Cubeb Oil Lures: Terpenoid Emissions, Trapping Efficacy, and Longevity for Attraction of Redbay Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae)

Community of Bark and Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae) in Agricultural and Forest Ecosystems with Laurel Wilt

Redbay ambrosia beetle, Xyleborus glabratus, is an invasive wood-boring pest first detected in the USA in 2002 in Georgia. The beetle's dominant fungal symbiont, Harringtonialauricola, causes laurel wilt, a lethal disease of trees in the Lauraceae. Over the past 20 years, X. glabratus and laurel wilt have spread to twelve southeastern states, resulting in high mortality of native Persea species, including redbay (P. borbonia), swampbay (P. palustris), and silkbay (P. humilis). Laurel wilt also threatens avocado (P. americana) in south Florida, but in contrast to the situation in forests, X. glabratus is detected at very low levels in affected groves. Moreover, other species of ambrosia beetle have acquired H. lauricola and now function as secondary vectors. To better understand the beetle communities in different ecosystems exhibiting laurel wilt, parallel field tests were conducted in an avocado grove in Miami-Dade County and a swampbay forest in Highlands County, FL. Sampling utilized ethanol lures (the best general attractant for ambrosia beetles) and essential oil lures (the best attractants for X. glabratus), alone and in combination, resulting in detection of 20 species. This study documents host-related differences in beetle diversity and population levels, and species-specific differences in chemical ecology, as reflected in efficacy of lures and lure combinations.

Use of Semiochemicals for the Management of the Redbay Ambrosia Beetle

Simple Summary

Laurel wilt is a devastating exotic fungal disease that threatens avocado and related members of the laurel family in North America. This disease has killed over 300 million redbay trees and has caused cascading ecological impacts across the landscape. Management strategies, especially in natural forests, are limited. The ambrosia beetles that vector this disease respond strongly to odors produced by the trees, and our research indicates that it is possible to repel the beetles away from trees in a forest setting with the use of verbenone. Other compounds have been identified that can be used to trap the beetles. If used together, these strategies can be used to develop a single “push-pull” system to manage this disease in natural systems where other management strategies are not feasible.

Abstract

This review highlights current advances in the management of the redbay ambrosia beetle, Xyleborus glabratus, a primary vector of the pathogenic fungus, Raffaelea lauricola, that causes laurel wilt. Laurel wilt has a detrimental effect on forest ecosystems of southeastern USA, with hundreds of millions of Lauraceae deaths. Currently, preventive measures mostly focus on infected-tree removal to potentially reduce local beetle populations and/or use of preventative fungicide applications in urban trees. Use of semiochemicals may offer an opportunity for the management of X. glabratus. Research on attractants has led to the development of α-copaene lures that are now the accepted standards for X. glabratus sampling. Research conducted on repellents first included methyl salicylate and verbenone and attained significant reduction in the number of X. glabratus captured on redbay and swamp bay trees treated with verbenone. However, the death rate of trees protected with verbenone, while lower compared to untreated trees, is still high. This work underscores the necessity of developing new control methods, including the integration of repellents and attractants into a single push-pull system.

A monograph of the Xyleborini (Coleoptera, Curculionidae, Scolytinae) of the Indochinese Peninsula (except Malaysia) and China

