Aggregation Pheromone Production Research Articles

Identification of Aggregation Pheromone as an Attractant for Odontothrips loti, A Serious Thrips Pest on Alfalfa.

Odontothrips loti (Haliday) (Thysanoptera: Thripidae) is one of the most serious pests on alfalfa, causing direct damage by feeding and indirect damage by transmitting plant viruses. This damage causes significant loss in alfalfa production. Semiochemicals offer opportunities to develop new approaches to thrips management. In this study, behavioral responses of female and male adults of O. loti to headspace volatiles from live female and male conspecifics were tested in a Y-tube olfactometer. The results showed that both male and female adults of O. loti were attracted to the odors released by conspecific males but not those released by females. Headspace volatiles released by female and male adults were collected using headspace solid-phase microextraction (HS-SPME). The active compound in the volatiles was identified by gas chromatography-mass spectrometry (GC-MS). The analysis showed that there was one major compound, (R)-lavandulyl (R)-2-methylbutanoate. The attractive activity of the synthetic aggregation pheromone compound was tested under laboratory and field conditions. In an olfactometer, both male and female adults showed significant preference for synthetic (R)-lavandulyl (R)-2-methylbutanoate at certain doses. Lures with synthetic (R)-lavandulyl (R)-2-methylbutanoate significantly increased the trap catches of sticky white traps at doses of 40-80µg in the field. This study confirmed the production of aggregation pheromone by O. loti male adults and identified its active compound as (R)-lavandulyl (R)-2-methylbutanoate, providing a basis for population monitoring and mass trapping of this pest.

Comparative Transcriptomics Analysis Reveals Rusty Grain Beetle's Aggregation Pheromone Biosynthesis Mechanism in Response to Starvation.

Pheromones are the basis of insect aggregation, mating, and other behaviors. Cucujoid grain beetles produce macrocyclic lactones as aggregation pheromones, yet research on their biosynthesis at the molecular level remains limited. The rusty grain beetle, C. ferrugineus, is an important economic species in China. Although two aggregation pheromone components have been identified, their suspected biosynthesis via the MVA pathway and the FAS pathway lacks molecular elucidation. Previous evidence supports that starvation affects the production of aggregation pheromones. Therefore, we constructed comparative transcriptome libraries of pheromone production sites in C. ferrugineus under starvation stress and identified genes related to pheromone biosynthesis and hormone regulation. A total of 2665 genes were significantly differentially expressed, of which 2029 genes were down-regulated in starved beetles. Putative C. ferrugineus genes directly involved in pheromone biosynthesis were identified, as well as some genes related to the juvenile hormone (JH) pathway and the insulin pathway, both of which were depressed in the starved beetles, suggesting possible functions in pheromone biosynthesis and regulation. The identification of genes involved in macrolide lactone biosynthesis in vivo holds great significance, aiding in the elucidation of the synthesis and regulatory mechanisms of cucujoid grain beetle pheromones.

A novel physiological function of pheromone biosynthesis-activating neuropeptide in production of aggregation pheromone

The western flower thrips, Frankliniella occidentalis, is an insect pest, and its aggregation pheromone (AP) plays a crucial role in the recruitment of both sexes. A novel pheromone biosynthesis-activating neuropeptide (PBAN)-like gene is encoded in F. occidentalis genome, but its physiological function has yet to be elucidated. This study hypothesized the physiological role played by PBAN in mediating AP production. AP has been known to be produced only by male adults in F. occidentalis. Surprisingly, our extraction of headspace volatiles contained two AP components in females as well as in males with similar composition. PBAN injection elevated the AP production whereas RNA interference (RNAi) of the gene expression suppressed the AP production in both sexes. A biosynthetic pathway to produce AP components were predicted and the enzymes catalyzing the main steps were confirmed in their expressions. Individual RNAi treatments of these genes significantly suppressed AP production. RNAi of PBAN gene downregulated the expressions of these biosynthesis-associated genes in both sexes. These results suggest that the novel neuropeptide acts as PBAN mediating AP production through stimulating its biosynthetic machinery in F. occidentalis.

