Invasive Ambrosia Beetle Research Articles

Native European ants can discourage host colonization and reduce reproductive success of the invasive ambrosia beetle Xylosandrus compactus

Due to their ubiquity and their nature as generalist predators, ants have long been used as biological control agents in forest and agricultural systems. Several exotic ambrosia beetles (Coleoptera: Curculionidae: Scolytinae, Platypodinae) are considered emerging widespread pests of various trees and shrubs growing in forests, nurseries, orchards, and urban areas. Among them, the Scolytinae Xylosandrus compactus (Eichhoff) is an invasive fungus-farming species native to Asia and able to cause serious damage to a broad range of natural and cultivated plants worldwide, exerting significant ecological and economic costs. Its biology makes conventional control strategies often ineffective, while little is known about natural enemies. We explored the potential of native European predators as natural enemy of this pest, conducting laboratory tests with four widespread ant species using chestnut and laurel as beetle hosts. In particular, we evaluated the interactions between X. compactus and four species of native Euro-Mediterranean ants that usually forage on plants: Crematogaster scutellaris (Olivier), Tapinoma magnum Mayr, Temnothorax affinis (Mayr), and Temnothorax mediterraneus Ward, Brady, Fisher & Schultz. Results indicate that ants may significantly limit the reproductive success of X. compactus, increasing the mortality of the beetle foundresses and reducing their offspring. Smaller ant species may also invade X. compactus nests, killing larvae, pupae and adults, while female beetles avoid nesting in twigs previously visited by ants. These results encourage to explore possible applications of ants in the biological control of X. compactus and the ecological implications of these interactions in the field.

Population structure of the invasive ambrosia beetle, Euwallacea fornicatus, indicates multiple introductions into South Africa

Population structure of the invasive ambrosia beetle, Euwallacea fornicatus, indicates multiple introductions into South Africa

Microbial mutualism suppression by Trichoderma and Bacillus species for controlling the invasive ambrosia beetle Xylosandrus compactus

Xylosandrus compactus (Eichhoff) (Coleoptera: Curculionidae: Scolytinae) is among the most invasive ambrosia beetles causing severe damage to host plants belonging to various ecosystems. Foundress females excavate galleries into the plant xylem introducing mutualistic ambrosia fungi which are the exclusive food source for their offspring. The cryptic habits of this fungus-farming insect and its wide host range facilitated its rapid spreading worldwide. Despite several advances in deepening the bio-ecology of this beetle, there is still a general lack of information about effective control strategies. In this context, microbials, such as antagonistic bacteria and mycoparasitic fungi, can have the potential to act as alternative management tools. Here, we evaluated, for the first time, the potential of commercially available microbial agents for suppressing the growth of the main beetle mutualist, Ambrosiella xylebori, and consequently to hamper the beetle progeny development. The antagonistic activity of five Trichoderma and two Bacillus-based biofungicides was first evaluated in vitro by means of dual-culture experiments in Petri dishes. Then, beetle bioassays were conducted by exposing carob twigs, previously treated with different concentrations of each biofungicide, to beetle foundresses. Tested microbial antagonists significantly suppressed the growth of A. xylebori on Petri dishes. A significant reduction of the beetle progeny was observed in galleries of treated twigs compared to controls. The higher reduction in mutualist growth and brood production was obtained within galleries of T. atroviride treated twigs. Our results show the potential of the tested microbials to suppress the beetle mutualist growth within galleries and consequently to affect the development of its progeny.

Characterization of Two Fusarium solani Species Complex Isolates from the Ambrosia Beetle Xylosandrus morigerus.

