Characterization of olfactory sensory neurons in the striped ambrosia beetle Trypodendron lineatum

Introduction: The striped ambrosia beetle Trypodendron lineatum (Coleoptera, Curculionidae, Scolytinae) is a major forest pest in the Holarctic region. It uses an aggregation pheromone and host and non-host volatiles to locate suitable host trees, primarily stressed or dying conifer trees. The beetles bore into the xylem and inoculate spores of their obligate fungal mutualist Phialophoropsis ferruginea inside their excavated egg galleries, with the fungus serving as the main food source for the developing larvae. Olfactory sensory neuron (OSN) responses to pheromones and host volatiles are poorly understood in T. lineatum and other ambrosia beetles, and nothing is known about potential responses to fungal volatiles. Methods: We screened responses of OSNs present in 170 antennal olfactory sensilla using single sensillum recordings (SSR) and 57 odor stimuli, including pheromones, host and non-host compounds, as well as volatiles produced by P. ferruginea and fungal symbionts of other scolytine beetles. Results and Discussion: Thirteen OSN classes were characterized based on their characteristic response profiles. An OSN class responding to the aggregation pheromone lineatin was clearly the most abundant on the antennae. In addition, four OSN classes responded specifically to volatile compounds originating from the obligate fungal mutualist and three responded to non-host plant volatiles. Our data also show that T. lineatum has OSN classes tuned to pheromones of other bark beetles. Several OSN classes showed similar response profiles to those previously described in the sympatric bark beetle Ips typographus, which may reflect their shared ancestry.

Sex Pheromone of the Introduced Pine Sawfly, Diprion similis, Revisited to Define a Useful Monitoring Lure: Deviating Chiral Composition and Behavioural Responses Compared to Earlier Reports

Extracts of Diprion similis females contained about 15 ng of the sex pheromone precursor 3,7-dimethylpentadecan-2-ol per female. After derivatisation with (S)-2-acetoxypropanoyl chloride, we found that the major stereoisomer in the extract was (2S,3R,7R)-3,7-dimethylpentadecan-2-ol. Small amounts of other stereoisomers of 3,7-dimethylpentadecan-2-ol were also identified in the extract, namely 1% of (2R,3S,7S), 0.3% (2R,3R,7R) and 0.4% of (2R,3R,7S). An unknown fifth substance showed a very similar spectrum to 3,7-dimethylpentadecan-2-ol, both in SIM and full scan mode. None of the earlier suggested behavioural synergistic isomers ((2S,3S,7S), (2S,3S,7R) and (2S,3R,7S)) were detected in the extracts. In field tests in Ontario, Canada, the earlier identified main pheromone component, viz. the propanoate of (2S,3R,7R)-3,7-dimethylpentadecan-2-ol, was tested alone and in combination with other stereoisomers, earlier reported to be synergistic. No synergistic effects were detected and the threo four-isomer blend was as attractive as the pure main compound. Thus, one of the few examples of a diprionid sawfly using more than one substance in its sex pheromone could not be confirmed. The results also suggest that monitoring programs can use the more easily synthesized threo-blend without losing efficiency. Furthermore, the study suggests that other diprionid pheromones may benefit from a reinvestigation, to clarify possible synergistic effects of stereoisomers.

Defense of Scots pine against sawfly eggs (Diprion pini) is primed by exposure to sawfly sex pheromones

Plants respond to insect infestation with defenses targeting insect eggs on their leaves and the feeding insects. Upon perceiving cues indicating imminent herbivory, such as damage-induced leaf odors emitted by neighboring plants, they are able to prime their defenses against feeding insects. Yet it remains unknown whether plants can amplify their defenses against insect eggs by responding to cues indicating imminent egg deposition. Here, we tested the hypothesis that a plant strengthens its defenses against insect eggs by responding to insect sex pheromones. Our study shows that preexposure of Pinus sylvestris to pine sawfly sex pheromones reduces the survival rate of subsequently laid sawfly eggs. Exposure to pheromones does not significantly affect the pine needle water content, but results in increased needle hydrogen peroxide concentrations and increased expression of defense-related pine genes such as SOD (superoxide dismutase), LOX (lipoxygenase), PAL (phenylalanine ammonia lyase), and PR-1 (pathogenesis related protein 1) after egg deposition. These results support our hypothesis that plant responses to sex pheromones emitted by an herbivorous insect can boost plant defensive responses to insect egg deposition, thus highlighting the ability of a plant to mobilize its defenses very early against an initial phase of insect attack, the egg deposition.

Characterization of olfactory sensory neurons in the red clover seed weevil, Protapion trifolii (Coleoptera: Brentidae) and comparison to the closely related species P. fulvipes

Protapion trifolii and P. fulvipes (Coleoptera: Brentidae) are major pests in European clover seed production. Previous studies have reported a high host plant fidelity of these weevils for red and white clover species, respectively, driven by host plant olfactory cues. Given the specific host preferences observed in these weevils, we aimed to elucidate to which extent such selectivity is reflected in their peripheral olfactory systems. Using an electrophysiological approach, we performed the first functional characterisation of olfactory sensory neurons (OSNs) in P. trifolii to a panel of volatile compounds emitted by red clover plants, and compared the results with the reported OSN types of P. fulvipes. Nineteen OSN classes were characterized in P. trifolii, with the majority of these neurons responding strongly to common volatiles released by the host plant. Based on response profiles, eight of these OSN classes have clear matches to OSN classes in P. fulvipes. The OSN colocalisation patterns and antennal frequency of these classes are similar in the two species. Additionally, the responses of these OSNs are generally highly conserved in the two species, with clear response shifts only revealed for two of the OSN classes. These response shifts in combination with additional response dissimilarities for compounds that vary in abundance between red and white clover plants may underlie the species-specific host preferences. Further behavioural and field experiments should focus on these differentially detected compounds to elucidate their potential role in host selection and use in semiochemical-based control of these pests.