A synopsis of the ecology of Protura (Arthropoda: Hexapoda)

This publication reviews the literature on the ecology of Protura. Current knowledge is scarce, fragmentary and scattered among papers which do not all strictly deal with ecology or soil arthropods communities. Therefore all available information is summarized in order to better understand the ecology of these arthropods. The density of Protura ranges from hundreds to thousands of individuals per m2. Their aggregate distribution is probably related to food (fungal hyphae) availability and quality, and to the production of aggregation pheromones. Protura tend to form species assemblages characterizing different habitats. Their populations often show an unbalanced sex ratio in favour of females, suggesting that a single male can fertilize several females, perhaps via spermatophores. For some species only females have been collected, which suggests the possibility of parthenogenesis. Our analysis of the available information on phenology and population dynamics of Protura points toward annual cycles with one, two or more peaks of reproductive activity.

Establishing Diorhabda carinulata: Impact of Release Disturbances on Pheromone Emission and Influence of Pheromone Lures on Establishment.

Before weed biocontrol insects are transported and released in a new area, they are commonly collected into small paper containers, chilled, and kept under dark conditions. This process can be termed a pre-release protocol. The influence of a pre-release protocol on establishment success of a gregarious biological control agent was assessed using the northern tamarisk beetle, Diorhabda carinulata (Desbrochers), and its exotic, invasive host plant saltcedar (Tamarix spp.). Pre-release protocol impacts on aggregation pheromone production by D. carinulata were characterized under controlled conditions. Additional experiments were undertaken to determine if deployment of aggregation pheromone lures might enhance the agent's persistence at release sites. Adults that experienced the pre-release protocol produced less aggregation pheromone compared to undisturbed adults. Olfactometer bioassays indicated that a cohort of adults subjected to the pre-release protocol were less attractive to other adults than a control cohort. Efficacy of aggregation pheromone-based lures to retain adults at release sites was evaluated by comparing capture numbers of adult beetles at paired treatment and control release sites, 10-14days after the release of 300, 500, or 1000 individuals. A greater number of adult D. carinulata were captured where the pheromone lures had been deployed compared to control release sites. Application of aggregation pheromone when a new release of D. carinulata is planned should allow biological control practitioners to increase retention of beetles at a release site.

Tryptophan Metabolism in Caenorhabditis elegans Links Aggregation Behavior to Nutritional Status.

Caenorhabditis elegans uses aggregation pheromones to communicate its nutritional status and recruit fellow members of its species to food sources. These aggregation pheromones include the IC-ascarosides, ascarosides modified with an indole-3-carbonyl (IC) group on the 4'-position of the ascarylose sugar. Nothing is known about the biosynthesis of the IC modification beyond the fact that it is derived from tryptophan. Here, we show that C. elegans produces endogenously several indole-containing metabolites, including indole-3-pyruvic acid (IPA), indole-3-acetic acid (IAA; auxin), and indole-3-carboxylic acid, and that these metabolites are intermediates in the biosynthetic pathway from tryptophan to the IC group. Stable isotope-labeled IPA and IAA are incorporated into the IC-ascarosides. Importantly, we show that flux through the biosynthetic pathway is affected by the activity of the pyruvate dehydrogenase complex (PDC). Knockdown of the PDC by RNA interference leads to an accumulation of upstream metabolites and a reduction in downstream metabolites in the pathway. Our results show that production of aggregation pheromones is linked to PDC activity and that aggregation behavior may reflect a favorable metabolic state in the worm. Lastly, we show that treatment of C. elegans with indole-containing metabolites in the pathway induces the biosynthesis of the IC-ascarosides. Because the natural environment of C. elegans is rotting plant material, indole-containing metabolites in this environment could potentially stimulate pheromone biosynthesis and aggregation behavior in the worm. Thus, there may be important links between tryptophan metabolism in C. elegans and in plants and bacteria that enable interkingdom signaling.

Olfactometric evidence for aggregation pheromone production by females of the four-eyed fir bark beetle Polygraphus proximus Blandf. (Coleoptera, Curculionidae: Scolytinae)

Chemical communication of the four-eyed fir bark beetle Polygraphus proximus Blandf., an aggressive invasive pest of the Siberian fir Abies sibirica Ledeb., was experimentally studied using a four-way olfactometer of a modified design, in which the tested insects were allowed to move on their own from a lightproof plastic container onto the lighted arena. Young hibernated adults of P. proximus were offered four variants of odor: fir log segments infested with (1) 10 males, (2) 10 females, (3) 10 couples of P. proximus, and (4) clean air as the control. The pheromone of P. proximus was shown to be produced by females; a similar response of both sexes characterized it as an aggregation pheromone. All the three variants with infested fir logs were much more attractive than the control variant with clean air. Volatiles from fir tissues not only seem to serve as markers facilitating host selection by the first-to-arrive beetles before direct contact with the tree bark, but also to be used as pheromone precursors or synergists. The absence of difference in response to the logs infested with males and couples of the bark beetle indicated that pheromone synthesis was inhibited after couple formation.