Ambrosia beetles are insect vectors of important plant diseases and have been considered as a threat to forest ecosystems, agriculture, and the timber industry. Several factors have been suggested as promoters of the pathogenic behavior of ambrosia beetles; one of them is the nature of the fungal mutualist and its ability to establish an infectious process. In Mexico, Xylosandrus morigerus is an invasive ambrosia beetle that damages many agroecosystems. Herein, two different isolates from the X. morigerus ambrosia beetle belonging to the Fusarium genus are reported. Both isolates belong to the Fusarium solani species complex (FSSC) but not to the Ambrosia Fusarium clade (AFC). The two closely related Fusarium isolates are pathogenic to different forest and agronomic species, and the morphological differences between them and the extracellular protease profile suggest intraspecific variability. This study shows the importance of considering these beetles as vectors of different species of fungal plant pathogens, with some of them even being phylogenetically closely related and having different pathogenic abilities, highlighting the relevance of the fungal mutualist as a factor for the ambrosia complex becoming a pest.

Can the invasive ambrosia beetle Xylosandrus germanus withstand an unusually cold winter in the West Carpathian forest in Central Europe?

Abstract The capability of a non-native species to withstand adverse weather is indicative of its establishment in a novel area. An unusually cold winter of 2016/2017 that occurred in the West Carpathians of Slovakia and other regions within Europe provided an opportunity to indirectly assess survival of the invasive ambrosia beetle Xylosandrus germanus (Coleoptera: Curculionidae, Scolytinae). We compared trap captures of this species in the year preceding and succeeding the respective cold winter. Ethanol-baited traps were deployed in 24 oak dominated forest stands within the southern and central area from April to August 2016, and again from April to August 2017 to encompass the seasonal flight activity of X. germanus and to get acquainted with temporal changes in the abundance of this species in these two distant areas. Dispersing X. germanus were recorded in all surveyed stands before and after the aforementioned cold winter. Their total seasonal trap captures were lower in the southern area following low winter temperatures, but remained similar in the central area. Our results suggest that X. germanus can withstand adverse winter weather in oak dominated forests of the West Carpathians within altitudes of 171 and 450 m asl. It is likely that minimum winter temperatures will not reduce the establishment or further spread of this successful invader in forests in Central Europe.

Xylosandrus germanus (Blandford, 1894) on Grapevines in Italy with a Compilation of World Scolytine Weevils Developing on Vitaceae

Simple SummaryXylosandrus germanus (Curculionidae: Scolytinae: Xyleborini) has been recorded attacking grapevines (cv Glera) in the Conegliano Valdobbiadene DOCG area (Vidor, Veneto, Northern Italy). Here, we documented the first case of this invasive species damaging Vitis vinifera in Italy, supplying the second record ever in Europe. The type of the attack is illustrated and the possible causes of the onset of the infestation are discussed. In addition, an updated checklist of world Scolytinae attacking Vitaceae is provided. A total of 34 scolytine species, in eight tribes and fifteen genera, are recorded.The invasive ambrosia beetle Xylosandrus germanus (Curculionidae: Scolytinae: Xyleborini) is recorded for the first time infesting wine grapes in Italy. The type of the attack is illustrated and the possible causes of the onset of the infestation are discussed. Furthermore, given the continuously increasing number of alien wood-borer beetles introduced worldwide, we provide and discuss the updated world checklist of Scolytinae attacking Vitaceae, and Vitis sp. in particular.

Scolytinae in Nursery and Fruit Crops of Western Kentucky and Seasonal Population Patterns of Four Invasive Ambrosia Beetles

AbstractAmbrosia beetles (Coleoptera: Curculionidae: Scolytinae) inoculate species specific symbiotic fungi into the sapwood of their hosts. Some fungi are innocuous, but others are pathogenic and can kill plants in a short time. The main objectives of this study were to identify ambrosia beetle species found in wholesale and retail nurseries and an apple orchard in western Kentucky and monitor population abundance and phenology of the more common invasive ambrosia beetles. Baker traps baited with ultra-high or standard release ethanol were deployed in late February or March and removed in either fall (2016 and 2017) or August (2018). Sixteen ambrosia beetle species were captured, and eight of them were invasive. The invasive species Cnestus mutilatus (Blandford), Xylosandrus crassiusculus (Motschulsky), Xylosandrus germanus (Blandford), and Xyleborinus saxesenii (Ratzeburg) were the most common and abundant species. The highest counts of these invasive species were recorded from April to May. In addition, we are reporting 13 bark beetle species captured in this study; among them, Phloeotribus dentrifrons (Blackman) and Thysanoes fimbricornis LeConte are reported for the first time for Kentucky, whereas Scolytus multistriatus (Marsham) was the only invasive bark beetle collected.

