Insect Pheromones Research Articles

Phase transitions in hydrophobe/phospholipid mixtures: hints at connections between pheromones and anaesthetic activity.

The phase behavior of a mixture of a typical insect pheromone (olean) and a phospholipid (DOPC)/water dispersion is extensively explored through SAXS, NMR and DSC experiments. The results mimic those obtained with anaesthetics in phospholipid/water systems. They also mimic the behavior and microstructure of ternary mixtures of a membrane mimetic, bilayer-forming double chained surfactants, oils and water. Taken together with recent models for conduction of the nervous impulse, all hint at lipid involvement and the underlying unity in mechanisms of pheromone, anaesthetic and hydrophobic drugs, where a local phase change in the lipid membrane architecture may be at least partly involved in the transmission of the signal.

Evaluation of Controlled-Release Property and Phytotoxicity Effect of Insect Pheromone Zinc-Layered Hydroxide Nanohybrid Intercalated with Hexenoic Acid.

A controlled release formulation for the insect pheromone hexenoic acid (HE) was successfully developed using zinc-layered hydroxide (ZLH) as host material through a simple coprecipitation technique, resulting in the formation of inorganic-organic nanolayered material with sustained release properties. The release of HE from its nanohybrid was found to occur in a controlled manner, governed by a pseudo-second order kinetics model. The maximum amount of HE released from the nanocomposite into solutions at pH 4, 6.5, and 8 was found to be 84, 73, and 83% for 1100 min, respectively. The hexenoate zinc-layered hydroxide nanomaterial (HEN) was found to be nontoxic for plants when green beans and wheat seeds were successfully germinated in all HEN concentrations tested in the experiment, with higher percentage of seed germination and higher radical seed growth as compared to its counter anion, HE. ZLH can be a promising carrier for insect pheromone toward a new generation of environmentally safe pesticide nanomaterial for crop protection.

Identification of Esters as Novel Aggregation Pheromone Components Produced by the Male Powder-Post Beetle, Lyctus africanus Lesne (Coleoptera: Lyctinae).

Lyctus africanus is a cosmopolitan powder-post beetle that is considered one of the major pests threatening timber and timber products. Because infestations of this beetle are inconspicuous, damage is difficult to detect and identification is often delayed. We identified the chemical compounds involved in the aggregation behavior of L. africanus using preparations of crude hexanic extracts from male and female beetles (ME and FE, respectively). Both male and female beetles showed significant preferences for ME, which was found to contain three esters. FE was ignored by both the sexes. Further bioassay confirmed the role of esters in the aggregation behavior of L. africanus. Three esters were identified as 2-propyl dodecanoate, 3-pentyl dodecanoate, and 3-pentyl tetradecanoate. Further behavioral bioassays revealed 3-pentyl dodecanoate to play the main role in the aggregation behavior of female L. africanus beetles. However, significantly more beetles aggregated on a paper disk treated with a blend of the three esters than on a paper disk treated with a single ester. This is the first report on pheromone identification in L. africanus; in addition, the study for the first time presents 3-pentyl dodecanoate as an insect pheromone.

Asymmetric Synthesis of Spiroketals with Aminothiourea Catalysts

AbstractChiral spiroketal skeletons are found as core structures in a range of bioactive compounds. These natural compounds and their analogues have attracted much attention in the field of drug discovery. However, methods for their enantioselective construction are limited, and easily available optically active spiroketals are rare. We demonstrate a novel catalytic asymmetric synthesis of spiroketal compounds that proceeds through an intramolecular hemiacetalization/oxy‐Michael addition cascade mediated by a bifunctional aminothiourea catalyst. This results in spiroketal structures through the relay formation of contiguous oxacycles, in which multipoint recognition by the catalyst through hydrogen bonding imparts high enantioselectivity. This method offers facile access to spiroketal frameworks bearing an alkyl group at the 2‐position, which are prevalent in insect pheromones. Optically active (2S,5S)‐chalcogran, a pheromone of the six‐spined spruce bark beetle, and an azide derivative could be readily synthesized from the bicyclic reaction product.

