Sex pheromone component ratios and mating isolation among three Lygus plant bug species of North America

Identification, synthesis, and field evaluation of components of the female-produced sex pheromone of Helopeltis cinchonae (Hemiptera: Miridae), an emerging pest of tea

BACKGROUND

Helopeltis cinchonae (Hemiptera: Miridae) is a major pest of tea plantations in Asia. Conventional control of pests with pesticides is unsustainable. Therefore, safe and eco-friendly alternatives, such as pheromones, are required to manage the pest.

RESULTS

In gas chromatography-electroantennographic detection (GC-EAD) analysis of whole-body extracts of virgin female H. cinchonae, two compounds elicited electroantennogram (EAG) responses from male antennae. These were identified as hexyl (R)-3-acetoxybutyrate and (R)-1-acetoxy-5-butyroxyhexane using gas chromatography-mass spectrometry (GC-MS) analysis compared to synthetic compounds. This is the first study to report 1-acetoxy-5-butyroxyhexane as an insect pheromone component. The synthetic compounds elicited dose-dependent EAG responses from the antennae of male H. cinchonae. In two field trapping experiments, the individual compounds were highly attractive to male H. cinchonae when dispensed from polyethylene vials. However, higher catches were obtained with blends of the two compounds in a 1:10 ratio. The blend of racemic compounds was as attractive as the blend of (R)-enantiomers.

CONCLUSIONS

We reported that 1-acetoxy-5-butyroxyhexane and hexyl 3-acetoxybutyrate are components of the female-produced sex pheromone of H. cinchonae, but further work is required on the blend and loading of pheromone and on trap design to provide an optimized system for monitoring and control of this pest. The results may also facilitate the identification of the pheromones of other Helopeltis species, which are major pests in many crops. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Zoophytophagous predator sex pheromone and visual cues of opposing reflectance spectra lure predator and invasive prey

INTRODUCTION

In sub-Saharan Africa, the invasive South American leafminer Phthorimaea absoluta is the most damaging tomato pest. Females of the pest can reproduce both sexually and through parthenogenesis and lay their eggs on all tomato plant parts. The mirid predator Nesidiocoris tenuis, a biological control agent for the pest, is also a tomato pest when prey population is low. To date, however, no study has developed an eco-friendly solution that targets both the predator and its host in a tomato farming system.

OBJECTIVE

To develop a bio-based management system for both pest and predator based on the combined use of sexual communication in the predator and visual cues.

METHODS

We collected volatiles from both sexes of the Kenyan population of the predator N. tenuis and identified candidate sex pheromone components by coupled gas chromatography-mass spectrometry (GC-MS). We used electrophysiological assays to identify antennally-active odorants in the volatiles, followed by field trials with different pheromone-baited colored traps to validate the responses of both predator and prey. Thereafter, we compared the reflectance spectra of the colored traps with those of different tomato plant tissues.

RESULTS

Our results reveal an interplay between different sensory cues which in the predator-prey interaction may favor the predator. Antennae of both sexes of predator and prey detect the predator sex pheromone identified as 1-octanol and hexyl hexanoate. Unexpectedly, our field experiments led to the discovery of a lure for P. absoluta females, which were lured distinctly into a pheromone-baited trap whose reflectance spectrum mimicked that of ripe tomato fruit (long wavelength), an egg-laying site for females. Contrastingly, N. tenuis males were lured into baited white trap (short wavelength) when the predator is actively searching for prey.

CONCLUSION

Our results demonstrate the novel use of a predator sex pheromone and different visual cues to assess complex trophic interactions on tomatoes.

Species- and sex-specific chemical composition from an internal gland-like tissue of an African frog family

Intraspecific chemical communication in frogs is understudied and the few published cases are limited to externally visible and male-specific breeding glands. Frogs of the family Odontobatrachidae, a West African endemic complex of five morphologically cryptic species, have large, fatty gland-like strands along their lower mandible. We investigated the general anatomy of this gland-like strand and analysed its chemical composition. We found the strand to be present in males and females of all species. The strand varies in markedness, with well-developed strands usually found in reproductively active individuals. The strands are situated under particularly thin skin sections, the vocal sac in male frogs and a respective area in females. Gas-chromatography/mass spectrometry and multivariate analysis revealed that the strands contain sex- and species-specific chemical profiles, which are consistent across geographically distant populations. The profiles varied between reproductive and non-reproductive individuals. These results indicate that the mandibular strands in the Odontobatrachidae comprise a so far overlooked structure (potentially a gland) that most likely plays a role in the mating and/or breeding behaviour of the five Odontobatrachus species. Our results highlight the relevance of multimodal signalling in anurans, and indicate that chemical communication in frogs may not be restricted to sexually dimorphic, apparent skin glands.