The Southeast Asian xyleborine ambrosia beetle fauna is reviewed for the first time. Thirty-four genera and 315 species are reviewed, illustrated, and keyed to genera and species. Sixty-three new species are described: Amasa cycloxyster sp. nov., Amasa galeoderma sp. nov., Amasa gibbosa sp. nov., Amasa lini sp. nov., Amasa tropidacron sp. nov., Amasa youlii sp. nov., Ambrosiophilus caliginestris sp. nov., Ambrosiophilus indicus sp. nov., Ambrosiophilus lannaensis sp. nov., Ambrosiophilus papilliferus sp. nov., Ambrosiophilus wantaneeae sp. nov., Anisandrus achaete sp. nov., Anisandrus auco sp. nov., Anisandrus auratipilus sp. nov., Anisandrus congruens sp. nov., Anisandrus cryphaloides sp. nov., Anisandrus feronia sp. nov., Anisandrus hera sp. nov., Anisandrus paragogus sp. nov., Anisandrus sinivali sp. nov., Anisandrus venustus sp. nov., Anisandrus xuannu sp. nov., Arixyleborus crassior sp. nov., Arixyleborus phiaoacensis sp. nov., Arixyleborus setosus sp. nov., Arixyleborus silvanus sp. nov., Arixyleborus sittichayai sp. nov., Arixyleborus titanus sp. nov., Coptodryas amydra sp. nov., Coptodryas carinata sp. nov., Coptodryas inornata sp. nov., Cyclorhipidion amasoides sp. nov., Cyclorhipidion amputatum sp. nov., Cyclorhipidion denticauda sp. nov., Cyclorhipidion muticum sp. nov., Cyclorhipidion obesulum sp. nov., Cyclorhipidion petrosum sp. nov., Cyclorhipidion truncaudinum sp. nov., Cyclorhipidion xeniolum sp. nov., Euwallacea geminus sp. nov., Euwallacea neptis sp. nov., Euwallacea subalpinus sp. nov., Euwallacea testudinatus sp. nov., Heteroborips fastigatus sp. nov., Heteroborips indicus sp. nov., Microperus latesalebrinus sp. nov., Microperus minax sp. nov., Microperus sagmatus sp. nov., Streptocranus petilus sp. nov., Truncaudum bullatum sp. nov., Xyleborinus cuneatus sp. nov., Xyleborinus disgregus sp. nov., Xyleborinus echinopterus sp. nov., Xyleborinus ephialtodes sp. nov., Xyleborinus huifenyinae sp. nov., Xyleborinus jianghuansuni sp. nov., Xyleborinus thaiphami sp. nov., Xyleborinus tritus sp. nov., Xyleborus opacus sp. nov., Xyleborus sunisae sp. nov., Xyleborus yunnanensis sp. nov., Xylosandrus bellinsulanus sp. nov., Xylosandrus spinifer sp. nov.. Thirteen new combinations are given: Ambrosiophilus consimilis (Eggers) comb. nov., Anisandrus carinensis (Eggers) comb. nov., Anisandrus cristatus (Hagedorn) comb. nov., Anisandrus klapperichi (Schedl) comb. nov., Anisandrus percristatus (Eggers) comb. nov., Arixyleborus resecans (Eggers) comb. nov., Cyclorhipidion armiger (Schedl) comb. nov., Debus quadrispinus (Motschulsky) comb. nov., Heteroborips tristis (Eggers) comb. nov., Leptoxyleborus machili (Niisima) comb. nov., Microperus cruralis (Schedl) comb. nov., Planiculus shiva (Maiti & Saha) comb. nov., Xylosandrus formosae (Wood) comb. nov. Twenty-four new synonyms are proposed: Ambrosiophilus osumiensis (Murayama, 1934) (= Xyleborus nodulosus Eggers, 1941 syn. nov.); Ambrosiophilus subnepotulus (Eggers, 1930) (= Xyleborus cristatuloides Schedl, 1971 syn. nov.); Ambrosiophilus sulcatus (Eggers, 1930) (= Xyleborus sinensis Eggers, 1941 syn. nov.; = Xyleborus sulcatulus Eggers, 1939 syn. nov.); Anisandrus hirtus (Hagedorn, 1904) (= Xyleborus hirtipes Schedl, 1969 syn. nov.); Cnestus protensus (Eggers, 1930) (= Cnestus rostratus Schedl, 1977 syn. nov.); Cyclorhipidion bodoanum (Reitter, 1913) (= Xyleborus misatoensis Nobuchi, 1981 syn. nov.); Cyclorhipidion distinguendum (Eggers, 1930) (= Xyleborus fukiensis Eggers, 1941 syn. nov.; = Xyleborus ganshoensis Murayama, 1952 syn. nov.); Cyclorhipidion inarmatum (Eggers, 1923) (= Xyleborus vagans Schedl, 1977 syn. nov.); Debus quadrispinus (Motschulsky, 1863) (= Xyleborus fallax Eichhoff, 1878 syn. nov.); Euwallacea gravelyi (Wichmann, 1914) (= Xyleborus barbatomorphus Schedl, 1951 syn. nov.); Euwallacea perbrevis (Schedl, 1951) (= Xyleborus molestulus Wood, 1975 syn. nov.; Euwallacea semirudis (Blandford, 1896) (= Xyleborus neohybridus Schedl, 1942 syn. nov.); Euwallacea sibsagaricus (Eggers, 1930) (= Xyleborus tonkinensis Schedl, 1934 syn. nov.); Euwallacea velatus (Sampson, 1913) (= Xyleborus rudis Eggers, 1930 syn. nov.); Microperus kadoyamaensis (Murayama, 1934) (= Xyleborus pubipennis Schedl, 1974 syn. nov.; =Xyleborus denseseriatus Eggers, 1941 syn. nov.); Stictodex dimidiatus (Eggers, 1927) (=Xyleborus dorsosulcatus Beeson, 1930 syn. nov.); Webbia trigintispinata Sampson, 1922 (= Webbia mucronatus Eggers, 1927 syn. nov.); Xyleborinus artestriatus (Eichhoff, 1878) (= Xyelborus angustior [sic] Eggers, 1925 syn. nov.; = Xyleborus undatus Schedl, 1974 syn. nov.); Xyleborinus exiguus (Walker, 1859) (= Xyleborus diversus Schedl, 1954 syn. nov.); Xyleborus muticus Blandford, 1894 (= Xyleborus conditus Schedl, 1971 syn. nov.; = Xyleborus lignographus Schedl, 1953 syn. nov.). Seven species are removed from synonymy and reinstated as valid species: Anisandrus cristatus (Hagedorn, 1908), Cyclorhipidion tenuigraphum (Schedl, 1953), Diuncus ciliatoformis (Schedl, 1953), Euwallacea gravelyi (Wichmann, 1914), Euwallacea semirudis (Blandford, 1896), Microperus fulvulus (Schedl, 1942), Xyleborinus subspinosus (Eggers, 1930).

