Effects of pheromone and plant volatile release rates and ratios on trapping Anoplophora glabripennis (Coleoptera: Cerambycidae) in China

Current and future control of the wood-boring pest Anoplophora glabripennis

The Asian longhorn beetle (ALB) Anoplophora glabripennis is one of the most successful and most feared invasive insect species worldwide. This review covers recent research concerning the distribution of and damage caused by ALB, as well as major efforts to control and manage ALB in China. The distribution and destruction range of ALB have continued to expand over the past decade worldwide, and the number of interceptions has remained high. Detection and monitoring methods for the early discovery of ALB have diversified, with advances in semiochemical research and using satellite remote sensing in China. Ecological control of ALB in China involves planting mixtures of preferred and resistant tree species, and this practice can prevent outbreaks. In addition, strategies for chemical and biological control of ALB have achieved promising results during the last decade in China, especially the development of insecticides targeting different stages of ALB, and applying Dastarcus helophoroides and Dendrocopos major as biocontrol agents. Finally, we analyze recommendations for ALB prevention and management strategies based on native range and invasive area research. This information will hopefully help some invaded areas where the target is containment of ALB.

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

BACKGROUND

The Asian longhorned beetle (ALB), Anoplophora glabripennis, is a serious wood borer of hardwood trees. Populus deltoides 'Shalinyang' (PdS) is attractive to ALB adults for oviposition but highly resistant to their offspring. Investigation of the chemicals regulating ALB oviposition is scarce in previous studies until now. To determine which chemicals emitted by PdS were attractive and induced oviposition behavior by ALB on non-host poplar tree species, we first: collected and identified the bio-active volatiles produced by PdS using coupled gas chromatography-mass spectrometry (GC-MS) and coupled gas chromatography-electroantennographic detector (GC-EAD); then evaluated which chemicals were attractive in a Y-tube olfactometer bioassay; and finally screened key compounds affecting ALB oviposition using a 'chemical-stimulated oviposition on non-host tree' bioassay.

RESULTS

(E)-2-Hexenal, hexyl acetate, (Z)-3-hexenol acetate, 1-hexanol, (Z)-3-hexenol, β-caryophyllene, and salicylaldehyde emitted from PdS were attractive to ALB. When (E)-2-hexenal, 1-hexanol, (Z)-3-hexenol acetate, and (Z)-3-hexenol were applied to the non-host tree Populus tomentosa, oviposition by ALB females was significantly increased. Furthermore, the mean number of oviposition pits increased as the (Z)-3-hexenol concentrations increased. Further tests on synergy between pairs of chemicals showed that (Z)-3-hexenol stimulated production of the most oviposition pits, but that the percentage of effective oviposition pits (those containing an egg and larva and not empty) decreased.

CONCLUSION

(Z)-3-Hexenol is the main chemical component inducing ALB oviposition. These results increase understanding about the oviposition behavior of ALB and could help improve management strategies that regulate ALB behavior by planting mixed-species forests resistant to ALB. © 2023 Society of Chemical Industry.

Research on Photoinduction-Based Technology for Trapping Asian Longhorned Beetle (Anoplophora glabripennis (Motschulsky, 1853) (Coleoptera: Cerambycidae)

Light traps play a crucial role in monitoring pest populations. However, the phototactic behavior of adult Asian longhorned beetle (ALB) remains enigmatic. To provide a theoretical foundation to select the suitable light emitting diode (LED)-based light sources used for monitoring ALB, we compared the effect of exposure time on the phototactic response rates of adults at wavelengths of 365 nm, 420 nm, 435 nm, and 515 nm, and found that the phototactic rate increased gradually when the exposure time was prolonged, but there was no significant difference between different exposure times. We evaluated the effect of diel rhythm and found the highest phototactic rate at night (0:00-2:00) under 420 nm and 435 nm illumination (74-82%). Finally, we determined the phototactic behavioral response of adults to 14 different wavelengths and found both females and males showed a preference for violet wavelengths (420 nm and 435 nm). Furthermore, the effect of the light intensity experiments showed that there were no significant differences in the trapping rate between different light intensities at 120 min exposure time. Our findings demonstrate that ALB is a positively phototactic insect, showing that 420 nm and 435 nm are the most suitable wavelengths for attracting adults.

