Identification of compounds in an HPLC fraction from female extracts that elicit mating responses in male screwworm flies,Cochliomyia hominivorax

Physiological and molecular correlates of the screwworm fly attraction to wound and animal odors

The screwworm fly, Cochliomyia hominivorax (Coquerel), was successfully eradicated from the United States by the sterile insect technique (SIT). However, recent detection of these flies in the Florida Keys, and increased risk of introductions to the other areas warrant novel tools for management of the flies. Surveillance, a key component of screwworm control programs, utilizes traps baited with rotting liver or a blend of synthetic chemicals such as swormlure-4. In this work, we evaluated the olfactory physiology of the screwworm fly and compared it with the non-obligate ectoparasitic secondary screwworm flies, C. macellaria, that invade necrotic wound and feed on dead tissue. These two species occur in geographically overlapping regions. C. macellaria, along with other blowflies such as the exotic C. megacephala, greatly outnumber C. hominivorax in the existing monitoring traps. Olfactory responses to swormlure-4 constituents between sex and mating status (mated vs unmated) in both species were recorded and compared. Overall, responses measured by the antennograms offered insights into the comparative olfactory physiology of the two fly species. We also present detailed analyses of the antennal transcriptome by RNA-Sequencing that reveal significant differences between male and female screwworm flies. The differential expression patterns were confirmed by quantitative PCR. Taken together, this integrated study provides insights into the physiological and molecular correlates of the screwworm’s attraction to wounds, and identifies molecular targets that will aid in the development of odorant-based fly management strategies.

Chiral methyl-branched pheromones

Insect pheromones are some of the most interesting natural products because they are utilized for interspecific communication between various insects, such as beetles, moths, ants, and cockroaches. A large number of compounds of many kinds have been identified as pheromone components, reflecting the diversity of insect species. While this review deals only with chiral methyl-branched pheromones, the chemical structures of more than one hundred non-terpene compounds have been determined by applying excellent analytical techniques. Furthermore, their stereoselective syntheses have been achieved by employing trustworthy chiral sources and ingenious enantioselective reactions. The information has been reviewed here not only to make them available for new research but also to understand the characteristic chemical structures of the chiral pheromones. Since biosynthetic studies are still limited, it might be meaningful to examine whether the structures, particularly the positions and configurations of the branched methyl groups, are correlated with the taxonomy of the pheromone producers and also with the function of the pheromones in communication systems.

Synthesis of the Enantiomers of 21-Methyl-7-hentriacontanone and a Stereoisomeric Mixture of 5-Acetoxy-19-methylnonacosane, Candidates for the Female Sex Pheromone of the Screwworm Fly…

The enantiomers of 21-methyl-7-hentriacontanone (1), which might show weak bioactivity as the female sex pheromone of the screwworm fly (Cochliomyia hominivorax), were synthesized by starting from the enantiomers of citronellal. (+/-)-Citronellol was converted to a racemic and diastereomeric mixture of 5-acetoxy-19-methylnonacosane (2), which was considered to be a candidate for the female sex pheromone of C. hominivorax. Synthetic 2 exhibited no pheromone activity against male C. hominivorax.

Determination by HPLC fluorescence analysis of the natural enantiomers of sex pheromones in the New World screwworm fly, Cochliomyia hominivorax

Bioassays of six racemic synthesized candidate sex pheromone compounds against male New World screwworm Cochliomyia hominivorax (Coquerel) flies showed that the most potent bioactivity was found with 6-acetoxy-19-methylnonacosane and 7-acetoxy-15-methylnonacosane compared with four other isomeric acetoxy nonacosanes and a larger aliphatic ketone. As all these methyl-branched compounds have two asymmetric carbons and four possible enantiomers, characterization of the natural enantiomers was essential. All four enantiomers for the two most bioactive isomers of the natural sex pheromone were synthesized for bioassay. Hydrolysis and derivatization of these enantiomers with different fluorescent reagents was followed by column-switched high-performance liquid chromatography. The use of two linked, reversed-phase columns of different polarity held at sub-ambient temperatures allowed good separation of each enantiomer. This analysis applied to natural material was successful, as (6R,19R)-6-acetoxy-19-methylnonanocosane, and (7R,15R)- and (7R,15S)-7-acetoxy-15-methylnonanocosane were detected in extracts of recently colonized female flies.

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.

Pheromonal communication involved in courtship behavior in Diptera

Sex pheromones are known for many dipteran species and play an important role in courtship behavior, together with visual, tactile, acoustic and other factors. Pheromones for a number of dipterans have been recently identified. This survey covers a number of species in all the families that have been studied. The review discusses diverse courtship behaviors in Diptera, with a special focus on the sex pheromones involved. In the Nematocera suborder, pheromones are volatile components, which act at a distance. They are derived from short-chain alkanes with acetoxy groups (Cecidomyidae) or terpenes (Psychodidae). In the Cyclorrhapha, pheromones may be volatile, derived from alkanes (Tephritidae) or terpenes (Agromyzidae), or non-volatile, unsaturated or methyl-branched hydrocarbons, which act by contact (the other subgenera). The behavioral roles and regulation of these pheromones are described, and their importance in species recognition is discussed.