Utility of essential oils for development of host-based lures for Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae), vector of laurel wilt

Redbay ambrosia beetle, Xyleborus glabratus, is native to Southeast Asia, but subsequent to introduction in Georgia in 2002, it has become a serious invasive pest in the USA, now established in nine southeastern states. Females vector Raffaelea lauricola, the fungus that causes laurel wilt, a lethal vascular disease of trees in the family Lauraceae. Laurel wilt has caused extensive mortality in native Persea species, including redbay (P. borbonia), swampbay (P. palustris), and silkbay (P. humilis). Avocado (P. americana) is now impacted in Florida, and with continued spread, laurel wilt has potential to affect avocado and native Lauraceae in California, Mexico, and throughout the American tropics. Effective lures for detection and control of X. glabratus are critical to slow the spread of laurel wilt. No pheromones are known for this species; primary attractants are volatile terpenoids emitted from host Lauraceae. This report provides a concise summary of the chemical ecology of X. glabratus, highlighting research to identify kairomones used by females for host location. It summarizes development of essential oil lures for pest detection, including discussions of the initial use of phoebe and manuka oil lures, the current cubeb oil lure, and a newly-developed distilled oil lure enriched in (-)-α-copaene.

Xyleborus bispinatus Reared on Artificial Media in the Presence or Absence of the Laurel Wilt Pathogen (Raffaelea lauricola)

Like other members of the tribe Xyleborini, Xyleborus bispinatus Eichhoff can cause economic damage in the Neotropics. X. bispinatus has been found to acquire the laurel wilt pathogen Raffaelea lauricola (T. C. Harr., Fraedrich & Aghayeva) when breeding in a host affected by the pathogen. Its role as a potential vector of R. lauricola is under investigation. The main objective of this study was to evaluate three artificial media, containing sawdust of avocado (Persea americana Mill.) and silkbay (Persea humilis Nash.), for rearing X. bispinatus under laboratory conditions. In addition, the media were inoculated with R. lauricola to evaluate its effect on the biology of X. bispinatus. There was a significant interaction between sawdust species and R. lauricola for all media. Two of the media supported the prolific reproduction of X. bispinatus, but the avocado-based medium was generally more effective than the silkbay-based medium, regardless whether or not it was inoculated with R. lauricola. R. lauricola had a neutral or positive effect on beetle reproduction. The pathogen was frequently recovered from beetle galleries, but only from a few individuals which were reared on inoculated media, and showed limited colonization of the beetle's mycangia. Two media with lower water content were most effective for rearing X. bispinatus.

Evaluation of Lure Combinations Containing Essential Oils and Volatile Spiroketals for Detection of Host-Seeking Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae)

The invasive redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), vectors the fungal pathogen (Raffaelea lauricola) that causes laurel wilt, a disease responsible for widespread mortality of trees in the Lauraceae in the southeastern United States. Early detection of incipient vector populations may allow for management practices that could successfully mitigate damage. Developing new, highly effective attractants is a priority for improving sensitivity of early detection efforts. In this study, two field tests were conducted to evaluate combinations of commercially available bark and ambrosia beetle lures for enhanced attraction of host-seeking female X. glabratus. In addition, lures were compared for capture of nontarget scolytine beetles. In the first experiment, traps baited with a combination of cubeb oil, conophthorin, chalcogran, and ethanol captured greater numbers of X. glabratus than cubeb oil alone, the current standard attractant. However, this combination lure resulted in higher nontarget scolytine captures than with the cubeb lure. In the second field test, an oil enriched in the sesquiterpene α-copaene caught significantly more X. glabratus than other lures currently available for monitoring this pest. There were no differences in efficacy between cubeb oil lures produced by two different manufacturers, and a combination lure containing copaiba and cubeb oils did not increase captures over the cubeb lure alone. Results of these two tests suggest that increased sensitivity for detection of X. glabratus may be achieved with a multicomponent lure that incorporates α-copaene, spiroketals, and low release of ethanol.

Flight Capacities and Diurnal Flight Patterns of the Ambrosia Beetles, Xyleborus glabratus and Monarthrum mali (Coleoptera: Curculionidae)

We compared the flight activity of Xyleborus glabratus Eichhoff, vector and symbiont of the causal agent of laurel wilt disease (Raffaelea lauricola), with a native species Monarthrum mali (Fitch) using flight mills. Flight mills were operated either for 24 h or for three 3-h time intervals. During the 3-h interval experiment, the shortest time to flight initiation for X. glabratus occurred at 1600-1900 hours. The average flight time and total flying distance during 1600-2100 hours were also higher than those quantified during the other two recording times investigated. However, total flight duration and proportion of fliers was highest at 1000-1300 hours. We compared several flight parameters. About 64.0% of tested X. glabratus flew <20 m. During 24-h recording periods, M. mali flew longer distances than X. glabratus. Over 50.0% of M. mali flew over 100 m on the flight mill. Xyleborus glabratus flight activity was greatest between 1200 and 1800 hours, while M. mali flew most frequently between 1500 and 2100 hours. Monarthrum mali flew more than five times more frequently than X. glabratus, and their longest single flight distance (37.5 ± 12.5 m) and total flight distance (213.7 ± 85.5 m) were greater than those of X. glabratus. These data will be useful for development of species-specific control and monitoring protocols for these ambrosia beetles based on greater understanding of their flight capacities and associated invasion distance.

