we mapped large oaks (d.b.h. >70 cm), hollow trees and three associated beetles including the hermit beetle (Osmoderma barnabita), the great capricorn beetle (Cerambyx cerdo) and the jewel beetle Eurythyrea quercus.

Results

The presence of large oaks, hollow trees and their associated beetle species are negatively related to recent high canopy closure, and the historical level of canopy closure matters, as in nowadays closed‐canopy stands, the beetles and veteran trees are more common in places that were rather open in 1938 than in the places with closed canopy already in 1938. Moreover, the health state of veteran trees highly depends on the canopy closure.

Main conclusion

The negative effect of canopy closure on veteran trees and their endangered inhabitants is several decades delayed and may thus often go undetected. In the forests, however, large and hollow trees and their associated biodiversity are relics of the past, more open conditions. The restoration of open woodlands is therefore vital for preventing their further decline. Conservation management planning needs to take this into account wherever, veteran trees and associated biota are concerned.

     

Dynamics of twolined chestnut borer Agrilus bilineatus as influenced by defoliation and selection thinning

1 The twolined chestnut borer, Agrilus bilineatus (Coleoptera: Buprestidae), is a major mortality agent of stressed oak trees. However, patterns of abundance and population change are not well understood. 2 We studied the spatial and temporal variation in abundance of twolined chestnut borer adults during a gypsy moth, Lymantria dispar (Lepidoptera: Lymnatriidae), outbreak and examined the influence of both defoliation and thinning on twolined chestnut borer abundance. 3 In stands that were defoliated by gypsy moth, extensive defoliation occurred in one year, and major overstory tree mortality followed in the next. Most mortality occurred in the year preceding the peak year of twolined chestnut borer abundance and abundance of twolined chestnut borer was positively associated with defoliation and mortality in the previous year. 4 Twolined chestnut borers were more frequently associated with poor or fair crown condition trees than trees with good crown condition and were more abundant on members of the red oak group than the white oak group.     

Increased openness around retained oaks increases species richness of saproxylic beetles

The decrease of old deciduous trees in northern Europe is a threat to the saproxylic fauna. In northern Europe, oak sustains the highest richness of saproxylic invertebrates, among which beetles is a large group. In order to preserve species associated with old trees, it has become common practice in commercial forestry to retain such trees at final felling. However, to create beneficial conditions for species associated with retained trees, the surrounding plantation has to be managed with regard to their specific demands. In the case of oak-associated species, including many red-listed species, several studies have shown that light is an important factor. The aim of this study was to analyze the effects of increased openness around oaks (Quercus robur) in spruce plantations (Picea abies) on species richness and abundance of oak-associated saproxylic beetles. The study was performed in nine spruce plantations located in southern Sweden, with mature oaks standing in a gradient of canopy openness. Beetles were collected from 54 oaks from May to September during two seasons, using window traps. The analyses revealed that increased openness around oaks increases species richness and abundance of oak-associated beetles. By including insolation angle in the analysis, we found that it is mainly the degree of openness directed south from the oak that has positive effects on beetle richness. These findings imply that it is desirable to maintain an open area around retained oaks, and that this area should be placed on the southern side of the oak to maximize the biodiversity benefit in relation to costs for the forest owner.     

Behaviours of phoretic mites (Acari) associated with Ips pini and Ips grandicollis (Coleoptera: Curculionidae) during host‐tree colonization

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Assemblages of saproxylic beetles on large downed trunks of oak

