Inhibitory Effects of Semiochemicals on the Attraction of an Ambrosia Beetle Euwallacea nr. fornicatus to Quercivorol

Volatiles from nutritional fungal symbiont influence the attraction of Anisandrus maiche (Coleoptera: Curculionidae) to ethanol-baited traps

Anisandrus maiche Stark (Coleoptera: Curculionidae: Scolytinae) is a non-native ambrosia beetle from central Asia that has been spreading throughout the eastern United States since 2005. Preferred hosts of A. maiche are not well characterized within its currently invaded range, but it is established in managed and natural forests throughout Indiana. Current monitoring and detection efforts for this beetle rely on ethanol-baited traps, but fungal volatiles may alter the attraction of A. maiche to ethanol. In this study, we conducted trapping experiments in Indiana to determine the extent to which a suite of common fungal alcohols influences the response of A. maiche to ethanol-baited traps. We then evaluated isoamyl and isobutyl alcohol as potential attractants for A. maiche and their ability to enhance attraction to ethanol. Lastly, we used SPME-GC-MS to identify volatiles from Ambrosiella cleistominuta (Mayers & Harr.), the fungal symbiont of A. maiche, grown for 7 and 14 days on malt extract agar. Benzyl alcohol, isobutyl alcohol, hexanol, methyl phenylacetate, phenethyl alcohol, and piperitone reduced the attraction of A. maiche to ethanol-baited traps in the field. Moreover, adding methyl benzoate and isoamyl alcohol individually to ethanol-baited traps did not further increase A. maiche capture. When paired with ethanol, isoamyl alcohol repelled beetles in the early flight period but did not significantly increase trap capture during the fall flight. These results represent a first step in understanding the role of fungal volatiles in the colonization behavior of A. maiche and may ultimately inform management strategies for this species.

Sequential Isolation of Essential Oils Repellent to the Red Palm Weevil Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae)

The push-pull approach using semiochemicals in pest control requires both an attractant and a repellent. Many previous studies have arbitrarily tested one or more known insect repellents or plant essential oils (EOs) hoping to find repellents of an insect pest. We used a comprehensive approach that synergistically tests in the field numerous natural volatiles from commercial EOs to identify repellents of the red palm weevil Rhynchophorus ferrugineus (Coleoptera: Curculionidae), a worldwide pest of palms and date palms. Volatiles from 79 EOs in slow-release devices were divided into five groups and tested in traps with attractive pheromone compared to traps with pheromone alone. EO-treatment groups exhibiting repellency due to significant trap shutdown, were further subdivided into subgroups of four EOs each and tested further. Two groups of four EOs (cypress, desert wormwood, elemi, and Eucalyptus citriodora) and (niaouli, nutmeg, oregano, and orange sweet), or their corresponding mixtures of major volatiles, caused pheromone trap reductions of up to 92%. Further tests showed that seven of the eight EOs are similarly repellent as the corresponding subgroup. This systematic approach of successively testing sub-fractions of EOs in the field for trap shutdown should be useful to identify repellents of other insect pests of crops.

A New Repellent for Redbay Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae), Primary Vector of the Mycopathogen That Causes Laurel Wilt

The redbay ambrosia beetle, Xyleborus glabratus, was detected in Georgia, USA, in 2002 and has since spread to 11 additional states. This wood-boring weevil carries a symbiotic fungus, Harringtonia lauricola, that causes laurel wilt, a lethal disease of trees in the Lauraceae family. Native ambrosia beetles that breed in infected trees can acquire H. lauricola and contribute to the spread of laurel wilt. Since 2002, laurel wilt has devastated native Persea species in coastal forests and has killed an estimated 200,000 avocado trees in Florida. Since laurel wilt is difficult to manage once it has entered a susceptible agrosystem, this study evaluated piperitone as a candidate repellent to deter attacks by X. glabratus and other ambrosia beetles. Additionally, piperitone was compared to the known repellent verbenone as a potential cost-effective alternative. The repellent efficacy was determined by comparing captures in traps baited with commercial beetle lures containing α-copaene versus captures in traps baited with lures plus a repellent. In parallel 10-week field tests, the addition of piperitone reduced the captures of X. glabratus in α-copaene-baited traps by 90%; however, there was no significant reduction in the captures of native ambrosia beetles in ethanol-baited traps. In two replicate 10-week comparative tests, piperitone and verbenone both reduced X. glabratus captures by 68-90%, with longevity over the full 10 weeks. This study identifies piperitone as a new X. glabratus repellent with potential for pest management.

