Male-produced Aggregation Pheromone Research Articles

Enantioselective synthesis of ( S)-3,7-dimethyl-2-oxo-6-octene-1,3-diol: a Colorado potato beetle pheromone

The recent identification of a male-produced aggregation pheromone [( S)-3,7-dimethyl-2-oxo-6-octene-1,3-diol, ( S)-CPB] offers a new tool for Colorado potato beetle (CPB) management. We developed a novel synthetic approach to produce CPB pheromone in seven steps and 46.54% overall yield. Grignard reaction, oxidation, and stereoselective methylation using organometallic reagent are the key steps in the commercially viable total synthesis, generating CPB pheromone in 98.6% enantiomeric purity and gram quantity.

Analysis of 2,4,6-Nonatrienal Geometrical Isomers from Male Flea Beetles, Epitrix hirtipennis and E. fuscula

Geometrical isomers of 2,4,6-nonatrienal have been reported from a variety of food- and insect-related sources. It was discovered recently that the eggplant flea beetle, Epitrix fuscula, uses the (2 E,4 E,6 Z) and (2 E,4 E,6 E) isomers as components of its male-produced aggregation pheromone. Here, we learned that the related species, E. hirtipennis, also emits a blend of 2,4,6-nonatrienals, including isomers not previously characterized. Patterns in emission and response suggest a pheromonal function. In an effort to acquire standards to aid in identification, we found that exposing (2 E,4 E,6 E)-2,4,6-nonatrienal (or other available 2,4,6-nonatrienals) to light readily generated a mixture of six geometrical isomers. Configurations of these were determined by NMR, and chromatographic properties (GC and HPLC) were documented. On the basis of chromatographic comparison to these standards, the most abundant, new compound from E. hirtipennis was concluded to be (2 E,4 Z,6 Z)-2,4,6-nonatrienal. Minor components from both E. hirtipennis and E. fuscula were also characterized. The analytical approach given here would also be of use in the food industry, where 2,4,6-nonatrienals are important as aroma compounds.

Host Plant Choice Experiments of Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Virginia

Field and laboratory-choice experiments were conducted to understand aspects of host plant orientation by the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in Virginia. In laboratory bioassays, L. decemlineata oriented to volatiles emitted by potato, Solanum tuberosum L., foliage over both tomato, Lycopersicon esculentum L., and eggplant, Solanum melongena L., foliage, and eggplant over tomato foliage, all of which had been mechanically damaged. Field choice tests revealed more L. decemlineata adults, larvae, and egg masses on eggplant than on tomato. In other experiments, counts of live L. decemlineata on untreated paired plants and counts of dead beetles on imidacloprid-treated plants did not differ between potato and eggplant. L. decemlineata was significantly attracted to eggplant over both tomato and pepper. To determine whether feeding adults affected orientation to host plants, an imidacloprid-treated eggplant or potato plant was paired with an untreated eggplant or potato plant covered in a mesh bag containing two adult male beetles. Significantly more adults were attracted to eggplant with feeding male beetles paired with another eggplant than any other treatment combination. These results indicate that the presence of male L. decemlineata on plants affects host plant orientation and suggests that the male-produced aggregation pheromone may be involved.

Early-summer pheromone biology of Galerucella calmariensis and relationship to dispersal and colonization

Galerucella calmariensis (Coleoptera: Chrysomelidae) has become an effective biological control agent for purple loosestrife ( Lythrum salicaria). A male-produced aggregation pheromone was recently identified in this mostly univoltine beetle, and attractiveness to both sexes was demonstrated in the spring, when overwintered adults reproduce. Nothing was known about whether the pheromone functioned for the summer generation, when some of the beetles may undergo a brief reproductive period before entering diapause. Our results showed that both sexes of the beetles responded strongly to synthetic pheromone during summer, and males collected in the field during early summer and held under the prevailing photoperiod were able to emit pheromone. These males mated readily with field-collected females, and fertile eggs were laid, indicating a reproductive role for the pheromone during early summer. Males emitted pheromone well only when fed L. salicaria. Adult beetles were able to persist on marginal hosts such Salix interior and Rosa spp., but almost no pheromone was detected. Emission ceased and resumed as host access changed, even after a long interruption. Attractiveness of L. salicaria foliage was investigated. Six “green-leaf” volatiles were identified that were readily sensed by beetle antennae, but a preliminary synthetic blend of these was not attractive in the field. A model is presented for pheromone-mediated host colonization after dispersal, and relationships among pheromone biology, diapause, photoperiod, and host quality are discussed. Practical uses for the pheromone are noted, and new information is given about longevity of pheromone lures.

