Emerson S. Lacey

Male-Produced Aggregation Pheromone of the Cerambycid Beetle Neoclytus acuminatus acuminatus

This is the first fully verified report of an aggregation pheromone produced by a cerambycid beetle species. Field bioassays with adultNeoclytus acuminatus acuminatus (F.) (Coleoptera: Cerambycidae) revealed that males produce a pheromone that attracts both sexes. Extracts of odors from males contained a single major male-specific compound, (2S,3S)-hexanediol. Field trials determined that both sexes were attracted by the racemic blend of (2S,3S)- and (2R,3R)-hexanediols and that activity was similar to enantiomerically enriched (2S,3S)-hexanediol (e.e. 80.2%). However, the blend of all four 2,3-hexanediol stereoisomers attracted few beetles, indicating inhibition by one or both of the (2R*,3S*)-stereoisomers. Females of the cerambycidCurius dentatus Newman were attracted to traps baited with the four component blend, suggesting that a male-produced sex pheromone for this species may contain (2R,3S)-hexanediol and/or (2S,3R)-hexanediol. The pheromone ofN. a. acuminatus, and presumed pheromone ofC. dentatus, bear structural similarities to those produced by males of six other species in the Cerambycinae (straight chains of 6, 8, or 10 carbons with hydroxyl or carbonyl groups at C2 and C3). It is likely that males of other species in this large subfamily produce pheromones that are variations on this structural motif.

Using Generic Pheromone Lures to Expedite Identification of Aggregation Pheromones for the Cerambycid Beetles Xylotrechus nauticus, Phymatodes lecontei, and Neoclytus modestus modestus

Males of several species of longhorned beetles in the subfamily Cerambycinae produce sex or aggregation pheromones consisting of 2,3-hexanediols and/or hydroxyhexanones. We tested the hypothesis that this diol/hydroxyketone pheromone motif is highly conserved within the subfamily, and the resulting prediction that multiple cerambycine species will be attracted to compounds of this type. We also tested the concept that live traps baited with generic blends of these compounds could be used as a source of live insects from which pheromones could be collected and identified. Traps placed in a mature oak woodland and baited with generic blends of racemic 2-hydroxyhexan-3-one and 3-hydroxyhexan-2-one captured adults of both sexes of three cerambycine species: Xylotrechus nauticus (Mannerheim), Phymatodes lecontei Linsley, and Phymatodes decussatus decussatus (LeConte). Odors collected from male X. nauticus contained a 9:1 ratio of two male-specific compounds, (R)- and (S)-3-hydroxyhexan-2-one. Field trials with synthetic compounds determined that traps baited with (R)-3-hydroxyhexan-2-one (94% ee), alone or in blends with other isomers, attracted similar numbers of X. nauticus of both sexes, whereas (S)-3-hydroxyhexan-2-one (94% ee) attracted significantly fewer beetles. Phymatodes lecontei and P. d. decussatus also were caught in traps baited with hydroxyhexanones, as well as a few specimens of two other cerambycine species, Neoclytus modestus modestus Fall (both sexes) and Brothylus gemmulatus LeConte (only females). Male N. m. modestus produced (R)-3-hydroxyhexan-2-one, which was not present in extracts from females. Neoclytus m. modestus of both sexes also responded to lures that included (R)-3-hydroxyhexan-2-one as one of the components. The only male-specific compound found in extracts from P. lecontei was (R)-2-methylbutan-1-ol, and adults of both sexes were attracted to racemic 2-methylbutan-1-ol in field bioassays. Surprisingly, P. lecontei of both sexes also were attracted to (R)- and (S)-3-hydroxyhexan-2-ones, although neither compound was detected in extracts from this species. Males of all five beetle species had gland pores on their prothoraces that were similar in structure to those that have been associated with volatile pheromone production in other cerambycine species. The attraction of multiple cerambycine species of two tribes to (R)-3-hydroxyhexan-2-one in this study, and in earlier studies with other cerambycine species, suggests that this compound is a widespread aggregation pheromone component in this large and diverse subfamily. Overall, the attraction of multiple species from different cerambycine tribes to this compound at a single field site supports the hypothesis that the hydroxyketone pheromone structural motif is highly conserved within this subfamily.

Male-produced aggregation pheromone of the cerambycid beetle Neoclytus mucronatus mucronatus

Adult male Neoclytus mucronatus mucronatus (F.) (Coleoptera: Cerambycidae: Cerambycinae) were observed to display behaviors identical to calling behaviors of the congener N. acuminatus acuminatus F., males of which produce an aggregation pheromone. Odors collected from male N. m. mucronatus contained one major male‐specific compound, identified as (R)‐3‐hydroxyhexan‐2‐one. Bioassays determined that both sexes were weakly attracted to racemic 3‐hydroxy‐2‐hexanone. Further field trials determined that enantiomerically enriched (R)‐3‐hydroxyhexan‐2‐one (94% ee) attracted more beetles of both sexes than did the racemic blend. This aggregation pheromone is produced by glands that discharge through pores lying within shallow cuticular depressions in the pronotum of male N. m. mucronatus.