Functional characterization of odorant receptors from Lampronia capitella suggests a non-ditrysian origin of the lepidopteran pheromone receptor clade

The odorant receptors (ORs) of insects are crucial for host and mate recognition. In moths (Lepidoptera), specialized ORs are involved in male detection of the sex pheromone produced by females. Most moth sex pheromones are C₁₀-C₁₈ acetates, alcohols, and aldehydes (Type I pheromones), and most pheromone receptors (PRs) characterized to date are from higher Lepidoptera (Ditrysia), responding to these types of compounds. With few exceptions, functionally characterized PRs fall into what has been called the "PR-clade", which also contains receptors that have yet to be characterized. While it has been suggested that moth PRs have evolved from plant odor-detecting ORs, it is not known when receptors for Type I pheromones arose. This is largely due to a lack of functionally characterized PRs from non-ditrysian Lepidoptera. The currant shoot borer moth, Lampronia capitella (Prodoxidae), belongs to a non-ditrysian lineage, and uses Type I pheromone compounds. We identified 53 ORs from antennal transcriptomes of this species, and analyzed their phylogenetic relationships with known lepidopteran ORs. Using a HEK293 cell-based assay, we showed that three of the LcapORs with male-biased expression (based on FPKM values) respond to Type I pheromone compounds. Two of them responded to pheromone components of L. capitella and one to a structurally related compound. These PRs are the first from a non-ditrysian moth species reported to respond to Type I compounds. They belong to two of the more early-diverging subfamilies of the PR-clade for which a role in pheromone detection had not previously been demonstrated. Hence, our definition of the monophyletic lepidopteran PR-clade includes these receptors from a non-ditrysian species, based on functional support.

Diversity of olfactory structures: A comparative study of antennal sensilla in Trichoptera and Lepidoptera

The antenna is the main sensory organ of insects, housing different types of sensilla dedicated to detect chemical cues, motion, humidity and temperature. Sensilla are divided into different types based on their wall structure and morphology. Among the olfactory sensilla, there is an enormous variation in the numbers and morphological types present in different insect taxa. The reasons for this variation remain obscure, though there may be a correlation between sensillum morphology and the characteristics of the stimulus that the olfactory sensory neurons inside the sensillum detect. Here, we report the first comparative analysis of the morphology and ultrastructure of sensilla from Rhyacophila nubila (Rhyacophilidae: Trichoptera) and three species of Lepidoptera, Eriocrania semipurpurella (Eriocraniidae), Lampronia capitella (Prodoxidae), and Bicyclus anynana (Nymphalidae), which use different chemical types of pheromones. Our results, together with a thorough literature review, suggest a shift in major types of olfactory sensilla, from a high proportion of sensilla placodea or auricillica in Trichoptera and the most basal moth lineages (including Eriocraniidae), respectively, to sensilla trichodea in the more derived Lepidoptera (including Prodoxidae and the Ditrysia clade), which parallels the change in the types of sex pheromones used.

Characterization of Odorant Receptors from a Non-ditrysian Moth, Eriocrania semipurpurella Sheds Light on the Origin of Sex Pheromone Receptors in Lepidoptera

Pheromone receptors (PRs) are essential in moths to detect sex pheromones for mate finding. However, it remains unknown from which ancestral proteins these specialized receptors arose. The oldest lineages of moths, so-called non-ditrysian moths, use short-chain pheromone components, secondary alcohols, or ketones, so called Type 0 pheromones that are similar to many common plant volatiles. It is, therefore, possible that receptors for these ancestral pheromones evolved from receptors detecting plant volatiles. Hence, we identified the odorant receptors (ORs) from a non-ditrysian moth, Eriocrania semipurpurella (Eriocraniidae, Lepidoptera), and performed functional characterization of ORs using HEK293 cells. We report the first receptors that respond to Type 0 pheromone compounds; EsemOR3 displayed highest sensitivity toward (2S, 6Z)-6-nonen-2-ol, whereas EsemOR5 was most sensitive to the behavioral antagonist (Z)-6-nonen-2-one. These receptors also respond to plant volatiles of similar chemical structures, but with lower sensitivity. Phylogenetically, EsemOR3 and EsemOR5 group with a plant volatile-responding receptor from the tortricid moth Epiphyas postvittana (EposOR3), which together reside outside the previously defined lepidopteran PR clade that contains the PRs from more derived lepidopteran families. In addition, one receptor (EsemOR1) that falls at the base of the lepidopteran PR clade, responded specifically to β-caryophyllene and not to any other additional plant or pheromone compounds. Our results suggest that PRs for Type 0 pheromones have evolved from ORs that detect structurally-related plant volatiles. They are unrelated to PRs detecting pheromones in more derived Lepidoptera, which, in turn, also independently may have evolved a novel function from ORs detecting plant volatiles.

Challenges of pheromone-based mating disruption of Cydia strobilella and Dioryctria abietella in spruce seed orchards

Seed orchards function as the primary source of high-quality seeds for reforestation in many European countries, but their seed yields can be severely reduced due to seed- and cone-feeding insects. We evaluated various parameters of pheromone-based mating disruption for control of the moths Cydia strobilella and Dioryctria abietella, which are major pests in European Picea abies seed orchards. We applied different types of pheromone dispensers (rubber septa or wax droplets) at different densities and heights, and with different amounts of active components, covering whole orchards or part of an orchard. The efficacy of the treatment was evaluated by analysing male captures in pheromone-baited assessment traps, and presence of larvae in cones. A dramatic decrease (94-100%) in capture of males in traps occurred in all pheromone-treated plots compared to control plots for both moth species. In contrast, a subsequent reduction in larval numbers in cones was only achieved when wax droplets were used as the dispensing formulation at high density and at the highest pheromone dose tested, and only in half of the trials for each pest species. Electrophysiological recordings using antennae of male C. strobilella indicated elevated pheromone concentrations in a treated plot versus a control plot. Our results show that mating disruption has potential to reduce cone damage in spruce seed orchards caused by C. strobilella and D. abietella, but optimisation of the technique is required to achieve consistent and efficient population suppression of these pests.

