Ability of stress‐related volatiles to attract and induce attacks by Xylosandrus germanus and other ambrosia beetles

• 1 Xylosandrus germanus typically colonizes physiologically‐stressed deciduous hosts but it is increasingly being recognized as a key pest of ornamental nursery stock. We tested the attractiveness of common plant stress‐related volatiles to ambrosia beetles occupying the nursery agroecosystem, as well as their ability to induce attacks on selected trees. Experiments were conducted in Ohio, U.S.A.
• 2 Stress volatile attractiveness was first assessed by positioning traps baited with acetaldehyde, acetone, ethanol and methanol in ornamental nurseries. Cumulative trap counts confirmed that ethanol was the most attractive stress‐related volatile to X. germanus. Methanol‐baited traps were slightly attractive to X. germanus, whereas traps baited with acetaldehyde and acetone were not attractive to any ambrosia beetle.
• 3 A series of tree injection experiments were also conducted to determine the ability of these volatiles to induce attacks by ambrosia beetles under field conditions. Injection of ethanol into Magnolia virginiana induced the largest number of attacks, whereas injection of acetaldehyde induced more attacks than methanol or acetone. Xylosandrus germanus was the most predominant species emerging from M. virginiana injected with each of the stress‐related volatiles. No attacks by wood‐boring beetles were observed on water injected or uninjected control trees.
• 4 Solid‐phase microextraction–gas chromatography–mass spectrometry confirmed the emission of acetaldehyde, acetone, ethanol and methanol after their injection into M. virginiana.
• 5 Xylosandrus germanus has an efficient olfactory‐based mechanism for differentiating among host volatile cues. Injecting select trees with stress‐related volatiles, particularly ethanol, shows promise as a trap tree strategy for X. germanus and other ambrosia beetles.

     

Influence of flood‐stress on ambrosia beetle host‐selection and implications for their management in a changing climate

• 1 Xylosandrus germanus (Blandford) is a key pest of ornamental nursery trees. Ethanol is the most attractive semiochemical known for X. germanus, and its emission from trees represents a primary host‐selection cue. Ethanol production is induced by a variety of abiotic and biotic stressors, which could thereby predispose trees to attack by ethanol‐responsive ambrosia beetles.
• 2 To better understand X. germanus host‐selection behaviour within ornamental nurseries, a series of experiments examined the influence of flood‐stress on the attractiveness and susceptibility of flowering dogwood Cornus florida L. Under field conditions, more X. germanus were attracted to experimentally flood‐stressed dogwoods than neighbouring nonflooded controls in 2009, 2010 and 2011. Flood‐stressed dogwoods were also preferentially attacked in 2009–2011, although no attacks occurred on any of the neighbouring nonflooded trees.
• 3 Solid‐phase microextraction‐gas chromatography‐mass spectrometry detected ethanol in stem tissue from flooded dogwoods but not nonflooded trees. Acetaldehyde, acetic acid and ethanol were also emitted from the outer bark of flooded dogwoods but not nonflooded trees.
• 4 These results demonstrate that X. germanus preferentially lands on and attacks physiologically‐stressed hosts, and further support the role of ethanol in mediating this interaction.
• 5 Attacks by X. germanus have previously been suspected to occur on trees viewed as ‘apparently‐healthy’, although the possibility of such trees being in apparently‐stressed at the time of attack cannot be ruled out given the results obtained in the present study. Minimizing the impact of stressors known to induce the production of ethanol should be the primary foundation of a management plan for X. germanus and other ethanol‐responsive ambrosia beetles.

     

The capacity of conophthorin to enhance the attraction of two Xylosandrus species (Coleoptera: Curculionidae: Scolytinae) to ethanol and the efficacy of verbenone as a deterrent

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Integrating repellent and attractant semiochemicals into a push–pull strategy for ambrosia beetles (Coleoptera: Curculionidae)