Old living oaks (Quercus robur) are known as a very species‐rich habitat for saproxylic beetles, but it is less clear to what extent such veteran trees differ from an even rarer feature: downed trunks of large oaks. In this study, we set out to sample this habitat, using window traps, with two aims: (1) to describe the variation of assemblages among downed trunks of different type and (2) to compare beetles on downed oaks with data from veteran standing trees. The results showed that trunk volume and sun exposure better explained assemblages as well as species numbers on downed trunks than did decay stage. Furthermore, species classified as facultative saproxylic species showed weak or no differentiation among downed trunks. Species with different feeding habits showed no apparent differentiation among downed trunks. Furthermore, species composition on dead, downed oak trunks differed sharply from that of living, veteran oaks. Wood or bark feeders were more common on veterans than downed trunks, but there was no difference for those species feeding on fungi or those feeding on insects and their remains. In conclusion, for a successful conservation of the saproxylic beetle fauna it is important to keep downed oak trunks, and particularly large ones, in forest and pastures as they constitute a saproxylic habitat that differs from that of living trees.     

Stand-level distribution and movement of Platypus quercivorus adults and patterns of incidence of new infestation

Abstract 1 Flying populations of an ambrosia beetle, Platypus quercivorus (Murayama), a vector of an ambrosia fungus Raffaelea quercivora, which causes deciduous oak diebacks in Japan, were determined by sticky screen traps. 2 Platypus quercivorus beetles tended to move upwards along slopes. The highest concentrations of flying beetles usually occured at the upper forest margins. 3 During the period when the number of flying beetles was increasing, the incidence of newly infested trees spread from the epicentre into the forest. During the period when the number of flying beetles was decreasing, the epicentre shrank into the upper forest edge. Newly infested trees did not occur in this period because most trees had already been infested. 4 Near the upper forest edge, where many beetles were highly concentrated throughout the season, the number of new entry holes decreased greatly after the initial attack early in the season, although many adults were present throughout the period.     

Leaf abscission phenology of a scrub oak: consequences for growth and survivorship of a leaf mining beetle

Brachys tessellatus is a leaf-mining beetle that attacks Quercus laevis (turkey oak), a deciduous scrub oak in the fall line Sandhills of the southeastern United States. This oak species varies substantially in leaf abscission phenology. In the fall of 1994 we examined leaf abscission patterns at three sites in central South Carolina and found that leaves containing active miners abscised earlier than leaves without active miners. To quantify the effect of leaf abscission phenology on the survivorship and body size of leaf miners within the abscised leaves, we marked naturally and manually abscised leaves, left leaves on the ground to over-winter, and then collected leaves before beetles emerged the following spring. We found that beetles inside leaves that were abscised early in the season were more likely to be killed by predators, and that they produced smaller pupae than beetles within leaves abscised later in the season. We also evaluated the relationship between adult beetle body size and fecundity; body size of B. tessellatus is positively correlated with lifetime fecundity and daily oviposition rate indicating that effects of leaf-abscission phenology on beetle body size likely translate into effects on beetle fitness. We discuss how B. tessellatus has adapted to variation of leaf abscission phenology of oaks by evolving developmental plasticity that permits successful completion of larval development over a range of season lengths.     

Comparisons of mountain pine beetle (Dendroctonus ponderosae Hopkins) reproduction within a novel and traditional host: effects of insect natal history,colonized host species and competitors

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Ten years after: Release cutting around old oaks still affects oak vitality and saproxylic beetles in a Norway spruce stand

1. It is often suggested to release oaks (Quercus robur) from competition, to ensure their survival and boost their conservational value. However, few studies have explored how long-lasting this effect is and how it affects saproxylic beetles.
2. Ten years after cutting, we investigated effects of different release cutting levels (high, medium, and no release) around 140-year-old retained oaks in a commercial forest with Norway spruce (Picea abies).
3. We evaluated oak vitality using crown and dead wood measurements. Saproxylic beetles were caught in window traps, identified to species level, and grouped according to their association with oak and/or Norway spruce.
4. Released oaks had more light, higher temperatures, greater crown growth, and less dead wood in the crown compared to the no-release control.
5. After 10 years we still found a higher abundance of oak-associated beetles and higher overall species richness of saproxylic beetles in the released oaks. Beetle species composition significantly differed between released oaks and control.
6. We suggest avoiding planting trees beneath retained oaks when regenerating conifer forests and to proceed with conservation management during subsequent thinning by removing regeneration under the oak crowns. We emphasize the benefits of monitoring the retained oaks to maintain tree vitality, habitat quality, and insolation.

