Science
Exploring plant volatile-mediated interactions between native and introduced plants and insects | Scientific Reports – Nature.com
Abstract
In invasion scenarios, native and introduced species co-occur creating new interactions and modifying existing ones. Many plant–plant and plant–insect interactions are mediated by volatile organic compounds (VOCs), however, these have seldom been studied in an invasion context. To fill this knowledge gap, we explored some interactions mediated by VOCs between native and introduced plants and insects in a New Zealand system. We investigated whether a native plant, Leptospermum scoparium (mānuka), changes its volatile profile when grown adjacent to two European introduced plants, Calluna vulgaris (heather) and Cytisus scoparius (Scotch broom), in a semi-field trial using potted plants without above- or below-ground physical contact. We also investigated the influence of plant cues on the host-searching behaviour of two beetles, the native Pyronota festiva (mānuka beetle), and the introduced biocontrol agent Lochmaea suturalis (heather beetle), by offering them their host-plant and non-host volatiles versus clean air, and their combination in a Y-tube olfactometer. As a follow-up, we performed preference/feeding tests in Petri dishes with fresh plant material. Results of the semi-field experiment show a significant reduction in green leaf volatiles, sesquiterpenes and total volatile emissions by mānuka plants neighbouring heather. In the Y-tube assays, the native beetle P. festiva performed poorly in discriminating between host and non-host plants based on plant volatile cues only. However, it performed relatively well in the Petri dish tests, where other cues (i.e., visual, gustatory or tactile) were present. In contrast, the introduced beetle L. suturalis showed high host-specificity in both Y-tube and Petri dish assays. This study illustrates the importance of VOCs in mediating interactions between introduced and native species, suggesting that invasive plants can disrupt native plants’ communication and affect the host-searching behaviour of native insects. It also reinforces the relevance of regular host testing on introduced weed biocontrol agents to avoid unwanted host shifts or host-range expansion.
Introduction
The introduction and establishment of organisms into new habitats is increasing globally with devastating consequences for native biodiversity and ecosystems1,2. Invasive species co-exist with one another and with natives creating new interactions and modifying existing ones3,4,5, with positive, negative or neutral consequences. Invasive plants modify the environments they colonise primarily by altering soil properties, microclimate, out-competing native counterparts, and displacing animals (mostly insects) that rely on them6,7,8,9. Chemically, invasive plants can alter the complexity of invaded habitats by releasing secondary metabolites mainly through root exudates and airborne emissions. A recent publication exploring the allelopathic potential (i.e., the production of chemicals by a plant species that can affect the growth, survival, development or reproduction of neighbouring organisms) of 524 invasive plants shows the majority of these plants produce allelochemicals with the potential to affect native species10,11. However, the databases used for this study mainly focus on allelopathic impacts caused through root exudates12,13, whereas the role of airborne emissions (volatile organic compounds) in invasion scenarios remains largely unexplored.
Volatile organic compounds (VOCs) are plant natural products with low molecular weight and high vapour pressure at room temperatures. Based on their biosynthetic origin they can be assigned to different classes including terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives (green leaf volatiles) and amino acid derivatives, as well as others not represented in these major classes14. Volatile organic compounds are species-specific but also responsive to biotic (e.g., herbivore and pathogen attack) and abiotic factors (e.g., temperature, UV radiation and drought), making them valuable cues about a plant’s identity and state for surrounding organisms15. Plant VOCs play an important role in plant–insect interactions by mediating host location and acceptance by pollinators, herbivores and their natural enemies16,17. Volatile organic compounds also mediate plant–plant interactions, including kin-recognition, priming and competition18,19,20. Moreover, plants are known to modify their VOC emissions in the presence of different neighbouring plants21 and even have ‘geographic dialects’22, responding strongly to cues of other plants from the same region.