Sternal gland structures in males of bean flower thrips, Megalurothrips sjostedti, and Poinsettia thrips, Echinothrips americanus, in comparison with those of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae)

Sternal pores are important features for identification of male thrips, especially within the subfamily Thripinae. They vary in shape, size and distribution even between species of one genus. Their functional role is speculated to be that of sex- and/or aggregation pheromone production. Yet, sexual aggregations are not reported in Echinothrips americanus, known to have sternal pores, while we observed aggregations in Megalurothrips sjostedti, previously reported to lack them.We examined the sternal glands and pores of the thripine species E. americanus and M. sjostedti males, in comparison with those of Frankliniella occidentalis using light microscopy, as well as scanning and transmission electron microscopy. Pore plates of F. occidentalis were ellipsoid and medial on sternites III–VII, while in E. americanus they were distributed as multiple micro pore plates on sternites III–VIII. In M. sjostedti they appeared as an extremely small pore in front of the posterior margin of each of sternites IV–VII. Pore plate and pore plate area were distributed similarly on sternites III–VII in F. occidentalis. However, in E. americanus the total pore plate area increased significantly from sternites III to VIII. Ultrastructure of cells associated with sternal glands showed typical characteristics of gland cells that differ in size, shape and number. The function of sternal glands is further discussed on the basis of morphological comparisons with other thrips species.

Influences of food sources on reproduction and aggregation pheromone production of Riptortus pedestris (Hemiptera: Alydidae) in its adult stage

AbstractThe dietary importance of sweet persimmon fruit (SPF) was determined in adult bean bug, Riptortus pedestris, by investigating the effect of feeding SPF and soybean seeds and peanut on longevity, weight change, fecundity and ability for pheromone production in the bean bug. Adult female R. pedestris fed on SPF had significantly shorter lifespans than those fed on soybean, while in males there was no significant difference. Males and females fed on SPF were significantly lighter than those fed on soybean seeds. Females fed on SPF did not lay eggs at all, but those fed on soybean laid 155.8 eggs, and those fed on soybean seed complemented with peanut seed laid 120.8 eggs in 50 days. The amount of pheromone components (E)‐2‐hexenyl (E)‐2‐hexenoate and (E)‐2‐hexenyl (Z)‐2‐hexenoate produced by male R. pedestris fed on SPF was significantly less than that produced by males fed on soybean. Other pheromone components, tetradecyl isobutyrate and octadecyl isobutyrate, were not produced by adult males fed on SPF. This difference was apparent at one week after emergence and was more at three weeks after emergence. In the present study, we demonstrated that SPF had adverse effect on female survivorship, reproduction of female adults and production of the aggregation pheromone by adult males, compared to soybean food. These results suggested that SPF is unsuitable for adult R. pedestris. Management of nearby vegetation of fruit orchards may play an important role in reducing damage by adult R. pedestris.

Exploring a key synapomorphy: correlations between structure and function in the sternum V glands of Trichoptera and Lepidoptera (Insecta)

The sternum V glands are a key synapomorphy that unites Trichoptera with Lepidoptera, but their functional aspects have not been analysed from an evolutionary perspective. We examine phylogenetic trends and correlations between chemical and morphological features of these glands. The most likely ancestral gland compounds are heptan-2-ol, 4-hepten-2-one and -ol, nonan-2-one, and 6-nonen-2-one and -ol, making pheromone production a plausible ancestral function. The most widespread gland compounds (heptan-2-one and -ol and nonan-2-one and -ol) are not known from Apataniidae + Limnephilidae (Trichoptera), which in turn uniquely produce a number of methylated 3-ketones and their corresponding alcohols, probably functioning as pheromones. We propose a functional connection between perforated patches on sternum IV in females and a scaly/dome-covered area around the gland openings, as well as between perforated patches and lack of Trichoptera-type opening muscles. We also propose a functional connection between the shape of the gland reservoirs and the presence of gland reservoir musculature. The perforated patches were significantly correlated with several gland compounds that had double bonds between carbon atoms: the double bonds may lower the viscosity of the compounds, facilitating secretion through the tiny pores of the perforated patches. The production of defensive substances in Pycnopsyche (Trichoptera: Limnephilidae) is probably connected to the presence of large, compartmentalized gland reservoirs. Large glands in male Hydropsyche (Trichoptera: Hydropsychidae) are probably linked to male aggregation pheromone production. The relative sizes of sternum V gland reservoirs and fenestral gland reservoirs in female philopotamids (Trichoptera) suggest a complementary function of the two structures. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 561–579.