Early Season Monitoring of Tarnished Plant Bug, Lygus lineolaris, in Wild Hosts Using Pheromone Traps

The tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), has a wide host range of over 700 plant species, including 130 crops of economic importance. During early spring, managing the field edges with weeds and other wild hosts is important in preventing early-season infestations of L. lineolaris in cotton to prevent damage to the squares and other fruiting structures. Scouting fields for L. lineolaris is time- and labor-intensive, and end-user variability associated with field sampling can lead to inaccuracies. Insect traps that combine visual cues and pheromones are more accurate, sustainable, and economically feasible in contrast to traditional insect detection methods. In this study, we investigated the application of red or white sticky cards baited with the female-produced sex pheromone to monitor overwintering L. lineolaris populations in early spring. Field experiments demonstrated that the red sticky cards baited with a pheromone blend containing hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal in 4:10:7 ratio are highly effective in trapping L. lineolaris adults in early spring before the row crops are planted, and in monitoring their movement into a cotton crop. The monitoring of L. lineolaris should help growers to make judicious decisions on insecticide applications to control early pest infestations, thereby reducing economic damage to cotton.

Combining visual cues and pheromone blends for monitoring and management of the tarnished plant bug Lygus lineolaris (Hemiptera: Miridae)

BACKGROUND

The tarnished plant bug Lygus lineolaris (Palisot de Beauvois) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States. Previous studies have reported the role of different ratios of volatile metathoracic gland components such as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal in eliciting low-level attraction of L. lineolaris. In this study, we tested different visual cues (colored sticky cards) in combination with olfactory cues (pheromone blends) to optimize the attraction and capture of L. lineolaris in the field.

RESULTS

Red-colored sticky cards were more attractive to L. lineolaris adults than white, blue or yellow cards. Red sticky cards combined with blends of three potential pheromone components attracted significantly more L. lineolaris adults than sticky cards without a blend added. Traps baited with a blend of hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal in 4:10:7 ratio, respectively, caught a significantly higher number of L. lineolaris than those baited with 10:4:2 or 7:10:4 blends or an unbaited control in the first week of the experiment.

CONCLUSIONS

Combining visual cues (red color) with olfactory cues (pheromone blends) significantly increased the capture of L. lineolaris in the field. This device or a future iteration could contribute towards sustainable and environmentally appropriate early-season monitoring and management of L. lineolaris in the field. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Mining Lygus hesperus (western tarnished plant bug) transcriptomic data for transient receptor potential channels: Expression profiling and functional characterization of a Painless homolog

The transient receptor potential (TRP) family of cation channels are evolutionarily conserved proteins with critical roles in sensory physiology. Despite extensive studies in model species, knowledge of TRP channel functional diversity and physiological impact remains limited in many non-model insect species. To assess the TRP channel repertoire in a non-model agriculture pest species (Lygus hesperus), publicly available transcriptomic datasets were mined for potential homologs. Among the transcripts identified, 30 are predicted to encompass complete open reading frames that encode proteins representing each of the seven TRP channel subfamilies. Although no homologs were identified for the Pyrexia and Brivido channels, the TRP complement in L. hesperus exceeded the 13-16 channels reported in most insects. This diversity appears to be driven by a combination of alternative splicing, which impacted members of six subfamilies, and gene expansion of the TRPP subfamily. To validate the in silico data and provide more detailed analyses of L. hesperus TRP functionality, the putative Painless homolog was selected for more in depth analysis and its functional role in thermosensation examined in vitro. RT-PCR expression profiling revealed near ubiquitous expression of the Painless transcript throughout nymphal and adult development. Electrophysiological data generated using a Xenopus oocyte recombinant expression system indicated activation parameters for L. hesperus Painless homolog that are consistent with a role in noxious heat (40°-45 °C) thermosensation.

