Sex recognition inDiglyphus isaea walker (Hymenoptera: Eulophidae): Role of an uncommon family of behaviorally active compounds

Identification and field bioassays of the sex pheromone of Eurytoma maslovskii (Hymenoptera: Eurytomidae)

Long-range sex pheromones are generally considered to be a main cue for mate recognition in the order Hymenoptera. Although considerable attention has been given to the identification of semiochemicals in the superfamily Chalcidoidea, which comprises 19 families, no study has identified active components in a field bioassay. We herein report the sensitive and selective pheromone communication system of the Korean apricot wasp, Eurytoma maslovskii (Eurytomidae), whose larvae feed on Prunus mume seeds. Using gas chromatography coupled with electroantennographic detection (GC-EAD) and mass spectrometry (GC-MS), we detected 2,10-dimethyldodecyl propionate and 2,8-dimethyldecyl propionate in thoracic extracts of female E. maslovskii at a ratio of 8:2 as the active pheromone components. Field experiments showed that the attractive effect of the two compounds is highly enantioselective. Racemic 2,10-dimethyldodecyl propionate and 2,8-dimethyldecyl propionate were not attractive to E. maslovskii males. In bioassays with single enantiomers, the (2 S,10 R)-enantiomer was highly attractive to male wasps, and the (2 S,8 S)-enantiomer was also attractive, although to a lesser degree. No synergistic effect between (2 S,10 R)- and (2 S,8 S)-enantiomers was identified, and the (2 S,10 R)-enantiomer alone caught significantly more males than the natural pheromone extracts. The addition of other enantiomers to the (2 S,10 R)-isomer significantly decreased the attraction of conspecific males. In addition, a very low dose of synthetic pheromone attracted conspecific males, showing that both female signaling and male response traits may have evolved to contribute to species-specific sexual communication in this species.

Sexy Mouth Odour? Male Oral Gland Pheromone in the Grain Beetle Parasitoid Lariophagus distinguendus (Förster) (Hymenoptera: Pteromalidae)

Throughout the animal kingdom, sexual pheromones are used for the attraction of mates and as courtship signals but also enable sexual isolation between species. In the parasitic wasp Lariophagus distinguendus, male courtship behaviour consisting of wing fanning, antennal stroking of the female antenna, and head nodding stimulates female receptivity leading to copulation. Recently L. distinguendus was reported to consist of two different lineages, which are sexually isolated because males fail to elicit receptivity in foreign females. It is unclear, however, which part of the courtship behaviour triggers female receptivity and therefore could be a mechanism causing sexual isolation. Here we show that in L. distinguendus a nonvolatile male oral pheromone is essential to release the female receptivity signal. In contrast, male wing fanning and antennal contact play a minor role. Additionally, the composition of the oral pheromone depends on the developmental host and females learn the composition upon emergence from the host substrate. These results will enable more detailed work on oral sexual pheromones to answer the question of how they are involved in the speciation process of L. distinguendus and other parasitoid species, for a better understanding of the huge biodiversity in this group.

Identification of sex pheromone components in Trissolcus brochymenae females

Long- and short-range sex pheromones appear to play a crucial role in the mate finding and courtship behaviour of most parasitic Hymenoptera. Yet these parasitoids have been rarely investigated and only a few pheromones have been identified. Recent studies have shown that sexual communication of Trissolcus brochymenae (Hymenoptera: Platygastridae), a quasi-gregarious egg parasitoid of the harlequin bug, Murgantia histrionica (Heteroptera: Pentatomidae), starts before contact between males and females when chemical compounds produced by virgin females trigger the courtship behaviour of males. In the present study, the pheromone components involved in the short-range recognition of T. brochymenae females by males were investigated using electrophysiological and behavioural methods. Female body extracts were analyzed through EAG and GC-EAD and the active compounds were identified through GC-MS. The behavioural responses of virgin males to the GC-EAD active compounds were subsequently evaluated in closed arena bioassays. Two active compounds in EAG and behavioural tests, tetradecyl acetate and (Z)-11-hexadecen-1-yl acetate, were identified as sex pheromone components. Both compounds triggered intense male antennation and mount when applied to solvent-washed female cadavers. Dose-response tests showed different curves for the two compounds. This is the first study on the identification of sexual pheromones in Platygastridae.

Differences in cuticular lipid composition of the antennae of Helicoverpa zea, Heliothis virescens, and Manduca sexta

Analyses of the hexane washes of antennae, forelegs and whole bodies of Helicoverpa zea, Heliothis virescens, and Manduca sexta revealed notable differences in the components of the cuticular coatings of each species. Most striking were the differences between the cuticular coatings of male and female antennae of both H. zea and H. virescens. Novel esters of short-chain acids (C2-C4) and long-chain secondary alcohols (C25-C32) were identified in the hexane washes of the male antenna and forelegs of H. zea and H. virescens. These compounds were found in only small amounts or were completely absent on the female antennae of both species. In H. zea, butyrates of 7- and 8-pentacosanol and 8- and 9-heptacosanol were found, whereas, in the foreleg extracts of H. virescens, acetates and propionates were detected in addition to butyrates. While cholesterol is a major component of antennal washes (10-15%), only traces were found in the foreleg extracts. Although the composition of the cuticular coating of M. sexta differed greatly from that of the other two species, the extractable coatings of the antennae of male and female M. sexta were nearly identical.