Asymmetric Synthesis of Spiroketals with Aminothiourea Catalysts.

Chiral spiroketal skeletons are found as core structures in a range of bioactive compounds. These natural compounds and their analogues have attracted much attention in the field of drug discovery. However, methods for their enantioselective construction are limited, and easily available optically active spiroketals are rare. We demonstrate a novel catalytic asymmetric synthesis of spiroketal compounds that proceeds through an intramolecular hemiacetalization/oxy-Michael addition cascade mediated by a bifunctional aminothiourea catalyst. This results in spiroketal structures through the relay formation of contiguous oxacycles, in which multipoint recognition by the catalyst through hydrogen bonding imparts high enantioselectivity. This method offers facile access to spiroketal frameworks bearing an alkyl group at the 2-position, which are prevalent in insect pheromones. Optically active (2S,5S)-chalcogran, a pheromone of the six-spined spruce bark beetle, and an azide derivative could be readily synthesized from the bicyclic reaction product.

Optimizing Crops for Biocontrol of Pests and Disease.

Volatile compounds and extrafloral nectar are common defenses of wild plants; however, in crops they bear an as-yet underused potential for biological control of pests and diseases. Odor emission and nectar secretion are multigene traits in wild plants, and thus form difficult targets for breeding. Furthermore, domestication has changed the capacity of crops to express these traits. We propose that breeding crops for an enhanced capacity for tritrophic interactions and volatile-mediated direct resistance to herbivores and pathogens can contribute to environmentally-friendly and sustainable agriculture. Natural plant volatiles with antifungal or repellent properties can serve as direct resistance agents. In addition, volatiles mediating tritrophic interactions can be combined with nectar-based food rewards for carnivores to boost indirect plant defense.

Chemoenzymatic Total Synthesis of (R)-Dodecanolide and (R)-4-Octanolide

A simple and efficient chemoenzymatic total synthesis of the naturally occurring insect pheromones, (4R)-dodecanolide and (4R)-octanolide is described.

Rapid evolution of chemosensory receptor genes in a pair of sibling species of orchid bees (Apidae: Euglossini).

BackgroundInsects rely more on chemical signals (semiochemicals) than on any other sensory modality to find, identify, and choose mates. In most insects, pheromone production is typically regulated through biosynthetic pathways, whereas pheromone sensory detection is controlled by the olfactory system. Orchid bees are exceptional in that their semiochemicals are not produced metabolically, but instead male bees collect odoriferous compounds (perfumes) from the environment and store them in specialized hind-leg pockets to subsequently expose during courtship display. Thus, the olfactory sensory system of orchid bees simultaneously controls male perfume traits (sender components) and female preferences (receiver components). This functional linkage increases the opportunities for parallel evolution of male traits and female preferences, particularly in response to genetic changes of chemosensory detection (e.g. Odorant Receptor genes). To identify whether shifts in pheromone composition among related lineages of orchid bees are associated with divergence in chemosensory genes of the olfactory periphery, we searched for patterns of divergent selection across the antennal transcriptomes of two recently diverged sibling species Euglossa dilemma and E. viridissima.ResultsWe identified 3185 orthologous genes including 94 chemosensory loci from five different gene families (Odorant Receptors, Ionotropic Receptors, Gustatory Receptors, Odorant Binding Proteins, and Chemosensory Proteins). Our results revealed that orthologs with signatures of divergent selection between E. dilemma and E. viridissima were significantly enriched for chemosensory genes. Notably, elevated signals of divergent selection were almost exclusively observed among chemosensory receptors (i.e. Odorant Receptors).ConclusionsOur results suggest that rapid changes in the chemosensory gene family occurred among closely related species of orchid bees. These findings are consistent with the hypothesis that strong divergent selection acting on chemosensory receptor genes plays an important role in the evolution and diversification of insect pheromone systems.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0451-9) contains supplementary material, which is available to authorized users.

