Attraction of bruchid beetles Callosobruchus chinensis (L.) (Coleoptera: Bruchidae) to host plant volatiles

Host-plant volatiles play an important role as cues for herbivores in search of resources, mates and oviposition sites in complex environments. Plant volatile-based attractants can be developed for pest monitoring and control. Previously, we indicated that mated female adults of Callosobruchus chinensis showed choice preference behavior toward 2-hexenal and benzaldehyde. Our objective here was to investigate the synergistic effect of host-derived attractive volatiles in attracting C. chinensis under laboratory and field conditions in Shanxi Province, China. We hypothesized that the ratio and concentration of volatiles derived from Vigna radiata play critical roles for C. chinensis in locating this host. Therefore, we collected and identified the volatiles of mungbean by using headspace collection and GC-MS. The effectiveness of different ratios and concentrations of two compounds (2-hexenal and benzaldehyde) that elicit C. chinensis searching behavior were examined in Y-tube olfactometer assays. The combination of 300 μg μL^–1 2-hexenal and 180 μg μL^–1 benzaldehyde loadings exhibited a synergistic effect on attracting C. chinensis (82.35%). Compared to control traps, the adults were significantly attracted to traps baited with blends, and more attraction to females than males was found for blend traps in the field experiments. Our results suggest that blends of this specific concentration and ratio of benzaldehyde and 2-hexenal can be used in traps as attractants for C. chinensis monitoring and control in the field.

Screening of Slow Release Solvents for Plant Volatiles

[Objective] The paper was to study the slow release effects of eight common kinds of slow release solvents on n-hexane, and to provide a reference for the construction of slow release system of attractants or repellents synthesized by plant volatiles. [Method] The effect of slow release solvents on volatile quantity and release rate of n-hexane was compared by weight loss method. [Result] Under indoor natural conditions [(22±2) ℃,RH 50%±10%], the slow release effect of lubricating oil on n-hexane was the best, followed by liquid paraffin. The best ratio of slow release solvent(lubricating oil and liquid paraffin) and n-hexane was 5∶1 and the best mixing time was 3 h, which improved the slow release effects of n-hexane by6.3 and 4.7 times, and prolonged the half-life of n-hexane by 1.3 and 1.0 times, respectively. Slow release solvents mainly affected the post-half-life period of n-hexane, and the release rates of n-hexane mixed with lubricating oil and liquid paraffin were decreased by 10.4 and 7.7 times, respec-tively. During the half-life period, the release rates of n-hexane were decreased by 1.3 and 1.0 times, respectively. [Conclusion] Two kinds of slow release solvents with good slow release effect on volatile n-hexane are screened out, and the proportion and mixing time of slow release solvent and volatile are determined, which will provide technical support for the construction of plant volatile slow release system.

Electroantennogram and behavioral responses of Cotesia plutellae to plant volatiles

Plant volatiles have been demonstrated to play an important role in regulat- ing the behavior of Cotesia plutellae, a major larval parasitoid of the diamondback moth （DBM）, Plutella xylostella, but little is currently known about the function of each volatile and their mixtures. We selected 13 volatiles of the DBM host plant, a cruciferous veg- etable, to study the electroantennogram （EAG） and behavioral responses of C. plutellae. EAG responses to each of the compounds generally increased with concentration. Strong EAG responses were to 100 μL/mL of trans-2-hexenal, benzaldehyde, nonanal and cis-3- hexenol, and 10/zL/mL of trans-2-hexenal and benzaldehyde with the strongest response provoked by trans-2-hexenal at 100μL/mL. In the Y-tube olfactometer, C. plutellae, was significantly attracted by 1μL/mL of trans-2-hexenal and benzaldehyde.β-caryophyllene, cis-3-hexenol or trans-2-hexenal significantly attracted C. plutellae at 10μL/mL, while nonanal, benzyl alcohol, cis-3-hexenol or benzyl cyanide at 100μL/mL significantly at- tracted C. plutellae. Trans-2-hexenal significantly repelled C. plutellae at 100 μL/mL. EAG of C. plutellae showed strong responses to all mixtures made of five various com- pounds with mixtures 3 （trans-2-hexenal, benzaldehyde, nonanal, cis-3-hexenol, benzyl cyanide, farnesene, eucalyptol） and 4 （trans-2-hexenal, benzaldehyde, benzyl alcohol, （R）- （＋）-limonene,β-ionone, farnesene, eucalyptol） significantly attracting C. plutellae. These findings demonstrate that the behavior of C. plutellae can be affected either by individual compounds or mixtures of plant volatiles, suggesting a potential of using plant volatiles to improve the efficiency of this parasitoid for biocontrol ofP. xylostella.