A Review of the Host Plant Location and Recognition Mechanisms of Asian Longhorn Beetle

The Asian longhorn beetle (ALB), Anoplophora glabripennis Motschulsky, is a polyphagous xylophage with dozens of reported host tree species. However, the mechanisms by which individuals locate and recognize host plants are still unknown. We summarize the current knowledge of the host plant list, host kairomones, odorant-binding proteins (OBPs) and microbial symbionts of this beetle and their practical applications, and finally discuss the host localization and recognition mechanisms. A total of 209 species (or cultivars) were reported as ALB host plants, including 101 species of higher sensitivity; host kairomones were preferentially bound to ALB recombinant OBPs, including cis-3-hexen-1-ol, δ-3-carene, nonanal, linalool, and β-caryophyllene. In addition, microbial symbionts may help ALB degrade their host. Complementarity of tree species with different levels of resistance may reduce damage, but trapping effectiveness for adults was limited using a combination of host kairomones and sex pheromones in the field. Therefore, we discuss host location behavior from a new perspective and show that multiple cues are used by ALB to locate and recognize host plants. Further research into host resistance mechanisms and visual signal recognition, and the interaction of sex pheromone synthesis, symbiont microbiota, and host plants may help reveal the host recognition mechanisms of ALBs.

Genome-Wide Identification of the Odorant Receptor Gene Family and Revealing Key Genes Involved in Sexual Communication in Anoplophora glabripennis

Insects use a powerful and complex olfactory recognition system to sense odor molecules in the external environment to guide behavior. A large family of odorant receptors (ORs) mediates the detection of pheromone compounds. Anoplophora glabripennis is a destructive pest that harms broad-leaved tree species. Although olfactory sensation is an important factor affecting the information exchange of A. glabripennis, little is known about the key ORs involved. Here, we identified ninety-eight AglaORs in the Agla2.0 genome and found that the AglaOR gene family had expanded with structural and functional diversity. RT-qPCR was used to analyze the expression of AglaORs in sex tissues and in adults at different developmental stages. Twenty-three AglaORs with antennal-biased expression were identified. Among these, eleven were male-biased and two were female-biased and were more significantly expressed in the sexual maturation stage than in the post-mating stage, suggesting that these genes play a role in sexual communication. Relatively, two female-biased AglaORs were overexpressed in females seeking spawning grounds after mating, indicating that these genes might be involved in the recognition of host plant volatiles that may regulate the selection of spawning grounds. Our study provides a theoretical basis for further studies into the molecular mechanism of A. glabripennis olfaction.

Effect of Soybean Volatiles on the Behavior of the Bean Bug, Riptortus pedestris

The bean bug, Riptortus pedestris, is a polyphagous insect that feeds primarily on leguminous plants, especially soybean (Glycine max). Although the bean bug is an economically important pest of soybean, little is known about how the insect locates soybean fields. In this study, we examined the electroantennogram responses of R. pedestris to soybean volatiles and examined the behavioral responses of the adult bean bugs. R. pedestris adults were attracted more to their host-plant soybean, even when physical contact was absent, than to air or a non-host plant. Accordingly, we hypothesized that R. pedestris can recognize soybean through a plant's volatile organic compounds (VOCs). Five VOCs were identified from intact soybean plants at the vegetative stage: (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, 4-ethylbenzaldehyde, α-farnesene, and methyl salicylate. Response spectra of the antennae to these volatiles clearly showed that both male and female R. pedestris can detect soybean volatiles. The adult bean bugs did not show behavioral orientation to any individual compounds but showed significant orientation to a particular blend of synthetic soybean volatiles when tested under laboratory conditions. In the field, this soybean volatile blend did not significantly attract the bean bugs, but it did interact synergistically with the aggregation pheromone to attract the bean bugs. These results highlight the role of host plant volatiles in the sensory ecology of R. pedestris and help explain colonization pattern of the bean bugs in soybean fields.

