Development of semiochemical attractants for monitoring bean seed beetle, Bruchus rufimanus

Transcriptome Analysis of Stigmas of Vicia faba L. Flowers

Pollination in angiosperms depends on complex communication between pollen grains and stigmas, classified as wet or dry, depending on the presence or absence of secretions at the stigma surface, respectively. In species with wet stigma, the cuticle is disrupted and the presence of exudates is indicative of their receptivity. Most stigma studies are focused on a few species and families, many of them with self-incompatibility systems. However, there is scarce knowledge about the stigma composition in Fabaceae, the third angiosperm family, whose stigmas have been classified as semidry. Here we report the first transcriptome profiling and DEGs of Vicia faba L. styles and stigmas from autofertile (flowers able to self-fertilize in the absence of manipulation, whose exudate is released spontaneously) and autosterile (flowers that need to be manipulated to break the cuticle and release the exudates to be receptive) inbred lines. From the 76,269 contigs obtained from the de novo assembly, only 45.1% of the sequences were annotated with at least one GO term. A total of 115,920, 75,489, and 70,801 annotations were assigned to Biological Process (BP), Cellular Component (CC), and Molecular Function (MF) categories, respectively, and 5918 differentially expressed genes (DEGs) were identified between the autofertile and the autosterile lines. Among the most enriched metabolic pathways in the DEGs subset were those related with amino acid biosynthesis, terpenoid metabolism, or signal transduction. Some DEGs have been related with previous QTLs identified for autofertility traits, and their putative functions are discussed. The results derived from this work provide an important transcriptomic reference for style-stigma processes to aid our understanding of the molecular mechanisms involved in faba bean fertilization.

A semiochemical view of the ecology of the seed beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae, Bruchinae)

The dried bean beetle, Acanthoscelides obtectus, is an economically important pest of stored legumes worldwide. Tracking the human-aided dispersion of its primary hosts, the Phaseolus vulgaris beans, it is now widespread in most bean-growing areas of the tropics and subtropics. In temperate regions where it can only occasionally overwinter in the field, A. obtectus proliferates in granaries, having multiple generations a year. Despite its negative impact on food production, no sensitive detection or monitoring tools exist, and the reduction of local populations still relies primarily on inorganic insecticides as fumigating agents. However, in the quest to produce more nutritious food more sustainably and healthily, the development of environmentally benign crop protection methods is vital against A. obtectus. For this, knowledge of the biology and chemistry of both the host plant and its herbivore will underpin the development of, among others, chemical ecology-based approaches to form an essential part of the toolkit of integrated bruchid management. We review the semiochemistry of the mate- and host-finding behaviour of A. obtectus and provide new information about the effect of seed chemistry on the sensory and behavioural ecology of host acceptance and larval development.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

Can Pheromones Contribute to Phylogenetic Hypotheses? A Case Study of Chrysomelidae

Pheromones mediate species-level communication in the search for mates, nesting, and feeding sites. Although the role of pheromones has long been discussed by various authors, their existence was not proven until the mid-twentieth century when the first sex pheromone was identified. From this finding, much has been speculated about whether this communication mechanism has acted as a regulatory agent in the process of speciation, competition, and sexual selection since it acts as an intraspecific barrier. Chrysomelidae is one of the major Phytophaga lineages, with approximately 40,000 species. Due to this immense diversity the internal relationships remain unstable when analyzed only with morphological data, consequently recent efforts have been directed to molecular analyses to establish clarity for the relationships and found their respective monophyly. Therefore, our goals are twofold 1) to synthesize the current literature on Chrysomelidae sex pheromones and 2) to test whether Chrysomelidae sex pheromones and their chemical structures could be used in phylogenetic analysis for the group. The results show that, although this is the first analysis in Chrysomelidae to use pheromones as a phylogenetic character, much can be observed in agreement with previous analyses, thus confirming that pheromones, when known in their entirety within lineages, can be used as characters in phylogenetic analyses, bringing elucidation to the relationships and evolution of organisms.

Bumblebee responses to variation in pollinator-attracting traits of Vicia faba flowers

Adaptations that attract pollinators to flowers are central to the reproductive success of insect-pollinated plants, including crops. Understanding the influence of these non-rewarding traits on pollinator preference is important for our future food security by maintaining sufficient crop pollination. We have identified substantial variation in flower shape, petal size, corolla-tube length, petal spot size and floral volatile compounds among a panel of 30 genetically distinct lines of Vicia faba. Using this variation, we found that Bombus terrestris was able to distinguish between natural variation in petal spot size, floral volatile emissions and corolla-tube length. Foragers showed some innate preference for spotted flowers over non-spotted flowers and preferred shorter corolla-tube lengths over longer tubes. Our results suggest that some floral traits may have significant potential to enhance pollinator attraction to V. faba crops, particularly if paired with optimised rewards.