Metarhizium robertsii in combination with Trichoderma asperellum reduce the malathion doses used to control ambrosia beetles: the case of Xyleborus affinis

ABSTRACT Invasive ambrosia beetles and their symbiotic fungi are responsible for destructive diseases like Laurel Wilt and Fusarium Dieback. Some biological treatments and chemical pesticides (e.g. malathion) have been proposed as alternatives to control these pests, however, to date there are no effective treatments. Here we evaluated the susceptibility of the ambrosia beetle Xyleborus affinis Eichhoff to the entomopathogenic fungus Metarhizium robertsii strain Xoch 8.1, and the efficacy of the mycopathogenic fungus Trichoderma asperellum strain Th-T4 (3) to inhibit the growth of the pathogenic ambrosia fungus Fusarium euwallaceae strain 744. Also, we compared the efficacy of a combination of M. robertsii Xoch 8.1 and T. asperellum Th-T4 (3) against X. affinis, and examined the feasibility of using this combination as an alternative to reduce the malathion doses that have been proposed to control ambrosia beetles. The treatment of X. affinis with M. robertsii (1 × 107 con/mL) alone or in combination with T. asperellum (1 × 106 con/mL) resulted in an average mortality of 76% (±7.5), which was statistically similar to that obtained with malathion at 600 ppm (96% ± 4.0). The combination of a lower concentration of malathion (60 ppm or 200 ppm) and both fungi was as efficient as malathion at 600 ppm. Mortality in negative controls (without fungal conidia or malathion) resulted in an average of 16% (±7.5). The proposed combined treatment reduces by up to one order of magnitude the required amount of malathion, and thus represents a potential alternative to control ambrosia beetle pests.

What Determines Host Range and Reproductive Performance of an Invasive Ambrosia Beetle Euwallacea fornicatus; Lessons From Israel and California

This study examined the polyphagous shot hole borer (PSHB) Euwallacea fornicatus (Coleoptera; Scolytinae) native to Southeast Asia and concentrated on its wide host range in two of the invaded areas, California and Israel. Among the 583 examined tree species, 55.9% were characterized as “non-reproductive hosts” and only 13.8% were characterized as “reproductive hosts,” suitable for the E. fornicatus reproduction. Families that included ≥20 species and genera with ≥10 were considered for further analysis. The highest percentage of tree species suitable for reproduction was obtained for Salicaceae and Sapindaceae, whereas the lowest percentage of tree species belonging to this category were within the Rosaceae, Myrtaceae, and Magnoliaceae. The genera Acer, Quercus and Acacia displayed the highest percentage within the “reproductive host” category, with the former significantly higher from all seven of the studied genera. We found that all Brachychiton and Erythrina were attacked and none of the examined 20 Eucalyptus spp. were suitable for E. fornicatus reproduction. The results suggest discordance between host tree phylogeny and susceptibility to the E. fornicatus, indicating that trait correlation of susceptibility of different tree species to the E. fornicatus are the results of convergent evolution and not of a common descent. A theoretical model, suggesting the different possibilities of potential tree species becoming attractive or non-attractive to E. fornicatus attack, is described. It is suggested that the beetle reproduction success rate over a wide host range, as well as the long list of species belonging to the “non-reproductive host” category, is the outcome of interactions between the beetle fungal symbiont, F. euwallaceae, and sapwood of the attacked tree. The model suggests that a tree selected by the E. fornicatus may fall in one of three groups, (i) those in which F. euwallaceae is unable to develop, (ii) those tree species that slow the development of the fungus, and (iii) those that enable F. euwallaceae to thrive. Hence, the host range suitable for beetle reproduction is determined by development of F. euwallaceae. In general, PSHB does not distinguish between host species of the “non-reproductive host” and “reproductive host” categories.