Pest detection dogs for wood boring longhorn beetles

Invasive alien species are increasing due to globalization. Their spread has resulted in global economic losses. Asian [Anoplophora glabripennis (Motschulsky)] (ALB) and citrus [A. chinensis (Forster)] (CLB) longhorn beetles are two introduced wood borers which contribute to these economic losses e.g. the destruction of tree plantations. Early detection is key to reduce the ecological influence alongside the detrimental and expensive eradication. Dogs (Canis lupus familiaris) can detect these insects, potentially at an early stage. We trained two privately owned dogs to investigate their use as detection tools. We tested the dog's ability to discriminate ALB and CLB from native wood borers by carrying out double-blind and randomized experiments in three search conditions; (1) laboratory, (2) semi-field and (3) standardized field. For condition one, a mean sensitivity of 80%, specificity of 95% and accuracy of 92% were achieved. For condition two and three, a mean sensitivity of 88% and 95%, specificity of 94% and 92% and accuracy of 92% and 93% were achieved. We conclude that dogs can detect all types of traces and remains of ALB and CLB and discriminate them from native wood borers and uninfested wood, but further tests on live insects should be initiated.

Chemical Ecology of the Asian Longhorn Beetle, Anoplophora glabripennis

The Asian longhorn beetle (ALB), Anoplophora glabripennis (Motschulsky), is a destructive forest pest in its native range, East Asia, or a high-risk invasive species in many other parts of the world. Extensive research has been directed toward the development of ALB management strategies. However, semiochemical-based trap lures, which are one of the effective tools for detecting, monitoring, and potentially assisting in eradicating cerambycids, have not reached operational efficacy for ALB to date, which is probably due to a grossly incomplete understanding of its chemical ecology. Here, we summarize the current progress in ALB chemical ecology including host selection and location, pheromone identification, trapping techniques, olfactory system, and related biology and behavior. We also briefly review the known semiochemicals in the subfamily Lamiinae, particularly the ALB congener, A. chinensis. Based on this knowledge, we highlight a potentially important role of some host-original chemicals, such as sesquiterpenes, in ALB host and mate location, and emphasize the basic studies on the biology and behavior of adult ALB. Last, we formulate suggestions for further research directions that may contribute to a better understanding of ALB chemical ecology and improved lure efficacy.

Optimizing Application Rates of Metarhizium brunneum (Hypocreales: Clavicipitaceae) Microsclerotia for Infecting the Invasive Asian Longhorned Beetle (Coleoptera: Cerambycidae)

The Asian longhorned beetle (Anoplophora glabripennis [Motschulsky]) is an invasive wood-boring beetle that threatens urban trees and forests in North America and Europe. The entomopathogenic fungus Metarhizium brunneum Petch strain F52 can infect and kill A. glabripennis adults. Products containing this fungus were available for commercial use in the United States but not registered for Asian longhorned beetle. This study tested different formulations and application rates of M. brunneum F52 microsclerotial granules for their potential development for management of A. glabripennis adults. Three application rates of M. brunneum microsclerotial granules relative to a 1× formulation from previous experiments (0.03 g/cm2; 2× = 0.06 g/cm2 and 3× = 0.09 g/cm2) were exposed on tree trunks for 4-wk periods during May-September. Increased application rates had better retention (% of initial g applied) than the 1× rate, rather than greater weathering loss. Microsclerotia at the 2× application produced 5.05 × 106 conidia/cm2, which was 18 times more conidia than the 1× application. Since A. glabripennis is under active eradication, bioassays with adult beetles were carried out in a quarantine laboratory, using the formulation samples from field exposures. The 2× application resulted in faster beetle mortality. The 3× and 2× rates were not significantly different in retention of the formulation, conidial production, or mortality, but 2× produced the most conidia per gram applied (3.92 × 109 conidia/g). An augmented formulation containing 70% M. brunneum by weight, rather than 50%, produced significantly more conidia and faster beetle mortality than the 50% formulation.