Non‐native ambrosia beetles (Coleoptera: Curculionidae), especially Xylosandrus compactus (Eichhoff), Xylosandrus crassiusculus (Motschulsky) and Xylosandrus germanus (Blandford), are destructive wood‐boring pests of trees in ornamental nurseries and tree fruit orchards. Previous studies have demonstrated the adults are repelled by verbenone and strongly attracted to ethanol. We tested a “push–pull” semiochemical strategy in Ohio, Virginia and Mississippi using verbenone emitters to “push” beetles away from vulnerable trees and ethanol lures to “pull” them into annihilative traps. Container‐grown trees were flood‐stressed to induce ambrosia beetle attacks and then deployed in the presence or absence of verbenone emitters and a perimeter of ethanol‐baited interception traps to achieve the following treatment combinations: (a) untreated control, (b) verbenone only, (c) ethanol only, and (d) verbenone plus ethanol. Verbenone and ethanol did not interact to reduce attacks on the flooded trees, nor did verbenone alone reduce attacks. The ethanol‐baited traps intercepted enough beetles to reduce attacks on trees deployed in Virginia and Mississippi in 2016, but not in 2017, or in Ohio in 2016. Xylosandrus germanus, X. crassiusculus and both Hypothenemus dissimilis Zimmermann and X. crassiusculus were among the predominant species collected in ethanol‐baited traps deployed in Ohio, Virginia and Mississippi, respectively. Xylosandrus germanus and X. crassiusculus were also the predominant species dissected from trees deployed in Ohio and Virginia, respectively. While the ethanol‐baited traps showed promise for helping to protect trees by intercepting ambrosia beetles, the repellent “push” component (i.e., verbenone) and attractant “pull” component (i.e., ethanol) will need to be further optimized in order to implement a “push–pull” semiochemical strategy.     

Conophthorin enhances the electroantennogram and field behavioural response of Xylosandrus germanus (Coleoptera: Curculionidae) to ethanol

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Habitat and climatic preferences drive invasions of non-native ambrosia beetles in deciduous temperate forests

The introduction of non-native ambrosia beetles can cause severe damage in forest ecosystems. Understanding the environmental drivers affecting their invasion at the local scale is of utmost importance to enhancing management strategies. Our objectives were: (1) to determine the influence of forest composition, forest structure, and climate on invasion success of non-native ambrosia beetles in deciduous temperate forests, and (2) to test the effect of host tree species on colonization success by non-native ambrosia beetles. In 2013, we sampled 25 forest stands located in North-East Italy belonging to three forest types dominated respectively by hop hornbeam, chestnut, and beech. Both ethanol-baited traps and trap-logs of five tree species (hop hornbeam, chestnut, beech, manna ash, and black locust) were used to sample non-native and native ambrosia beetle communities. We found a clear effect of forest composition on non-native species richness and activity-density, as measured in ethanol-baited traps, both of which were higher in chestnut-dominated forests. Furthermore, we found a positive effect of temperature on both the number of trapped non-native species and their activity-density, with cold temperatures limiting beetle spread in high-elevation forests. Only Xylosandrus germanus successfully colonized the trap-logs. The number of colonized logs was higher for chestnut and in chestnut-dominated forests. Both trapping and log-baiting indicated that chestnut-dominated forests were at greater risk of invasion than hop hornbeam- and beech-dominated forests. Given the economic and ecological importance of chestnut, ambrosia beetle communities present in chestnut-dominated forests should be monitored to determine where protective measures must be taken.     

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

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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.     

Freeze stress of deciduous trees induces attacks by opportunistic ambrosia beetles

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The ambrosia beetle Anisandrus maiche (Stark) is repelled by conophthorin and verbenone and attracted to ethanol in a dose-dependent manner

1. Anisandrus maiche (Stark) (Coleoptera: Curculionidae: Scolytinae) is a non-native ambrosia beetle recently detected in northwestern Indiana. There is a critical need for advanced methods to detect and manage this potentially destructive beetle. Identifying semiochemicals that function as attractants or repellents can inform management practices to protect high-value plantings of hardwood trees.
2. We evaluated the extent to which (S)-(−)-verbenone, (E)-(±)-conophthorin and ethanol influence trap capture of A. maiche using two trap types and heights. We also investigated the effect of ethanol release rate on trap capture.
3. Traps baited with ethanol alone captured the most beetles, while traps baited with (S)-(−)-verbenone or (E)-(±)-conophthorin alone captured few A. maiche, and each compound decreased capture when paired with ethanol lures.
4. There was no difference in mean capture of A. maiche between trap types across treatments, and the height of ethanol-baited traps did not influence the capture rate suggesting this species is widely distributed throughout the canopy.
5. Our results suggest that (S)-(−)-verbenone and (E)-(±)-conophthorin are effective repellents for A. maiche and a release rate of at least 3 g/day of ethanol enhances trap to capture.