Visual cues of oviposition sites and spectral sensitivity of Cydia strobilella L

We investigated whether the spruce seed moth (Cydia strobilella L., Tortricidae: Grapholitini), an important pest in seed orchards of Norway spruce (Picea abies (L.) Karst.), can make use of the spectral properties of its host when searching for flowers to oviposit on. Spectral measurements showed that the flowers, and the cones they develop into, differ from a background of P. abies needles by a higher reflectance of long wavelengths. These differences increase as the flowers develop into mature cones. Electroretinograms (ERGs) in combination with spectral adaptation suggest that C. strobilella has at least three spectral types of photoreceptor; an abundant green-sensitive receptor with maximal sensitivity at wavelength λ_max=526nm, a blue-sensitive receptor with λ_max=436nm, and an ultraviolet-sensitive receptor with λ_max=352nm. Based on our spectral measurements and the receptor properties inferred from the ERGs, we calculated that open flowers, which are suitable oviposition sites, provide detectable achromatic, but almost no chromatic contrasts to the background of needles. In field trials using traps of different spectral properties with or without a female sex pheromone lure, only pheromone-baited traps caught moths. Catches in baited traps were not correlated with the visual contrast of the traps against the background. Thus, visual contrast is probably not the primary cue for finding open host flowers, but it could potentially complement olfaction as a secondary cue, since traps with certain spectral properties caught significantly more moths than others.

Attraction of the Larval Parasitoid Spintherus dubius (Hymenoptera: Pteromalidae) to Feces Volatiles from the Adult Apion Weevil Host

The behavioral response of the larval parasitoid Spintherus dubius (Hymenoptera: Pteromalidae) to volatile compounds derived from its Apion weevil hosts was investigated in two-choice bioassays. Odor source candidates were the larval and adult stages of weevils, clover flowers, and feces from adult weevils. Despite S. dubius being a larval parasitoid, the odor of weevil larvae isolated from the clover flowers was not attractive to female parasitoids. Surprisingly, S. dubius females were instead attracted by the odor from the feces of adult weevils. The female parasitoids were similarly attracted to the feces produced by the two main hosts, the red clover weevil (A. trifolii) and the white clover weevil (A. fulvipes). Chemical analysis of the volatile composition of feces produced by the two hosts revealed qualitatively similar odor profiles, correlating with the observed attraction by the parasitoid towards both odor sources. Some of the identified volatile compounds are commonly present in clover plant headspace fractions and may function as a kairomone to facilitate orientation by S. dubius to Apion-infested clover flowers. Larval and adult weevils were not attractive for parasitoid females, whereas, for the white clover weevil-plant association, infested flowers were highly attractive. These data show the use by the clover weevil parasitoid of an alternative source of olfactory information for locating its host.

Enhanced science-stakeholder communication to improve ecosystem model performances for climate change impact assessments

In recent years, climate impact assessments of relevance to the agricultural and forestry sectors have received considerable attention. Current ecosystem models commonly capture the effect of a warmer climate on biomass production, but they rarely sufficiently capture potential losses caused by pests, pathogens and extreme weather events. In addition, alternative management regimes may not be integrated in the models. A way to improve the quality of climate impact assessments is to increase the science-stakeholder collaboration, and in a two-way dialog link empirical experience and impact modelling with policy and strategies for sustainable management. In this paper we give a brief overview of different ecosystem modelling methods, discuss how to include ecological and management aspects, and highlight the importance of science-stakeholder communication. By this, we hope to stimulate a discussion among the science-stakeholder communities on how to quantify the potential for climate change adaptation by improving the realism in the models.

Field Abundance Patterns and Odor-Mediated Host Choice by Clover Seed Weevils, Apion fulvipes and Apion trifolii (Coleoptera: Apionidae)

The clover seed weevils Apion fulvipes Geoffroy, 1785 and Apion trifolii L., 1768 (Coleoptera: Apionidae) cause major losses to seed production of white clover (Trifolium repens L.) and red clover (Trifolium pratense L.), respectively. Clover is important as animal forage and an alternative to inorganic fertilizers. Because clover is mainly pollinated by bees, the use of insecticides in management of these weevils is discouraged. To gain basic knowledge for development of alternative management strategies, we investigated weevil field abundance over two growing seasons, as well as feeding and olfactory host preferences by A. fulvipes and A. trifolii. Field trap catches in southern Sweden revealed that white clover was dominated by A. fulvipes and red clover by A. trifolii. For both weevil species, female catches were positively correlated to the number of clover buds and flowers in the field. In feeding and olfactory bioassays, females of A. fulvipes and A. trifolii showed a preference for T. repens and T. pratense, respectively. However, the feeding preference was lost when the antennae were removed, indicating a significant role of olfaction in host choice. Male weevils of both species did not show clear olfactory or feeding preferences for host plant species. The field study and laboratory bioassays demonstrate that, at least for female weevils, olfaction is important for selection of host plants. We discuss these novel results in the context of managing these important pests of clover by exploiting olfaction and behavioral attraction to host plant volatiles.

(Z)-3-Dodecenoic acid is the main component of full-body n-hexane extracts from two Acacia gall-inducing thrips (Thysanoptera) and may function as an alarm pheromone

A major interest in the gall-inducing thrips of Australia began with the discovery that some species have eusocial colonies. The origin of social castes remains one of the outstanding questions in evolutionary biology. The inference of the ancestral stage from study of solitary species is important to understanding the evolutionary history of semiochemicals in social species. Here we investigated two solitary species, Kladothrips nicolsoni and K. rugosus. Whole body extracts revealed that (Z)-3-dodecenoic acid, here reported for the first time in a thrips species, is the main component. (Z)-3-Dodecenoic acid and (E)-3-dodecenoic acid were synthesized in high stereoisomeric purity (> 99.8%) and exposed to K. nicolsoni 2nd-instar larvae in a contact chemoreception bioassay to test for potential bioactivity. Both isomers decreased the average time spent in the treated area per entry suggesting repellence at the tested dose. (Z)-3-Dodecenoic acid may function as alarm pheromone. (E)-3-Dodecenoic acid increased also the absolute change in direction of larvae compared to an n-hexane control and could potentially function as a repellent.