The Punky Wood Ambrosia Beetle and Fungus in Florida that Cause Wood Rot: Ambrosiodmus minor and Flavodon subulatus


 
 
 
 
 
 
 Ambrosiodmus minor is an invasive ambrosia beetle in the southeastern United States, including Florida. It is considered of low importance because evident economic or ecological impacts have not been observed. However, it is associated with a unique ambrosia fungus, Flavodon subulatus, which causes rapid wood rot. Wood decay caused by this association between Ambrosiodmus and Flavodon is increasing in dead trees across the introduced range, especially in Florida. This 4-page fact sheet written by Demian F. Gomez and Jiri Hulcr and published by the UF/IFAS School of Forest Resources and Conservation offers guidance in identification of the pest, the symptoms of an infestation, and explanation of the insect?s biology. In addition, we provide an updated overview of contemporary management and monitoring of the species.https://edis.ifas.ufl.edu/fr434
 
 
 
 
 
 

Shifts in the structure of rhizosphere bacterial communities of avocado after Fusarium dieback

The rhizosphere microbiome is critical for plant growth and protection against plant pathogens. However, rhizosphere microbial communities are likely to be restructured upon plant infection by fungal pathogens. Our objective was to determine the shifts in rhizosphere bacterial communities of avocado trees (Persea americana Mill.) after Fusarium dieback (FD), a disease triggered by the symbiotic fungi of invasive ambrosia beetles (Euwallacea kuroshio and Euwallacea sp. nr. fornicatus), using 16S rDNA gene amplicon sequencing and a culture-dependent approach. Rhizosphere soil samples were collected from five asymptomatic and five FD-symptomatic avocado trees in a Californian orchard. Sequence analysis showed that diversity metrics of the rhizosphere bacterial communities associated with asymptomatic avocado trees were larger than those of communities from FD-symptomatic trees. Moreover, FD produced significant shifts in rhizobacterial community structure, which were mainly caused by rare OTUs. Bacterial taxa such as Armatimonadetes, Sporocytophaga or Cellvibrio were exclusively associated with the rhizosphere of asymptomatic trees and may act as an insurance mechanism against fungal invasions. Conversely, genera such as Myxococcus or Lysobacter, which have been described as effective biocontrol agents against Fusarium oxysporum, Colletotrichum gloeosporioides or Rhizoctonia spp., among other phytopathogens, were only found in the rhizosphere of FD-symptomatic trees. The culturable bacterial communities in the rhizosphere of both FD-symptomatic and asymptomatic trees were dominated by isolates from the Bacillus and Pseudomonas genera, indicating that potential biocontrol agents against FD may be isolated from healthy and diseased avocado trees. Altogether, our results showed that FD elicited shifts in the avocado rhizosphere microbiome, which could potentially affect soil microbial processes, and provide a basis for the selection of biocontrol agents that could be used for FD prevention.

In-vitro evaluation of copper nanoparticles as a potential control agent against the fungal symbionts of the invasive ambrosia beetle Euwallacea fornicatus

The tea shot-hole borer (THSB), a member of the Euwallacea fornicatus (Eichhoff 1868) complex of species, harboring the plant pathogenic symbiotic fungi (AF-6, AF-8, and Fusarium sp.) (Curculionidae: Scolytinae) attacks avocado (Persea americana Miller) and other tree species in Florida. Currently, their management is limited to prevention and sanitation; therefore, the development of novel control alternatives is critical to mitigate pest outbreaks and avoid massive crop losses. Here, we report on the antifungal activity of copper nanoparticles (Cu-NPs) against the beetle/fungus complex and their effect on the beetle's reproduction. The results revealed that the synthesized Cu-NPs were pure metallic Cu with an average size of 240.88 ± 62.66 nm measured by electron microscopy. The antifungal test for symbionts showed that 0.75 mg/mL of Cu-NPs caused growth inhibition above 60%. However, strong alterations in the morphology of fungal cells were observed at Cu-NPs concentrations as low as 0.1 mg/mL. Additionally, treatments with 0.25, 0.5, and 1 mg/mL of Cu-NPs led to a reduction in offspring production in a concentration dependent manner. According to our findings, the application of Cu-NPs could be potentially considered as an alternative for the control of the beetle-fungi complex or even be integrated into novel disease management strategies.