Isolation and extreme sex‐specific expression of cytochrome P450 genes in the bark beetle, Ips paraconfusus, following feeding on the phloem of host ponderosa pine, Pinus ponderosa

We have identified cDNAs and characterized the expression of 13 novel cytochrome P450 genes of potential importance in host colonization and reproduction by the California fivespined ips, Ips paraconfusus. Twelve are of the Cyp4 family and one is of the Cyp9 family. Following feeding on host Pinus ponderosa phloem, bark beetle transcript levels of several of the Cyp4 genes increased or decreased in males only or in both sexes. In one instance (IparaCyp4A5) transcript accumulated significantly in females, but declined significantly in males. The Cyp9 gene (Cyp9T1) transcript levels in males were > 85 000 x higher at 8 h and > 25 000 x higher at 24 h after feeding compared with nonfed controls. Transcript levels in females were approximately 150 x higher at 24 h compared with nonfed controls. Cyp4G27 transcript was present constitutively regardless of sex or feeding and served as a better housekeeping gene than beta-actin or 18S rRNA for the real-time TaqMan polymerase chain reaction analysis. The expression patterns of Cyp4AY1, Cyp4BG1, and, especially, Cyp9T1 in males suggest roles for these genes in male-specific aggregation pheromone production. The differential transcript accumulation patterns of these bark beetle P450s provide insight into ecological interactions of I. paraconfusus with its host pines.

Spatio-temporal analysis of trap catches of Tribolium confusum du Val in a semolina-mill, with a comparison of female and male distributions

By using food-bait traps, we evaluated the presence and the spatio-temporal distribution of insect pests in an industrial semolina-mill, with particular attention to Tribolium confusum du Val in which the spatio-temporal dynamics of females and males were also studied separately. A total of 1401 insect specimens was captured in the traps, belonging to 14 taxa, mainly Coleoptera. The most abundant species were T. confusum (with 1002 adults), followed by Typhaea stercorea (L.) (with 158 adults) and T. castaneum (Herbst) (with 110 adults). Of particular interest was the presence in the food-bait traps of T. confusum and T. castaneum adults in a mixed population with equal numbers of males and females. Furthermore, analysis of the spatio-temporal dynamics suggested that the distribution of the two sexes in T. confusum was almost the same during the entire sampling period. The findings of our study can usefully be applied to the management of Tribolium infestations, but further and more detailed studies are needed to better understand the ecology and behaviour of the species in association with searching for food and production of aggregation pheromones.

Coordinated gene expression for pheromone biosynthesis in the pine engraver beetle, Ips pini (Coleoptera: Scolytidae).

In several pine bark beetle species, phloem feeding induces aggregation pheromone production to coordinate a mass attack on the host tree. Male pine engraver beetles, Ips pini (Say) (Coleoptera: Scolytidae), produce the monoterpenoid pheromone component ipsdienol de novo via the mevalonate pathway in the anterior midgut upon feeding. To understand how pheromone production is regulated in this tissue, we used quantitative real-time PCR to examine feeding-induced changes in gene expression of seven mevalonate pathway genes: acetoacetyl-coenzyme A thiolase, 3-hydroxy-3-methylglutaryl coenzyme A synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, mevalonate 5-diphosphate decarboxylase, isopentenyl-diphosphate isomerase, geranyl-diphosphate synthase (GPPS), and farnesyl-diphosphate synthase (FPPS). In males, expression of all these genes significantly increased upon feeding. In females, the expression of the early mevalonate pathway genes (up to and including the isomerase) increased significantly, but the expression of the later genes (GPPS and FPPS) was unaffected or decreased upon feeding. Thus, feeding coordinately regulates expression of the mevalonate pathway genes necessary for pheromone biosynthesis in male, but not female, midguts. Furthermore, basal mRNA levels were 5- to 41-fold more abundant in male midguts compared to female midguts. This is the first report of coordinated regulation of mevalonate pathway genes in an invertebrate model consistent with their sex-specific role in de novo pheromone biosynthesis.