Visual attraction of the European tarnished plant bug Lygus rugulipennis (Hemiptera: Miridae) to a water trap with LED light in chrysanthemum greenhouses and olfactory attraction to novel compounds in Y-tube tests

BACKGROUND

The European tarnished plant bug Lygus rugulipennis Poppius (Hemiptera: Miridae) can cause several types of damage to crops grown in greenhouses and fields, including flower abortion in eggplant, stem and fruit damage in cucumbers, and splits in chrysanthemums. Studies suggest that both male and female L. rugulipennis may be more attracted to traps based on visual attraction than pheromone-based trap. Therefore, the aim of this study was to evaluate the effectiveness of a water trap with LED lights and semiochemicals in trapping L. rugulipennis in the laboratory and greenhouse.

RESULTS

The results showed that water traps equipped with white LED light caught 20 - 30 times more bugs than did the sex pheromone-based traps in greenhouse experiment. During the week of peak flight, the LED water trap caught a total of 29 males and females, whereas the sex pheromone caught only one male. Among the semiochemicals tested in a Y-tube, both males and females were attracted to ß-caryophyllene, but not in the presence of the sex pheromone, whereas both males and females were attracted to pentyl butyrate in the presence of the sex pheromone. The pheromone plus bean plant odor was attractive to the insects, suggesting an interaction between plant odor and pheromone.

CONCLUSION

Overall, the findings of the study showed that the water trap with LED light could be an effective method for trapping L. rugulipennis in greenhouses. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

Simple Summary

The tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.

Abstract

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Identification and functional characterization of sex pheromone receptors in mirid bugs (Heteroptera: Miridae)

Mirid bugs are a group of important insect pests that cause large annual losses in agricultural production. Many studies have focused on the isolation and identification of sex pheromones in mirid bugs, and the components and biological activity of the sex pheromones have also been studied as a way to control these pests. However, few studies have focused on the mechanisms of pheromone perception. In this study, we identified the odorant receptor repertoire in three mirid bug species, Apolygus lucorum, Adelphocoris lineolatus, and Adelphocoris suturalis using antennal transcriptome sequencing and bioinformatics analysis. The candidate pheromone receptor (PR) genes were then identified by comparative transcriptomic and expression pattern analysis. Importantly, in vitro functional studies have shown that the candidate PRs have robust responses to the main mirid bug sex pheromone components (E)-2-hexenyl butyrate (E2HB) and hexyl butyrate (HB). Our study uncovered the mechanism of pheromone peripheral coding in these three species and elucidated the mechanism by which mirid bugs can specifically recognize a mate. Moreover, the results of our study will provide a theoretical basis for screening effective sex attractants or mating disturbance agents at the molecular and neural levels for enhanced control of these destructive pests.

Circadian rhythms of insect pheromone titer, calling, emission, and response: a review

Many insect species have circadian rhythms of pheromone production/titer, calling, emission, and response that are involved in intraspecific communication and impact pest management practices. Rhythms of pheromone biosynthesis, most studied in moths affecting forestry and agriculture, contribute to a periodicity of pheromone concentration or titer within glands or hemolymph. Calling rhythms by the pheromone-emitting sex are physical movements (pumping, vibrating wings) that aid in release and dispersion of the volatile pheromone components attractive to the opposite conspecific sex or both sexes. Circadian rhythms of emission of pheromone also occur as a result of an interaction between calling and the titer of pheromone available for release. Responding individuals usually show a coincidental rhythm of dispersal flight while seeking pheromone plumes in which, by orienting upwind, the insects find mates or food resources. However, some species begin searching an hour or more before the emitting sex initiates calling and emission, which benefits mass trapping control programs because the baited traps do not compete initially with natural pheromone sources. In our review, data of daily rhythms of moths and other insects were extracted from the literature by screen capture software to calculate mean time of activity and standard deviation and fit to normal curves. These methods are illustrated for various insects and as a basis for discussion of interactions of pheromonal circadian rhythms of the well-studied gypsy moth Lymantria dispar, spruce budworm moth Choristoneura fumiferana, turnip moth Agrotis segetum, and cabbage looper moth Trichoplusia ni. The various circadian rhythms are discussed in relation to application of species-specific sex and aggregation pheromones for benign biological control and management of pest insects.