Synthesis and absolute configuration of the male aggregation pheromone of the stink bug Erysarcoris lewisi (Distant), (2 Z,6 R,1′ S,5′ S)-2-methyl-6-(4′-methylenebicyclo[3.1.0]hexyl)hept-2-en-1-ol

The structure including the absolute configuration of the male-produced aggregation pheromone of the stink bug Erysarcoris lewisi (Distant) was determined to be (2 Z,6 R,1′ S,5′ S)-2-methyl-6-(4′-methylenebicyclo[3.1.0]hexyl)hept-2-en-1-ol 1 by bioassay and comparison of the 1H NMR spectrum of the natural pheromone with those of (2 Z,6 R,1′ S,5′ S)- and (2 Z,6 R,1′ R,5′ R)-isomers. These two diastereomers were synthesized from the corresponding ketones (6 R,1′ S,5′ R)- and (6 R,1′ R,5′ S)- 2, which were prepared by lipase-catalyzed asymmetric acetylation of a mixture of (6 R,1′ S,4′ S,5′ R)- and (6 R,1′ R,4′ R,5′ S)-7′-norsesquisabinen-4′-ol 3. The absolute configuration of ketone 2 was assigned by its CD comparison with (1 R,5 S)-sabina ketone 4. An alternative synthesis of (2 Z,6 R,1′ S,5′ S)- 1 was achieved without recourse to enzyme by employing Hodgson’s diastereoselective intramolecular cyclopropanation as the key step.

A Male-produced Aggregation Pheromone Blend Consisting of Alkanediols, Terpenoids, and an Aromatic Alcohol from the Cerambycid Beetle Megacyllene caryae

Bioassays conducted with a Y-tube olfactometer provided evidence that both sexes of the cerambycid beetle Megacyllene caryae (Gahan) were attracted to odor produced by males. Odor collected from male M. caryae contained eight male-specific compounds: a 10:1 blend of (2S,3R)- and (2R,3S)-2,3-hexanediols (representing 3.2 +/- 1.3% of the total male-specific compounds), (S)-(-)-limonene (3.1 +/- 1.7%), 2-phenylethanol (8.0 +/- 2.4%), (-)-alpha-terpineol (10.0 +/- 2.8%), nerol (2.1 +/- 1.5%), neral (63.3 +/- 7.3%), and geranial (8.8 +/- 2.4%). Initial field bioassays determined that none of these compounds was attractive as a single component. Further field trials that used a subtractive bioassay strategy determined that both sexes were attracted to the complete blend of synthetic components, but the elimination of any one component resulted in a decline in trap captures. Blends that were missing (2S,3R)-2,3-hexanediol, (2R,3S)-2,3-hexanediol, or citral (a 1:1 mixture of neral and geranial) attracted no more beetles than did controls. A pheromone blend of this complexity, composed of alkanediols, terpenoids, and aromatic alcohols, is unprecedented for cerambycid species.

Identification, Synthesis, and Bioassay of a Male-Specific Aggregation Pheromone from the Harlequin Bug, Murgantia histrionica

Sexually mature male harlequin bugs produced a sex-specific compound, identified as one of the stereoisomers of the sesquiterpene epoxyalcohol 4-[3-(3,3-dimethyloxiran-2-yl)-1-methylpropyl]-1-methylcyclohex-2-en-1-ol (henceforth murgantiol), a compound with four chiral centers and 16 possible stereoisomers. Production of the compound was highest during the middle of the day. Individual virgin male bugs in separate containers produced the compound at a higher rate than virgin males in groups. The carbon skeleton was verified by synthesis of several mixtures which, in total, contained all possible isomers, one of which matched the insect-produced compound. The relative and absolute configurations of the insect-produced compound remain to be determined. In laboratory bioassays, insect-produced and synthetic murgantiol attracted harlequin bugs of both sexes, suggesting that murgantiol is a male-produced aggregation pheromone, analogous to those found in a number of other phytophagous bug species.

Stereoselective synthesis of (+)-sordidin, the male-produced aggregation pheromone of the banana weevil Cosmopolites sordidus

Stereoselective synthesis of (1 S,3 R,5 R,7 S)-(+)-sordidin, the natural male-produced aggregation pheromone of the banana weevil Cosmopolites sordidus (Germar) starting from 5-benzyloxy-(2 E)-pentene-1-ol is described. The key transformations employed in the synthesis are Sharpless asymmetric epoxidation, Ueno–Stork cyclization, and Jacobsen kinetic resolution.

