BackgroundThe European spruce bark beetle, Ips typographus, and the North American mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae: Scolytinae), are severe pests of coniferous forests. Both bark beetle species utilize aggregation pheromones to coordinate mass-attacks on host trees, while odorants from host and non-host trees modulate the pheromone response. Thus, the bark beetle olfactory sense is of utmost importance for fitness. However, information on the genes underlying olfactory detection has been lacking in bark beetles and is limited in Coleoptera. We assembled antennal transcriptomes from next-generation sequencing of I. typographus and D. ponderosae to identify members of the major chemosensory multi-gene families.ResultsGene ontology (GO) annotation indicated that the relative abundance of transcripts associated with specific GO terms was highly similar in the two species. Transcripts with terms related to olfactory function were found in both species. Focusing on the chemosensory gene families, we identified 15 putative odorant binding proteins (OBP), 6 chemosensory proteins (CSP), 3 sensory neuron membrane proteins (SNMP), 43 odorant receptors (OR), 6 gustatory receptors (GR), and 7 ionotropic receptors (IR) in I. typographus; and 31 putative OBPs, 11 CSPs, 3 SNMPs, 49 ORs, 2 GRs, and 15 IRs in D. ponderosae. Predicted protein sequences were compared with counterparts in the flour beetle, Tribolium castaneum, the cerambycid beetle, Megacyllene caryae, and the fruit fly, Drosophila melanogaster. The most notable result was found among the ORs, for which large bark beetle-specific expansions were found. However, some clades contained receptors from all four beetle species, indicating a degree of conservation among some coleopteran OR lineages. Putative GRs for carbon dioxide and orthologues for the conserved antennal IRs were included in the identified receptor sets.ConclusionsThe protein families important for chemoreception have now been identified in three coleopteran species (four species for the ORs). Thus, this study allows for improved evolutionary analyses of coleopteran olfaction. Identification of these proteins in two of the most destructive forest pests, sharing many semiochemicals, is especially important as they might represent novel targets for population control.

Our results demonstrate that a single dedicated olfactory pathway determines oviposition fruit substrate choice. Moreover, our work suggests that the fly's fruit preference--reflected in the functional properties of the identified neuron population--stem from a need to escape parasitism from endoparasitoid wasps.

The family of cecidomyiid midges (Diptera: Cecidomyiidae) exhibits diversified patterns of life history, behavior, host range, population dynamics and other ecological traits. Those that feed on plants include many important agricultural pests; most cultivated plants are attacked by at least one midge species. Several features of the reproductive biology of cecidomyiid midges point to an important role for chemical communication, with this topic last reviewed comprehensively 12 years ago. Here, we review progress on identification of sex pheromones, chemicals involved in location of host plants, the neurophysiology of reception of volatile chemicals, and application of semiochemicals to management of pest species of cecidomyiid midges that has occurred during the last decade. We hope this review will stimulate and sustain further research in these fields.

Coupled gas chromatographic-electroantennographic detection analyses of ovipositor extracts of calling Contarinia nasturtii females revealed two compounds that elicited responses from antennae of male midges. Using synthetic reference samples, these components were identified by gas chromatography mass spectrometry and enantioselective GC as (2S,9S)-diacetoxyundecane and (2S,10S)-diacetoxyundecane. In addition, trace amounts of 2-acetoxyundecane were found in ovipositor extracts, and the (S)-enantiomer was synthesized. When tested in the wind tunnel, a blend of 5 ng (2S,9S)-diacetoxyundecane and 10 ng (2S,10S)-diacetoxyundecane (mimicking the ratio found in the extracts) did not attract any of the males tested, but when 0.1 ng (S)-2-acetoxyundecane was added to the blend, 86.8% of the males were attracted to the bait. Three-component blends with lower or higher relative concentrations than 1% of (S)-2-acetoxyundecane [relative to (2S,10S)-diacetoxyundecane] were less attractive. In a field trapping experiment with released laboratory-reared C. nasturtii adults, traps baited with 500:1000:10 ng of (2S,9S)-diacetoxyundecane/(2S,10S)-diacetoxyundecane/(S)-2-acetoxyundecane applied to rubber septa or dental cotton rolls were tested. Traps without dispensers were used as controls. All three treatments were tested at 20 and 50 cm above ground. The estimated recapture rate was 30-50%, and 81.9% of the recaptured males were caught in traps positioned at 20 cm above ground, and 88.4% in traps with dental cotton rolls as dispensers.

The Hessian fly, Mayetiola destructor Say (Diptera, Cecidomyiidae), is a pest of wheat and belongs to a group of gall-inducing herbivores. This species has a unique life history and several ecological features that differentiate it from other Diptera such as Drosophila melanogaster and blood-feeding mosquitoes. These features include a short, non-feeding adult life stage (1–2 days) and the use of a long-range sex pheromone produced and released by adult females. Sex pheromones are detected by members of the odorant receptor (OR) family within the Lepidoptera, but no receptors for similar long-range sex pheromones have been characterized from the Diptera. Previously, 122 OR genes have been annotated from the Hessian fly genome, with many of them showing sex-biased expression in the antennae. Here we have expressed, in HEK293 cells, five MdesORs that display male-biased expression in antennae, and we have identified MdesOR115 as a Hessian fly sex pheromone receptor. MdesOR115 responds primarily to the sex pheromone component (2S,8E,10E)-8,10-tridecadien-2-yl acetate, and secondarily to the corresponding Z,E-isomer. Certain sensory neuron membrane proteins (i.e., SNMP1) are important for responses of pheromone receptors in flies and moths. The Hessian fly genome is unusual in that it encodes six SNMP1 paralogs, of which five are expressed in antennae. We co-expressed each of the five antennal SNMP1 paralogs together with each of the five candidate sex pheromone receptors from the Hessian fly and found that they do not influence the response of MdesOR115, nor do they confer responsiveness in any of the non-responsive ORs to any of the sex pheromone components identified to date in the Hessian fly. Using Western blots, we detected protein expression of MdesOrco, all MdesSNMPs, and all MdesORs except for MdesOR113, potentially explaining the lack of response from this OR. In conclusion, we report the first functional characterization of an OR from the Cecidomyiidae, extending the role of ORs as long-range sex pheromone detectors from the Lepidoptera into the Diptera.