     

Species characterization and responses of subcortical insects to trap‐logs and ethanol in a hardwood biomass plantation

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Earwig preying on ambrosia beetle: Evaluating predatory process and prey preference

Earwigs (Dermaptera), such as Forficula auricularia L., are important euryphagous predators for a wide variety of prey and can markedly influence the populations of orchard pests. Most previous studies on earwig feeding behaviour have not used adult beetles of the prey species; few researchers have focused on prey preference in earwigs. Some fragments of beetle exoskeleton and an earwig adult, Anisolabella marginalis (Dohrn), were found in the same cage, where adults of ambrosia beetle, Euwallacea interjectus (Blandford), were emerging from the logs of a fig tree infected with Ceratocystis canker (fig wilt disease). Thus, A. marginalis was suspected of being a predator of E. interjectus. To shed light on this issue, in the laboratory, we set up a test arena and observed and recorded behavioural interactions between A. marginalis and E. interjectus. E. interjectus was collected from the logs of fig trees and reared on an artificial diet, along with six different ambrosia beetle species, which were collected from a trap (baited with ethanol) and a fallen maple tree. A series of laboratory experiments demonstrated that A. marginalis is actually a predator of E. interjectus and other species of ambrosia beetle, indicating its a potential for use in effective pest control in the field. The predators frequently consume and tend to select their prey depending on prey size, rather than sex and beetle species. Furthermore, earwigs have alternative predatory strategies for dealing with seven different species, although they use their forceps to cut the body of most tested beetles.     

Short-term development of ambrosia and bark beetle assemblages following a windstorm in French broadleaved temperate forests

Abstract: In most temperate deciduous forests, windstorm is the main source of dead wood. However, the effects of this natural disturbance on ambrosia and bark beetle communities are poorly known. In managed oak‐hornbeam forests storm‐damaged in France in 1999, we sampled ambrosia (and second bark beetles) by ethanol‐baited window‐flight traps in 2001. By comparing uncleared gaps, undisturbed closed‐canopy controls and seedling‐sapling stands, we investigated the short‐term effects of gap formation, gap size and surrounding landscape to provide a snapshot of scolytid response. Contrary to expectations, neither the abundance nor the richness of ambrosia beetle species was significantly higher in gaps than in undisturbed stands. Few responses in abundance at the species level and only a slight difference in assemblage composition were detected between gaps and closed‐canopy controls. Gaps were more dissimilar from seedling‐sapling stands, than from closed‐canopy controls. More scolytid individuals and species were caught in gaps than in seedling‐sapling stands. Mean local and cumulative richness peaked in mid‐size gaps. Only mid‐size gaps differed from closed‐canopy controls in terms of species composition. We identified generalist gap species (Xyleborus saxesenii, X. cryptographus), but also species significantly more abundant in mid‐size gaps (Platypus cylindrus, Xyloterus signatus). The faunistic peculiarity of mid‐size gaps seemed to be partly related to a bias in oak density among gap size classes. Few landscape effects were observed. Only the scolytids on the whole and X. dispar were slightly favoured by an increasing density in fellings at the 78 ha scale. We did not find any correlation between scolytid abundance and the surrounding closed‐forest percentage area. We confirmed that temperate, deciduous, managed stands did not come under threat by ambrosia and bark beetle pests after the 1999 windstorm. Nonetheless, our data stressed the current expansion in Western Europe of two invasive species, X. peregrinus and especially X. germanus, now the predominant scolytid in the three oak forests studied.     

Distribution of Norway spruce bark and wood‐boring beetles along Alpine elevational gradients

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Phenological observations and trapping tactics for the granulate ambrosia beetle Xylosandrus crassiusculus (Coleoptera: Curculionidae,Scolytinae) in New Zealand

1. The granulate ambrosia beetle (GAB) Xylosandrus crassiusculus, was first formally detected in New Zealand in 2019. Since then, GAB has subsequently been found infesting numerous tree species in the Auckland region.
2. Flight intercept traps baited with ethanol lures were deployed from October 2019 to May 2021 at three sites in the Auckland region to ascertain the phenology of GAB in New Zealand. Two distinct peak flight periods were identified in early and late summer, while a smaller and inconsistent third peak was detected in early autumn. Logistical analysis of GAB captures in the ethanol-lured traps and degree-day (DD) accumulation indicated that 90% of flight activity is completed by 800 DD.
3. To assess monitoring tactics, flight intercept traps were baited with three different ethanol lures with varying release rates or ethanol-soaked or non-soaked wood bolts from three species of trees. A lure releasing 2 g ethanol per day was most effective at capturing GAB. Ethanol-soaked bolts were less effective than the lures.
4. Xylosandrus crassiusculus represents a significant risk for shrubs and trees native to New Zealand, as well as commercial horticultural and forestry trees. We recommend using ethanol-lured panel traps for monitoring purposes.