Sex Pheromone of the Alfalfa Plant Bug, Adelphocoris lineolatus: Pheromone Composition and Antagonistic Effect of 1-Hexanol (Hemiptera: Miridae)

The sex pheromone composition of alfalfa plant bugs, Adelphocoris lineolatus (Goeze), from Central Europe was investigated to test the hypothesis that insect species across a wide geographical area can vary in pheromone composition. Potential interactions between the pheromone and a known attractant, (E)-cinnamaldehyde, were also assessed. Coupled gas chromatography-electroantennography (GC-EAG) using male antennae and volatile extracts collected from females, previously shown to attract males in field experiments, revealed the presence of three physiologically active compounds. These were identified by coupled GC/mass spectrometry (GC/MS) and peak enhancement as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal. A ternary blend of these compounds in a 5.4:9.0:1.0 ratio attracted male A. lineolatus in field trials in Hungary. Omission of either (E)-2-hexenyl-butyrate or (E)-4-oxo-2-hexenal from the ternary blend or substitution of (E)-4-oxo-2-hexenal by (E)-2-hexenal resulted in loss of activity. These results indicate that this Central European population is similar in pheromone composition to that previously reported for an East Asian population. Interestingly, another EAG-active compound, 1-hexanol, was also present in female extract. When 1-hexanol was tested in combination with the ternary pheromone blend, male catches were reduced. This compound showed a dose-response effect with small doses showing a strong behavioral effect, suggesting that 1-hexanol may act as a sex pheromone antagonist in A. lineolatus. Furthermore, when (E)-cinnamaldehyde was field tested in combination with the sex pheromone, there was no increase in male catch, but the combination attracted both males and females. Prospects for practical application are discussed.

Optimization and field demonstration of the Lygus pratensis (Hemiptera: Miridae) sex pheromone

BACKGROUND

The plant bug Lygus pratensis Linnaeus is a widely distributed polyphagous herbivore that increasingly attains outbreak population levels on cotton in northwestern China. Although the sex pheromone of L. pratensis from the United Kingdom has been identified as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal, at a ratio of 100:25:24, this volatile blend does not prove attractive to Chinese field populations.

RESULTS

In this study, we identified and optimized the sex pheromone of L. pratensis strains from northwestern China. In coupled gas chromatography and electro-antennogram detection (GC-EAD) assays, three compounds within whole-body extracts of virgin L. pratensis females elicited antennal responses: hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal. In field trials, a 20:1:30 ratio blend was the most attractive to L. pratensis males.

CONCLUSION

Traps baited with this synthetic pheromone blend present considerable advantages over traditional sweep-net sampling for L. pratensis population monitoring. It can readily be incorporated into monitoring schemes and integrated pest management packages.

Molecular cloning and comparative analysis of transcripts encoding chemosensory proteins from two plant bugs, Lygus lineolaris and Lygus hesperus

Chemosensory proteins (CSPs) are soluble carrier proteins typically characterized by a six-helix bundle structure joined by two disulfide bridges and a conserved Cys spacing pattern (C1-X_6-8 -C2-X_16-21 -C3-X₂ -C4). CSPs are functionally diverse with reported roles in chemosensation, immunity, development, and resistance. To expand our molecular understanding of CSP function in plant bugs, we used recently developed transcriptomic resources for Lygus lineolaris and Lygus hesperus to identify 17 and 14 CSP-like sequences, respectively. The Lygus CSPs are orthologous and share significant sequence identity with previously annotated CSPs. Three of the CSPs are predicted to deviate from the typical CSP structure with either five or seven helical segments rather than six. The seven helix CSP is further differentiated by an atypical C3-X₃ -C4 Cys spacing motif. Reverse transcriptase PCR-based profiling of CSP transcript abundance in adult L. lineolaris tissues revealed broad expression for most of the CSPs with antenna specific expression limited to a subset of the CSPs. Comparative sequence analyses and homology modeling suggest that variations in the amino acids that comprise the Lygus CSP binding pockets affect the size and nature of the ligands accommodated.

Identification and field evaluation of the sex pheromone of Apolygus lucorum (Hemiptera: Miridae) in China

BACKGROUND

The plant bug, Apolygus lucorum Meyer-Dür, has begun a resurgence and has become a key pest in cotton in northern China, with the wide-scale adoption of transgenic Bt cotton. We attempted to develop a new approach to the control of this plant bug by identifying and utilizing its sex pheromone.