Assessing Niche Shifts and Conservatism by Comparing the Native and Post-Invasion Niches of Major Forest Invasive Species

Invasive species experience biotic and abiotic conditions that may (or may not) resemble their native environment. We explored the methodology of determining climatic niches and compared the native and post-invasion niches of four invasive forest pests to determine if these species experienced shifts or changes in their new climatic niches. We used environmental principle components analysis (PCA-env) method to quantify climatic niche shifts, expansions, and temporal changes. Furthermore, we assessed the effect of variable selection in the delineation and comparison of niche space. We found that variable selection influenced the delineation and overlap of each niche, whereas the subset of climatic variables selected from the first two PCA-env axes explained more variance in environmental conditions than the complete set of climatic variables for all four species. Most focal species showed climatic niche shifts in their invasive range and had not yet fully occupied the available niche within the invaded range. Our species varied the proportion of niche overlap between the native and invasive ranges. By comparing native and invasive niches, we can help predict a species’ potential range expansion and invasion potential. Our results can guide monitoring and help inform management of these and other invasive species.

Inter- and Intrasexual Interactions in Anoplophora glabripennis (Coleoptera: Cerambycidae) and the Impact of Different Sex Ratios

The behaviors of Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae) during inter- and intrasexual interactions between both solitary and paired individuals at different sex ratios were observed on Acer platanoides L. (Sapindales: Sapindaceae) branches in the laboratory. Intrasexual contact was generally ignored by females, but between males resulted in battles from which one male ultimately retreated. When male size differed, larger males won battles, whereas equally sized males split the wins and battled longer. When males initiated intersexual contact, they quickly found and mounted the female. The female apparently determined if and how long the male could copulate with her by controlling access to her genital opening and males would eventually dismount if the female remained unreceptive. After successful copulation, males ignored female intruders and fought off male challengers, generally without dismounting. Some males dismounted females without attempting to copulate. Individual age and size were not predictive of either female or male choice in a mate. Mating duration was affected by both female receptivity and sex ratios present. Male interruptions of the pair shortened time in copula. Male-skewed sex ratios (1F:2M) significantly shortened the time a male would stay with an unreceptive female. Female-skewed sex ratios (2F:1M) did not impact mating duration. Probability of dispersal both from and within the branch was greater for smaller individuals of both sexes and for males when sex ratios were male-skewed. This information demonstrates how reproductive activity might be impacted as population densities decline during efforts at eradication of this species in North America.

Reproductive Behaviors of Anoplophora glabripennis (Coleoptera: Cerambycidae) in the Laboratory

The reproductive behaviors of individual pairs of Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae)-all combinations of three populations and three different ages-were observed in glass jars in the laboratory on Acer saccharum Marshall (Sapindales: Sapindaceae) host material. The virgin female occasionally made first contact, but mounting did not occur until the male antennated or palpated the female. If the female was receptive (older females initially less receptive than younger ones), the male mated with her immediately after mounting and initiated a prolonged pair-bond. When the female was not receptive, some males abandoned the attempt while most performed a short antennal wagging behavior. During the pair-bond, the male continuously grasped the female's elytral margins with his prothoracic tarsi or both pro- and mesothoracic tarsi. The male copulated in a series of three to four bouts (averaging three to five copulations each) during which the female chewed oviposition sites or walked on the host. Between bouts, the female oviposited and fertile eggs were deposited as soon as 43 min after the first copulation. Females became unreceptive again after copulation and the duration of the pair-bond depended on the male's ability to remain mounted. Some population differences were seen which may be climatic adaptations. A single pair-bond was sufficient for the female to achieve ~60% fertility for her lifetime, but female fecundity declined with age at mating. Under eradication conditions, mates will become more difficult to find and females that find mates will likely produce fewer progeny because they will be older at the time of mating.