The Fungus Raffaelea lauricola Modifies Behavior of Its Symbiont and Vector, the Redbay Ambrosia Beetle (Xyleborus Glabratus), by Altering Host Plant Volatile Production

The redbay ambrosia beetle Xyleborus glabratus is the vector of the symbiotic fungus, Raffaelea lauricola that causes laurel wilt, a highly lethal disease to members of the Lauraceae family. Pioneer X. glabratus beetles infect live trees with R. lauricola, and only when tree health starts declining more X. glabratus are attracted to the infected tree. Until now this sequence of events was not well understood. In this study, we investigated the temporal patterns of host volatiles and phytohormone production and vector attraction in relation to laurel wilt symptomology. Following inoculations with R. lauricola, volatile collections and behavioral tests were performed at different time points. Three days after infection (DAI), we found significant repellency of X. glabratus by leaf odors of infected swamp bay Persea palustris as compared with controls. However, at 10 and 20 DAI, X. glabratus were more attracted to leaf odors from infected than non-infected host plants. GC-MS analysis revealed an increase in methyl salicylate (MeSA) 3 DAI, whereas an increase of sesquiterpenes and leaf aldehydes was observed 10 and 20 DAI in leaf volatiles. MeSA was the only behaviorally active repellent of X. glabratus in laboratory bioassays. In contrast, X. glabratus did not prefer infected wood over healthy wood, and there was no associated significant difference in their volatile profiles. Analyses of phytohormone profiles revealed an initial increase in the amount of salicylic acid (SA) in leaf tissues following fungal infection, suggesting that the SA pathway was activated by R. lauricola infection, and this activation caused increased release of MeSA. Overall, our findings provide a better understanding of X. glabratus ecology and underline chemical interactions with its symbiotic fungus. Our work also demonstrates how the laurel wilt pathosystem alters host defenses to impact vector behavior and suggests manipulation of host odor by the fungus that attract more vectors.

Efficacy of α-Copaene, Cubeb, and Eucalyptol Lures for Detection of Redbay Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae)

Redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is a wood-boring pest that has now invaded nine states in the southeastern United States. The beetle's dominant fungal symbiont (Raffaelea lauricola) is phytopathogenic, inducing laurel wilt in trees within the family Lauraceae. Members of the genus Persea are particularly susceptible to the lethal disease, including native redbay (P. borbonia) and swampbay (P. palustris), as well as commercial avocado (P. americana). Cubeb oil lures are the current standard for detection of X. glabratus, but recently eucalyptol and a 50% α-copaene oil have been identified as additional attractants. This study used a combination of binary-choice bioassays, field cage release-and-recapture assays, and a 12-wk field trial to compare efficacy of eucalyptol and copaene lures relative to commercial cubeb lures. In addition, GC-MS was used to quantify emissions from lures field-aged for 12 wk. In laboratory bioassays, copaene lures were more attractive than eucalyptol lures. In field cage assays, copaene lures recaptured a higher percentage of released beetles than cubeb lures. In the field test, cubeb lures captured fewer beetles than copaene lures, and lowest captures were obtained with eucalyptol lures. Combining eucalyptol with either copaene or cubeb lures did not increase captures over those lures deployed alone. Both copaene and cubeb lures were effective in attracting X. glabratus for 12 wk, but field life of eucalyptol lures was only 4 wk, consistent with the quantification of lure emissions. Results suggest that the 50% α-copaene lure provides the best pest detection currently available for X. glabratus.

Species Diversity, Phenology, and Temporal Flight Patterns of Hypothenemus Pygmy Borers (Coleoptera: Curculionidae: Scolytinae) in South Florida