Optimizing Insecticide Application Timing for Broad Bean Weevil Control and Minimizing Crop Damage in Broad Bean (Vicia faba Linn.)

During the growing seasons of 2018 to 2020, a field experiment in broad bean (Vicia faba L.) was conducted at the Lithuanian Research Centre for Agriculture and Forestry. The objective of the study was to explore the effects of the timing of insecticide application on the abundance, damage, and control of the broad bean weevil (Bruchus rufimanus Boh.). The experiment included four spray regimes and an untreated control. Yellow water traps were utilized to monitor the broad bean weevil from germination to senescence. Results indicate that broad bean weevil infestation occurred in all study years, with the highest density of adults observed during the flowering stage. Damage to seeds ranged from 23% to 59.62%. The data suggest that B. rufimanus infestation can result in a 19.1% reduction in seed yield. However, spraying when the daily temperature exceeded the threshold for adult activity for 3 days and at the end of flowering produced a significant increase in yield of 13.3% and 6.6%, respectively. Additionally, the spray at the end of flowering reduced damaged seeds by 21.4-48%.

Impacts of Semiochemical Traps Designed for Bruchus rufimanus Boheman 1833 (Coleoptera: Chrysomelidae) on Nontarget Beneficial Entomofauna in Field Bean Crops

Broad bean weevils (BBWs-Coleoptera: Chrysomelidae) are serious pests of field bean seeds that hamper the promotion of this crop in the diversification of European cropping systems. Recent research has identified different semiochemical lures and trap devices for the development of semiochemical-based control strategies of BBWs. In this study, two field trials were carried out in order to provide necessary information supporting the implementation of sustainable field use of semiochemical traps against BBWs. More particularly, three principal objectives were followed including (i) the identification of the most efficient traps for BBWs capture and the influence of trapping modality on BBWs sex-ratio, (ii) the assessment of eventual collateral effects on crop benefits including aphidophagous and pollinator insects such as Apidae, Syrphidae and Coccinellidae, (iii) the assessment of the crop developmental stage influence on the capture by semiochemical traps. Three different semiochemical lures were tested in combination with two trapping devices across two field trials in early and late flowering field bean crops. The crop phenology and climate parameters were integrated into the analyses to interpret the spatiotemporal evolution of the captured insect populations. A total of 1380 BBWs and 1424 beneficials were captured. White pan traps combined with floral kairomones were the most efficient traps for the capture of BBWs. We demonstrated that the crop phenology (c.f., the flowering stage) exerted strong competition on the attractiveness of semiochemical traps. Community analysis revealed that only one species of BBWs was captured in field bean crops (i.e., Bruchus rufimanus), and no trend was highlighted concerning the sex ratios according to the trapping devices. The beneficial insect community included 67 different species belonging to bees, hoverflies and ladybeetles. Semiochemical traps manifested a strong impact on beneficial insect communities that included some species under extinction threats and need to be further adapted to minimize such collateral effects. Based on these results, recommendations are provided for the implementation of the most sustainable BBWs control method that minimizes the impact on the recruitment of beneficial insects, which is an important ecosystem service for faba bean crops.

Development of a Phytochemical-Based Lure for the Dried Bean Beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae)

The dried bean beetle, Acanthoscelides obtectus, is an economically important, worldwide pest of legume crops including dry beans, Phaseolus vulgaris. Assessment of A. obtectus infestation levels in pre-harvest field crops and post-harvest granaries is difficult to achieve because there is no effective monitoring tool for early detection so that interventions can be deployed as needed. Because A. obtectus is a generic pollen and nectar feeder, we adopted an electrophysiological (EAG) screening approach, using the antennae of female A. obtectus to identify physiologically active, volatile phytochemicals, which could then be investigated for their attractiveness to A. obtectus in laboratory behavioral assays and preliminary field tests. Of the 27 compounds tested in EAG screening, 5 compounds, i.e., methyl anthranilate, methyl eugenol, benzyl alcohol, (RS)-lavandulol, and 2-phenylethanol, elicited stronger EAG responses than the standard (1-phenylethanol). In 4-arm olfactometer bioassays, female A. obtectus preferred the olfactometer arm containing the odor of either methyl anthranilate or benzyl alcohol compared to the solvent control. In preliminary field tests using these 2 compounds as a binary mixture, at least 5 times as many beetles were caught on baited traps compared to non-baited traps. The field data also suggested that benzyl alcohol was primarily responsible for the field activity of the blend. We hypothesize that the attraction of A. obtectus to the combined benzyl alcohol/methyl anthranilate and the single benzyl alcohol baits is connected to the species` nectar- and pollen-feeding behaviour and not to its intraspecific communication. To our knowledge, this is the first evidence that A. obtectus behavior in the field can be modified by the deployment of plant-derived semiochemicals.