Differential flight responses of two ambrosia beetles to ethanol as indicators of invasion biology: the case with Kuroshio shot hole borer (Euwallacea kuroshio) and fruit‐tree pinhole borer (Xyleborinus saxesenii)

1. Host selection and utilization by ambrosia beetles ranges from healthy trees to weakened, dying, or dead trees. Compared to weakened trees, healthy trees emit little to no ethanol, which is stress‐induced and a by‐product of anaerobic respiration. The current study tested the attraction of two invasive ambrosia beetles, Kuroshio shot hole borer (KSHB), one member of the species complex, Euwallacea nr. fornicatus, and fruit‐tree pinhole borer, Xyleborinus saxesenii, to four treatments with or without ethanol.2. GC–MS analyses confirmed the release of ethanol from the ethanol lure and boxelder log filled with ethanol and not from the other two treatments. Kuroshio shot hole borer was not preferentially attracted to any ethanol treatment, whereas X. saxesenii responded positively to the ethanol treatments. The boxelder bolt infused with ethanol was the most attractive treatment to X. saxesenii.3. We propose that the differential behavioural responses of these two ambrosia beetles to ethanol correspond to their differential aggressiveness for attacking healthy trees: KSHB attacks healthy trees, whereas X. saxesenii attacks weakened trees. The proposal is further substantiated by a literature survey on bark and ambrosia beetles from Scolytinae. The survey also indicates that the majority of bark and ambrosia beetles from Scolytinae respond positively to ethanol.4. Although ethanol is widely used and is an effective lure for attraction of many bark and ambrosia beetles, findings from this current study and many others necessitate research and development of alternative lures for more aggressive species which are ecologically and economically more devastating.

Continued eastward spread of the invasive ambrosia beetle Cyclorhipidion bodoanum (Reitter, 1913) in Europe and its distribution in the world

Continued eastward spread of the invasive ambrosia beetle Cyclorhipidion bodoanum (Reitter, 1913) in Europe and its distribution in the world

The utility of Trichoderma spp. isolates to control of Xylosandrus germanus Blandford (Coleoptera: Curculionidae: Scolytinae)

The invasive ambrosia beetle, Xylosandrus germanus Blandford (Coleoptera: Curculionidae: Scolytinae), is a serious pest of hazelnut in Turkey, which is the biggest hazelnut producer in the world. In this study, the utility of four isolates representing different Trichoderma species (T. harzianum, T. hamatum, T. asperellum, and T. atroviride) was evaluated on survival, gallery behavior and brood production of X. germanus by effecting the symbiotic fungal development at laboratory conditions. Hazelnut branches were exposed to fungal suspensions (1 × 106 and 1 × 108 conidia mL−1 doses) for about 30 s. and transferred to individual plastic boxes. Ten healthy females of X. germanus were released into each box to determine the effect of the treatment of mycoparasite isolates. The antagonistic effect of Trichoderma species on symbiotic fungus was evaluated in dual-culture experiments in Petri dishes. The survival and gallery production of the pest were not directly affected by treatment of two different doses of all four Trichoderma species. The growth of the symbiotic fungus, however, was suppressed significantly by Trichoderma isolates in beetle galleries as well as on Petri dishes. Moreover, symbiotic fungal growth and eggs, larvae, and pupae of the beetle were not observed in the galleries carved out by females within the branches treated with two concentrations of T. harzianum, T. asperellum, and T. atroviride. Some of the galleries in the branches treated with T. hamatum had very sparse mycelial growth and fewer broods compared to the control. Our findings showed that the Trichoderma species may be potential biological control agents against X. germanus.

Reproduction and Control of the Invasive Polyphagous Shot Hole Borer, Euwallacea nr. fornicatus (Coleoptera: Curculionidae: Scolytinae), in Three Species of Hardwoods: Effective Sanitation Through Felling and Chipping.