Predicted taxonomic patterns in pheromone production by longhorned beetles

Males of five species of three tribes in the longhorned beetle subfamily Cerambycinae produce volatile pheromones that share a structural motif (hydroxyl or carbonyl groups at carbons two and three in straight-chains of six, eight, or ten carbons). Pheromone gland pores are present on the prothoraces of males, but are absent in females, suggesting that male-specific gland pores could provide a convenient morphological indication that a species uses volatile pheromones. In this article, we assess the taxonomic distribution of gland pores within the Cerambycinae by examining males and females of 65 species in 24 tribes using scanning electron microscopy. Gland pores were present in males and absent in females of 49 species, but absent in both sexes of the remaining 16 species. Pores were confined to indentations in the cuticle. Among the species that had male-specific gland pores were four species already known to produce volatile compounds consistent with the structural motif. These findings support the initial assumption that gland pores are associated with the production of pheromones by males. There were apparently no taxonomic patterns in the presence of gland pores. These findings suggest that volatile pheromones play an important role in reproduction for many species of the Cerambycinae, and that the trait is evolutionarily labile.

7-methylheptacosane is a major component of the contact sex pheromone of the cerambycid beetle Neoclytus acuminatus acuminatus

Abstract Male Neoclytus acuminatus acuminatus (F.) (Coleoptera: Cerambycidae) attempt to mate with females only after touching them with their antennae, suggesting that mate recognition is mediated by contact pheromones in the cuticular wax layer of females. Consistent with that hypothesis, males exhibit similar responses to dead females in laboratory bioassays, but not to solvent‐washed dead females with their cuticular hydrocarbons removed. The mating response of males is restored when solvent extracts are reapplied to carcasses of solvent‐washed females, indicating that the contact pheromone is present in solvent extracts. Solvent extracts of the female cuticle contain six methylalkanes that are not present in extracts of males, three of which (7Me‐C25, 7Me‐C27 and 9Me‐C27) constitute almost 40% of the total hydrocarbons. The bioactivity of these three compounds is tested by applying synthetic standards to solvent‐washed carcasses of females and presenting them to males. Standards are tested singly, pairwise and as the complete blend; freeze‐killed females serve as controls. Males attempt to couple with solvent‐washed female carcasses treated with 7Me‐C27 alone and in combination with 9Me‐C27 but only the complete blend elicits the same number of mounting and coupling attempts as does the control. These findings suggest that 7Me‐C27 (7‐methylheptacosane) is the major component of the contact sex pheromone of N. a. acuminatus and that 7Me‐C25 and 9Me‐C27 act as synergists.

Cuticular hydrocarbons mediate mate recognition in a species of longhorned beetle (Coleoptera: Cerambycidae) of the primitive subfamily prioninae

Abstract We tested the hypothesis that contact pheromones mediate mate recognition in Prionus californicus Motschulsky, a species of longhorned beetle (Coleoptera: Cerambycidae) in the primitive subfamily Prioninae. Males attempted to mate with live females only after contacting them with their antennae, and 80% of males showed an identical response to freshly killed females. Males did not attempt to mate with dead females that had been extracted with solvent, suggesting that mate recognition cues had been eliminated. When the solvent extract was applied to carcasses of the same dead females, however, 56% of the males again attempted to mate with them. A preliminary analysis of crude solvent extracts of adult beetles revealed that adults have at least 24 different cuticular hydrocarbons and that the sexes differ in relative proportions of some compounds that may serve as the contact pheromone. This report provides the first evidence that contact pheromones play an important role in mate recognition in the more primitive longhorned beetles.

Calling Behavior in the Primitive Longhorned Beetle Prionus californicus Mots.

Many prionine species share morphological and behavioral traits commonly associated with production of volatile pheromones by females. Adults Prionus californicus Mots. are sexually dimorphic, males being smaller and having antennae that are much more strongly serrate than those of females. Females of this species produce a volatile pheromone that attracts males. We conducted studies characterizing calling behavior of P. californicus females. In these studies females typically lowered their heads and raised their abdomens while extending their ovipositors. The extended ovipositor was often flexed and the abdomen rhythmically contracted during these bouts which lasted up to 10 min. In some cases females everted a membranous, cylindrical sac from the dorsal surface of the ovipositor which was retracted before the ovipositor was withdrawn. This eversible sac has not reported for a cerambycid species, and is likely to be involved in production and/or release of pheromone.

First Documentation of a Volatile Sex Pheromone in a Longhorned Beetle (Coleoptera: Cerambyicidae) of the Primitive Subfamily Prioninae

Abstract We conducted laboratory and field studies to test the hypothesis that volatile pheromones mediate mate location in the longhorned beetle Prionus californicus Motschulsky (Coleoptera: Cerambyicidae), an important pest of many agricultural and ornamental plants. Males were strongly attracted to live females and to carcasses of freshly killed females in olfactometer bioassays. Males also responded strongly to excised ovipositors of freshly killed females but not to their excised heads, thoraces, or abdomens. In field studies, males were strongly attracted to cages baited with live females. These findings demonstrate that female P. californicus produce a volatile pheromone from the ovipositor that attracts males over a distance, and they provide the first conclusive evidence of a volatile sex pheromone for a species of the primitive cerambycid subfamily Prioninae.

Calling behavior of the cerambycid beetle Neoclytus acuminatus acuminatus (F.)

Males of the cerambycid beetle Neoclytus acuminatus acuminatus (F.) assume a body posture, never displayed by females, that appears to be associated with release of an aggregation pheromone: they periodically stop walking and fully extend their front legs, elevating their head and thorax above the substrate. In this article, we demonstrate that this body posture, the “pushup stance,” coincides with release of pheromone and that it serves to elevate pheromone glands above the substrate. We also use a pheromone proxy system (sublimation of naphthalene) to demonstrate that the pushup stance increases rates of pheromone dissemination. The pushup stance provides a convenient indictor for studying the role of pheromones in reproductive behavior and facilitating collection of pheromone in the laboratory.