Hypothenemus are some of the most common and diverse bark beetles in natural as well as urban habitats, particularly in tropical and subtropical regions. Despite their ecological success and ubiquitous presence, very little is known about the habits of this genus. This study aimed to understand species diversity and daily and seasonal trends in host-seeking flight patterns of Hypothenemus in a suburban environment by systematic collections with ethanol baiting over a 15-mo period in South Florida. A total of 481 specimens were collected and identified as eight species, most of them nonnative. Hypothenemus formed the overwhelming majority of bark beetles (Scolytinae) collected, confirming the dominance of the genus in urban environments. Hypothenemus brunneus (Hopkins) and Hypothenemus seriatus (Eichhoff) were most abundant, comprising 74% of the capture. Rarefaction showed that the sample was sufficient to characterize the local diversity and composition. The seasonal pattern in Hypothenemus capture was positively correlated to day-time temperature, not to season as in most temperate Scolytinae. Another significant observation in the community dynamics was the synchronized occurrence of two common species (H. birmanus and H. javanus), unrelated to season. Hypothenemus were predominantly diurnal with a broad flight window. Females flew as early as 11:00 hours (EDST), with peak flight occurring at 15:00 hours, significantly earlier than flight patterns of most other Scolytinae. Surprisingly, male Hypothenemus were frequently collected, despite their lack of functional wings. Several potential explanations are discussed. This is the first study into the ecology of an entire community of the twig-feeding Hypothenemus.

Influence of Trap Distance From a Source Population and Multiple Traps on Captures and Attack Densities of the Redbay Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae)

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is the principal vector of laurel wilt disease in North America. Lures incorporating essential oils of manuka plants ( Leptospermum scoparium J. R. Forster & G. Forster) or cubeb seeds ( Piper cubeba L.f.) are the most effective in-flight attractants to date. Using grids of traps baited with these essential oil lures, we evaluated 1) the effect of trap distance from a source beetle population on beetle captures, 2) the feasibility of trapping out low-density beetle populations, and 3) the effect of trap spacing on beetle captures. In the first experiment, increasing trap distance up to 300 m from a source X. glabratus population had little effect on beetle captures. In a second experiment conducted in a study area with very low beetle densities, trapping for 5 mo prior to deploying freshly cut, uninfested redbay bolts had no effect on subsequent attack densities. In a third experiment, numbers of X. glabratus captured in traps in the center of a grid of nine traps spaced 1 or 5 m apart were compared with lone baited or unbaited traps 30 m away. Relative to the more distant traps, the grid of baited traps neither increased captures in the unbaited center trap nor decreased captures in the baited center trap, regardless of spacing. The results suggest that the effective trapping distance of essential oil lures for X. glabratus is <1 m, and that newer, more attractive lures will be needed to be useful in managing X. glabratus populations.

Attraction of Redbay Ambrosia Beetle, Xyleborus Glabratus, To Leaf Volatiles of its Host Plants in North America

The redbay ambrosia beetle, Xyleborus glabratus, is an important pest of redbay (Persea borbonia) and swamp bay (P. palustris) trees in forests of the southeastern USA. It is also a threat to commercially grown avocado. The beetle is attracted to host wood volatiles, particularly sesquiterpenes. Contrary to other ambrosia beetles that attack stressed, possibly pathogen-infected, and dying trees, X. glabratus readily attacks healthy trees. To date little is known about the role of leaf volatiles in the host selection behavior and ecology of X. glabratus. To address this question, an olfactometer bioassay was developed to test the behavioral response of X. glabratus to plant leaf volatiles. We found that X. glabratus was attracted to the leaf odors of their hosts, redbay and swamp bay, with no attraction to a non-host tree tested (live oak, Quercus virginiana), which served as a negative control. Gas chromatography-mass spectrometry (GS/MS) analysis of leaves revealed the absence of sesquiterpenes known to be attractive to X. glabratus and present in host wood, suggesting that additional leaf-derived semiochemicals may serve as attractants for this beetle. An artificial blend of chemicals was developed based on GC/MS analyses of leaf volatiles and behavioral assays. This blend was attractive to X. glabratus at a level that rivaled currently used lures for practical monitoring of this pest. This synthetic redbay leaf blend also was tested in the field. Baited traps captured more X. glabratus than unbaited controls and equivalently to manuka oil lures. We hypothesize that leaf volatiles may be used by X. glabratus as an additional cue for host location.