(2E,6Z,9Z)-2,6,9-Pentadecatrienal as a Male-Produced Aggregation-Sex Pheromone of the Cerambycid Beetle Elaphidion mucronatum

Recent advances in the synthesis of insect pheromones: an overview from 2013 to 2022

Covering: 2013 to June 2022Pheromones are usually produced by insects in sub-microgram amounts, which prevents the elucidation of their structures by nuclear magnetic resonance (NMR). Instead, a synthetic reference material is needed to confirm the structure of the natural compounds. In addition, the provision of synthetic pheromones enables large-scale field trials for the development of environmentally friendly pest management tools. Because of these potential applications in pest control, insect pheromones are attractive targets for the development of synthetic procedures and the synthesis of these intraspecific chemical messengers has been at the core of numerous research efforts in the field of pheromone chemistry. The present review is a quick reference guide for the syntheses of insect pheromones published from 2013 to mid-2022, listing the synthesized compounds and highlighting current methodologies in organic synthesis, such as carbon-carbon coupling reactions, organo-transition metal chemistry including ring-closing olefin metathesis, asymmetric epoxidations and dihydroxylations, and enzymatic reactions.

A Novel Trisubstituted Tetrahydropyran as a Possible Pheromone Component for the South American Cerambycid Beetle Macropophora accentifer

A novel trisubstituted tetrahydropyran was isolated and identified from the sex-specific volatiles produced by males of the cerambycid beetle Macropophora accentifer (Olivier), a serious pest of citrus and other fruit crops in South America. The compound was the major component in the headspace volatiles, and it was synthesized in racemic form. However, in field trials, the racemate was only weakly attractive to beetles of both sexes, suggesting that attraction might be inhibited by the presence of the "unnatural" enantiomer in the racemate. Alternatively, the male-produced volatiles contained a number of minor and trace components, including a compound tentatively identified as a homolog of the major component, as well as a number of unsaturated 8-carbon alcohols and aldehydes. Further work is required to conclusively identify and synthesize these minor components, to determine whether one or more of them are crucial components of the active pheromone blend for this species.

Methionol, a Sulfur-Containing Pheromone Component from the North American Cerambycid Beetle Knulliana cincta cincta

We describe the identification and field testing of 3-methylthiopropan-1-ol (methionol) as a male-produced aggregation-sex pheromone for the cerambycid beetle Knulliana cincta cincta (Drury) (subfamily Cerambycinae, tribe Bothriospilini). The corresponding sulfoxide, 3-methylsulfinylpropan-1-ol, was also produced sex-specifically by males, but its function remains unclear because the measured release rates of this compound from five different types of release devices were very low to undetectable. Unexpectedly, adults of the cerambycine Elaphidion mucronatum (Say) (Elaphidiini), primarily females, also were attracted by methionol, despite males of this species producing an aggregation-sex pheromone of entirely different structure, (2E,6Z,9Z)-2,6,9-pentadecatrienal.

Identification and field verification of an aggregation pheromone from the white-spotted flower chafer, Protaetia brevitarsis Lewis (Coleoptera: Scarabaeidae)

The white-spotted flower chafer (WSFC), Protaetia brevitarsis Lewis, is native to East Asia. Although their larvae are considered a potential resource insect for degrading plant residues, producing protein fodder, and processing to traditional medicine, adult WSFCs inflict damage to dozens of fruit and economic crops. The control of the WSFC still relies heavily on pesticides and the inefficient manual extraction of adults. Here, we report the identification and evaluation of the aggregation pheromone of WSFCs. From the headspace volatiles emitted from WSFC adults, anisole, 4-methylanisole, 2-heptanone and 2-nonanone were identified as WSFC-specific components. However, only anisole and 4-methylanisole elicited positive dose-response relationship in electroantennography tests, and only 4-methylanisole significantly attracted WSFCs of both sexes in olfactometer bioassays and field experiments. These results concluded that 4-methylanisole is the aggregation pheromone of WSFCs. Furthermore, we developed polyethylene vials as long-term dispensers of 4-methylanisole to attract and kill WSFCs. The polyethylene vial lures could effectively attracted WSFCs for more than four weeks. Pheromone-based lures can be developed as an environmentally friendly protocol for monitoring and controlling WSFC adults.

2-Nonanone is a Critical Pheromone Component for Cerambycid Beetle Species Native to North and South America

An increasing body of evidence indicates that cerambycid beetles native to different continents may share pheromone components, suggesting that these compounds arose as pheromone components early in the evolution of the family. Here, we describe the identification and field testing of the pheromone blends of two species in the subfamily Cerambycinae that share 2-nonanone as an important component of their male-produced aggregation-sex pheromones, the South American Stizocera consobrina Gounelle (tribe Elaphidiini) and the North American Heterachthes quadrimaculatus Haldeman (tribe Neoibidionini). Along with 2-nonanone, males of S. consobrina also produce 1-(1H-pyrrol-2-yl)-1,2-propanedione, whereas males of H. quadrimaculatus produce 10-methyldodecanol. Field bioassays conducted in Brazil (targeting S. consobrina) and Illinois (targeting H. quadrimaculatus) demonstrated that adults of both species were attracted only by the blends of both their pheromone components, and not to the individual components. The use of the pyrrole as a critical component for the former species is further evidence that this compound is a common pheromone structure among cerambycines in different biogeographical regions of the world.