Odorant receptors and antennal lobe morphology offer a new approach to understanding olfaction in the Asian longhorned beetle

The Asian longhorned beetle Anoplophora glabripennis (Motchulsky) is an exotic forest pest that has repeatedly invaded North America and Europe from Asia, and has the potential to kill millions of trees and cause billions of dollars in damage. Traps baited with an attractive mixture of volatile organic compounds from hosts have been of limited success in monitoring invasion sites. We propose that lures might be improved through studying the olfactory system of adult beetles, especially the gene family of odorant receptors (ORs) and the structure of the antennal lobes of the brain. Here, we report identification of 132 ORs in the genome of A. glabripennis (inclusive of one Orco gene and 11 pseudogenes), some of which are orthologous to known pheromone receptors of other cerambycid beetles. We also identified three ORs that are strongly biased toward expression in the female transcriptome, and a single OR strongly biased toward males. Three-dimensional reconstruction of the antennal lobes of adults suggested a male-specific macroglomerulus and several enlarged glomeruli in females. We predict that functional characterization of ORs and glomeruli will lead to identification of key odorants in the life history of A. glabripennis that may aid in monitoring and controlling future invasions.

A Variable-Instar Climate-Driven Individual Beetle-Based Phenology Model for the Invasive Asian Longhorned Beetle (Coleoptera: Cerambycidae)

Efforts to manage and eradicate invasive species can benefit from an improved understanding of the physiology, biology, and behavior of the target species, and ongoing efforts to eradicate the Asian longhorned beetle (Anoplophora glabripennis Motschulsky) highlight the roles this information may play. Here, we present a climate-driven phenology model for A. glabripennis that provides simulated life-tables for populations of individual beetles under variable climatic conditions that takes into account the variable number of instars beetles may undergo as larvae. Phenology parameters in the model are based on a synthesis of published data and studies of A. glabripennis, and the model output was evaluated using a laboratory-reared population maintained under varying temperatures mimicking those typical of Central Park in New York City. The model was stable under variations in population size, simulation length, and the Julian dates used to initiate individual beetles within the population. Comparison of model results with previously published field-based phenology studies in native and invasive populations indicates both this new phenology model, and the previously published heating-degree-day model show good agreement in the prediction of the beginning of the flight season for adults. However, the phenology model described here avoids underpredicting the cumulative emergence of adults through the season, in addition to providing tables of life stages and estimations of voltinism for local populations. This information can play a key role in evaluating risk by predicting the potential for population growth, and may facilitate the optimization of management and eradication efforts.

The Influence of Host Plant Volatiles on the Attraction of Longhorn Beetles to Pheromones

Host plant volatiles have been shown to strongly synergize the attraction of some longhorn beetle species (Coleoptera: Cerambycidae) to their pheromones. This synergism is well documented among species that infest conifers, but less so for angiosperm-infesting species. To explore the extent of this phenomenon in the Cerambycidae, we first tested the responses of a cerambycid community to a generic pheromone blend in the presence or absence of chipped material from host plants as a source of host volatiles. In the second phase, blends of oak and conifer volatiles were reconstructed, and tested at low, medium, and high release rates with the pheromone blend. For conifer-infesting species in the subfamilies Spondylidinae and Lamiinae, conifer volatiles released at the high rate synergized attraction of some species to the pheromone blend. When comparing high-release rate conifer blend with high-release rate α-pinene as a single component, species responses varied, with Asemum nitidum LeConte being most attracted to pheromones plus α-pinene, whereas Neospondylis upiformis (Mannerheim) were most attracted to pheromones plus conifer blend and ethanol. For oak-infesting species in the subfamily Cerambycinae, with the exception of Phymatodes grandis Casey, which were most attracted to pheromones plus ethanol, neither synthetic oak blend nor ethanol increased attraction to pheromones. The results indicate that the responses to combinations of pheromones with host plant volatiles varied from synergistic to antagonistic, depending on beetle species. Release rates of host plant volatiles also were important, with some high release rates being antagonistic for oak-infesting species, but acting synergistically for conifer-infesting species.