The Sex Pheromones of Two Pine Sawfly Species, Gilpinia frutetorum and Gilpinia socia: Chemical Identification, Synthesis and Biological Activity

3,7-Dimethylpentadecan-2-ol and 3-methylpentadecan-2-ol were identified in female whole body extracts from the two pine sawfly species Gilpinia frutetorum and Gilpinia socia. This is the first observation of 3-methylpentadecan-2-ol in extracts of a female pine sawfly species. Synthetic and highly pure stereoisomers of 3,7-dimethylpentadecan-2-ol and 3-methylpentadecan-2-ol were used to verify that the (2S,3R,7R)-isomer of 3,7-dimethylpentadecan- 2-ol and (2S,3R)-3-methylpentadecan-2-ol were present in the extracts. The four stereoisomers of 3-methylpentadecan-2-ol and their biologically active esters were produced via chemoenzymatic methods and the synthesis is described in detail. Male G. socia antennae responded strongly in EAG recordings to the (2S,3R)-isomer of the acetate and propionate of 3-methylpentadecan-2-ol. Male antennae of both G. frutetorum and G. socia also responded to the (2S,3R,7R)- and (2S,3R,7S)-acetates of 3,7-dimethylpentadecan-2-ol

Identification, synthesis, and behavioral activity of 5,11-dimethylpentacosane, a novel sex pheromone component of the greater wax moth, Galleria mellonella (L.)

The greater wax moth, Galleria mellonella (L.), is a serious and widespread pest of the honeybee, Apis mellifera L. In contrast to most moths, for which long-range mate finding is mediated by female-produced sex pheromones, G. mellonella males attract conspecific females over long distances by emitting large amounts of a characteristic scent in combination with bursts of ultrasonic calls. The male scent for this species was previously identified as a blend of nonanal and undecanal. When these compounds were bioassayed, characteristic short-range sexual behavior, including wing fanning, was triggered in conspecific females, but the aldehyde blend failed to elicit attraction over longer distances. We identified, via analysis and synthesis, a third male-specific compound, 5,11-dimethylpentacosane. We show that it acts as a behavioral synergist to the aldehydes. In wind tunnel experiments, very few female moths responded to the aldehyde blend or to 5,11-dimethylpentacosane tested separately, but consistently showed orientation and source contact when a combination of all three compounds was applied. The level of attraction to the three-component mixture was still lower than that to male extract, indicating that the composition of compounds in the synthetic blend is suboptimal, or that additional pheromone components of G. mellonella are yet to be identified. The identification of 5,11-dimethylpentacosane is an important step for the development of an efficient long-range attractant that will be integrated with other environmentally safe strategies to reduce damage to beehives caused by wax moths.

Effective attraction radius : A method for comparing species attractants and determining densities of flying insects

The catches of bark beetles (Coleoptera: Scolytidae) were compared between attractive traps releasing semiochemicals and passive traps (cylindrical sticky screens hung, at 10 heights of 0.7-11.5 m, on poles). A central attractive-trap pole was surrounded by three passive-trap poles spaced 50 or 100 m away at the apices of an equilateral triangle. The catches ofTomicus piniperda and other scolytid species on the attractive-trap pole baited with host monoterpenes, or the catches ofIps typographus attracted to synthetic pheromone, were compared to passive trap catches in a Scots pine forest or in a Norway spruce clear-cut, respectively. Information about flight height distributions of the above scolytid species, andHylurgops palliatus, Cryphalus abietis, Pityogenes chalcographus, P. quadridens, P. bidentatus, andTrypodendron domesticum were obtained on the passive and attractive trap poles. A new method is presented for determining the densities of flying insects based on the passive trap's dimensions and catch, duration of test, and speed of insect. Also, a novel concept, the effective attraction radius (EAR), is presented for comparing attractants of species, which is independent of insect density, locality, or duration of test. The EAR is obtained by the ratio of attractive and passive trap catches and the dimensions of the passive trap, and thus should correlate positively with the strength of the attractant and the distance of attraction. EARs are determined from catch data ofT. piniperda andI. typographus as well as from the data of previous investigations on the same or other bark beetles.

Field response of the pine sawflyNeodiprion sertifer to controlled release of diprionyl acetate, diprionyl propionate andtrans-perillenal

Two dispenser types for pine sawfly (Hymenoptera: Diprionidae) pheromones-glass capillaries and dental cotton rolls-are described, and release rates reported. Glass capillaries of different diameters were used in field tests to determine dose-response relationships of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate (diprionyl acetate), diprionyl propionate, andtrans-perillenal on the trap catch of maleNeodiprion sertifer. A linear relationship between the logarithm of the capillary cross-sectional area and the logarithm of the release rate was found. However, capillaries of the same diameter could vary in the amount released by as much as a factor of 10. Both the acetate and propionate were attractive alone, but no synergistic effect was found.trans-Perillenal did not show any behavioral activity. Dental cotton rolls have been used extensively in diprionid pheromone research without knowledge about release rates. The release rate from rolls loaded with different amounts of diprionyl acetate was determined by extracting rolls after different times under constant temperature and wind conditions or after use in field tests. Quantification of diprionyl acetate was done on GC. The release rate was found to be proportional to the amount applied over several orders of magnitude, and persisted for several weeks. Capillaries and rolls with similar release rates caught similar numbers of sawflies.