     

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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Ambrosia beetles (Curculionidae: Scolytinae and Platypodinae) on Fagus crenata Blume: community structure,seasonal population trends and resource utilization patterns

Ambrosia beetles (many Scolytinae and all Platypodinae) are one of the most important insect pests for forestry worldwide, but little is known about the community structure of ambrosia beetles in terms of their vertical variations and resource utilization. We clarified the community structure and seasonal population trends of ambrosia beetles on 11 living and three newly dead Fagus crenata Blume trees using individual tube traps placed up to 10 m high from May to November in 2007 and 2008. We captured seven scolytine species (Ambrosiodmus lewisi (Blandford), Euwallacea validus (Eichhoff), Trypodendron proximum (Niisima), Xyleborinus saxeseni (Ratzeburg), Xyleborus atratus Eichhoff, Xylosandrus brevis (Eichhoff) and Xylosandrus germanus (Blandford)) and three platypodine species (Crossotarsus niponicus Blandford, Platypus hamatus Blandford and Platypus severini Blandford). The ambrosia beetles were suggested to breed at species‐specific height ranges, with the equal host resource use per individual among the species. Of the three major species, C. niponicus, P. hamatus and P. severini, two (C. niponicus and P. hamatus) had male‐biased sex ratios, which is considered a reproductive strategy to increase maternal fitness. Morphological characteristics of the mandibles may play an important role in the difference of sex roles on reproduction in the three major species.     

Attraction of ambrosia beetles to ethanol baited traps in a Slovakian oak forest

The attractiveness of ultra high release ethanol lures to ambrosia beetles in Slovakian oak forests was tested from 2010 to 2012. A total of 24,705 specimens were captured during this three year period with Xyleborinus saxesenii (Ratzeburg, 1837) representing 49.28% (12,174 specimens) of the total. Other dominant species captured in the traps were Anisandrus dispar (F., 1792) (27.84%), Xyleborus monographus (F., 1792) (9.72%) and Trypodendron signatum (F., 1792) (6.04%). During this experiment, Xylosandrus germanus (Blandford, 1894) was detected for the first time in Slovakia with an increase in capture each year (19, 40 and 77 specimens, respectively). Flight period for ambrosia beetles in Slovakia occurs from the beginning of April through the end of September. This is the first time that ethanol baited traps were deployed in Slovakian oak forests and the lures were an effective tool for monitoring native and non-native ambrosia beetles.     

Optimizing early detection strategies: defining the effective attraction radius of attractants for emerald ash borer Agrilus planipennis Fairmaire

1. Adult emerald ash borers are attracted to green prism traps baited with the ash host volatile (3Z)-hexenol and the sex pheromone of emerald ash borer (3Z)-dodecen-12-olide [(3Z)-lactone]. Quantifying the heretofore unknown range of attraction of such traps would help optimize deployment strategies for early detection.
2. Examining trap captures of traps deployed in pairs at variable distances offers insight into the range of attraction. Recent work has shown the range of attraction can be estimated as half the intertrap distance at which trap catch begins to decrease, which should occur when proximate traps overlap their respective attractive ranges.
3. We estimated these traps' attractive range for emerald ash borer using 98 baited dark green prism traps deployed in pairs, one trap per tree, in an urban park in Saint Paul, Minnesota, USA in summer 2020.
4. We estimate attractive range by fitting a logistic model to trap catch data using Bayesian inferential methods and describe advantages thereof.
5. The attractive range of these baited traps was estimated to be between 16 and 73 m, with a median of 28 m. We recommend that dark green prism traps baited with these semiochemicals be placed 25–35 m apart near high-risk entry points.

     

Attraction of the cerambycid beetles Tetropium gabrieli,T. castaneum and T. fuscum to pheromones and host tree volatiles

1. Tetropium gabrieli is native to the European Alps where it breeds in European larch and may be an important pest during drought periods by killing trees. It has spread to larch plantations in several European countries including Sweden.
2. In trapping studies conducted in Sweden, we tested whether T. gabrieli was attracted to E-fuscumol, E,Z-fuscumol, E,Z-fuscumol acetate and the host volatile combination of α-pinene plus ethanol. We also compared its response with those of the native congeners, T. fuscum and T. castaneum.
3. All three Tetropium species were caught in significantly higher numbers in traps baited with E-fuscumol plus host volatiles than in traps baited with host volatiles alone or in unbaited traps.
4. There was no difference in catch of any Tetropium species between traps baited with E-fuscumol plus host volatiles versus traps baited with E,Z-fuscumol plus host volatiles, but the latter treatment caught more T. fuscum and T. castaneum than did E,Z-fuscumol acetate plus host volatiles.
5. The addition of E-fuscumol to host volatile-baited traps significantly reduced mean catch of T. gabrieli, significantly increased mean catch of T. castaneum, and had no significant effect on catch of T. fuscum. Mean catch of all three species was significantly greater in traps baited with E-fuscumol alone than in traps baited with host volatiles alone.
6. All three species were caught from May to August. The median date of captures was about 2 weeks earlier for T. fuscum compared with the other two species.