Synthetic studies aimed at the elucidation of the stereostructure of the aggregation pheromone, 2-methyl-6-(4′-methylenebicyclo[3.1.0]hexyl)hept-2-en-1-ol, produced by the male stink bug Erysarcoris lewisi

The male-produced aggregation pheromone of the stink bug Erysarcoris lewisi Distant was shown to be one of the two diastereomers of (2 Z,6 R)-2-methyl-6-(4′-methylenebicyclo[3.1.0]hexyl)hept-2-en-1-ol by synthesizing and bioassaying (2 E,6 R)-, (2 E,6 S)-, (2 Z,6 R)-, and (2 Z,6 S)-isomers. These were synthesized from the enantiomers of citronellal by employing an intramolecular α-ketocarbene addition to a double bond and the E-selective or Z-selective olefination of a formyl group as the key steps. A reliable method was developed for the preparation of ethyl 2-(di- o-tolylphosphono)propanoate, Ando’s reagent for Z-selective olefination.

Male-specific volatiles released by the brazilian papaya weevil, pseudopiazurus obesus: partial identification and evidence of an aggregation pheromone

The behavioral responses of adult male and female Pseudopiazurus obesus (Boheman, 1838) (Coleoptera: Curculionidae) to several odour sources were evaluated in a Y-tube olfactometer. Males and females insects were significantly more attracted to a combination of volatiles released by males of the species and host plant, suggesting the existence of a male-produced aggregation pheromone. Comparative analysis of the volatiles released by males and females revealed three male-specific compounds, in a ratio of 77:14:9, providing a chemical support to the behavioral observations. (1R,2S)-(+)-Grandisal and (1R,2S)-(+)-grandisol were identified as the major and intermediate compounds, respectively, while the chemical structure of the minor compound, that seems to be a new grandisol derivative, still remains to be determined. These three compounds are the most important pheromone candidates in the species.

Behaviorally Active Green Leaf Volatiles for Monitoring the Leaf Beetle, Diorhabda elongata, a Biocontrol Agent of Saltcedar, Tamarix spp.

Biological activity and chemistry of host plant volatiles were investigated for Diorhabda elongata, Brullé (Coleoptera: Chrysomelidae), a biological control agent for the invasive tree, saltcedar (Tamarix spp., Tamaricaceae). Gas chromatographic-electroantennographic detection (GC-EAD) analysis of volatiles collected from adult D. elongata feeding on saltcedar foliage or from saltcedar foliage alone showed 15 antennally active compounds. These compounds were more abundant in collections from beetle-infested foliage. Antennally active compounds were identified by GC-mass spectrometry (MS) and confirmed with authentic standards. The emissions of the most abundant GC-EAD-active compounds, green leaf volatiles (GLV), were quantitated by GC-MS. A blend of four GLV compounds, mimicking the natural blend ratio, was highly attractive to male and female D. elongata in the field, and a combination of GLV and male-produced aggregation pheromone attracted significantly greater numbers of D. elongata than did either bait alone. A preliminary experiment with a blend of seven additional GC-EAD-active saltcedar volatiles did not show any behavioral activity. The combination of the pheromone and the green leaf odor blend could be a useful attractant in detecting the presence of the biocontrol agent, D. elongata, in stands of saltcedar newly colonized by the beetle.

Male-Produced Aggregation Pheromone Compounds from the Eggplant Flea Beetle (Epitrix fuscula): Identification, Synthesis, and Field Biossays

Volatiles from the eggplant flea beetle, Epitrix fuscula Crotch (Coleoptera: Chrysomelidae), feeding on host foliage, were investigated. Six male-specific compounds were detected and were identified through the use of mass spectrometry, nuclear magnetic resonance (NMR) spectrometry, chiral and achiral gas chromatography, high-performance liquid chromatography, electrophysiology (gas chromatography-electroantennography, GC-EAD), and microchemical tests. The two most abundant of the six compounds were (2E,4E,6Z)-2,4,6-nonatrienal (1) and (2E,4E,6E)-2,4,6-nonatrienal (2). The other four compounds, present in minor amounts, were identified as himachalene sesquiterpenes; two of these, 3 and 4, were hydrocarbons and two, 5 and 6, were alcohols. All four sesquiterpenes were previously encountered from male flea beetles of Aphthona spp. and Phyllotreta cruciferae. Synthetic 1 and 2 matched the natural products by GC retention times, mass spectra, and NMR spectra. Sesquiterpenes 3-6 similarly matched synthetic standards and natural samples from the previously studied species in all ways, including chirality. Both natural and synthetic 1 and 2 gave positive GC-EAD responses, as did sesquiterpenes 3, 5, and 6. Field trials were conducted with a mixture of 1 and 2, and the baited traps were significantly more attractive than control traps to both male and female E. fuscula. The E. fuscula pheromone has potential for monitoring or controlling these pests in eggplants.