Complex Blends of Synthetic Pheromones are Effective Multi-Species Attractants for Longhorned Beetles (Coleoptera: Cerambycidae)

The wood-boring larvae of longhorned beetles (Coleoptera: Cerambycidae) can be important pests of woody plants, particularly as invasive species introduced by international commerce. Previous research has revealed that cerambycid species native to different parts of the world often share the same aggregation-sex pheromones and that pheromones of different species can be combined to create multi-species attractants that would be advantageous for surveillance monitoring for a number of species simultaneously. To explore the extent to which these chemicals can be combined into single lures, we developed four different blends of six to eight compounds and tested their effects as attractants for a community of longhorned beetle species in Iowa. The blends included known pheromones of species native to the study site, as well as pheromones identified from cerambycid species native to other parts of the world. The experiment confirmed that several cerambycid species were attracted by specific blends, in accordance with their known pheromone chemistry, and despite the presence of pheromone components of heterospecifics. This finding lends further support to developing multi-component blends that can effectively monitor for new incursions of multiple exotic species concurrently.

The Role of Minor Pheromone Components in Segregating 14 Species of Longhorned Beetles (Coleoptera: Cerambycidae) of the Subfamily Cerambycinae

We present research on the chemical ecology of 14 species of longhorned beetles (Coleoptera: Cerambycidae), in four tribes of the subfamily Cerambycinae, conducted in east-central Illinois over 8 yr. Adult males produce aggregation-sex pheromones that attract both sexes. Twenty independent field bioassays explored the pheromone chemistry of the species and tested the possible attractive or antagonistic effects of compounds that are not produced by a given species, but are pheromone components of other species. Analyses of beetle-produced volatiles revealed compounds that had not been reported previously from several of the species. The most common pheromone component was (R)-3-hydroxyhexan-2-one, but pheromones of some species included isomers of the related 2,3-hexanediols. Males of the congeners Phymatodes amoenus (Say) and Phymatodes testaceus (L.) produced pure (R)-2-methylbutan-1-ol. Enantiomers of 2-methylbutan-1-ol also proved to be powerful synergists for Megacyllene caryae (Gahan), Sarosesthes fulminans (F.), and Xylotrechus colonus (F.). The major components of pheromone blends were consistently present in collections of headspace volatiles from male beetles, and only the major components were inherently attractive to a subset of species when tested as single components. Minor components of some species acted as powerful synergists, but in other cases appeared not to influence attraction. Among the minor components identified in headspace extracts from males, 2,3-hexanedione and 2-hydroxyhexan-3-one appeared to be analytical artifacts or biosynthetic by-products, and were neither attractants nor synergists. The antagonistic effects of minor compounds produced by heterospecific males suggest that these compounds serve to maintain prezygotic reproductive isolation among some species that share pheromone components.

Identifying Possible Pheromones of Cerambycid Beetles by Field Testing Known Pheromone Components in Four Widely Separated Regions of the United States

The pheromone components of many cerambycid beetles appear to be broadly shared among related species, including species native to different regions of the world. This apparent conservation of pheromone structures within the family suggests that field trials of common pheromone components could be used as a means of attracting multiple species, which then could be targeted for full identification of their pheromones. Here, we describe the results of such field trials that were conducted in nine states in the northeastern, midwestern, southern, and western United States. Traps captured 12,742 cerambycid beetles of 153 species and subspecies. Species attracted in significant numbers to a particular treatment (some in multiple regions) included 19 species in the subfamily Cerambycinae, 15 species in the Lamiinae, one species in the Prioninae, and two species in the Spondylidinae. Pheromones or likely pheromones for many of these species, such as 3-hydroxyhexan-2-one and syn- and anti-2,3-hexanediols for cerambycine species, and fuscumol and/or fuscumol acetate for lamiine species, had already been identified. New information about attractants (in most cases likely pheromone components) was found for five cerambycine species (Ancylocera bicolor [Olivier], Elaphidion mucronatum [Say], Knulliana cincta cincta [Drury], Phymatodes aeneus LeConte, and Rusticoclytus annosus emotus [Brown]), and five lamiine species (Ecyrus dasycerus dasycerus [Say], Lepturges symmetricus [Haldeman], Sternidius misellus [LeConte], Styloleptus biustus biustus [LeConte], and Urgleptes signatus [LeConte]). Consistent attraction of some species to the same compounds in independent bioassays demonstrated the utility and reliability of pheromone-based methods for sampling cerambycid populations across broad spatial scales.