Is Bigger Better? Size and Pheromone Production in the Mountain Pine Beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae)

Reproductive success in the mountain pine beetle, Dendroctonus ponderosae Hopkins, is determined by the production of aggregation and antiaggregation pheromones, as well as body size. In a laboratory experiment with beetles that emerged from naturally attacked hosts, there was no relationship between body size and the production of aggregation pheromones in either sex. In contrast, there were significant relationships between body size and the production of antiaggregation pheromones in males that were paired with females. Pheromone amounts decreased in paired females and antiaggregation pheromones correspondingly increased in paired males, suggesting that after pairing, males take over the role of pheromone production. Although males could potentially select large females by evaluating gallery size, and females could select large males on the basis of their strength in stridulation or physical courtship, we propose that mate choice occurs primarily by olfaction. Small individuals that produce large amounts of pheromone during initial attack could “sabotage” mate choice based on size-related criteria. This hypothesis is consistent with a lack of evidence for size assortative mating in 92 pairs of beetles. The production of antiaggregants by large male D. ponderosae after pairing with females appears to be an important factor in intraspecific resource partitioning, population regulation, and reproductive success.

Midgut tissue of male pine engraver, Ips pini, synthesizes monoterpenoid pheromone component ipsdienol de novo.

For over three decades the site and pathways of bark beetle aggregation pheromone production have remained elusive. Studies on pheromone production in Ips spp. bark beetles have recently shown de novo biosynthesis of pheromone components via the mevalonate pathway. The gene encoding a key regulated enzyme in this pathway, 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R), showed high transcript levels in the anterior midgut of male pine engravers, Ips pini (Say) (Coleoptera:Scolytidae). HMG-R expression in the midgut was sex, juvenile hormone, and feeding dependent, providing strong evidence that this is the site of acyclic monoterpenoid (ipsdienol) pheromone production in male beetles. Additionally, isolated midgut tissue from fed or juvenile hormone III (JH III)-treated males converted radiolabeled acetate to ipsdienol, as assayed by radio-HPLC. These data support the de novo production of this frass-associated aggregation pheromone component by the mevalonate pathway. The induction of a metazoan HMG-R in this process does not support the postulated role of microorganisms in ipsdienol production.

OPPOSING EFFECTS OF HOST MONOTERPENES ON RESPONSES BY TWO SYMPATRIC SPECIES OF BARK BEETLES TO THEIR AGGREGATION PHEROMONES

The effects of host tree monoterpenes on primary and secondary attraction of the bark beetles, Ips pini and Ips grandicollis, and their associated phloeophagous insects were investigated. Monoterpenes alone were not attractive to I. pini. However, monoterpenes mediated the attraction of I. pini to its aggregation pheromones. With the exception of 3–carene, the effect of monoterpenes on I. pini's response to its pheromone, ipsdienol plus lanierone, was inhibitory. In contrast, (−)-α-pinene both attracted I. grandicollis and enhanced the attraction of I. grandicollis to its pheromone, ipsenol. No monoterpene inhibited the response of I. grandicollis to its pheromone. The inhibitory effect of host monoterpenes on I. pini response to its aggregation pheromone differs from previous work, in which monoterpenes either synergized responses or had no effect. In addition to possible geographic differences, the concentrations used in our study simulated trees that had begun to respond to attack, whereas previous studies deployed lower concentrations, which simulated constitutive phloem from unattacked trees. These results support the view that trees that undergo induced responses to bark beetles sometimes inhibit attraction of additional beetles, despite the beetles' production of aggregation pheromones. Neither species displayed cross-attraction to the pheromone of the other. The red turpentine beetle, Dendroctonus valens, showed weak and consistent attraction to (+)-α-pinene and in some cases to (−)-α-pinene. Attraction to (−)-α-pinene was usually enhanced by Ips spp. pheromones. The absence of strong attraction to (+)-α-pinene and partial attraction to (−)-α-pinene suggest that the effects of different stereoisomers of α-pinene on D. valens vary throughout its geographical range. Hylastes porculus was also attracted to some monoterpenes, particularly (−)-α-pinene. An additional 10 species of phloeophagous insects were caught in response to monoterpenes and/or pheromones, including the pine root weevils, Hylobius pales and Pachylobius picivorus, and the longhorned beetle, Monochamus carolinensis.