Sex pheromone of the alfalfa plant bug, Adelphocoris lineolatus

AbstractIn northern China, due to the large‐scale adoption of transgenic Bacillus thuringiensis Berliner (Bt) cotton, the number of Adelphocoris lineolatus (Goeze) (Hemiptera: Miridae) has increased quickly, causing significant loss in cotton and alfalfa production. One of the environmentally safe strategies without use of pesticides is the application of insect pheromone for mating disruption. In our study, we aim to identify the active components in sexually mature virgin female A. lineolatus, and activity and optimal ratio of these components. By using gas chromatography–mass spectrometry (GC‐MS) and gas chromatography–electroantennographic detection (GC‐EAD), we identified three active compounds: hexyl butyrate (HB), (E)‐2‐hexenyl butyrate (E2HB), and (E)‐4‐oxo‐2‐hexenal (4‐OHE). We examined the release rate of septum and tube dispensers in a wind tunnel. In a field experiment, deletion of 4‐OHE or E2HB resulted in significant suppression of male trap catches, indicating that E2HB or 4‐OHE may be the active pheromone components. Traps baited with a blend of 4‐OHE and E2HB at 2:5, 3:4, and 4:3 caught significantly more males, suggesting that the optimal ratio of 4‐OHE and E2HB could be in the range of 1:1 to 1:2. The addition of a large amount of HB could strongly reduce the attractive activity of both virgin females and artificial lures. We also compared the attractiveness of septum lures and tube lures in field experiments. The septum lures attracted males in the first 3 days. The tube lures caught more males after 3 days and the attractive effects existed up to 5 weeks, suggesting them as a tool for long‐term monitoring and control of plant bugs.

Genes involved in sex pheromone biosynthesis of Ephestia cautella, an important food storage pest, are determined by transcriptome sequencing.

BackgroundInsects use pheromones, chemical signals that underlie all animal behaviors, for communication and for attracting mates. Synthetic pheromones are widely used in pest control strategies because they are environmentally safe. The production of insect pheromones in transgenic plants, which could be more economical and effective in producing isomerically pure compounds, has recently been successfully demonstrated. This research requires information regarding the pheromone biosynthetic pathways and the characterization of pheromone biosynthetic enzymes (PBEs). We used Illumina sequencing to characterize the pheromone gland (PG) transcriptome of the Pyralid moth, Ephestia cautella, a destructive storage pest, to reveal putative candidate genes involved in pheromone biosynthesis, release, transport and degradation.ResultsWe isolated the E. cautella pheromone compound as (Z,E)-9,12-tetradecadienyl acetate, and the major pheromone precursors 16:acyl, 14:acyl, E14-16:acyl, E12-14:acyl and Z9,E12-14:acyl. Based on the abundance of precursors, two possible pheromone biosynthetic pathways are proposed. Both pathways initiate from C16:acyl-CoA, with one involving ∆14 and ∆9 desaturation to generate Z9,E12-14:acyl, and the other involving the chain shortening of C16:acyl-CoA to C14:acyl-CoA, followed by ∆12 and ∆9 desaturation to generate Z9,E12-14:acyl-CoA. Then, a final reduction and acetylation generates Z9,E12-14:OAc. Illumina sequencing yielded 83,792 transcripts, and we obtained a PG transcriptome of ~49.5 Mb. A total of 191 PBE transcripts, which included pheromone biosynthesis activating neuropeptides, fatty acid transport proteins, acetyl-CoA carboxylases, fatty acid synthases, desaturases, β-oxidation enzymes, fatty acyl-CoA reductases (FARs) and fatty acetyltransferases (FATs), were selected from the dataset. A comparison of the E. cautella transcriptome data with three other Lepidoptera PG datasets revealed that 45 % of the sequences were shared. Phylogenetic trees were constructed for desaturases, FARs and FATs, and transcripts that clustered with the ∆14, ∆12 and ∆9 desaturases, PG-specific FARs and potential candidate FATs, respectively, were identified. Transcripts encoding putative pheromone degrading enzymes, and candidate pheromone carrier and receptor proteins expressed in the E. cautella PG, were also identified.ConclusionsOur study provides important background information on the enzymes involved in pheromone biosynthesis. This information will be useful for the in vitro production of E. cautella sex pheromones and may provide potential targets for disrupting the pheromone-based communication system of E. cautella to prevent infestations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1710-2) contains supplementary material, which is available to authorized users.

