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

The avoidance of conspecific cues during egg-laying decision-making in the Asian long-horned beetle Anoplophora glabripennis

For insects whose larvae are incapable of moving between food resources, the selection of oviposition sites by females is critical to the survival and development of their offspring. In such insects, it is known that females utilise and benefit from conspecific cues for oviposition choice. Studying how information from the behaviour of conspecifics affects egg-laying decision-making is crucial for understanding the biology of insects, which can lead to novel strategies for pest management. We focused on the reproductive behaviour of the Asian long-horned beetle Anoplophora glabripennis, which has become an invasive pest species throughout the world. Here, we show that A. glabripennis avoids sites already containing conspecific cues during egg-laying decision-making. The field survey measuring the distance between neighbouring oviposition scars (in this species, females make scars through the bark of host branches for laying eggs) suggested that the selection of oviposition sites by females is not random. In laboratory oviposition-choice bioassays, females made less oviposition scars on branches containing scars made by other females than those without scars. In addition, female oviposition was also deterred by the presence of their own oviposition scars. Our results indicate that avoiding sites containing conspecific (and their own) traces realises fitness benefit such as reducing resource competition among larvae. This study provides insights into the reproductive behaviour of this invasive longhorn beetle, which is useful for developing environmentally friendly control methods such as oviposition deterrents.

Fraxinus foliage: does host species during adult maturation feeding alter the fecundity of emerald ash borers, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)?

Herbivorous insects can have their reproductive potential influenced by the quality and species of host plants they feed upon. The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive pest of ash trees (Fraxinus spp.) within its introduced range. As adults, EAB must feed upon foliage to sexually mature. We compared the influence of 4 North American ash species on EAB via foliage feeding to assess impacts on female lifespan and reproductive metrics. We fed 136 female EAB, 34 in each foliage group, either black, green, tropical, or white ash throughout their adult life. We performed daily inspections for adult mortality, oviposition, and egg hatching. We found that the mean female lifespan, fertility rate, and mean egg development time were not affected by the ash species. Potential and realized fecundity each increased with summed female group lifespan (days), but this rate differed among ash species. Consequently, there was a statistically significant interaction effect of the summed female group lifespan and the host foliage. Green ash-fed EAB laid (2.94 ± 0.86 eggs/female days) and hatched (1.67 ± 0.59 eggs/female days) the most eggs, more than double the rates of EAB feeding on black (1.39 ± 0.48 laid and 0.75 ± 0.30 hatched eggs/female days) and white (1.08 ± 0.35 laid and 0.65 ± 0.22 hatched eggs/female days) ash. Adults feeding on green ash resulted in the greatest EAB fecundity suggesting that the presence of green ash may promote population growth and provide a pathway to overwhelm other ash species nearby.

Interspecific Mating Is Trivial and Asymmetrical Between Two Destructive Anoplophora Beetles

The Asian longhorn beetle (ALB), Anoplophora glabripennis, and citrus longhorn beetle (CLB), Anoplophora chinensis, are two destructive invasive wood-boring pests, with high similarities in morphology, geographical distribution, host range, life cycle, adult behaviors and male-produced pheromone, implying a potential existence of interspecific interactions. Matings have been found to occur across females and males of the two species when manually paired in confined spaces. However, interspecific mating and its regulating factors are unclear between sympatric populations on hosts. Herein, by observing mountings and tracking the beetles that freely coexisted on host branches in cages, we found that the majority of mountings appeared within species; however, interspecific mountings occasionally occurred between male CLBs and female ALBs. The CLB was more active than the ALB at night. It seems that males actively searched for female ALBs, while the inverse was the case with CLBs. The main release periods of shared pheromone components overlapped between the two species, while compound ratios had significant differences. Our results unveil a trivial and asymmetrical interspecific mating between ALBs and CLBs, implying a risk of co-outbreaks of the two species in either native or invaded areas.

Potential Functions and Transmission Dynamics of Fungi Associated with Anoplophora glabripennis Across Different Life Stages, Between Sexes, and Between Habitats

The fungi residing in the gut and associated habitats play a crucial role in the growth and development of Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), a wood-boring pest. Yet, how they are acquired and maintained across generations, and their respective roles throughout the life cycle, remain unknown. To this end, we used high-throughput ITS sequencing analysis to characterize the fungal composition and diversity associated with A. glabripennis across three different life stages, between sexes, and between its habitats. Overall, the fungi composition was stage specific, with adult gut communities being more diverse than those of larvae and eggs. Male fungal communities differed significantly, while frass and female communities were more similar to each other. The top 10 most abundant genera were investigated, with Fusarium consistently observed in all samples and exhibiting the highest overall abundance. Function predictions revealed the presence of potentially beneficial fungi that may support A. glabripennis invasion across all groups. Additionally, we observed complex network structures in the fungal communities associated with eggs and males, and stronger positive correlations in those of eggs and newly hatched larvae. Source tracking analysis suggested that these fungi were vertically transmitted, following a transmission pathway of 'female gut-frass-egg-larval gut', occurring via frass deposited in oviposition sites. Our findings provide a nuanced understanding of the intricate interactions among plants, insects, and fungi, shedding light on the acquisition, maintenance, and roles of gut-associated fungi in A. glabripennis.