Haemolymph ecdysteroids and the prothoracic glands in the solitary and gregarious adults of Schistocerca gregaria

The haemolymph titre of ecdysteroids rises in the adults of both sexes to a brief peak in the first week after emergence. A major rise begins on days 8–10, coincidentally with intensive vitellogenesis in the females and aggregation pheromone production in the males. The titre reaches about 400 ng of 20-hydroxyecdysone (20E) equiv./ml in the solitary, but less than 150 ng/ml in the gregarious adults of both sexes. In the females, the titre drops after oviposition (prior to day 20) and remains low until the next egg batch matures; then it increases in either phase to 150–180 ng/ml. A similar titre reduction in the males occurs just after day 20: in the solitary males the titre declines slowly to about 110 ng/ml on day 40, whereas in the gregarious males ecdysteroids virtually disappear by day 25. The blood of females contains similar levels of 20E and ecdysone, whereas in the males 20E makes up 73% (solitary) or 94% (gregarious) of total ecdysteroids. Minor components include a compound behaving as makisterone A and highly polar metabolites. The prothoracic glands are well preserved in both solitary and gregarious adults for at least 1 week after fledging and in some females they seem to persist for the lifetime, but in contrast to the glands of larvae, do not produce significant amounts of ecdysteroids when cultured in vitro.

Influence of Tapeworm Infection on the Production of Aggregation Pheromone and Defensive Compounds in Tribolium castaneum

Recent studies suggest that parasites affect host development, reproduction, and behavior through alterations of host hormones and pheromones, or other hormone-triggered biochemical events. We previously reported that Hymenolepis diminuta infection affects surface-seeking and cannibalism behaviors, and reduces male sperm precedence of Tribolium castaneum beetles. This study examined the quantitative effects of H. diminuta on the production of aggregation pheromone and 3 defensive compounds in male T. castaneum beetles, using 2 wild-caught, geographically distinct T. castaneum strains. For the c-Madison strain, infected beetles exhibited a 2- to 22-fold increase in defensive compounds; conversely, no changes were observed in strain c-Africa. Parasite infection did not significantly influence aggregation pheromone secretion in either strain. Because defensive compounds function as repellents or deterrents to other insects, parasite-induced increases in the secretion of defensive compounds may be a physiologic clue for the behavioral changes in infected T. castaneum beetles. Significant among-strain variation in defensive compound production seen in infected beetles suggests that caution is needed before generalizing about changes in volatile production and in host behavior induced by a parasite.

Investigation of the effect of female larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), and their residues on the production of aggregation pheromone by males

The rate of production of aggregation pheromone by male larger grain borer beetles, Prostephanus truncatus (Horn), is greatly reduced in the presence of live, conspecific female beetles. A similar effect is observed in the absence of live female beetles when males are placed on maize that was previously infested with males and females, suggesting that it is due to some chemical residue left by the females. This was shown to persist for at least 15 days, to be involatile and not perceived by receptors on the antennae of the males. Attempts to extract the chemical(s) responsible and transfer it to a new substrate gave variable results. Extraction of previously-infested maize with hexane, ether, dichloromethane, butanone or water under different conditions probably did not remove the suppression effect, but Soxhlet extraction with methanol did. However, when the resulting extract was recoated onto various substrates, no reduction in pheromone production by males could be demonstrated, suggesting that the methanol is extracting and/or destroying the chemical(s) responsible.

Role of chirality in olfactory-directed behavior: Aggregation of pine engraver beetles in the genusIps (Coleoptera: Scolytidae)

There has been a renaissance of interest in the significance of enantiomeric composition in biological systems. Three chiral monoterpene alcohol aggregation pheromone components (ipsenol, ipsdienol, andcis-verbenol) commonly isolated from engraver beetles (Ips spp.) provide a paradigm for this theme as it relates to olfactory-guided insect behavior. The literature pertaining to this system is reviewed and the effects of the enantiomeric composition of these semiochemicals on theIps spp. community is explored on two trophic levels. Hypotheses generated from the well-studied aggregation pheromone production and response patterns forI. paraconfusus Lanier andI. pini (Say) are generalized to the North American species in the genus. Despite the progress withI. paraconfusus andI. pini, substantial deficiencies exist in our understanding of the role of enantiomeric composition in pheromonal/allomonal effects in different subgeneric groups, in the regulation and mechanisms of stereoselective biosynthesis of the monoterpene alcohols, and in the benefits derived by individual insects that produce relatively large proportions of inactive or interruptive enantiomers with attractive enantiomers.