The first crop plant genetically engineered to release an insect pheromone for defence.

Insect pheromones offer potential for managing pests of crop plants. Volatility and instability are problems for deployment in agriculture but could be solved by expressing genes for the biosynthesis of pheromones in the crop plants. This has now been achieved by genetically engineering a hexaploid variety of wheat to release (E)-β-farnesene (Eβf), the alarm pheromone for many pest aphids, using a synthetic gene based on a sequence from peppermint with a plastid targeting amino acid sequence, with or without a gene for biosynthesis of the precursor farnesyl diphosphate. Pure Eβf was produced in stably transformed wheat lines with no other detectable phenotype but requiring targeting of the gene produced to the plastid. In laboratory behavioural assays, three species of cereal aphids were repelled and foraging was increased for a parasitic natural enemy. Although these studies show considerable potential for aphid control, field trials employing the single and double constructs showed no reduction in aphids or increase in parasitism. Insect numbers were low and climatic conditions erratic suggesting the need for further trials or a closer imitation, in the plant, of alarm pheromone release.

Identification of hydroxymethylpyrazines using mass spectrometry.

Pyrazines are well-known natural products that are present in bacterial odours and food flavouring agents and are used as insect pheromones. Recently, a number of hydroxymethylpyrazines have been identified as thynnine wasp pheromones and orchid semiochemicals that are essential for pollination in sexually deceptive plants. These compounds are present in low amounts in complex blends, making GC-MS (including high-resolution techniques) the method of choice for their structure elucidation. We report the EI mass spectra for 14 representative compounds and have found that based on characteristic fragmentations, it is possible to distinguish between different positional isomers of hydroxymethylpyrazines. The presence or absence of either [M - 17]+ , [M - 18]+· or [M - 19]+ fragment species provides characteristic information to allow the distinction between the different isomers. Considering the importance of pyrazines as a group of bioactive natural products, and the recent findings of biological activity for hydroxymethylpyrazines, our results presented here will aid the identification of these compounds in other biological systems. Copyright © 2015 John Wiley & Sons, Ltd.

The importance of natural habitats to Brazilian free-tailed bats in intensive agricultural landscapes in the Winter Garden region of Texas, United States

The conversion of natural lands to agriculture is a leading cause of the worldwide loss of biodiversity. In particular, cropland monocultures alter insect abundance and diversity compared to adjacent natural habitats. While agricultural lands can provide large numbers of insect pests as prey items to predators such as bats, insect pest population size vary greatly throughout growing seasons. This study assesses the importance of land use and corn earworm moth availability as spatial and temporal drivers of bat activity. We quantified spatial variation in land use patterns at fifteen sites located within the Winter Garden region in south central Texas and used bat detectors and insect pheromone traps to monitor nightly bat activity and corn earworm moth abundance across the landscape and throughout most of the year. Our temporal analyses show that bat activity was positively correlated with moth abundance, but only early in the growing season when moth abundance is at its peak. The key result from this study is a positive relationship between bat activity and natural habitat cover during late summer months, corresponding to periods of low moth abundance and a peak in bat activity. During the late summer period, bats were more active at sites containing a larger percentage of natural habitats than those containing a larger percentage of agricultural land. Our results strongly suggest that intensive agricultural practices create systems providing bats with inconsistent resource supply, but the persistence of natural habitats provides consistency in food supply though time. Taken together, these findings illustrate the importance of protecting and restoring natural habitats for the conservation for bats and the pest-suppression services they provide in agricultural ecosystems.

ChemInform Abstract: Ozonolysis of Unsaturated Compounds in the Synthesis of Insect Pheromones and Juvenoids

AbstractReview: 96 refs.