Specificity and sensitivity of plant odor-detecting olfactory sensory neurons in Ctenarytaina eucalypti (Sternorrhyncha: Psyllidae)

The blue gum psyllid, Ctenarytaina eucalypti (Sternorrhyncha: Psyllidae), is an economic threat to Eucalyptus subgenus Symphyomyrtus plantations worldwide. To date, no generally applicable control method is available and the potential for semiochemical-based monitoring or control methods has not yet been investigated. Hence, we conducted the first study on the olfactory sense of C. eucalypti, investigating the specificity and sensitivity of its olfactory sensory neurons (OSNs) to host plant volatiles using single sensillum recordings (SSR). Synthetic compounds were selected from published identifications of Eucalyptus volatiles and after analysis of headspace collections from Eucalyptus cordata. The antenna of C. eucalypti carries four cavities containing olfactory sensilla (S1-S4). Our recordings revealed that each of these sensilla houses three OSNs that could be distinguished electrophysiologically based on spike amplitude differences (A, B, and C neuron with large, intermediate, and small amplitude, respectively). The A neuron in sensillum S1 responded primarily to β-caryophyllene and weaker to β-ocimene, whereas the accompanying B-neuron responded strongly and very specifically to linalool. Furthermore, the B-neuron in both S2 and S3 responded strongly to 1-hexanol, Z3-hexenol, and Z3-hexenyl acetate. OSNs in S4 responded only weakly to a few of the synthetic compounds. Response thresholds in strongly responding OSNs to putative key compounds were close to the 1ng dose on the filter paper and responses exhibited a phasic-tonic profile irrespective of compound dose. C. eucalypti may use the physiologically active compounds for long-range host finding. Future laboratory and field experiments will reveal whether plant volatiles can be used in the management and monitoring of C. eucalypti.

Characterization of olfactory sensory neurons in the white clover seed weevil, Apion fulvipes (Coleoptera: Apionidae)

Seed-eating Apion weevils (Coleoptera: Apionidae) cause large economic losses in white and red clover seed production across Europe. Monitoring and control of clover weevils would be facilitated by semiochemical-based methods. Until now, however, nothing was known about physiological or behavioral responses to semiochemicals in this insect group. Here we analyzed the antenna of the white clover (Trifolium repens L.) specialist Apion fulvipes Geoffroy with scanning electron microscopy, and used single sensillum recordings with a set of 28 host compounds to characterize 18 classes of olfactory sensory neurons (OSNs). Nine of the OSN classes responded strongly to synthetic compounds with high abundance in clover leaves, flowers, or buds. Eight classes responded only weakly to the synthetic stimuli, whereas one collective class responded exclusively to volatiles released from a crushed clover leaf. The OSNs showed a remarkable degree of specificity, responding to only one or a few chemically related compounds. In addition, we recorded a marked difference in the temporal dynamics of responses between different neurons, compounds, and doses. The identified physiologically active compounds will be screened for behavioral activity, with the ultimate goal to develop an odor-based control strategy for this pest.

First Report of "Candidatus Liberibacter solanacearum" Associated with Psyllid-Affected Carrots in Sweden

Carrot (Daucus carota) plants with symptoms resembling those associated with the carrot psyllid Trioza apicalis and the bacterium "Candidatus Liberibacter solanacearum" (1-4) were observed in 70% of commercial fields in southern Sweden in August 2011, with approximately 1 to 45% symptomatic plants per field. T. apicalis, a pest of carrot in northern and central Europe, including Sweden, can cause as much as 100% crop loss and is associated with "Ca. L. solanacearum" (1-4). Symptoms on affected plants include leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots (3). Carrot plant and psyllid samples were collected from fields in the province of Halland. Total DNA was extracted from petiole and root tissues of 33 symptomatic and 16 asymptomatic plants (cvs. Nevis and Florida), with the cetyltrimethylammonium bromide (CTAB) buffer extraction method (2,3). DNA was also extracted from 155 psyllids (3). DNA samples were tested by PCR using primer pairs OA2/OI2c (5''-GCGCTTATTTTTAATAGGAGCGGCA-3'/5'-GCCTCGCGACTTCGCAACCCAT-3') and CL514F/R (5'-CTCTAAGATTTCGGTTGGTT-3'/5'-TATATCTATCGTTGCACCAG-3'), to amplify a portion of 16S rDNA and rplJ/rplL ribosomal protein genes, respectively, of "Ca. L. solanacearum" (2,3). A 1,168-bp 16S rDNA fragment was detected in the DNA from all 33 symptomatic and two asymptomatic plants, and a 668-bp rplJ/rplL fragment was amplified from the DNA of all 33 symptomatic and four asymptomatic plants, indicating the presence of liberibacter. DNA from 23 and 49 psyllid samples yielded similar amplicons with OA2/OI2c and CL514F/R primer pairs, respectively. Amplicons from the DNA of four carrot roots and three T. apicalis with each primer pair were cloned (pCR2.1-TOPO; Invitrogen, Carlsbad, CA) and three clones of each of the 14 amplicons were sequenced (MCLAB, San Francisco, CA). BLAST analysis of the 16S rDNA consensus sequences from carrot (GenBank Accession No. JN863095) and T. apicalis (GenBank Accession No. NJ863096) showed 100% identity to those of "Ca. L. solanacearum" previously amplified from carrot (GU373048 and GU373049) and T. apicalis (GU477254 and GU477255) from Finland (2,3). The rplJ/rplL consensus sequences from carrot (GenBank Accession No. JN863093) and T. apicalis (GenBank Accession No. JN863094) were 99% identical to the sequences of rplJ/rplL "Ca. L. solanacearum" ribosomal protein gene from carrots in Finland (GU373050 and GU373051). To our knowledge, this is the first report of "Ca. L. solanacearum" associated with carrot and T. apicalis in Sweden. The disease associated with this bacterium caused millions of dollars in losses to potato and several other solanaceous crops in North and Central America and New Zealand (1). This plant pathogen is also associated with significant economic damage to carrot crops observed in Finland (2,3). References: (1) J. E. Munyaneza. Southwest. Entomol. 35:471, 2010. (2) J. E. Munyaneza et al. Plant Dis. 94:639, 2010. (3) J. E. Munyaneza et al. J. Econ. Entomol. 103:1060, 2010. (4) A. Nissinen et al. Entomol. Exp. Appl. 125:277, 2007.