     

Colonization, survival, and causes of mortality of Camerariu hamadryadella (Lepidoptera: Gracillariidae) on four species of host plants

Abstract.

• 1 The abundance, survival, and causes of mortality of Cameraria hamadryadella (Clemens) (Lepidoptera: Gracillariidae) were examined on four host plant species in Virginia, U.S.A. Quercus alba L. and Q.rubra L. are native within the geographic range of C.hamadryadella, and Q.robur L. and Q.benderi Baenitz are exotic. Q.robur is native to Europe, North Africa, and Asia and was probably introduced prior to 1850, and Q.benderi is of hybrid origin and introduced to cultivation before 1900. Q.alba and Q.robur are in the subgenus Lepidobalanus (white oaks), and Q.rubra and Q.benderi are in the subgenus Erythrobalanus (red oaks).
• 2 Larval mines of C. hamadryadella were abundant on both white oak species, including the exotic Q.robur, but were rare on host plants in the red oak subgenus. Un-hatched eggs of C.hamadryadella were not observed on red oaks. Other observations on host distribution indicate that C.hamadryadella is rarely found on red oaks. These observations are interpreted as circumstantial evidence that C. hamadryadella generally avoids ovipositing on red oaks.
• 3 Survival of C.hamadryadella to the adult stage was similar among all host species, but larvae tended to survive longer on hosts in the red oak subgenus. The observation of higher survival rates of early instar larvae on red oaks suggests that no nutritional or secondary chemical barrier reinforces the observed pattern of oviposition.
• 4 Significant differences in the distribution of the causes of mortality were detected between native and exotic host plant species. Larvae and pupae on native hosts were more likely to die because of predation, while those on exotic host plants were more likely to die because of parasitism and host feeding by adult female parasitoids. This pattern could arise because parasitoids prefer to forage on exotic host plants or because predators avoid foraging on exotic plants.
• 5 This study shows for C. hamadryadella that the only barriers to colonization and use of exotic hosts, in the white and red oak subgenera, are the presence of cues sufficient to stimulate oviposition and/or the absence of cues to deter oviposition. It also suggests that the presence of closely related native host plants in the region of introduction will increase the probability that exotic plants will be colonized by phytophagous insects.

     

Ethanol‐injection induces attacks by ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) on a variety of tree species

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Influence of temperature on the reproductive success,brood development and brood fitness of the eastern larch beetle Dendroctonus simplex LeConte

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Testing temperature effects on woodboring beetles associated with oak dieback

A warmer climate may potentially have a strong effect on the health status of European oak forests by weakening oak trees and facilitating mass reproduction of wood boring insects. We did a laboratory experiment in Slovakia to study the response of major pest beetles of oak and their parasitoids to different temperature regimes as background for predicting climatic effects and improving management tools of European oak forests. With higher temperatures the most important oak pest Scolytus intricatus emerged much earlier, which indicate that completion of a second generation and increased damage further north in European oak forests may be possible. Lower temperatures gave longer larval galleries and more offspring per parents but still lower beetle production due to semivoltine life cycle. For buprestids and longhorn beetles warmer temperatures resulted in more emerging offspring and a shift towards earlier emergence in the same season, but no emergence in the first season indicated that a change to univoltine populations is not likely. Reduced development success of parasitoids at the highest temperatures (25/30 °C) indicates a loss of population regulation for pest beetle populations. A warmer climate may lead to invasion of other population-regulating parasitoids, but also new serious pest may invade. With expected temperature increases it is recommended to use trap trees both in April and in June, and trap trees should be removed within 2 months instead 1 year as described in the current standard.