Multiple functions of fire ant Solenopsis invicta mandibular gland products

AbstractAlarm pheromones of social insects are best known for their role in the defence and maintenance of colony integrity. Previous studies with the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) demonstrate that the mandibular glands of workers (sterile females) and male and female sexuals produce an alarm pheromone, 2‐ethyl‐3,6‐dimethylpyrazine. The function of alarm pheromones in worker ants is well understood and divergent from the function of these compounds in the winged sexual forms. The present study quantifies the amount of pyrazine in the mandibular glands from male and female alate sexuals, as well as queens. Pyrazine production in female alates starts in the late pupal stage and increases until they reach mating flight‐ready maturity; however, after mating flight participation, the pyrazine level declines by >50%. Interestingly, mature male alates lose >85% of their mandibular gland pyrazine during mating flight activity. The results of the present study indicate that male and female sexuals use mandibular gland secretions for mating flight initiation and during mating flights. Furthermore, the ontogeny of mandibular gland products (pyrazine as the marker) from newly‐mated queens to mature colony queens shows a more than two‐fold increase in the amount of pyrazine by 6 months after mating. However, this is followed by a decline to trace amounts in mature colony queens (>2 years old), suggesting a function for mandibular gland products during colony development. Multifunctional use of social insect pheromones is well documented and data are reported in the present study suggesting new roles for mandibular gland products in fire ants.

Size Exclusion High Performance Liquid Chromatography: Re-Discovery of a Rapid and Versatile Method for Clean-Up and Fractionation in Chemical Ecology.

Solvent extraction of bioactive molecules from glands, tissues, or whole organisms is a common first step in chemoecological studies. Co-extraction of a surplus of high boiling materials such as triacylglycerides (TAGs) and other lipids with higher molecular weight might hamper the identification of volatile or medium-volatile semiochemicals by high resolution chromatographic and spectroscopic techniques. Therefore, effective clean-up procedures are needed to separate potential semiochemicals from the accompanying materials. Size exclusion high performance liquid chromatography (SE-HPLC), a technique often disregarded by chemoecologists, has proved to be a rapid and efficient clean-up method for complex crude extracts. We demonstrated that TAGs can be baseline separated from typical semiochemicals within less than 10 min on a porous gel stationary phase based on highly cross-linked polystyrene/divinylbenzene. We applied the method as a rapid one-step clean-up procedure for the analysis of juvenile hormone III in insect hemolymph by gas chromatography-mass spectrometry. We furthermore introduced some recent application examples on insect pheromones to demonstrate that SE-HPLC is not only an effective method for the purification of crude extracts, but can as well be used as a first fractionation step for the bioassay-guided identification of behavior modifying natural products. SE-HPLC can be well operated with low-boiling solvents such as dichloromethane, and results in fraction volumes of typically less than one ml, which decreases the danger of losing volatile analytes during subsequent concentration steps.

Males and females of the social wasp Ropalidia marginata do not differ in their cuticular hydrocarbon profiles and do not seem to use any long-distance volatile mate attraction cues

Sex pheromones are vital in communication between individuals belonging to opposite sexes and form an integral part of the reproductive biology of various species. Among insects, sexual dimorphism in CHCs has been reported from diverse taxa spanning seven different orders, and thereby CHCs have been implicated as sex pheromones. Because males and females of the primitively eusocial wasp Ropalidia marginata touch each other with their antennae during mating, before engaging in sperm transfer, a sex pheromone that is perceived via contact chemosensation through the antennae can possibly exist in this species. Since CHCs have been implied as sex pheromones in various insects (including hymenopterans), and since sexual dimorphism of CHCs should be an obligatory prerequisite for them to act as sex pheromones, we investigated whether males and females of R. marginata differ in their CHC profiles. We found only nonvolatile CHCs, and our results show absence of sexual dimorphism in CHCs, suggesting that CHCs do not function as sex pheromone in this species. A behavioral assay failed to show presence of mate attraction at a distance, thereby showing the absence of volatile long-distance mate attraction cues (that may originate from sources other than and in addition to CHCs).

Trail following response of larval Cactoblastis cactorum to 2-acyl-1,3-cyclohexanediones.

