Search

Classical biological control of invasive alien weeds depends on the use of arthropod herbivores that are sufficiently host specific to avoid risk of injuring nontarget plants. Host plant specificity is usually evaluated by using a combination of behavioral and developmental experiments under choice, no-choice and field conditions. Secondary plant compounds are likely to have an important influence on host plant specificity. However, relatively little is known about the volatile organic compounds (VOCs) that are emitted by target and nontarget plants, and how environmental conditions may affect their emission. Previous studies have shown that mechanical damage of leaves increases the composition and content of VOCs emitted. In this study we measured the VOC emissions of five species of plants in the subtribe Centaureinae (Asteraceae) – Carthamus tinctorius , Centaurea cineraria , Centaurea melitensis , Centaurea rothrockii , and Centaurea solstitialis – that have previously been used in host specificity experiments for a prospective biological control agent of yellow starthistle ( C. solstitialis ). Leaves of each plant were punctured with a needle and the VOCs were collected by solid-phase microextraction (SPME) periodically over 48 h and analyzed by GC–MS. A total of 49 compounds were detected. Damage caused an immediate increase of 200–600% in the composition of VOCs emitted from each plant species, and the amounts generally remained high for at least 48 h. The results indicate that a very unspecific mechanical damage can cause a prolonged change in the VOC profile of plants. [ABSTRACT FROM AUTHOR]

Over the years various tissues of almond and pistachio have been evaluated for their ability to attract the navel orangeworm moth, a major insect pest in California tree nut orchards. Almond meal, which typically consists of ground almond kernels, is a monitoring tool for navel orangeworm populations in almond and pistachio orchards. Recently, ground pistachio and almond mummies have been re-visited in field trapping studies for their potential to attract navel orangeworm moths. Surprisingly, the volatile profiles of these two systems have not been reported. The objective of this study was to survey and then compare and contrast the volatile profiles of both ground almond and pistachio mummies over the course of a week. Principal component analysis (PCA) of the headspace volatiles showed a distinct difference between ground almond and pistachio mummies. The volatile emission profile of the almond mummies remained consistent over the one-week period, albeit in low content and composition; whereas the profile of the pistachio mummies changed over time as shown by PCA. Seven compounds were identified as being common volatiles to both matrices. These data may help explain results from recent navel orangeworm field trapping studies using almond and pistachio mummies, as well as with the formulation of future synthetic blends. [ABSTRACT FROM AUTHOR]

Highlights: [•] Volatile analysis of ground and wet almond and pistachio mummies. [•] Pistachio mummy volatile profile comprises 86 volatiles, 22 unique to wet matrix. [•] Almond mummy volatile profile comprises 57 volatiles, 37 unique to wet matrix. [•] The two wet matrices have 19 compounds in common. [Copyright &y& Elsevier]

Highlights: [•] Analysis of ground almond hull and shell emissions detected the spiroketals conophthorin and chalcogran. [•] Conophthorin is an important semiochemical of the insect pest navel orangeworm. [•] The spiroketals appear to be produced by damaged hull tissue. [•] The fatty acid composition, water activity, and water content of developing almond and pistachio hulls were determined. [Copyright &y& Elsevier]

Abstract: The volatile emissions of various plant parts of almonds have been studied via various techniques in the past. These analyses have typically been performed on single cultivars and hence may not be representative of the volatiles found in an entire almond orchard. Recent reports suggest some almond volatiles exhibit semiochemical activities for the navel orangeworm (NOW), a major insect pest of almonds; thus, the volatile composition of the comprehensive almond orchard would be helpful to research concerning NOW. The ambient volatile emissions of an almond orchard containing the cultivar Nonpareil and associated pollenizers were collected at four intervals during the 2009 growing season from orchards in the south Central Valley of California. The volatiles hexanal, octanal, nonanal, benzaldehyde, acetophenone, ethyl benzoate, methyl salicylate, and phenol were consistent in their presence and in relatively high amounts. The orchard volatile composition was analyzed via electroantennogram (EAG) analysis, which produced strong responses from NOW antennae. [Copyright &y& Elsevier]