The invasive ambrosia beetle polyphagous shot hole borer is one member of the cryptic species, Euwallacea nr. fornicatus (Eichhoff), and poses a great ecological and environmental threat to ornamental and native hardwood trees and agriculturally important tree crops in southern California, United States. We monitored the emergence of polyphagous shot hole borer adults from chipped and unchipped cut logs of infested boxelder, Acer negundo L. (Sapindales: Sapindaceae), California sycamore, Platanus racemosa Nutt. (Proteales: Platanaceae), coast live oak, Quercus agrifolia Née (Fagales: Fagaceae), and red willow, Salix laevigata Bebb (Malpighiales: Salicaceae), every week for 4 to 5 mo. No polyphagous shot hole borer adults emerged from chipped or unchipped coast live oak logs, suggesting this species is not a preferred reproductive host. However, following chipping, a small number of polyphagous shot hole borer adults emerged from boxelder (up to 7 wk) and from California sycamore and red willow (both up to 9 wk). A significantly greater number of polyphagous shot hole borer adults emerged from unchipped logs of boxelder (up to 14 wk) and California sycamore and red willow (both up to 5 mo). Chipping of boxelder, California sycamore, and red willow by using common commercially available chippers reduced polyphagous shot hole borer emergence by over 97%. Emerged polyphagous shot hole borer adults were strongly female-biased, regardless of host. Chipping treatments were highly effective, but for the complete elimination of polyphagous shot hole borer from woody material, other sanitation measures such as solarization in conjunction with chipping are recommended. Environmental and ecological impact of polyphagous shot hole borer is reviewed and discussed.

Effect of temperature on fecundity, development, and emergence of the invasive ambrosia beetle Euwallacea kuroshio (Coleoptera: Scolytinae)

The Kuroshio shot hole borer (KSHB) Euwallacea kuroshio is an invasive ambrosia beetle pest in Southern California, where it causes Fusarium dieback in a number of different host tree species. Since its discovery in California in about 2014, the KSHB has established or been identified across a wide geographic range along the California coast, spanning north from the Mexican border to San Luis Obispo. KSHB were reared at temperatures ranging from 16 to 32 °C to determine the effect of temperature on development and emergence rates, brood size, and colonization success. The highest total emergence and number of successful colonies occurred when KSHB was reared at 28 °C. Mean days until first offspring emergence decreased as temperature increased up to 30 °C, after which emergence ceased. The thermal constant was estimated to be 318 degree‐days. Using this approximation in conjunction with weather data from the California Irrigation Management Information System, we predict the annual number of generations of KSHB in several locations across its invasive range in California. Results can be used to predict the timing and number of generations in other invaded areas, as well as estimate the range of this pest.

Evaluation of trunk-injected emamectin benzoate as a potential management strategy for Kuroshio shot hole borer in avocado trees

The polyphagous shot hole borer (PSHB) and the Kuroshio shot hole borer (KSHB) are newly invasive ambrosia beetles in California. They are vectors of the plant pathogen Fusarium euwallaceae (S. Freeman, Z. Mendel, T. Aoki, K. O’ Donnell), the causal agent of Fusarium dieback in a broad host range that includes commercial avocados, landscape trees, and native tree species in urban and wildland environments. Management of these beetles using contact insecticides is challenging because the beetles spend little time outside their hosts. Trunk injection of systemic insecticides has been proposed as an alternative to contact treatments because insecticides can more effectively target the vascular tissues where the beetles establish their colonies. In this study, several field trials were conducted to evaluate the efficacy of trunk injections of the systemic insecticide emamectin benzoate in avocado trees. The uptake and persistence of emamectin benzoate were determined by quantifying residues in wood cores sampled at various heights within the trees where beetles would likely target. In conjunction with the field trials, a series of bioassays was conducted with a KSHB colony using an avocado-based artificial diet infused with the insecticide. The bioassays showed a dose-dependent effect of emamectin benzoate on the survival and development of the beetle in diet. We derived a tentative working threshold of 300 ng/g insecticide from the bioassay data that we subsequently used as a guide in evaluating the efficacy of the trunk injections. Emamectin benzoate established quickly within trees at the threshold concentration in the areas most vulnerable to attack and colonization by KSHB. Injection of the insecticide in a more dilute form promoted both faster uptake and more rapid establishment of effective concentrations than the undiluted form, thereby providing potential options in how the material is injected based on the levels of infestation of groves.