Integration of Visual and Olfactory Cues in Host Plant Identification by the Asian Longhorned Beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae)

Some insects use host and mate cues, including odor, color, and shape, to locate and recognize their preferred hosts and mates. Previous research has shown that the Asian longicorn beetle, Anoplophora glabripennis (Motschulsky), uses olfactory cues to locate host plants and differentiate them from non-host plants. However, whether A. glabripennis adults use visual cues or a combination of visual and olfactory cues remains unclear. In this study, we tested the host location and recognition behavior in A. glabripennis, which infests a number of hardwood species and causes considerable economic losses in North America, Europe and Asia. We determined the relative importance of visual and olfactory cues from Acer negundo in host plant location and recognition, as well as in the discrimination of non-host plants (Sabina chinensis and Pinus bungeana), by female and male A. glabripennis. Visual and olfactory cues from the host plants (A. negundo), alone and combined, attracted significantly more females and males than equivalent cues from non-host plants (S. chinensis and P. bungeana). Furthermore, the combination of visual and olfactory cues of host plants attracted more adults than either cue alone, and visual cues alone attracted significantly more adults than olfactory cues alone. This finding suggests that adult A. glabripennis has an innate preference for the visual and/or olfactory cues of its host plants (A. negundo) over those of the non-host plant and visual cues are initially more important than olfactory cues for orientation; furthermore, this finding also suggests that adults integrate visual and olfactory cues to find their host plants. Our results indicate that different modalities of host plant cues should be considered together to understand fully the communication between host plants and Asian longhorned beetles.

Effects of Pheromone Release Rate and Trap Placement on Trapping of Agrilus planipennis (Coleoptera: Buprestidae) in Canada

The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a devastating insect pest in its introduced range. A trapping system that increases trap catches or detection rates in low-density populations would be beneficial for survey programs. Five trapping experiments were conducted to investigate factors influencing capture rates of male beetles on dark green traps baited with the A. planipennis pheromone, (3Z)-dodecen-12-olide ((3Z)-lactone), plus the green leaf volatile, (3Z)-hexenol. Low doses (0.001-1.0 mg) of (3Z)-lactone + (3Z)-hexenol did not consistently increase captures of male A. planipennis. In other experiments, mean captures of males were significantly higher on traps baited with a moderate dose (3.0 mg/septum) of (3Z)-lactone + (3Z)-hexenol, compared with lower doses (0.001, 0.1, and 1.0 mg) or (3Z)-hexenol alone. Next, we demonstrated that addition of (3Z)-lactone to traps baited with (3Z)-hexenol resulted in significantly greater increases in male captures when pairs of traps were placed on the same tree, than when traps were placed on adjacent trees. Moreover, significantly more A. planipennis were captured on pheromone-baited traps placed in the southern versus northern aspect of the crown. These results highlight the importance of experimental set-up for elucidating lure treatment effects and also suggests the (3Z)-lactone may be more active at close range. Our findings increase our understanding of the pheromone ecology of this species and lend support toward the use of dark green traps baited with 3.0 mg (3Z)-lactone + (3Z)-hexenol deployed in the south aspect of the canopy for detection programs for this insect.

Identification of a potential third component of the male-produced pheromone of Anoplophora glabripennis and its effect on behavior

The Asian longhorned beetle, Anoplophora glabripennis, is considered to be one of the most serious invasive pests of deciduous trees in North America. An efficient monitoring trap is needed to detect and delimit new introductions and assess population densities of established infestations. Previous studies on A. glabripennis have shown that males produce a two-component aggregation pheromone that consists of a 1:1 blend of 4-(n-heptyloxy)butan-1-ol and 4-(n-heptyloxy)butanal. Moderate attraction in field trapping studies suggested that there may be additional chemical cues missing. Volatiles from male A. glabripennis were examined to identify other potential pheromone components. Gas chromatographic / electroantennographic (GC/EAD) analyses of male aerations detected a consistent EAD-active response to a previously unidentified compound. This compound was identified as (3E,6E)-α-farnesene. Both male and female beetles were antennally responsive to this sesquiterpene, and both sexes were attracted to it in olfactometer bioassays at different doses. When (3E,6E)-α-farnesene was combined with 4-(n-heptyloxy)butan-1-ol and 4-(n-heptyloxy)butanal, attraction of both sexes increased compared to assays using 4-(n-heptyloxy)butan-1-ol and 4-(n-heptyloxy)butanal alone.