Pheromone-based Arrestment Behavior in the Common Silverfish, Lepisma saccharina, and Giant Silverfish, Ctenolepisma longicaudata

Aggregations of the common silverfish, Lepisma saccharina, and giant silverfish, Ctenolepisma longicaudata (both Thysanura: Lepismatidae), are mediated by species-specific pheromones. In dual-choice, still-air olfactometer experiments, filter paper previously exposed to 12 male, female, or juvenile L. saccharina or C. longicaudata arrested conspecifics regardless of developmental stage or sex. Arrestment responses required physical contact with the pheromone. Insect-derived frass, scales, antennae, and setae, as well as salivary gland content, are not the source of the contact pheromone in L. saccharina. Lepisma saccharina did not respond to the pheromone of C. longicaudata, nor to that of another thysanuran, the firebrat Thermobia domestica. However, C. longicaudata responded to pheromones of both L. saccharina and T domestica, whereas T. domestica responded to the C. longicaudata but not L. saccharina pheromone. These results support the hypothesis that a closer phylogenetic relationship exists between C. longicaudata and T domestica than between C. longicaudata and L. saccharina, but a definitive conclusion must await molecular genetic analyses of all three species.

Pheromone components from body scales of female Anarsia lineatella induce contacts by conspecific males

Pheromonal communication of adult peach twig borers, Anarsia lineatella Zeller (Lepidoptera: Gelechiidae), was reinvestigated based on recent findings that virgin female-baited traps were more attractive to mate-seeking males than a two-component synthetic sex pheromone consisting of (E)-5-decen-1-yl acetate (1000 microg) and (E)-5-decen-1-ol (100 microg), suggesting that females use additional pheromone components. Hypothesizing that these additional components may be released from body parts other than abdominal sex pheromone glands, we extracted female body scales and analyzed aliquots by coupled gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometry. Eight straight-chain and four methylated aliphatic hydrocarbons, as well as two acetates, all elicited responses from excised male antennae. In laboratory experiments with synthetic candidate pheromone components, a combination of octadecyl acetate, (R)-11-methyltricosane, and (S)-11-methyltricosane in the presence of gland-derived sex pheromone components were shown to elicit contact of female decoys by males. However, body pheromone components did not enhance attractiveness of sex pheromone components in field trapping experiments, suggesting that they are effective only at close range and that other stimuli are responsible for superior attractiveness of female-baited traps.

Effect of 20-hydroxyecdysone on cannibalism, sexual behavior, and contact sex pheromone in the solitary female spider, Tegenaria atrica

We investigated the effect of exogenously administered 20-hydroxyecdysone (20E) on sexual behavior and on contact sex signals of adult females of the spider Tegenaria atrica. In untreated or control females cannibalism occurred in 36-47% of encounters, whereas no cannibalism at all was observed with 20E-treated females. The frequency of sexual receptivity was low (42%) in untreated or control females and high (100%) in 20E-treated females. Variability of female sexual behavior could be related to quantitative changes in web and cuticular compounds. We showed that 20E altered the production of polar contact sex pheromones on web and cuticle: methylesters and fatty acids are produced in higher amounts in 20E-treated females. Bioassays demonstrated clearly that methylesters and fatty acids of webs and cuticles were involved in attraction of males. Moreover, bioassays with synthetic substances showed that four fatty acids (myristic, pentadecanoic, hexadecanoic, and oleic acids) and one methylester (methyl stearate) are particularly effective in eliciting sexual behavior in males. In T. atrica, 20E inhibits cannibalism during sexual activity and changes sex pheromone production.

Novel wax esters and hydrocarbons in the cuticular surface lipids of the red harvester ant, Pogonomyrmex barbatus

The cuticular surface lipids of the red harvester ant, Pogonomyrmex barbatus, were found to contain minor amounts of novel wax esters, in addition to the major components, hydrocarbons. The wax esters ranged in carbon number from C19 to C31 and consisted of esters of both odd- and even-numbered alcohols and acids. Each wax ester with a given carbon number eluted at several different retention times indicating possible methyl branching in either the fatty acid or alcohol moiety, or in both moieties. Each eluting peak of wax esters consisted of a mixture of wax esters of the same carbon number in which the fatty acid moiety ranged from C8 to C18, and the alcohol moiety ranged from C8 to C17. Some wax esters were largely found on the head indicating they may be of a glandular origin. The hydrocarbons consisted of: n-alkanes, C23 to C33; odd-numbered n-alkenes, C27 to C35; and the major components, methyl-branched alkanes, C26 to over C49. Notable components of the methyl-branched alkanes were 2-methyltriacontane, and the novel trimethylalkanes with a single methylene between the first and second branch points, 13,15,19-trimethylhentriacontane and 13,15,21-trimethyltritriacontane.

Effect of age and sex on the production of internal and external hydrocarbons and pheromones in the housefly, Musca domestica

The epicuticular and internal waxes of male and female houseflies were examined by capillary gas chromatography-mass spectrometry at closely timed intervals from emergence until day-6 of adulthood. New components identified included tricosan-10-one, 9,10-epoxyheptacosane, heptacosen-12-one, a series of odd-carbon numbered dienes from C31 to C39, several positional isomers of monoenes including (Z)-9- and 7-pentacosene and a number of methyl- and dimethylalkanes. (Z)-9-tricosene appears in internal lipids prior to appearing on the surface of the insect, suggesting that it is transported in the hemolymph to its site of deposition on the epicuticle. The large increases in the amount of (Z)-9-tricosene in females from day-2 until day-6 is compensated for by a concomitant decrease in (Z)-9-heptacosene. The C23 epoxide and ketone only appear in females after the production of (Z)-9-tricosene is induced, and are only abundant in epicuticular waxes, suggesting they are formed after (Z)-9-tricosene is transported to the cells which are involved in taking them to the surface of the insect. Mathematical analysis indicated that the time shift between internal production and external accumulation in females is more than 24 h. The divergence between male and female lipid production occurs at an early stage, when insects are less than one day old.