Flagellar sensilla of the eusocial gall-inducing thrips Kladothrips intermedius and its kleptoparasite, Koptothrips dyskritus (Thysanoptera: Phlaeothripinae)

Insect antennal flagella host a multitude of sensory organs fulfilling different functions. Chemoreception, for example, is essential for insects in many contexts. Both olfaction and contact chemoreception are involved in host-plant selection, as well as in the integrity of insect societies, especially for nestmate recognition. Kladothrips intermedius is a eusocial gall-inducing thrips with two castes: dispersers and soldiers. Koptothrips dyskritus is a specialist in invading Kl. intermedius galls, killing the occupants, and thereby gaining the food and shelter offered by galls. In this study, we compared the morphology and ultrastructure of the flagellar sensilla of Kl. intermedius and Ko. dyskritus via scanning and transmission electron microscopy in order to facilitate future investigations of their sensory ecology, with an emphasis on chemical ecology. The two species show a very similar sensillar array. There are a few mechanosensory trichoid and a second type of mechanosensory sensilla, thermo-hygroreceptive sensilla, olfactory single-walled basiconic and double-walled coeloconic sensilla as well as contact chemoreceptive chaetic sensilla. The latter are sexually dimorphic in Kl. intermedius. Dispersers and soldiers of Kl. intermedius do not present noteworthy morphological differences, but the ultrastructural investigations revealed that soldiers have fewer ORNs, possibly an adaptation to their gall-cloistered lifestyle.

Field response of male pine sawflies, Neodiprion sertifer (Diprionidae), to sex pheromone analogs in Japan and Sweden

The pine sawfly Neodiprion sertifer (Geoffroy) uses the acetate or propionate of (2S,3S,7S)-3,7-dimethyl-2-pentadecanol (diprionol) as pheromone components, with the (2S,3R,7R)-isomer being antagonistic, synergistic, or inactive according to the population tested. In this study, we tested the attraction of males to the acetates of three analogs of diprionol, each missing one methyl group, viz. (2S,7S)-7-methyl-2-pentadecanol, (2S,6S)-2,6-dimethyl-1-tetradecanol, and (2S,3S)-3-methyl-2-pentadecanol. None of the analogs alone, or in combination with diprionol acetate, was attractive in Sweden, even at 100 times the amount of diprionol acetate attractive to N. sertifer. In Japan, the acetate of (2S,3S)-3-methyl-2-pentadecanol attracted males when tested in amounts 10-20 times higher than the acetate pheromone component. The acetate esters of the (2S,3R)-analog and the (2S,3R,7R)-isomer of diprionol also were tested in combination with the pheromone compound (acetate ester). Both compounds caused an almost total trap-catch reduction in Sweden, whereas in Japan they appear to have relatively little effect on trap capture when added to diprionol acetate. Butyrate and iso-butyrate esters of diprionol were unattractive to N. sertifer in Sweden. In summary, there exists geographic variation in N. sertifer in responses to both diprionyl acetate and some of its analogs.

Functional characteristics of a tiny but specialized olfactory system: olfactory receptor neurons of carrot psyllids (Homoptera: Triozidae)

With only approximately 50 olfactory receptor neurons (ORNs), the carrot psyllid Trioza apicalis (Homoptera: Psylloidea) may have the smallest olfactory system described in adult Neopteran insects. Using single sensillum recordings (SSR) and gas chromatograph-linked SSR, we characterized 4 olfactory sensilla forming a distinct morphological type, which together house approximately 25% of all ORNs. We recorded responses to extracts and single constituents from Daucus carota ssp. sativus, from the conifers Picea abies, Pinus sylvestris, and Juniperus communis, as well as from male and female T. apicalis. Receptor neurons were highly selective; only 9 compounds in total elicited repeatable responses, and each neuron responded to at most 3 individual compounds. Chemical profiles of carrot and conifers showed significant overlap, with 4 out of 9 electrophysiologically active compounds occurring in more than one type of extract, but a carrot-specific compound elicited the most repeated responses. We identified 4 tentative neuron classes and found a rather high degree of neuronal redundancy, with 1 neuron class present in 3 and another present in all 4 of the sensilla, respectively.

Aglomerular hemipteran antennal lobes--basic neuroanatomy of a small nose

We have compared the basic organization of the primary olfactory centre, the antennal lobe (AL), in 4 hemipteran species representing the 2 major lineages in this order. The Homoptera were represented by the psyllid Trioza apicalis and its aphid relatives the grain aphid Sitobion avenae Fabricius and the rose-grain aphid Metopolophium dirhodum Walker, whereas the Heteroptera were represented by the pentatomid stink bug Euschistus heros Fabricius. The olfactory systems of psyllids and aphids are generally very small, with low numbers of afferents in comparison to other insect groups, and the smallest described so far belongs to T. apicalis, comprising less than 50 olfactory receptor neurons (ORNs). Originally, we tried to estimate numbers of olfactory glomeruli in the AL of T. apicalis, which in insects generally correspond closely to the number of different types of ORNs. Neither immunocytochemical staining nor anterograde staining of ORNs revealed any glomerular structures in the ALs of T. apicalis or the 2 aphids that were included for comparison. In contrast, the ALs of the pentatomid stink bug E. heros displayed numerous distinct and well-delineated glomeruli, showing that aglomerular ALs are not typical of all insects within the order Hemiptera. Glomeruli are hallmark features of olfactory lobes in many different phyla, and the absence of glomerular structures in psyllids and aphids appears to be unique in insects that depend on olfactory orientation.