Olfactory Response of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to Volatiles Emitted by Mungbean Plants

Intercropping maize with the prostrate variety of mungbean, Vigna radiata （L.） Wilczek which grows flat along the ground can increase parasitism of the eggs of the Asian corn borer, Ostrinia furnacalis （Guenée）, a crucial insect pest of maize in China, by Trichogramma ostriniae Pang Chen. This study investigated the behavioural responses of T. ostriniae to plant volatiles emitted from whole plants, leaves, and flowers of prostrate and erect varieties of mungbean in a 4-armed olfactometer. Female parasitiods were significantly attracted to the odours from some varieties of prostrate mungbean when the visit duration and the number of visits were considered, but were not attracted to the odours from any erect varieties. The attractive odours were shown to emanate from the leaves, rather than from the flowers of prostrate mungbean plants. These results have implications for the augmentation of Trichogramma parasitoids in bio-control of O. furnacalis and other crop pests.

Plant-Derived Enzymes Producing Chiral Aroma Compounds and Potential Application

Aroma(volatile)compounds play important ecological functions in plants,and also contribute to the quality of plant-derived foods.Moreover,chiral aroma compounds affect their functions in plants and lead to different flavor quality properties.Formations of chiral aroma compounds are due to the presence of enzymes producing these compounds in plants,which are generally involved in the final biosynthetic step of the aroma compounds.Here,we review recent progress in research on the plant-derived enzymes producing chiral aroma compounds,and their changes in response to environmental factors.The chiral aroma enzymes that have been reported produce(R)-linalool,(S)-linalool,(R)-limonene,and(S)-limonene,etc.,and these enzymes are found in various plant species.We also discuss the origins of enantioselectivity in the plant-derived enzymes producing chiral aroma compounds and summarize the potential use of plants containing enzymes producing chiral aroma compounds for producing chiral flavors/fragrances.

WTV2.0:A high-coverage plant volatilomics method with a comprehensive selective ion monitoring acquisition mode

Volatilomics is essential for understanding the biological functions and fragrance contributions of plant volatiles.However,the annotation coverage achieved using current untargeted and widely targeted volatomics(WTV)methods has been limited by low sensitivity and/or low acquisition coverage.Here,we introduce WTV 2.0,which enabled the construction of a high-coverage library containing 2111 plant volatiles,and report the development of a comprehensive selective ion monitoring(cSIM)acquisition method,including the selection of characteristic qualitative ions with the minimal ion number for each compound and an optimized segmentation method,that can acquire the smallest but sufficient number of ions for most plant volatiles,as well as the automatic qualitative and semi-quantitative analysis of cSIM data.Importantly,the library and acquisition method we developed can be self-expanded by incorporating compounds not present in the library,utilizing the obtained cSIM data.We showed that WTV 2.0 increases the median signal-to-noise ratio by 7.6-fold compared with the untargeted method,doubled the annotation coverage compared with the untargeted and WTV 1.0 methods in tomato fruit,and led to the discovery of menthofuran as a novel flavor compound in passion fruit.WTV 2.0 is a Python library with a user-friendly interface and is applicable to profiling of volatiles and primary metabolites in any species.

Evaluation of trap effi ciency for the Asian longhorned beetle,Anoplophora glabripennis

The Asian longhorned beetle(ALB),Anoplophora glabripennis,is a well-known stem borer with high polyphagous properties causing frequent outbreaks in northeast China.An attractant-based trap is needed to improve the sensitivity,reliability,and effi ciency for detection of the beetle.In this study,the eff ects of attractants,trap types and color synergy of a trapping system were evaluated.Attractant blends comprised of the male-produced,two-component pheromone plus plant volatiles were used in the fi eld in Hengshui city.Plant volatiles(e.g.,1-pentanol,and 2-pentanol)in combination with male pheromones increased the mean number of trapped ALB compared to the pheromone alone.Males responded better than females to traps baited with plant volatiles alone,whereas traps emitting plant volatiles plus pheromone,regardless of trap type,captured more females than males.The ALB-trapping effi ciency of a modifi ed fl ight intercept panel trap was more than ten times as high as a woodborer panel trap and 1.2 times a fl ight intercept panel trap.The 1-pentanol and 2-pentanol attractants alone or in combination with male-produced pheromone were more eff ective for monitoring ALB than common lures.In laboratory Y-tube olfactometer experiments,the color brown was better at increasing attraction of both males and females to 1-pentanol,2-pentanol,1-pentanol+pheromone,and 2-pentanol+pheromone compared to the clear-glass control arm.The fi ndings provide a reliable and eff ective trap system to monitor ALB infestations.