Coupled gas chromatographic (GC)-electroantennographic detection (EAD) analyses of ovipositor extract of calling Hessian fly, Mayetiola destructor, females revealed that seven compounds elicited responses from male antennae. Four of the compounds-(2S)-tridec-2-yl acetate, (2S,10Z)-10-tridecen-2-yl acetate, (2S,10E)-10-tridecen-2-yl acetate, and (2S,10E)-10-tridecen-2-ol-were identified previously in female extracts. Two new EAD-active compounds, (2S,8Z,10E)-8,10-tridecadien-2-yl acetate and (2S,8E,10E)-8,10-tridecadien-2-yl acetate, were identified by GC-mass spectroscopy (MS) and the use of synthetic reference samples. In a Y-tube bioassay, a five-component blend (1 ng (2S)-tridec-2-yl acetate, 10 ng (2S,10E)-10-tridecen-2-yl acetate, 1 ng (2S,10E)-10-tridecen-2-ol, 1 ng (2S,8Z,10E)-8,10-tridecadien-2-yl acetate, and 1 ng (2S,8E,10E)-8,10-tridecadien-2-yl acetate) was as attractive to male Hessian flies as a similar amount of female extract (with respect to the main compound, (2S,10E)-10-tridecen-2-yl acetate). The five-component blend was more attractive to male flies than a three-component blend lacking the two dienes. Furthermore, the five-component blend was more attractive than a blend with the same compounds but that contained one tenth the concentration of (2S,8E,10E)-8,10-tridecadien-2-yl acetate (more accurately mimicking the ratios found in female extract). This suggests that the ratios emitted by females might deviate from those in gland extracts. In a field-trapping experiment, the five-component blend applied to polyethylene cap dispensers in a 100:10 microg ratio between the main component and each of the other blend components attracted a significant number of male Hessian flies. Also, a small-plot field test demonstrated the attractiveness of the five-component blend to male Hessian flies and suggests that this pheromone blend may be useful for monitoring and predicting Hessian fly outbreaks in agricultural systems.

Identification of host-derived volatiles is an important step towards the development of novel surveillance and control tools for Culicoides biting midges. In this study, we identified compounds from headspace collections of cattle hair and urine that modulate the behavioral response of Culicoides nubeculosus, a research model species with a similar hostrange as the vectors of Bluetongue disease and Schmallenberg disease in Europe. Combined gas chromatography and electroantennographic detection (GC-EAD) analysis revealed 23 bioactive compounds, of which 17, together with octanal, were evaluated in a two-choice behavioral assay in the presence of CO2. Decanal, 2-phenylethanal, 1-octen-3-ol, 2-ethylhexanol, 3-methylindole, phenol, and 3-ethylphenol elicited attraction of host seeking C. nubeculosus, whereas heptanal, octanal, nonanal, 3-propylphenol, and 4-action to CO2, when compared to CO2 alone. 6-Methyl-5-hepten-2-one, 3-methylphenol, 4-methylphenol, and 4-ethylphenol elicited both attraction and inhibition. The behavioral responses were dependent on the concentration tested. Our results show that cattle-derived odors have the potential to be used for the manipulation of the behavior of Culicoides biting midges.

Bactrocera invadens, an invasive fruit fly species in the Afro-tropical region belonging to the Bactrocera dorsalis complex, causes considerable damage to fruit production and productivity. We sought to find attractants from hosts of B. invadens that could serve as baits in traps for monitoring and management of this pest. The attractiveness of volatiles from four different fruit species (mango, guava, banana and orange) at two stages of ripeness (ripe or unripe) was tested in an olfactometer assay. All fruits were attractive against a clean air control. Using hexane extracts of volatile collections of fruits, we demonstrated that male flies preferred the volatiles of ripe guava and orange over unripe fruit extracts. There was a slight difference in preference between females and males; females preferred orange to guava and mango, whereas males preferred mango and guava to orange. Gas chromatography/electroantennographic detection (GC/EAD) and GC/mass spectrometry (GC/MS) were used to identify compounds to which B. invadens antennae were sensitive. GC/EAD recordings from distal and medio-central parts of the fly antenna showed responses to a number of compounds from each fruit species, with esters dominating the responses. Synthetic blends were made for each fruit species using the shared antennally active compounds in ratios found in the extracts. In the olfactometer, B. invadens was most attracted to the banana and orange blends, followed by the mango and guava blends. The synthetic banana blend was as attractive as the volatile collection of banana, although both were less attractive than the fruit. The results demonstrate that composing attractive blends from GC/EAD-active constituents shared by host fruits can be effective for formulating attractive synthetic host mimics for generalist fruit fly species, such as B. invadens.