Evaluation of long-term mating disruption of Ephestia kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae) in indoor storage facilities by pheromone traps and monitoring of relative aerial concentrations of pheromone

The potential for pheromone-based mating disruption (MD) of Ephestia kuehniella (Walker) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) was investigated in two flour mills and a pet food distributor. Plastic sachets emitting 2-3 mg per d (Z,E)-9,12-tetradecadienyl acetate, the major pheromone component of both moth species, were used as MD dispensers, which were applied in grid systems resulting in one dispenser per 100 m(3) of air volume. Pheromone traps with sticky inserts were used to monitor moth population fluctuations. To monitor pheromone levels in the air before, during, and after the treatment, electroantennographic (EAG) measurements were performed using a portable device. All localities showed decreased trap catches after application of MD. In two localities with low initial population densities, trap catches were reduced immediately after application of MD and remained very low, even several months after the MD treatment was terminated. In contrast, in a locality with a higher initial population density the reduction in trap catches was slower, and trap catches increased again soon after the termination of the MD treatment. Electrophysiological data showed not only increased aerial levels of pheromone during the treatment period but also levels that were higher than during pretreatment, even 12 mo after removal of MD dispensers. The localities had good ventilation, and the memory effect observed indicates that the pheromone adhered to surfaces that subsequently functioned as secondary dispensers. Customer complaints registered by one of the mills were 49% less in 2004, after 2 yr of MD compared with 2002, the year before the treatments began.

Sex pheromone of the pine sawfly, Gilpinia pallida: chemical identification, synthesis, and biological activity

We present the identification of the sex pheromone in the pine sawfly, Gilpinia pallida, including analysis of the female pheromone content, male antennal response and attraction in the field, and synthesis of the most active pheromone component. Several 3,7-dimethyl-2-alkanols were identified from female whole-body extracts, including some compounds with a 2R configuration. This is the first observation of such compounds in a pine sawfly species. Antennae of male G. pallida responded strongly in electroantennograph (EAG) recordings to the (2S,3R,7R)-isomers of the propionates of 3,7-dimethyl-2-tridecanol, 3,7-dimethyl-2-tetradecanol, and 3,7-dimethyl-2-pentadecanol, as well as to the acetates of the tri- and pentadecanols (the acetate of the tetradecanol was not tested). The propionate of (2S,3R,7R)-3,7-dimethyl-2-tetradecanol caught more males in the field than the corresponding isomer of tri- or pentadecanol. We suggest that the (2S,3R,7R)-isomer of 3,7-dimethyl-2-tetradecanol is likely the main sex pheromone precursor in G. pallida, with a subsidiary role for the (2S,3R,7R)-isomer of the tridecanol. Preparation of highly pure (2R,3R,7R)- and (2S,3R,7R)-stereoisomers of 3,7-dimethyl-2-tetradecanol, including the biological active esters, was performed via chemoenzymatic methods and is described in detail.

Reduction in an almond moth Ephestia cautella (Lepidoptera: Pyralidae) population by means of mating disruption

Pheromone-based mating disruption of the almond moth (Ephestia cautella) (Walk.) (Lepidoptera: Pyralidae) was carried out in a chocolate factory in Sweden. Population monitoring was conducted with pheromone-baited traps and water traps. Pheromone traps showed a 94% catch reduction, and monitoring with water traps showed a significant decrease in total catch (5.0 and 1.6 individuals per trap per week before and during treatment respectively). The significance of the results was tested by fitting the observed data to a first-order autoregressive model. This made it possible to test the data with a 95% confidence interval, comparing trap catches before mating disruption treatment with trapping data during the experiment. It is suggested that this statistical approach may be used more frequently in mating disruption experiments where it is extremely difficult to control external factors and therefore equally difficult to use a comparable control plot to evaluate the treatment.

Sparse sensillar array on Trioza apicalis (Homoptera, Triozidae) antennae-an adaptation to high stimulus levels?

To investigate the morphological basis for olfactory reception in the carrot psyllid (Trioza apicalis) we used scanning and transmission electron microscopy. Our study reveals a very sparse sensillar setup. We identify and describe several different types of single-walled sensilla likely to have an olfactory function, as well as mechanosensory hairs and intracuticular sensilla. A T. apicalis antenna is about 0.6 mm long and has 10 segments. Apically on the flagellum there are two conspicuous multi-porous single-walled bristles. There are six cuticular cavities on the flagellum; two smaller on the apical flagellomere, and four larger located on the lateral side of the antenna on flagellomeres 2, 4, 6 and 7. Each cavity contains two sensilla and there are three varieties of cavity sensilla. Mechano- and chemosensory hairs appear in low numbers on all segments but the third. Carrot psyllids most likely use olfactory cues to locate their rather strongly smelling host plants, and we argue that the low number of olfactory sensilla found in this insect may accommodate high concentrations of odour stimuli. There is no sexual dimorphism in the sensillar setup. In concordance with this, no sex pheromones have been described in the Psylloidea so far.

Electrophysiological and behavioral responses to chocolate volatiles in both sexes of the pyralid moths Ephestia cautella and Plodia interpunctella

Volatiles from chocolate mediate upwind flight behavior in Ephestia cautella and Plodia interpunctella. We used gas chromatography with electroantennographic detection and found 12 active compounds derived from three different chocolate types, i.e., plain, nut-containing, and rum-flavored. Eight of the compounds were identified with mass spectrometry, and the activity of three compounds, ethyl vanillin, nonanal, and phenylacetaldehyde (PAA), was subsequently confirmed in both electrophysiological and behavioral assays. In the electroantennogram experiment, PAA and nonanal were consistently eliciting responses in both species and sexes. Ethyl vanillin was active in males of both species, and also in P. interpunctella females. E. cautella females showed no antennal activity in response to ethyl vanillin. All three volatiles were attractive to E. cautella males and P. interpunctella females in a flight tunnel. E. cautella females were significantly attracted only to ethyl vanillin. P. interpunctella males were attracted to PAA. Ethyl vanillin is a novel insect attractant, whereas both nonanal and phenylacetaldehyde mediate behavior in many insect species. A final experiment revealed that a blend of the three volatiles was required to induce landing in the flight tunnel bioassay, and that the landing rate was dependent on dose. The three-component blend attracted both sexes of P. interpunctella and females of E. cautella, whereas E. cautella males were not attracted.