Piperitone (p-Menth-1-En-3-One): A New Repellent for Tea Shot Hole Borer (Coleoptera: Curculionidae) in Florida Avocado Groves

The tea shot hole borer, Euwallacea perbrevis, has been recently established in Florida, USA, where it vectors fungal pathogens that cause Fusarium dieback in avocado. Pest monitoring uses a two-component lure containing quercivorol and α-copaene. Incorporation of a repellent into IPM programs may reduce the incidence of dieback in avocado groves, particularly if combined with lures in a push-pull system. This study evaluated piperitone and α-farnesene as potential repellents for E. perbrevis, comparing their efficacy to that of verbenone. Replicate 12-week field tests were conducted in commercial avocado groves. Each test compared beetle captures in traps baited with two-component lures versus captures in traps containing lures plus repellent. To complement field trials, Super-Q collections followed by GC analyses were performed to quantify emissions from repellent dispensers field-aged for 12 weeks. Electroantennography (EAG) was also used to measure beetle olfactory response to each repellent. Results indicated that α-farnesene was ineffective; however, piperitone and verbenone were comparable in repellency, achieving 50-70% reduction in captures, with longevity of 10-12 weeks. EAG responses to piperitone and verbenone were equivalent, and significantly greater than response to α-farnesene. Since piperitone is less expensive than verbenone, this study identifies a potential new E. perbrevis repellent.

The bark and ambrosia beetles of Bhutan (Coleoptera: Curculionidae: Scolytinae and Platypodinae): a synopsis with three new species of Scolytinae

The present state of knowledge of the bark and ambrosia beetles of Bhutan is summarised as a basis for future studies of the fauna, and its economic importance in forestry, timber production and crop tree plantations. We describe three new species of Scolytinae: Cyclorhipidion druk Smith & Beaver, Euwallacea insolitus Smith & Beaver, and Xylosandrus geduensis Smith & Beaver. Thirty-four species of Scolytinae, and 13 species of Platypodinae are now known to occur in Bhutan, of which 14 species of Scolytinae, including the three new species, and four species of Platypodinae, are recorded for the first time. A checklist of the fauna is provided, with information on local and world distribution, host trees and biology, and taxonomy.  

Modelling push-pull management of pest insects using repellents and attractive traps in fruit tree orchards

BACKGROUND

Push-pull with semiochemicals in pest management uses repellents to reduce response of pests to food-mate resources (push) and attractive traps to reduce populations (pull). Simulation models of push-pull can aid understanding of plant-insect interactions in nature and suggest hypotheses for field tests that improve management. A previous model indicated advantages of push-pull for controlling ambrosia beetle, Euwallacea fornicatus, pest of avocado trees. However, the simulated behavior of repellency was inconsistent with field observations.

RESULTS

We simulated individual-based movement of insects in push-pull to reveal relationships between parameters of radii (strength) of attractive traps, pest aggregations, and repellents with densities of each in an avocado orchard to visualize and understand the interactions and significance. Simulations indicated placement of traps along a 1-ha area periphery as a barrier resulted in similar trapping and mating as when traps were in a grid, either when insects originated randomly inside the plot or came from outside the plot. However, when insects originated from outside, both arrangements caught slightly more than when insects originated within the plot.

CONCLUSION

There were no differences in capture rates whether traps were spaced in a barrier along the plot's periphery or in a grid covering the plot. Push-pull was more effective than pull (mass trapping) alone. Repellent behavior of individuals when encountering a repellent radius was modelled by approximate 90° turns (right or left at random) when about to enter an infestation, consistent with earlier observations of effects of repellents on bark beetles orienting to aggregation pheromone. © 2022 Society of Chemical Industry.

The Role of Wind and Semiochemicals in Mediating Switching Behavior in the Southern Pine Beetle (Coleoptera: Curculionidae: Scolytinae)

Aggressive bark beetles colonize and kill healthy conifers through pheromone-mediated mass aggregation. In several species, the focal point of aggregation moves progressively from mass-attacked 'focus trees' to adjacent, unattacked 'recipient trees', resulting in infestation growth. This process, termed 'switching', is hypothesized to be mediated in whole or in part by antiaggregation pheromones released by beetles as colonization intensifies on a focus tree. We tested this hypothesis with the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae), by using a windvane apparatus that maintained an unbaited, black, cylindrical trap (surrogate for a recipient tree) continuously 4 m downwind from an identical trap baited with synthetic aggregation attractant (surrogate for a focus tree). In two of three replicated trials, addition of pheromone components with antiaggregation activity, endo-brevicomin or verbenone, to the upwind trap caused a significant but small (<15%) increase in the proportion of beetles caught in the downwind trap. In one of two trials with endo-brevicomin, this shift was associated with a significant reduction in catches in the downwind trap and an overall reduction in catches of beetles by the trap pair. This suggests that an inhibitor-induced increase in landings on the recipient relative to the focus tree may be countered by the radial effects of the inhibitor, which at sufficiently high release may reduce responses to both the focus and recipient tree. We discuss spatial factors that might govern the role of antiaggregation pheromones in stimulating infestation growth as well as additional factors that likely govern switching behavior.