Plant-derived volatiles are important mediators of plant-insect interactions as they can provide cues for host location and quality, or act as direct or indirect defense molecules. The volatiles produced by Zea mays (maize) include a range of terpenes, likely produced by several of the terpene synthases (TPS) present in maize. Determining the roles of specific terpene volatiles and individual TPSs in maize-insect interactions is challenging due to the promiscuous nature of TPSs in vitro and their potential for functional redundancy. In this study, we used metabolite GWAS of a sweetcorn diversity panel infested with Spodoptera frugiperda (fall armyworm) to identify genetic correlations between TPSs and individual volatiles. This analysis revealed a correlation between maize terpene synthase 1 (Zm TPS1) and emission of the monoterpene volatiles linalool and β -myrcene. Electroantennogram assays showed gravid S. frugiperda could detect both linalool and β -myrcene. Quantification of headspace volatiles in a maize tps1 loss-of-function mutant confirmed that Zm TPS1 is an important contributor to linalool and β -myrcene emission in maize. Furthermore, pairwise choice assays between tps1 mutant and wild-type plants showed that Zm TPS1, and by extension its volatile products, aid host location in the chewing insect S. frugiperda, yet repel the sap-sucking pest, Rhopalosiphum maidis (corn leaf aphid). On the other hand, Zm TPS1 had no impact on indirect defense via the recruitment of the parasitoid Cotesia marginiventris. Zm TPS1 is therefore an important mediator of the interactions between maize and its insect pests. [Display omitted] • Plant volatiles mediate plant-insect interactions. • Metabolite GWAS and functional genetics identified a maize monoterpene synthase. • This monoterpene synthase has opposite effects on the chewing and piercing insect pests tested. [ABSTRACT FROM AUTHOR]

Infestation of agricultural commodities by insect pests results in significant economic, import and export, food safety, and invasive insect introduction issues for growers, consumers, and inspectors. The Oriental fruit fly (Bactrocera dorsalis) is considered a highly invasive insect pest with populations reported in more than 60 countries, with prevalent distributions in Asia and Africa. B. dorsalis is phytophagous with a host range encompassing hundreds of fruits and vegetables. Damage to the fruit or vegetable is inflicted through oviposition and subsequent larval feeding resulting in spoilage. Early detection of insect pest infestations is a critical component for ensuring food safety as well as controlling introduction and spread of invasive insects. However, detection of ovipositional activity and early larval development is visually difficult, thus rapid and non-destructive detection often relies on odors associated with infestation. We investigated the odors of mangoes (Mangifera indica L.) infested with B. dorsalis and compared the volatile profiles of infested mangoes to non-infested and mechanically damaged mangoes 24 h post-infestation. GC-MS and multivariate analyses provided the identification of eleven compounds unique to infested mangoes compared to mechanically damaged or non-infested fruit. Results indicated compositional and quantitative differentiation of volatile profiles among treatments for detection of infested fruit at quality checks or points of commerce. Eleven biomarkers were detected as volatile compounds from Bactrocera dorsalis infested mango treatments when compared to mechanically damaged and intact, non-infested mango treatments. [Display omitted] • Bactrocera dorsalis infested mangoes emitted unique volatile biomarkers. • The biomarkers can be used to detect early infestations of mangoes. • Infestation detection is vital for food safety and early recognition of invasive insect import. [ABSTRACT FROM AUTHOR]

The codling moth ( Cydia pomonella ) and navel orangeworm ( Amyelois transitella ) are insect pests that inflict serious economic damage to California walnuts. Feeding by these larvae causes physical damage to the nut and can lead to contamination by aflatoxigenic fungi. Over the years volatile natural products have played a critical role in efforts to control or monitor these and other insect pest moths. The ex situ volatile emissions from intact and mechanically damaged Howard variety walnuts from the California Central Valley were evaluated over the course of a typical growing season. The volatile profiles were compared and differences in emission considered as a means to identify candidate volatiles for use in host plant-based attractants or in conjunction with pheromone blends to enhance attractancy. Walnut volatiles were extracted by headspace solid phase microextraction (HS-SPME) in a semi-closed system and analyzed by gas chromatography mass spectrometry (GC–MS). Ninety two volatiles were identified, including monoterpenes as the predominant class of compounds. A multivariate analysis of the data highlighted two sampling periods (late July–late August) where intact walnuts and mechanically damaged walnuts can be distinguished due to their volatile profile composition. The results of this study provide relevant information regarding potential host plant-based semiochemicals of two insect pests, valuable data regarding the ambient odors these insects encounter in walnut orchards and add some potentially interesting volatile compounds to the existing literature. [ABSTRACT FROM AUTHOR]