Caterpillars of Cactoblastis cactorum secrete onto the surface of host cactuses droplets of an oily fluid that issues from the orifices of their paired mandibular glands. The fluid contains a series of 2-acyl-1,3-cyclohexanediones that, collectively, have been shown to elicit trail-following behavior from the caterpillars. This study reports the results of bioassays to determine the ability of two specific compounds, previously shown to be prominent components of the mandibular glands of pyralid caterpillars, 4-hydroxy-2-oleoyl-1,3-cyclohexanedione and 2-oleoyl-1,3-cyclohexanedione, to elicit trail-following behavior from the larvae of C. cactorum. Additionally bioassayed were structural fragments of these molecules. The relative effectiveness of the chemicals in eliciting trail following, the effect of varying concentration on the trail-following response, the importance of specific functional groups to the trail-following response, and the threshold sensitivity of the caterpillar to the pheromone were determined. The study showed that while all the tested compounds elicited some degree of trail following, they differed significantly in their effectiveness. The most effective of the compounds was 4-hydroxy-2-oleoyl-1,3-cyclohexanedione, which, on a per unit volume basis, was as effective as whole gland extract. Caterpillars secreted large quantities of fluid from the glands, and the threshold response to 4-hydroxy-2-oleoyl-1,3-cyclohexanedione occurred at a relative high application rate compared to trail pheromones of other social caterpillars and eusocial insects. This and the observation that the trail marker is secreted from the mandibular glands suggests that the use of 2-acyl-1,3-cyclohexanediones as trail markers is secondary, and that these compounds function primarily in some other, as yet undetermined, context.

Queen pheromone promotes production of salivary lysozyme by workers in a termite

Social insects have highly elaborated communication systems. In particular, communication via pheromones is important for maintaining complex social roles and behaviors. Brood care is a typical activity that involves pheromonal communication among colony members. In termites, eggs cannot survive without grooming by workers. The workers coat the eggs with their saliva, which contains an antibacterial protein lysozyme that protects the eggs against bacterial pathogens. The more eggs a colony has, the more salivary lysozyme the workers need to produce for egg grooming. However, it is unknown how termite workers regulate their lysozyme production. Here we show that the queen pheromone, which is emitted by both queens and eggs, promotes lysozyme production by workers in the termite Reticulitermes speratus. Exposure to artificial queen pheromone significantly increased the production of salivary lysozyme by workers as well as the artificial addition of eggs. Furthermore, our survey of field colonies revealed clear seasonality in the production of salivary lysozyme. The seasonal pattern of lysozyme production matched well with the seasonal change of the number of eggs per colony. In addition to the known function of the queen pheromone as an inhibitor of neotenic queen differentiation, this study reveals that the same pheromone also acts as a promoter of lysozyme production in workers. We describe a novel function of the multifunctional queen pheromone in termites and provide new insights into the evolutionary parsimony of social insect pheromones.

Varying importance of cuticular hydrocarbons and iridoids in the species-specific mate recognition pheromones of three closely related Leptopilina species

Finding a suitable mate for reproduction is one of the most important tasks for almost all animals. In insects this task is often facilitated by pheromone-mediated communication. While insect pheromones in general show enormous chemical diversity, closely related species often use structurally similar compounds in their pheromones. Despite this similarity, pheromones of congeneric species living in sympatry need to be species specific. We investigated the pheromone-mediated mate recognition by males of three closely related species of Leptopilina, a genus of parasitoid wasps that utilize the larvae of Drosophila as hosts. The study species, L. heterotoma, L. boulardi, and L. victoriae, occur sympatrically and have a similar ecology and life history. We have found that mate recognition is species specific in all three species. This species specificity is achieved by a differing importance of cuticular hydrocarbons (CHCs) and iridoids in the female mate recognition pheromones. In L. heterotoma the iridoids are of major importance while CHCs play a negligible role. In L. boulardi, however, the CHCs are as important as the iridoids, while in L. victoriae, the CHCs alone elicit a full behavioral response of males. Our results provide novel insights into pheromone evolution in insects by showing that selection on two completely different classes of chemical compounds may generate conditions where compounds from both classes contribute to a varying degree to the chemical communication of closely related species and that this variation also generates the species specificity of the signals.