Physiological Synchrony of the Broad Bean Weevil, Bruchus rufimanus Boh., to the Host Plant Phenology, Vicia faba L

The aims of the study were to understand the physiological and phenological relationship between Bruchus rufimanus and Vicia faba in the perspective of IPM strategies. V. faba, an important food resource for humans and livestock is the main host plant of B. rufimanus. Adults feed on the pollen, females lay eggs on pods, and larvae develop into the seeds. Pending the blooming phase, the weevil may feed on the pollen from wild plants. Depending on the sowing date, the phenological time lag should lead the plant parts, most utilized by the weevil, less or more available during the key life stages of the pest. The aims of the study were therefore (1) to assess the impact of the sowing date (i.e., cultivars) on the phenological relationship between B. rufimanus and V. faba, and (2) to identify alternative pollen resources during the vegetative phase. Insects were collected weekly on two cultivars: winter-sown and spring-sown fields. Ovarian development, fecundity, and diet were monitored using dissected adults. Results showed that immature adults colonized the blooming winter-sown field and then 2 weeks later, the blooming spring-sown field. Sexual maturity of the weevils is related with V. faba pollen consumption. The sexual maturity of females increased with the growing density of flowers and the first pods were quickly covered with eggs. In spring-sown field, first pods grew 19 days later, while collected females in winter sown field had already laid most of their eggs. Feeding tests were carried using flowers collected from plants growing close to the fields: wild chervil, oilseed rape and wild Prunus. All this pollen were consumed by the weevils. The study showed a perfect synchrony between the host and the pest. Late sowing date and control of the early blooming wild plants surrounding the crops might reduce the attacks in field beans. More broadly, the study helps to understand the eco-ethology of the insect in cultivated areas.

Peach volatile emission and attractiveness of different host plant volatiles blends to Cydia molesta in adjacent peach and pear orchards

The oriental fruit moth (OFM), Cydia (= Grapholitha) molesta, is a highly damaging pest; peaches are its primary host, and pears serve as post-peach secondary hosts during the late season in China. We collected volatiles from detached peach shoots and fruits, and identified them with gas chromatography-mass spectrometry (GC-MS). Antennally active compounds were identified by gas chromatography-electroantennogram detection (GC-EAD), and these were further tested in the laboratory and field. We detected consistent electroantennographic activity was for ten compounds. Significantly more C. molesta females were caught with a mixture of female EAD-active compounds identified from the detached matured peach fruits (nonanal, butyl acetate, 3-methylbutyl acetate, hexyl acetate, (Z)-3-hexenyl acetate, linalool and farnesene) than other mixtures mimicking the volatile profile from detached matured fruits or shoots. We identified a new GC-EAD active mixture from intact peach shoots composed of nonanal, (Z)-3-hexenyl acetate, (E)-β-ocimene, and 6-methyl-5-hepten-2-one. In the field test, the background odour of orchards could affect trap catches, and two peach-derived blends together with two previously known pear-derived blends were proven to be able to monitor the seasonal OFM population dispersal in adjacent orchards. These host plant blends will be effective for further designing candidate attractants for season-long C. molesta population dynamic monitoring.