Given the important ecological roles of VOCs in the context of plant invasion, it is relevant to explore, among other questions, if invasive plants affect the volatile emissions of native plant species, and whether VOCs emitted by invasive plants disrupt communication between native plants and insects. Another aspect that remains poorly explored in the literature is how biological control agents (insects), introduced to control invasive weeds, respond to volatiles from non-host native plants, despite increasing awareness that volatile cues are essential for host selection of these phytophagous insects23,24.
To address these knowledge gaps, we explored interactions between native and introduced plant and insect species that coexist on the North Island Central Plateau of New Zealand. This is a sub-alpine environment where the European introduced plants, Cytisus scoparius (Scotch broom; henceforth broom) and Calluna vulgaris (heather) are highly invasive. Information about broom’s introduction and establishment is scarce. Its potential to invade the area was only realised in the 1960s25 and although several biocontrol agents have been introduced in this region, they have only been partially successful26. Heather was deliberately introduced to the Central Plateau in 191227 and is now widespread, contributing to a decline in plant and arthropod biodiversity28,29,30. To help control the spread of heather in this region, Lochmaea suturalis (heather beetle), imported from the United Kingdom, was released in 1996 and despite initial poor performance, it is now successfully controlling this plant in some areas26,31.
To determine the impact of invasive plants’ airborne cues on a native plant’s VOCs, we explored the volatile emissions of the native shrub, Leptospermun scoparium (mānuka), when grown adjacent to heather or broom in a semi-field experiment using potted plants without above- or below-ground physical contact. Mānuka is an economic and culturally relevant plant species in New Zealand, due to its use in premium honey production and being considered a ‘treasured’ (Taonga) species for indigenous Māori communities32. Mānuka above-ground volatile emissions have only recently been characterised33,34, and under field conditions, VOC emissions of mānuka were observed to be lower at sites where it co-occurs with invasive species, suggesting that invasive species could disrupt the communication networks of this native shrub33. However, the ability of this native plant to perceive and respond to invaders’ VOCs has not been previously investigated.
To explore potential disruption in native plant–insect communication by invasive plant species, we performed a series of laboratory assays to investigate the host-selection of the endemic mānuka beetle, Pyronota festiva when presented with volatiles from its host plant (mānuka) or heather individually, and the two plants simultaneously, and conducted follow up preference/feeding assays using plant foliage. In a previous field study, we recorded lower numbers of P. festiva on its preferred mānuka host in areas invaded by exotic weeds33, and we have on several occasions observed the beetle on heather in the field (personal observations; Fig. 1). However, whether P. festiva will feed on heather when mānuka is scarce remains unknown. Similar bioassays were conducted for the introduced biocontrol agent (the heather beetle, L. suturalis) to explore its behaviour towards a native plant and to confirm that it retains its host specificity.
Materials and methods
All the methods, including plant and invertebrate collection, followed relevant institutional and national guidelines and legislation.
Volatile emissions of mānuka neighbouring conspecifics or invasive species
Potted wild mānuka plants (≈ one year old) were purchased from TreesforBees Plant Nursery, New Zealand, in May 2019. These plants were transplanted into 3.3 L plastic pots with the following soil mix: 80% bark fines, 20% pumice, 6 kg Agroblend, 3 kg dolomite, 1 kg aglime and 1 kg gypsum per m3. Young heather and broom plants were collected from a wild population on the North Island’s Central Plateau, New Zealand, in August 2018 and transplanted into 3.3 L plastic pots, keeping the root-bound soil intact. All plants were maintained under the same conditions in an outdoor cage before commencement of experiments.
In September 2019, the potted plants were transferred to experimental plots (2 m × 3 m) in open pasture land (Long. 175.612167–Lat. − 40.387417) at Massey University. The plants were placed on weed matting and, using an automatic sprinkler system, watered twice and four times daily during spring and summer, respectively. The vegetation surrounding each plot was kept low by periodic scything. Each plot consisted of 10 mānuka plants intermingled with and an equal number of conspecifics or one of the two invaders (heather or broom), ensuring no above-ground or below-ground physical contact. Each treatment was replicated twice (×2), and all plots were set ≥ 6 m apart (Supplementary Fig. S1).