Diel Periodicity of <I>Euschistus conspersus</I> (Heteroptera: Pentatomidae) Aggregation, Mating, and Feeding

The diel periodicity of pheromone-mediated aggregations and mating and feeding cycles of Euschistus conspersus Uhler (Heteroptera: Pentatomidae) was investigated in a series of laboratory and field experiments. The aggregation response of adult E. conspersus to lures loaded with the male-produced aggregation pheromone component methyl E2,Z4-decadienoate placed on common mullein, Verbascum thapsus L., peaked in the early hours of the scotophase, at ≈2100 hours. Peak mating occurred at 2300 hours, with 78.5% of the insects in aggregations mating at this time. Aggregations dispersed and declined to 30% of their maximum level by dawn on pheromone-baited plants. Equal numbers of males and females were found within aggregations. Aggregations continued to form nightly and disperse by morning throughout a 72-h observation period on pheromone-baited and unbaited mullein plants. A laboratory analysis of feeding periodicity indicated that although feeding occurred throughout the 24-h observation period, the percentage of feeding insects was significantly higher during the scotophase. There were no differences between feeding rates of males and females. The implications of these findings for monitoring and management of E. conspersus are discussed.

Evaluation of Two Pheromone Baits for Containment and Concentration of Attack by the Western Balsam Bark Beetle, Dryocoetes confusus (Coleoptera: Curculionidae)

Abstract In past studies, the greatest response by the western balsam bark beetle Dryocoetes confusus Swaine (Coleoptera: Scolytidae) to traps and baited trees was obtained with blend of (+)-exo- and (±)-endo-brevicomin, which mimic the natural male-produced aggregation pheromone. We conducted a tree-baiting experiment to determine whether low-release enantiospecific blends [9:1 (+) exo-brevicomin:(+)-endo-brevicomin, or 9:2 (+)-exo-brevicomin: (±)-endo-brevicomin released at 0.3, 0.1, or 0.03 mg/day] could compete with or improve the efficacy of the standard (±)-exo-brevicomin bait released at 1.2 mg/day. In this experiment, the standard and experimental baits were almost 90% effective in inducing attack by D. confusus. Two subsequent 9-ha block experiments compared the ability of the standard and 9:2 (+)-exo-brevicomin:(±)-endo-brevicomin baits to contain and concentrate infestations before harvesting. Again, both baits were equally effective as potential stand management tools based on almost 100% attack on baited trees, green-to-red tree ratios between 3:1 and 5:1, and redistribution of the majority of attack around baited rather than red trees from which beetles could emerge. We recommend that the standard bait continue to be offered commercially for treatment of stands infested by D. confusus.

Rhynchophorus palmarum

<i>Rhynchophorus palmarum</i>

Responses of Flea Beetle Phyllotreta cruciferae to Synthetic Aggregation Pheromone Components and Host Plant Volatiles in Field Trials

Male-specific compounds, previously identified from Phyllotreta cruciferae and synthesized or isolated from natural sources, attracted both sexes of the beetle in field trials and therefore function as components of a male-produced aggregation pheromone. Six field experiments of 7 to 10 d duration each were conducted over 2 yr using modified boll weevil traps and two doses of pheromone. Treatments containing two doses of allyl isothiocyanate (AITC), a breakdown product of glucosinolates in Brassica napus L., a host plant of the beetles, were included in the study. A dose response was observed for both the pheromone components and AITC, and combinations of the pheromone and AITC generally attracted greater numbers of flea beetles than did either component itself. This increased attraction to a combination of beetle-produced compounds and host odors has not been previously demonstrated in halticine beetles and could help explain patterns of movement by P. cruciferae into field crops.