Flower and Pod Source Influence on Pea Weevil (Bruchus pisorum) Oviposition Capacity and Preference

Bruchus pisorum is an insect pest causing major damage to pea seeds worldwide. Control is difficult and limited resistance is available. In this work we studied the effects of pollen and pod source on insect fecundity and oviposition by comparing resistant and susceptible Pisum spp. accessions and non-host (Lathyrus sativus and Vicia faba) species. A first no-choice assay revealed that the source of flower offered to adults for feeding might retard oviposition (the case of V. faba), reduce fertility (Pisum sativum ssp. syriacum, P. fulvum, and V. faba) or increase adult mortality (V. faba and P. sativum ssp. syriacum). A second no-choice assay with all adults fed with pollen of the same pea cultivar showed significant effect of the source of pods offered. Oviposition was reduced on pods of some resistant Pisum accessions, but particularly low on pods of the non-hosts, being retarded if ever happening and coupled with high mortality of adults. This was confirmed in a third experiment consisting on dual-choice assays showing reduced egg laying in V. faba, L. sativus, P. fulvum, and P. sativum ssp. syriacum compared to the commercial variety pea used as a control (Messire).

Isolation and identification of floral attractants from a nectar plant for the dried bean beetle, Acanthoscelides obtectus (Coleoptera: Chrysomelidae, Bruchinae)

BACKGROUND

The response of virgin females of the legume pest Acanthoscelides obtectus (Coleoptera: Bruchidae) to headspace extracts of volatiles collected from flowers of a nectar plant, Daucus carota, was investigated using behaviour (four-arm olfactometry) and coupled gas chromatography-electroantennography (GC-EAG).

RESULTS

Odours from inflorescences were significantly more attractive to virgin female beetles than clean air. Similarly, a sample of volatile organic compounds (VOCs) collected by air entrainment (dynamic headspace collection) was more attractive to beetles than a solvent control. In coupled GC-EAG experiments with beetle antennae and the VOC extract, six components showed EAG activity. Using coupled GC-mass spectrometry (GC-MS) and GC peak enhancement with authentic standards, the components were identified as α-pinene (S:R 16:1), sabinene, myrcene, limonene (S:R 1:3), terpinolene and (S)-bornyl acetate. Females preferred the synthetic blend of D. carota EAG-active volatiles to the solvent control in bioassays. When compared directly, odours of D. carota inflorescences elicited stronger positive behaviour than the synthetic blend.

CONCLUSION

This is the first report of behaviourally active volatiles linked to pollen location for A. obtectus, and development of the six-component blend is being pursued, which could underpin the design of semiochemical-based field management approaches against this major pest of stored products. © 2018 Society of Chemical Industry.

Plant volatile-mediated signalling and its application in agriculture: successes and challenges

856 I. 856 II. 857 III. 858 IV. 859 V. 860 VI. 862 VII. 863 VIII. 864 IX. 866 866 References 866 SUMMARY: The mediation of volatile secondary metabolites in signalling between plants and other organisms has long been seen as presenting opportunities for sustainable crop protection. Initially, exploitation of interactions between plants and other organisms, particularly insect pests, foundered because of difficulties in delivering, sustainably, the signal systems for crop protection. We now have mounting and, in some cases, clear practical evidence for successful delivery by companion cropping or next-generation genetic modification (GM). At the same time, the type of plant signalling being exploited has expanded to signalling from plants to organisms antagonistic to pests, and to plant stress-induced, or primed, plant-to-plant signalling for defence and growth stimulation.

Identification and field evaluation of pear fruit volatiles attractive to the oriental fruit moth, Cydia molesta

Plant volatiles play a key role in host plant location of phytophagous insects. Cydia molesta is an important pest of pear fruit late in the growing season. We identified and quantified volatiles from immature and mature fruits of six pear varieties by using gas chromatography-mass spectrometry (GC-MS). Attractiveness of synthetic blends to adults based on gas chromatography-electroantennogram detection (GC-EAD) activity was investigated in both field and laboratory. Consistent electroantennographic activity was obtained for 12 compounds from headspace collections of the mature fruits of the six pear varieties. Qualitative and quantitative differences were found among six odor profiles. Among the six mixtures, the mixture of 1-hexanol, nonanal, ethyl butanoate, butyl acetate, ethyl hexanoate, hexyl acetate, hexyl butanoate, and farnesene (different isomers) with a 1:1:100:70:7:5:1:4 ratio from the variety Jimi and the mixture of nonanal, ethyl butanoate, 3-methylbutyl acetate, ethyl hexanoate, hexyl acetate, and farnesene with a 1:100:1:32:1:2 ratio from the variety Huangjin were highly attractive to both sexes in the field. However, male captures were much higher than those of females. Further wind tunnel tests proved that both sexes exhibited upwind flight to the lures, but only males landed on the source. Our finding indicates that mixtures mimicking Jimi and Huangjin volatiles attract both females and males of C. molesta, and these host volatiles may be involved in mate finding behavior.