A female sterilization method for use in field-based behavioral studies of the invasive Asian longhorned beetle (Anoplophora glabripennis)

Asian longhorned beetle (Anoplophora glabripennis Motschulsky), a wood borer (Coleoptera: Cerambycidae) native to China, has been unintentionally and repeatedly introduced to North American and European landscapes as a stow-away in the wood packing material commonly used in international trade. Asian longhorned beetle causes extensive damage and mortality in multiple deciduous tree species and in response, countries in both North America and Europe have adopted policies of eradication. Models that integrate patterns of Asian longhorned beetle dispersal with records of infested trees are critical in optimizing survey and eradication efforts and tracking eradication progress. While these tools continue to be developed, they have been limited by the availability of experimental dispersal data. Existing data is restricted to observations made in the beetle's native range in China or based on inference of dispersal in invaded landscapes. Direct observation of beetle dispersal behavior in invaded landscapes could provide critical behavioral information, but the experimental release of gravid females has been incompatible with eradication program efforts. To fill this knowledge gap, there is a need to identify field-portable methods of effectively sterilizing mated females that do not alter ovipositional behavior. Here, we present a protocol for cauterizing a beetle's ovipositor to prevent successful oviposition. Results of lab trials demonstrate the efficacy of ovipositor cauterization in inhibiting successful oviposition without altering the egg-laying behavior of gravid Asian longhorned beetle females. This method enables research to inform models of beetle dispersal and infestation risk without adding to actual or perceived risk of exacerbating infestations in an eradication program.

Is there hybridization between 2 species of the same genus in sympatry?-The genetic relationships between Anoplophora glabripennis, Anoplophora chinensis, and putative hybrids

Anoplophora glabripennis (Asian longhorn beetle, ALB) and Anoplophora chinensis (Citrus longhorn beetle, CLB) are native forest pests in China; they have become important international quarantine pests. They are found using the same Salix aureo-pendula host tree of Cixi, Zhejiang province, China. On this host tree, we collected additional beetles that appeared to be morphologically intermediate between ALB and CLB. By using a stereoscope, we observed that there were several bumps on the base of the elytra, which was inconsistent with ALB, which typically has a smooth elytral base, but was more like CLB, which has numerous short tubercles on the elytral base. Given their sympatry and intermediate morphology, we hypothesized that these may represent ALB × CLB hybrids. We studied the genomic profiles for 46 samples (ALB, CLB, and putative hybrids) using genotyping-by-sequencing (GBS) providing a reduced representation of the entire genome. Employing principal component analyses on the 163 GBS-derived single nucleotide polymorphism data, we found putative hybrids tightly clustered with ALB, but genetically distinct from the CLB individuals. Therefore, our initial hybrid hypothesis was not supported by genomic data. Further, while mating experiments between adult ALB and CLB were successful in 4 separate years (2017, 2018, 2020, and 2021), and oviposition behavior was observed, no progeny was produced. Having employed population genomic analysis and biological hybridization experiments, we conclude that the putative hybrids represent newly discovered morphological variants within ALB. Our approach further confirmed the advantage of genome-wide information for Anoplophora species assignment in certain ambiguous classification cases.

Hybridization Potential of Two Invasive Asian Longhorn Beetles

The Asian longhorned beetle (ALB), Anoplophora glabripennis (Motschulsky) and citrus longhorned beetle (CLB), Anoplophora chinensis (Förster) (both Coleoptera: Cerambycidae: Lamiinae), are high-risk invasive pests that attack various healthy hardwood trees. These two species share some similar host plants and overlapping distributions in large parts of their native ranges in China and the Korean peninsula as well as similar reproductive behaviors. The original Anoplophora malasiaca (Thomson) occurs in Japan and has been synonymized as CLB (hereafter referred to JCLB). In this study, a 30-min behavioral observation of paired adults, followed by a four-week exposure to host bolts, showed that ALB could not successfully cross with CLB. Mating was observed between female CLB and male ALB but not between female ALB and male CLB, no laid eggs hatched. JCLB males successfully crossed with ALB females to produce viable eggs although the overall percentage of hatched eggs was lower than those from conspecific mating pairs. However, ALB males could not successfully cross with JCLB females. CLB and JCLB mated and produced viable hybrid offspring and the hybrid F1 offspring eggs were fertile. These results suggest an asymmetrical hybridization between ALB and JCLB, and that both CLB and JCLB might be considered as two subspecies with different hybridization potential with congeneric ALB. Given their potential impacts on ecosystems and many economically important tree hosts, invasion of these geographically isolated species (ALB and JCLB) or distant subspecies (CLB and JCLB) into the same region may facilitate potential hybridization, which could be a potential concern for the management of these two globally important invasive forest pests. Further studies are needed to determine if fertile hybrid offspring are capable of breeding continually or backcrossing with parental offspring successfully.

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.

Factors That Influence Flight Propensity in Anoplophora glabripennis (Coleoptera: Cerambycidae)

The effects of mating status, sex, beetle age, host quality, temperature, and wind speed on the propensity of Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae) to take flight were evaluated using a free flight test in the laboratory. Time to initiate flight, the angle of flight, and flight capability (when beetles were enticed to take flight) were also evaluated. Host quality, mating status, beetle age, sex, temperature, and the interactions between one or more of these were all found to be significant predictors of flight in A. glabripennis in one or more of the experiments. Female flight propensity peaked at sexual maturity and declined thereafter. Both sexes had a higher propensity to take flight from a stem section of dry host material than from a fresh one. Most (78%) males flew at least once during the four mating status/ages tested from a fresh host stem section, while only 43% of the females flew at least once after chewing an oviposition pit. Flight propensity and distance flown increased with temperature and there was no voluntary flight at 15°C. Flight propensity did not increase with wind speeds 0.0-1.0 m/s, but no ascending flight was observed at 0.5 or 1.0 m/s. Time to flight initiation did not vary with the factors evaluated. Implications these results could have on the success of eradication programs are discussed. Specifically, what factors increase the propensity of mated females to disperse, effectively expanding the infestation zone.

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.