Candidate sex pheromones of the New World screwworm Cochliomyia hominivorax

Five novel homologous acetate derivatives of long-chain secondary alcohols and a related ketone were tested for their efficacy as contact mating stimulants for Cochliomyia hominivorax Coquerel (Diptera: Calliphoridae). Full copulatory behaviour at a high percentage was found in tests with racemic 6-acetoxy-19-methylnonacosane at 2.5-20 microg using fertile males from three strains. Males of two strains responded nearly as well to 7-acetoxy-15-methylnonacosane, but an older strain first colonized in 1992 did not respond to this compound. Few or no copulatory responses were obtained to the other secondary alcohol acetates and a related ketone. These two acetate derivatives are the first sex pheromones identified in a calliphorid fly. The threshold of response was also tested, but could not be pinpointed.

Antennal sensilla of the New World screwworm fly, Cochliomyia hominivorax (Diptera: Calliphoridae)

Antennal sensilla of the Cochliomyia hominivorax were studied by scanning electron microscopy. Thirteen subtypes of sensilla were identified in the fly antenna. In the antennal funiculus, nine subtypes were found: one trichoid, three basiconic, and five coeloconic. Among these, olfactory sensilla were morphologically recognized. Long bristle sensilla presenting various sizes and distribution patterns were observed in the scape and pedicel. In this segment, two other types of tricoid sensilla were still observed. The three antennal segments were shown to be coved by smaller spinules of the microtrichia type. No type of sensillum was seen in the aristas of C. hominivorax. Consistent differences between the sexes in typology, topography, and quantity of antennal sensilla were verified. The great variety of sensillary subtypes, presenting wall pores and/or grooves, found in the funiculus of C. hominivorax, indicates the olfaction should play an important role in this species behavior and communication. The data of the current study, besides corroborating in the amplification of the morphologic and ultrastructural knowledge of C. hominivorax, can foment future electrophysiological studies for the development of volatile semiochemicals, to be uses as attractants in traps, as a new alternative to monitoring and/or controlling this fly.

Syntheses of four methyl-branched secondary acetates and a methyl-branched ketone as possible candidates for the female pheromone of the screwworm fly, Cochliomyia hominivorax

6-Acetoxy-19-methylnonacosane (1), 7-acetoxy-19-methylnonacosane (2), 8-acetoxy-19-methylnonacosane (3), 7-acetoxy-15-methylnonacosane (4), and 21-methyl-7-hentriacontanone (5) were synthesized as racemic and diastereomeric mixtures. These are new compounds isolated from an HPLC fraction of the female hexane extract which elicited mating responses in the male screwworm fly, Cochliomyia hominivorax.

(Z)-3-hexenyl (R)-3-hydroxybutanoate: a male specific compound in three North American decorator wasps Eucerceris rubripes, E. conata and E. tricolor

The males of the decorator wasps Eucerceris have been observed to display abdomen-dragging behavior on plants surrounding their nest. It is thought that this applies a territorial-marking sex pheromone that serves to alert females to the males' territory for courtship and mating. The extracts of three species E. rubripes, E. conata, and E. tricolor have been analyzed by GC-MS. The gas chromatograms revealed the presence, in large quantities, of one common volatile compound in the male head extracts. By analogy with the closely related bee wolves Philanthus, we believe the pheromone is produced in the mandibular glands. Utilizing mass spectrometry, microreactions, FT-IR, and 1H and 13C NMR spectroscopy the structure of the pheromone was proposed to be (Z)-3-hexenyl 3-hydroxybutanoate, which was confirmed by synthesis. The absolute configuration of the chiral center was determined to be R for the three species by preparing the Mosher esters of the insect samples and comparing their GC retention times with a synthetic sample of known absolute configuration. In addition 2- and 3-hexenoic acid and some aromatic compounds were also found in varying quantities in both males and females along with hydrocarbons and fatty acids, although no species-specific profiles emerged.

The pheromone system of the male danaine butterfly, Idea leuconoe

Male Idea leuconoe butterflies release a complex mixture of volatiles from their pheromone glands (hairpencils) during courtship. The pheromone components geranyl methyl thioether (2), viridifloric beta-lactone (3) and 6-hydroxy-4-dodecanolide (10) have been synthesized for the first time. Therefore, the structural assignment of these new natural products could be proved. Related 7-hydroxy-5-alkanoides are also present in the extract. The volatiles are embedded in a lipidic, matrix with more than 150 components. This matrix consists of alkanes, alkenes, 2,5-dialkyltetrahydrofurans, secondary alkanols and alkenols as well as alkanones and alkenones. Several regioisomers of the oxidized hydrocarbons occur. The elucidation of double bond positions has been performed by MS using DMDS adducts.