VOCs were collected from 6 healthy mānuka plants per plot from 7 to 9th January 2020. All volatile collections were done under sunny, dry conditions, and samples were collected from treatments simultaneously to account for collection time effects. Headspace volatiles of mānuka were collected using the “push–pull” sampling technique35. Briefly, proportions of mānuka foliage were bagged in new Glad ® oven bags. Carbon-filtered air was simultaneously pushed into and pulled out of bags through PTFE tubes connected to a portable volatile collection system pump (PVAS22; Volatile Assay Systems Rensselaer NY, USA). Compounds were trapped onto volatile collection filters containing 30 mg HayeSep Q adsorbent (Volatile Assay Systems Rensselaer, NY, USA). Each volatile collection lasted 2 h. The bagged foliage was then excised, oven-dried (60 °C for 72 h) and used to estimate VOC emission per dry weight (g).
Volatile collection filters were eluted using 200 μL of 99% hexane (Sigma Aldrich) containing 10 ng/mL nonyl acetate (C11H22O2) (Sigma Aldrich) as an internal standard. The eluted samples were analysed using gas chromatography coupled to mass spectrometry (GC–MS) (QP2010; GCMS Solution version 2.70, Shimadzu Corporations, Kyoto, Japan) with a 30 m × 250 μm × 0.25 μm TG-5MS column (Thermo Fisher Scientific, Waltham, MA, USA). The GC–MS programme followed35, and compounds were tentatively identified by comparing them to the National Institute of Standards library and confirmed using commercial standards when available. The air in clean oven bags without plants (blanks) was analysed, and contaminants were excluded from the analysis. Compounds identified from plants in both plots were pooled for respective treatments for analysis.
Host-selection and feeding behaviours of adult Pyronota festiva (mānuka beetle) and Lochmaea suturalis (heather beetle)
Beetle and plant collection
Adult Pyronota festiva and Lochmaea suturalis were collected from the Central Plateau in early summer 2021 using a beating tray. The collected beetles were maintained in cages and fed with their host plant foliage under temperature-controlled conditions (20 °C) with a 12:12 h light/dark cycle. Young heather plants were collected from the Central Plateau, while mānuka plants (≈ 6 months old) were purchased from a commercial nursery. Both plant species were maintained in an outdoor cage for ≈ 7 months before the experiment. Each plant used for the bioassays was healthy and undamaged. Plants were removed from the outdoor cage once their foliage was excised for bioassays to avoid inducing changes in the volatile profiles of the remaining healthy plants. Beetles were starved 24 h prior to their trial, and each beetle was tested only once.
Y-tube bioassays
We tested the preference of adult P. festiva and L. suturalis using a glass Y-tube olfactometer. The Y-tube was laid horizontally without any inclination on a benchtop with a white background. Y-tube arms were 2 cm internal diameter × 13.2 cm long. Using a portable volatile collection pump (PVAS22; Volatile Assay Systems Rensselaer NY), connected with PTFE tubes, carbon-filtered air was pushed at a rate of 0.8 L min−1 into two separate 20 cm × 24 cm glass chambers. Each chamber contained a different treatment (i.e., clean air, heather, or mānuka foliage). For the plant treatments, 4 g of the respective plant foliage were placed in each chamber. Air from the chambers was then pushed into the assigned Y-tube arm. The trials were conducted in a temperature-controlled room (22 °C), with no overhead lighting but the Y-tube was illuminated by a centrally positioned 50-W incandescent lamp.