Capture rates of the European pine sawfly, Neodiprion sertifer, in pheromone traps, with special regard to effects of wind speed

Males of the European pine sawfly, Neodiprion sertifer Geoffr., were marked and released downwind from pheromone traps, baited with 100 micrograms of the sex pheromone (2S,3S,7S)-3,7-dimethyl-2-pentadecyl acetate. Males were released 5 m downwind from one trap, or downwind from five traps, 50 m or 200 m away. The average capture rates after 24 hr were 21.5%, 17.7% and 3.8%, respectively. The capture rate was highest at moderate wind speeds (1-2 m/sec) in the 50 m experiments, whereas it decreased above wind speeds of 1.5 m/sec in the 200 m experiments. With no precipitation and > 13.5 degrees C during overcast, wind speed is presumably the most important climatic factor for N. sertifer males flying upwind to a pheromone source. Travel time, the elapsed time form take-off to landing on the trap, varied considerably, and the shortest recorded travel times were 1, 6 and 45 min for the 5, 50, and 200 m experiments, respectively. The trap efficiency i.e., number of captured males per number of males that landed on the trap, was estimated at 52% in the 5 m experiments. The sampling range after 24 hr was calculated at approximately 400 m by regression analysis. The combination of the males' flight ability during upwind progress and their longevity (12 days), suggests a potentially large seasonal sampling range of the traps used in this study.

Release rates for pine sawfly pheromones from two types of dispensers and phenology of Neodiprion sertifer

Comparisons of release rates, duration in the field, and catch efficiency of polyethylene and cotton roll dispensers for the sex pheromones of sawflies (Hymenoptera: Diprionidae) were conducted. The release rates of the Neodiprion sertifer (Geoffr.) and Diprion pini (L.) sex pheromones, the acetates of pentadecanol and (2S,3S,7S)-3,7-dimethyl (2S,3R,7R)-3,7-dimethyl-2-tridecanol from polyethylene dispensers were measured at different temperatures in the laboratory. The release rates for the substances depended on both the temperature and initial load in the vials. The catch from cotton rolls baited with 100 micrograms of the acetate or propionate of 3,7-dimethyl-2-pentadecanol was compared to the catch from regularly renewed cotton rolls baited with 10 micrograms of the same acetate. The catch was higher for the 100-microgram cotton rolls for, at most, 45 days, and there was no significant differences in catch between the acetate and the propionate. The catch in traps baited with polyethylene or cotton roll dispensers loaded with the acetate of 3,7-dimethyl-2-pentadecanol was compared and showed that cotton roll traps mirrored the decreasing release of the substance rather than the actual flight activity. The length of the flight period of N. sertifer in Sweden, the Czech Republic, Italy, and Greece did not exceed 100 days in any of the countries. By adjusting the initial pheromone load of the polyethylene vials to the expected temperatures, it should be possible to get a constant and sufficiently high release rate during the entire flight period.

Sex pheromone of the pine sawfly Macrodiprion nemoralis (Hymenoptera:Diprionidae): identification of (2S,3R,7R,9S)-3,7, 9-trimethyl-2-tridecanol as the precursor for the active pheromone acetate

The main component of the sex pheromone precursor in females of Macrodiprion nemoralis was identified as a threo-3,7, 9-trimethyl-2-tridecanol isomer, approximately 800 pg per female, by gas chromatography-mass spectrometry. Comparison of mass spectrometric ion chromatograms showed that the natural compound in the female extract has the same retention time and mass spectrum as one of the two synthetic threo peaks. The acetate of the synthetic 16-isomer mixture caught a large number of males in the field, confirming the structure of the active pheromone. Comparison of gas chromatograms of the natural female extract with the eight synthetic threo stereoisomers showed that the pheromone is the (2S,3R,7R, 9S)-stereoisomer of 3,7,9-trimethyl-2-tridecyl acetate.

Sex pheromone perception in male pine sawflies, Neodiprion sertifer (Hymenoptera; Diprionidae)

Electroantennographic and single sensillum recordings were performed on male pine sawfly, Neodiprion sertifer, antennae. Responses to the sex pheromone component (2S, 3S, 7S)- 3,7-dimethyl-2-pentadecenyl (diprionyl) acetate (SSS:OAc), to the behavioral inhibitor (2S, 3R, 7R)-diprionyl acetate (SRR:OAc), to the six other enantiomers of diprionyl acetate, and to the biosynthetic precursor diprionol were recorded. Responses to trans-perillenal, a monoterpene identified in female gland extracts and to (2S, 3S, 7S)-diprionyl propionate (SSS:OPr), a field attractant for N. sertifer and some related sawfly species were also recorded. EAG recordings demonstrated a high antennal sensitivity to SSS:OAc and to SSS:OPr. A somewhat lower response was elicited by SRR:OAc. Single sensillum recordings revealed 8-12 different cells firing in each sensillum, corresponding to the number of cells observed in earlier morphological investigations. Out of these cells all, except one, responded to SSS:OAc and to SSS:OPr. No differences in the response to the two components could be observed. The largest amplitude cell in each sensillum was specifically tuned to the behavioral antagonist, SRR:OAc. The pheromone perception system encountered in male pine sawflies thus differs clearly from that observed in moths.