RESULTS

Extracts from A. lucorum adults and nymphs were analyzed using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-electroantennogram detection (GC-EAD) to identify the sex pheromone components. (E)-4-Oxo-2-hexenal and (E)-2-hexenyl butyrate were the major sex pheromone components from females and were also electrophysiology-active towards male antennae. For males, (E)-4-oxo-2-hexenal and hexyl butyrate were the major sex pheromone components. These three components, however, were not detected in nymphs. Field tests showed that binary blends of (E)-4-oxo-2-hexenal and (E)-2-hexenyl butyrate at a ratio of 3:2 resulted in trapping the greatest numbers of A. lucorum males. A long-term dispenser was developed by loading the pheromone components dissolved in sunflower oil into polyethylene vials. Further field evaluation showed that the polyethylene dispensers attracted significantly more bugs even when deployed in the field for 5 weeks.

CONCLUSION

We identified the sex pheromone of A. lucorum and developed a type of high-efficiency and long-term lure. Our results could expand knowledge of the pheromones of plant bugs, and provide novel technologies to monitor and control this pest. © 2019 Society of Chemical Industry.

TRPA1 modulates noxious odor responses in Lygus hesperus

Lygus hesperus isa key pest of many economically important crops across western North America. Central to many aspects of the lives of these insects is chemical signalling, with identified roles in host plant selection, aggregation and passive mate guarding. The development of novel monitoring and control approaches for this insect will rely on a sound understanding of how these cues are perceived and processed, and their impact on behavior. Towards this end, we investigated allyl isothiocyanate, cinnamaldehyde and citronellal, compounds that are noxious repellents to other insects. We found that L. hesperus avoided areas containing the three compounds and that exposure induced increases in movement velocity and duration in both nymphs and adults. This suggests these compounds may work as repellents. To better understand the underlying physiology of this response, RNA interference by dsRNA injection was used to inhibit the expression of two chemosensory-associated proteins, the odorant receptor co-receptor (Orco) and the transient receptor potential A (TRPA1) channel. While knockdown of Orco did not change the reaction of adult females to citronellal, TRPA1 silencing effectively eliminated the induced increase to movement, suggesting a chemoperceptory role in citronellal detection.

Sensilla localization and sex pheromone recognition of odorant binding protein OBP4 in the mirid plant bug Adelphocoris lineolatus (Goeze)

Pheromone binding proteins (PBPs) are well studied in lepidopteran moths and are considered to be crucial in detection of sex pheromones as well as some green leaf volatiles. In contrast, evidence that PBPs interact with sex pheromones of hemipteran species is not available. The mirid plant bug, Adelphocoris lineolatus (Goeze), is a notorious hemipteran pest that uses two butyrate esters, trans-2-hexenyl butyrate (E2HB) and hexyl butyrate (HB), and one hexenoic aldehyde trans-4-oxo-2-hexenal (E4O2H), as sex pheromones. In the present study, we report on an odorant binding protein, AlinOBP4, with particular focus on its potential physiological roles in the detection of A. lineolatus sex pheromone components. Phylogenetic analyses indicated that AlinOBP4 and two mirid orthologs clustered in a general phylogenetic clade with the lepidopteran ABX OBPs, the fly LUSH and the OBP83a/b subfamily. Cellular localization by fluorescence in situ hybridization and immunolabeling further demonstrated that AlinOBP4 was strongly expressed in the multiporous sensilla trichodea (str) and middle long sensilla basiconica (mlsba) of male A. lineolatus adults, suggesting a key role associated with sex pheromone and odorant detection. A ligand binding assay revealed that recombinant AlinOBP4 protein highly bound not only to the sex pheromone components E4O2H but also to some host plant volatiles. These findings together with the evidence of insect PBPs available in the literature support the view that AlinOBP4 is involved in sex pheromone detection in male A. lineolatus and provide foundational information for further elucidating the molecular mechanisms of chemosensory based mating behavior in hemipteran mirid bugs.

Functional characterization of one sex pheromone receptor (AlucOR4) in Apolygus lucorum (Meyer-Dür)

Traps baited with female-produced sex pheromones have been very effective in the monitoring and management of mirid bugs in numerous field trials. However, none of the target odorant receptors for sex pheromone components in Apolygus lucorum have been identified. Here, we identified one candidate sex pheromone receptor, AlucOR4, from A. lucorum. Quantitative real-time PCR (qPCR) analysis revealed that AlucOR4 was antennae-enriched and male-biased in adult A. lucorum. Xenopus oocyte expression system assays demonstrated that AlucOR4/AlucOrco was sensitive to two major sex pheromone constituents and exhibited high sensitivity to (E)-2-hexenyl butyrate (E2HB) and lower sensitivity to hexyl butyrate (HB). The expression level of target mRNA was significantly reduced (>80%) in dsAlucOR4-injected bugs after five days. The electroantennogram (EAG) responses of male antennae to E2HB and HB were also reduced significantly (~40%). Our findings suggest that AlucOR4 is essential to sex pheromone perception in A. lucorum.