Pyronota festiva and L. suturalis were separately offered a choice between Y-tube arms with the following olfactory cues: (1) heather or clean air, (2) mānuka or clean air and (3) heather or mānuka. Each beetle was placed at the release point and given 10 min to respond to the treatment. A choice was recorded when a beetle moved past an arm’s halfway mark and stayed there for 30 s. Beetles that did not choose within the allocated time were noted as a no choice. Thirty (30) insects were tested for each treatment per beetle species, and the Y-tube was cleaned and rotated after each trial. Foliage in the glass chambers was replaced with fresh material after 10 trials, and the Y-tube system was thoroughly cleaned with non-scented soap and oven-dried for 30 min (80 °C) between treatments to prevent cross contamination.
Petri dish trials
Adult P. festiva and L. suturalis’ preference for their host and non-host plants was investigated in 9 cm × 1.5 cm Petri dishes lined with moistened filter paper. Twigs of healthy heather and mānuka plants inserted in separate water-filled Eppendorf tubes were used as the tested plant materials, while a green non-scented plastic was used as a blank. The following treatment combinations were tested for each beetle species: (1) heather + blank, (2) mānuka + blank and (3) heather + mānuka. One beetle was placed in the middle of a Petri dish containing one of the treatments, with 30 replicates conducted for each beetle species. The location of each beetle on either plant or blank was recorded at 0.25, 0.5, 1, 2, 16 and 32 h, after which the foliage was visually examined and recorded as damaged or undamaged. The trials were conducted in a temperature-controlled room (22 °C) with a 16:8 h light/dark cycle.
Data analysis
All statistical analyses were performed using R version 4.1.036. To assess the effect of invasive plants’ airborne cues on mānuka VOC emissions, we used linear discriminant analysis (LDA) to establish if we could classify mānuka into the the three neighbour-treatments (i.e., heather, broom or conspecifics) based on the individual volatile compounds. The data was standardised, and LDA was performed using the package “Mass”37. In addition, we counted the number of compounds that were abundant in the plants’ headspace and compared them between treatments using a generalised linear model (GLM) with Poisson distribution (log-link). The likelihood ratio test was used to estimate the significance of the predictor, and when significant, the “relevel” function was used to construct a series of pairwise comparisons. We also grouped the volatile compounds into their major chemical classes (Supplementary Table S1) and compared them between treatments using GLM, as already described, but with Gamma distribution (log-link). The beetle bioassay data were analysed using the two-tailed Chi-squared (Χ2) test.
Results
Volatile emissions of mānuka neighbouring conspecifics or invasive species
Thirty-two volatile compounds, predominantly sesquiterpenes and monoterpenes, were identified as most abundant in the headspace of mānuka (Supplementary Tables S1 and S2). Based on these compounds, we used linear discriminant analysis (LDA) to classify mānuka into three distinct groups, with the results showing a clear separation between conspecific and heterospecific groupings (Fig. 2). Compounds including (E)-β-Caryophyllene, (Z)-β-Ocimene, (Z,E)-α-Farnesene, α-Amorphene, α-Selinene, β-Elemene, Calamenene, δ-Cadinene, Humulene, Isoledene, Limonene, Methyl salicylate and Nerol had higher loading scores, which correspond with the higher emission of these compounds by mānuka neighbouring conspecifics (Supplementary Tables S2 and S3).
The total number of compounds in the headspace of mānuka did not differ significantly between the three treatments (X2 = 1.67, df = 2, P = 0.433, Fig. 3a). Total emissions (X2 = 7.91, df = 2, P = 0.019, Fig. 3b) and those of specific chemical classes differed between treatments (Supplementary Table S4). Green leaf volatiles (X2 = 6.82, df = 2, P = 0.033) and sesquiterpenes (X2 = 10.93, df = 2, P = 0.004) were emitted in significantly higher amounts in the mānuka-mānuka treatment, while monoterpenoids (X2 = 0.73, df = 2, P = 0.698) and other volatiles (X2 = 2.79, df = 2, P = 0.248) did not show significant differences between treatments.