Variability and stability of tea weevil-induced volatile emissions from tea plants with different weevil densities, photoperiod and infestation duration

After herbivore attack, many plants emit herbivore-induced plant volatiles （HIPVs）. HIPVs can attract carnivores and/or repel herbivores, thereby mediating tritrophic plant-herbivore-carnivore interactions. HIPVs act as chemical information between or- ganisms; hence, their variability and stability are vital. In the present study, variations in the volatile emissions, from the tea plant Camellia sinensis （O. Ktze） damaged by the tea weevil Myllocerinus aurolineatus （Voss） （Coleoptera： Curculionidae）, with weevil densities, pho- toperiod and infestation duration, were investigated. The volatiles induced by high-density weevils were more abundant in composition and amount than those induced by low-density weevils, whether at noon, night or after weevil removal. The induced volatile emissions were similar on the second and third day after infestation, and the emissions of the major induced compounds displayed diurnal cycles. Linalool, （E,E）-α-farnesene, and benzyl ni- trile were emitted mainly at noon, whereas 1,3,8-p-menthatriene and （E）-β-ocimene were maximally emitted at night. Given the different emission dynamics, significant differences were found between noon- and night-induced volatiles. In summary, tea plants damaged by different weevil densities emitted a relatively stable signal at a particular time. This stability could be attributed to the similarities under the two densities of the main induced volatile compounds, their relative ratios and the emission dynamics of the induced volatiles.

Beyond hypoxia: Occurrence and characteristics of black blooms due to the decomposition of the submerged plant Potamogeton crispus in a shallow lake

Organic matter-induced black blooms （hypoxia and an offensive odor） are a serious ecosystem disasters that have occurred in some large eutrophic shallow lakes in China. In this study, we investigated two separate black blooms that were induced by Potamogeton crispus in Lake Taihu, China. The main physical and chemical characteristics, including color- and odor-related substances, of the black blooms were analyzed. The black blooms were characterized by low dissolved oxygen concentration （close to 0 mg/L）, low oxidation-reduction potential, and relatively low pH of overlying water. Notably higher Fe^2＋ and ∑S2- were found in the black-bloom waters than in waters not affected by black blooms. The black color of the water may be attributable to the high concentration of these elements, as black FeS was considered to be the main substance causing the black color of blooms in freshwater lakes. Volatile organic sulfur compounds, including dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, were very abundant in the black-bloom waters. The massive anoxic degradation of dead Potamogeton crispus plants released dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, which were the main odor-causing compounds in the black blooms. The black blooms also induced an increase in ammonium nitrogen and soluble reactive phosphorus levels in the overlying waters. This extreme phenomenon not only heavily influenced the original lake ecosystem but also greatly changed the cycling of Fe, S, and nutrients in the water column.

Language of plants: Where is the word?

Plants emit biogenic volatile organic compounds（BVOCs） causing transcriptomic, metabolomic and behavioral responses in receiver organisms. Volatiles involved in such responses are often called ＂plant language＂. Arthropods having sensitive chemoreceptors can recognize language released by plants. Insect herbivores, pollinators and natural enemies respond to composition of volatiles from plants with specialized receptors responding to different types of compounds. In contrast, the mechanism of how plants＂hear＂ volatiles has remained obscured. In a plant-plant communication, several individually emitted compounds are known to prime defense response in receiver plants with a specific manner according to the chemical structure of each volatile compound. Further, composition and ratio of volatile compounds in the plant-released plume is important in plantinsect and plant-plant interactions mediated by plant volatiles. Studies on volatile-mediated plant-plant signaling indicate that the signaling distances are rather short, usually not longer than one meter. Volatile communication from plants to insects such as pollinators could be across distances of hundreds of meters. As many of the herbivore induced VOCs have rather short atmospheric life times, we suggest that in long-distant communications with plant volatiles,reaction products in the original emitted compounds may have additional information value of the distance to emission source together with the original plant-emitted compounds.

Olive fruits infested with olive fly larvae respond with an ethylene burst and the emission of specific volatiles

Olive fly（Bactrocera oleae R.） is the most harmful insect pest of olive（Olea europaea L.） which strongly affects fruits and oil production. Despite the expanding economic importance of olive cultivation, up to now, only limited information on plant responses to B. oleae is available. Here,we demonstrate that olive fruits respond to B. oleae attack by producing changes in an array of different defensive compounds including phytohormones, volatile organic compounds（VOCs）, and defense proteins. Bactrocera oleaeinfested fruits induced a strong ethylene burst and transcript levels of several putative ethylene-responsive transcription factors became significantly upregulated. Moreover, infested fruits induced significant changes in the levels of 12-oxophytodienoic acid and C12 derivatives of the hydroperoxide lyase. The emission of VOCs was also changed quantitatively and qualitatively in insect-damaged fruits, indicating that B.oleae larval feeding can specifically affect the volatile blend offruits. Finally, we show that larval infestation maintained high levels of trypsin protease inhibitors in ripe fruits, probably by affecting post-transcriptional mechanisms. Our results provide novel and important information to understand the response of the olive fruit to B. oleae attack; information that can shed light onto potential new strategies to combat this pest.