Diel Periodicity of 3-Methyl-2-Butenyl Butyrate Emissions by Bronze Bug Males Is Suppressed in the Presence of Females

The bronze bug, Thaumastocoris peregrinus Carpintero & Dellapé (Heteroptera: Thaumastocoridae), is an exotic emerging pest in Eucalyptus commercial forests in South America, Africa, and southern Europe. Information on the chemical communication system and reproductive ecology of this insect is scant, and it may be relevant for designing management strategies for eucalypt plantations. Males emit large amounts of 3-methyl-2-butenyl butyrate, which attracts conspecific adult males but not females. To learn more about the biological function of this putative male-produced pheromone, we quantified this compound in volatile emissions collected from males, females, and couples, in three 4-h collecting periods during the morning, afternoon, and night of a single 24-h cycle. Our results showed that virgin males emit 3-methyl-2-butenyl butyrate in a diel time pattern, with an almost sevenfold difference between the afternoon emission peak compared to morning or night hours. In addition, we show that in the presence of females, males emit the compound in the same amounts throughout the photocycle. While a definite function cannot yet be attributed to the emission of 3-methyl-2-butenyl butyrate by T. peregrinus males, our findings point to an intraspecific function, possibly one related to male-male competition.

An insect anti-antiaphrodisiac

Passive mechanisms of mate guarding are used by males to promote sperm precedence with little cost, but these tactics can be disadvantageous for their mates and other males. Mated females of the plant bug Lygus hesperus are rendered temporarily unattractive by seminal fluids containing myristyl acetate and geranylgeranyl acetate. These antiaphrodisiac pheromones are gradually released from the female's gonopore, declining until they no longer suppress male courtship. Because starting quantities of these compounds can vary widely, the repellant signal becomes less reliable over time. Evidence was found of a complimentary mechanism that more accurately conveys female mating status. Once inside the female, geranylgeranyl acetate is progressively converted to geranylgeraniol then externalized. Geranylgeraniol counteracts the antiaphrodisiac effect despite having no inherent attractant properties of its own. This is the first evidence for such an anti-antiaphrodisiac pheromone, adding a new element to the communication mechanisms regulating reproductive behaviors.

Bacteria may contribute to distant species recognition in ant-aphid mutualistic relationships

Mutualistic interactions between ant and aphid species have been the subject of considerable historical and contemporary investigations, the primary benefits being cleaning and protection for the aphids and carbohydrate-rich honeydew for the ants. Questions remained, however, as to the volatile semiochemical factor influencing this relationship. A recent study highlighted the role of bacterial honeydew volatile compounds in ant attraction. Here, ant's ability to distantly discriminate 2 aphid species was investigated based on bacterial honeydew semiochemicals emissions using a two-way olfactometer. Both the mutualistic aphid Aphis fabae L. and the nonmyrmecophilous aphid Acyrthosiphon pisum Harris were found to be attractive for the ant Lasius niger L. The level of attraction was similar in both assays (control vs. one of the aphid species). However, when given a choice between these 2 aphid species, ants showed a significant preference for Aphis fabae. Honeydew volatiles, mostly from bacterial origins, are known to be a key element in ant attraction. Using the same olfactometry protocol, the relative attractiveness of volatiles emitted by honeydews collected from each aphid species and by bacteria isolated from each honeydew was investigated. Again, ants significantly preferred volatiles released by Aphis fabae honeydew and bacteria. This information suggests that microbial honeydew volatiles enable ants to distantly discriminate aphid species. These results strengthen the interest of studying the occurrence and potential impact of microorganisms in insect symbioses.

Field Evaluation of Potential Pheromone Lures for Lygus lineolaris (Hemiptera: Miridae) in the Mid-South

Plant bugs (Hemiptera: Miridae) are phytophagous pests of cultivated plants around the world. In the mid-South region of the United States, Lygus lineolaris (Palisot de Beauvois) is a primary pest of cotton, and causes economic damage. Previously published research about the volatiles produced by members of the genus Lygus, and other closely related groups, indicated that they produce blends of hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal. Varying ratios of the three compounds were loaded into pipette tips, and screened in combination with non-UV white sticky cards for attractiveness to field populations of L. lineolaris in Mississippi. Field screening indicated that a lure expressing a ratio of 4:10:7 was the most effective at collecting L. lineolaris, and collected similar numbers of individuals to those reported in other studies using traps baited with live virgin insects over a similar period of time. Availability of a synthetic pheromone usable in the climate of the mid-South will enable broader scale landscape level monitoring for populations of L. lineolaris before movement into cotton fields and resulting economic damage.