Identification of a Male-produced Aggregation Pheromone in the Western Flower Thrips Frankliniella occidentalis

Two major components have been detected in the headspace volatiles of adult male Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) that are not present in the headspace volatiles of adult females. The compounds were identified as (R)-lavandulyl acetate and neryl (S)-2-methylbutanoate by comparison with synthetic standards using gas chromatography (GC), GC mass spectrometry (MS), and chiral GC. Field trials were conducted with synthetic compounds in naturally infested crops of sweet pepper grown in large plastic greenhouses in Spain. The catch of adult females and males on blue sticky traps was increased by neryl (S)-2-methylbutanoate alone or by a 1:1 blend of (R)-lavandulyl acetate and neryl (S)-2-methylbutanoate, but (R)-lavandulyl acetate was not active alone. This is the first identification of an aggregation pheromone in the order Thysanoptera. The possible role of (R)-lavandulyl acetate is discussed.

Chemical communication with volatile semiochemicals in Phyllotreta species (Coleoptera, Chrysomelidae): a minireview

Phyllotreta species (Coleoptera, Chrysomelidae, Halticinae) rank among the most important horticultural pests in the Northern Hemisphere. Leaf damage caused by flea beetles upsets the water balance, blocks plant growth and sometimes causes a high level of mortality of seedlings. Several species are known to act as vectors of numerous pathogens as well. Chemical communication plays an important role in the host finding, feeding and oviposition behaviour of flea beetles. In the first phase volatile mustard oils (isothiocyanates and thiocyanates) are released from the host plants through the decomposition of non-volatile glucosinolates (chemicals specific to Cruciferae) by myrosinase, and beetles are attracted to the source of release from a distance. Among the isothiocyanates, allyl isothiocyanate is the longest known and widespread compound utilized in the host-plant location of Phyllotreta species, but some species may have a stronger preference to other isothiocyanates or thiocyanates. The attractive effect of the plant volatiles is enhanced by the emission of a male-produced aggregation pheromone. The presence of such a pheromone was first demonstrated in Phyllotreta cruciferae Goeze. In this species R5R,5aS)-1,1,5,8-tetramethy1-1,2,3,4,5,6,5a-heptahydrobenzo[1,2-a][7]annulene] was found to be the main pheromone component. Significant attraction by the pheromone was recorded only in the presence of ALLYL ITCN. The biological activity of the pheromone compound was connected to the plus (+) chirality. The same component seems to be occurring also in the pheromones of several other Phyllotreta spp. as well, suggesting a wider occurence in the genus. Once attracted by the joint effect of plant volatiles and aggregation pheromone, the presence of the non-volatile glucosinolates in the plant tissues is necessary for continuous feeding. Aggregations of flea beetles on suitable host plants, which result from the joint effects of plant-derived and pheromonal chemical cues detailed above may also be good rendez-vous occasions, increasing the probability of encounters with the opposite sex and mating in the vicinity of the optimal oviposition site. Due to the horticultural importance of Phyllotreta spp., deciphering details of their chemical communication has considerable significance in the development of new methods of integrated control.

Male-produced sex pheromone in Tribolium confusum: Behaviour and investigation of pheromone production locations

It is generally accepted that mating in flour beetles of the genus Tribolium is mediated by a male-produced aggregation pheromone. The pheromone production site in T. castaneum is believed to be glands on the ventral side of the femur. Behavioural experiments with the confused flour beetle T. confusum were conducted using extracts of beetles and different body parts as well as live beetles to investigate the responses to the complete odour bouquet released from the beetles. In our experiments, females but not males were attracted to male-produced volatiles, corresponding to the definition of a sex pheromone rather than an aggregation pheromone. SEM pictures confirm the occurrence of glands on all three pairs of legs of male T. confusum, but behavioural experiments show that females are attracted not only to extracts of male legs but also to whole body extracts and extracts of bodies without legs. These data suggest that in this species attractive compounds are produced not only in the glands on the femurs but also at multiple locations. Thus the pheromone systems involved in mating of flour beetles may be more complex than previously reported and differ among closely related species.

Enzyme-assisted synthesis of ( S)-1,3-dihydroxy-3,7-dimethyl-6-octen-2-one, the male-produced aggregation pheromone of the Colorado potato beetle, and its ( R)-enantiomer

( S)-1,3-Dihydroxy-3,7-dimethyl-6-octen-2-one, the male-produced aggregation pheromone of the Colorado potato beetle ( Leptinotarsa decemlineata), and its ( R)-isomer were synthesized by employing lipase-catalyzed asymmetric acetylation of (±)-2,3-epoxynerol as the key step.