Erratum to "Spatial and Climatic Factors Influence Ambrosia Beetle (Coleoptera: Curculionidae) Abundance in Intensively Managed Plantations of Eastern Black Walnut".

Invasive ambrosia beetles are among the most economically important pests of forest and plantation trees worldwide.The development of effective management guidelines for these pests in plantations of high-value hardwood species is hindered by a lack of baseline information regarding their seasonal abundance and dispersal behavior. By analyzing long-term monitoring data from intensively-managed plantations of eastern black walnut (Juglans nigra L.) in north-central Indiana, we identified key spatial and climatic variables that could improve the timing and precision of management actions to reduce ambrosia beetle populations. We also used geospatial analyses to compare species-specific spatial patterns of population density and evaluate the sensitivity of the trap density deployed in our long-term monitoring efforts. Xyleborinus saxesenii Ratzeburg and Xylosandrus crassiusculus Matschulsky (Coleoptera: Curculionidae) were more abundant during the spring in years preceded by a hot, dry growing season, and cold winter. Both species were positively associated with plantation edges during the fall flight period. However, X. saxesenii was less abundant in plantations close to forest corridors, whereas X. crassiusculus was more abundant in plantations closer to woodlots and other walnut plantations. Geospatial analysis revealed X. crassiusculus is active in larger, more spatially continuous patches than X. saxesenii, and that 200-m trap spacing is likely to be sufficient to detect both species in the spring flight period but may be insufficient to detect X. saxesenii during the fall flight period. Our findings underscore the power and utility of long-term monitoring to improve management strategies.

Fungal symbionts of the polyphagous and Kuroshio shot hole borers (Coleoptera: Scolytinae, Euwallacea spp.) in California can support both ambrosia beetle systems on artificial media

The specificity of ambrosia beetle-fungus relationships is unknown for the vast majority of ambrosia symbioses, yet has important implications for the success of these beetles and fungi in their surrounding environments. The polyphagous shot hole borer and the Kuroshio shot hole borer (Euwallacea spp.) are invasive ambrosia beetles that exist sympatrically in California, and together with their fungi cause Fusarium Dieback in a variety of hosts. The potential for the two beetle species to exchange symbionts is unknown, but has important ecological consequences. Here we perform symbiont switching experiments, to determine if the polyphagous and Kuroshio shot hole borers can survive and reproduce on each other’s symbiotic fungi in their invasive range in California. Aposymbiotic foundresses were assessed on their ability to reproduce on each of the beetles’ primary (Fusarium spp.) and auxiliary (Graphium spp., Paracremonium pembeum) fungal symbionts, grown on sawdust-based artificial media. Offspring were collected to confirm which fungi were present in the different sexes and life stages. Additionally, the ability of aposymbiotic and non-aposymbiotic foundresses to survive and reproduce on non-ambrosial Fusarium species was tested. We found that reproduction is maximized on the beetles’ primary Fusarium symbionts, regardless of whether a beetle was paired with its own Fusarium symbiont or its congener’s, indicating that there is potential for symbiont switching in natural populations of these beetles. The addition of auxiliary fungi to treatments containing Fusarium spp. had no effect on overall offspring production, and females that were fed solely on auxiliary fungi produced significantly fewer offspring. Females that were fed non-ambrosial Fusarium species produced significantly fewer offspring than when reared on symbiotic Fusarium, and this was especially pronounced in aposymbiotic females. From our experiments, the putative roles of the primary versus auxiliary fungal symbionts, as well as the implications of these roles for beetle reproduction and development in their surrounding environment, are discussed.