Semiochemicals Affecting Attraction of Ambrosia Beetle Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae) to Quercivorol: Developing Push-Pull Control

Euwallacea fornicatus (Eichhoff), the polyphagous shot hole borer (PSHB), is an ambrosia beetle infesting avocado Persea americana Mill. limbs in North America and Israel. We conducted field experiments with sticky traps in avocado orchards to develop push-pull semiochemical methods of managing PSHB. Traps baited with 10-fold increasing doses (0.01 to 100× or 1.26 µg to 12.6 mg/d) of attractant quercivorol were previously shown to increasingly capture female PSHB (males flightless). We converted trap catch of this relationship to a standardized effective attraction radius (EAR) that predicts capture power of baited-traps regardless of insect flight density. Earlier, piperitone and verbenone were shown to strongly inhibit attraction of PSHB to quercivorol-traps. We tested increasing numbers of 1× piperitone dispensers at 0.75-m distance surrounding a quercivorol-trap and found PSHB catch to decline exponentially. Increasing decadic doses (0.01 to 10×) of either verbenone or piperitone released at 1× quercivorol-traps caused a sigmoidal first-order kinetic-decay in catch. Verbenone (1×) placed at increasing distances (0, 0.25, 0.5, 1, and 2 m) from a 1× quercivorol-trap became increasingly ineffective in reducing catch of PSHB. We found no evidence that ethanol released from 7.5 to 480 mg/d affected attraction of PSHB, but Scobicia chevrieri (Villa and Villa) (Coleoptera: Bostrichidae) was increasingly attracted. Due to their relatively short-range (<0.5 m) inhibition of attractive sources, piperitone, and verbenone dispensers should be placed on avocado trunks where PSHB aggregations occur before the flight season.

A Review of the Ecology and Management of Black Turpentine Beetle (Coleoptera: Curculionidae)

The black turpentine beetle, Dendroctonus terebrans Olivier is the largest pine-infesting bark beetle native to the southern and eastern United States. It generally reproduces in fresh stumps and bases of trees weakened or killed by other biotic or abiotic agents, although it can also infest and sometimes kills apparently healthy trees. Its numbers can build when large amounts of host material become available (typically through a disturbance), and black turpentine beetle-caused mortality at a local scale can become considerable. Here, we provide a complete review of the literature on this species, including its taxonomy, host, life history, chemical ecology, arthropod and microbial associates, and management options. We also provide original data on numbers of instars, acoustic signals, and pheromone chirality in this species. Our survey of the existing literature revealed that key biological characteristics of black turpentine beetles are known, but interactions with closely associated organisms, economic and ecological impacts, and improvements to monitoring and management practices have been only partially investigated.

Semiochemical Regulation of the Intraspecific and Interspecific Behavior of Tomicus yunnanensis and Tomicus minor during the Shoot-Feeding Phase

Two pine shoot beetles, Tomicus yunnanensis and Tomicus minor, are the most destructive pests of Pinus yunnanensis in southwestern China. We investigated behavioral responses within and between these two species during the shoot-feeding phase using walking bioassays. We also identified the pheromonal aspects of beetles by static solid phase microextraction (SPME) and hindgut extraction following interactive communication by gas chromatography-mass spectroscopy (GC-MS). Both species were significantly attracted by their own species and the same sex, and attraction was inhibited by exposure to additional beetles or to the hindgut extracts of beetles which had shown interaction. Female and male T. minor and T. yunnanensis hindguts contained 0.19, 0.09, 0.22, and 0.05 ng/individual of (-)-trans-verbenol, respectively; following interaction with additional beetles, this increased to 16.74-292.71 ng/individual in T. minor females. Mean concentration of verbenone detected in the hindguts of female/male individuals of T. minor and T. yunnanensis under natural conditions were 0.16, 0.06, 0.03, and 0.05 ng/individual, respectively, but these correspondingly increased to 5.90, 2.43, 0.06, and 0.19 ng/individual after exposure to additional insects. In T. yunnanensis, the amounts of detectable (-)-trans-verbenol and verbenone extracted from hindguts were lower than those from T. minor. The levels of cis-verbenol and (-)-trans-verbenol most attractive to walking T. yunnanensis and T. minor were 0.1 and 1.0 ng/μl, respectively. Verbenone was not attractive at any of the concentrations tested. The addition of verbenone to cis-verbenol or (-)-trans-verbenol reduced the attraction responses. We conclude that the (-)-trans-verbenol produced by these two pine shoot beetles is attractive at low concentrations and repellant at high concentrations, thereby fostering intraspecific competition. Verbenone is produced to prevent overcrowding via interspecific inhibition, and to expel beetles during shoot-feeding.