Neuroethology of Olfactory-Guided Behavior and Its Potential Application in the Control of Harmful Insects

Harmful insects include pests of crops and storage goods, and vectors of human and animal diseases. Throughout their history, humans have been fighting them using diverse methods. The fairly recent development of synthetic chemical insecticides promised efficient crop and health protection at a relatively low cost. However, the negative effects of those insecticides on human health and the environment, as well as the development of insect resistance, have been fueling the search for alternative control tools. New and promising alternative methods to fight harmful insects include the manipulation of their behavior using synthetic versions of "semiochemicals", which are natural volatile and non-volatile substances involved in the intra- and/or inter-specific communication between organisms. Synthetic semiochemicals can be used as trap baits to monitor the presence of insects, so that insecticide spraying can be planned rationally (i.e., only when and where insects are actually present). Other methods that use semiochemicals include insect annihilation by mass trapping, attract-and- kill techniques, behavioral disruption, and the use of repellents. In the last decades many investigations focused on the neural bases of insect's responses to semiochemicals. Those studies help understand how the olfactory system detects and processes information about odors, which could lead to the design of efficient control tools, including odor baits, repellents or ways to confound insects. Here we review our current knowledge about the neural mechanisms controlling olfactory responses to semiochemicals in harmful insects. We also discuss how this neuroethology approach can be used to design or improve pest/vector management strategies.

Sex pheromones and reproductive isolation in five mirid species

Mate location in many mirid bugs (Heteroptera: Miridae) is mediated by female-released sex pheromones. To elucidate the potential role of the pheromones in prezygotic reproductive isolation between sympatric species, we investigated differences in the pheromone systems of five mirid species, Apolygus lucorum, Apolygus spinolae, Orthops campestris, Stenotus rubrovittatus and Taylorilygus apicalis. GC/MS analyses of metathoracic scent gland extracts of virgin females showed that all five species produced mixtures of hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal, but in quite different ratios. (E)-2-hexenyl butyrate was the major component of A. spinolae, while hexyl butyrate was the most abundant component in the pheromone blends of the other four species. In addition to the three compounds, a fourth component, (E)-2-octenyl butyrate, was present in the gland extracts of A. lucorum and T. apicalis females. Field tests suggest that the ternary blends of hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal as found in the extracts of the females of each species do not inhibit attraction of conspecific males but ensure species-specificity of attraction between A. lucorum, O. campestris and T. apicalis. Furthermore, (E)-2-octenyl butyrate was essential for attraction of A. lucorum and T. apicalis males, but strongly inhibited attraction of male A. spinolae, O. campestris and S. rubrovittatus. The combined results from this study and previous studies suggest that the minor component and pheromone dose in addition to the relative ratio of the major components play an important role in reproductive isolation between mirid species.

Molecular Cloning and Characterization of G Alpha Proteins from the Western Tarnished Plant Bug, Lygus hesperus

The Gα subunits of heterotrimeric G proteins play critical roles in the activation of diverse signal transduction cascades. However, the role of these genes in chemosensation remains to be fully elucidated. To initiate a comprehensive survey of signal transduction genes, we used homology-based cloning methods and transcriptome data mining to identity Gα subunits in the western tarnished plant bug (Lygus hesperus Knight). Among the nine sequences identified were single variants of the Gαi, Gαo, Gαs, and Gα12 subfamilies and five alternative splice variants of the Gαq subfamily. Sequence alignment and phylogenetic analyses of the putative L. hesperus Gα subunits support initial classifications and are consistent with established evolutionary relationships. End-point PCR-based profiling of the transcripts indicated head specific expression for LhGαq4, and largely ubiquitous expression, albeit at varying levels, for the other LhGα transcripts. All subfamilies were amplified from L. hesperus chemosensory tissues, suggesting potential roles in olfaction and/or gustation. Immunohistochemical staining of cultured insect cells transiently expressing recombinant His-tagged LhGαi, LhGαs, and LhGαq1 revealed plasma membrane targeting, suggesting the respective sequences encode functional G protein subunits.