Host-selection and feeding behaviours of adult Pyronota festiva (mānuka beetle) and Lochmaea suturalis (heather beetle)
In the Y-tube olfactometer trials, when plants were paired with blank (clean air), P. festiva was significantly attracted to its host plant (X2 = 10.15, df = 1, P = 0.001) and had a slight, but not significant, preference for the invasive heather over clean air (X2 = 0.77, df = 1, P = 0.381, Fig. 4a). However, P. festiva could not differentiate between its host plant volatiles and those of heather in the paired choice test and selected equally the respective Y-tube arms (X2 = 0.00, df = 1, P = 1.000, Fig. 4b).
Adult L. suturalis, on the other hand, showed a significant preference for one of the treatments in all trials, where it preferred its host plant’s volatiles (X2 = 22.84, df = 1, P < 0.001), and those of mānuka (X2 = 4.51, df = 1, P = 0.034) compared to clean air (Fig. 4a). But, unlike P. festiva, L. suturalis preferred the volatiles of its host plant when offered the two plants simultaneously (X2 = 11.74, df = 1, P = 0.001, Fig. 4b).
Beetle host selection and feeding preferences for their host and non-host plants were also assessed in Petri dishes for 32 h, with observations at 0.5, 1, 2, 16 and 32 h. At any measured time, P. festiva showed a significant preference for mānuka and heather cues over a blank (Fig. 5a,b). When offered mānuka and heather cues simultaneously, P. festiva showed a stronger preference for its host plant, although heather attracted some individuals (Fig. 5c, Supplementary Table S5).
Similarly, L. suturalis showed a significant preference for its host plant at all measured times and sometimes for mānuka when heather was not available (Fig. 6a,b). The beetle selected its host plant over mānuka when presented with the two simultaneously (Fig. 6c, Supplementary Table S5).
After 32 h, beetles were removed from the Petri dishes, and foliar feeding damage was visually inspected. We found significant damage when P. festiva (X2 = 5.40, P = 0.020) and L. suturalis (X2 = 54.07, P < 0.001) were only offered their respective host plants (Fig. 7a). However, when offered only their non-host plants, damage signs were extremely low on heather offered to P. festiva (X2 = 19.27, P < 0.001) and on mānuka offered to L. suturalis (X2 = 11.27, P = 0.001), (Fig. 7a). About 60% of P. festiva (X2 = 24.96, P < 0.001) and 90% of L. suturalis (X2 = 46.84, P < 0.001) fed on their respective host when offered simultaneously with a non-host plant, with none of the beetles feeding on the non-host plant (Fig. 7b).
Discussion
There is a vast body of literature exploring the ecological roles of plant volatiles and allelopathic potential of invasive plants—focused mainly on root exudates (see excellent reviews by6,38,39,40) but comparatively few studies have explored the role of volatile organic compounds (VOCs) in interactions between native and invasive species. In this study, we investigated some interactions between native and introduced plants and insects mediated by VOCs, including (1) the effect of invasive plants on a native plant’s VOC emissions, and (2) the host-selection and feeding preference of a native insect and an introduced biocontrol agent when presented with volatiles only and a combination of cues from host and non-host plants.
Impacts of neighbouring plant identity on native plants’ VOC emissions
The notion of ‘talking plants’ has been around the scientific literature for about fifty years, since Rhoades first reported that uninfested Sitka willow (Salix sitchensis) in close proximity to herbivore-infested conspecifics expressed higher levels of herbivore resistance than plants of the same species growing further away41,42. Since then, this phenomenon has been reported for multiple species43, and it is now widely accepted that healthy plants or plant parts can detect herbivore-induced volatiles from a neighbour (or attacked plant part) and initiate changes in their defensive chemistry to prepare for future attack (e.g., through priming). Work by Barbosa et al.44 highlighted that plant associations could increase (associational susceptibility) or decrease (associational resistance) the likelihood of plant detection by herbivores, suggesting volatiles might play a role. Further to this, several reports (e.g.,21,45) showed that the volatile compounds emitted by a plant depended on the neighbouring species and that responses would depend on whether the plant is surrounded by kin or non-kin. Karban and co-workers described the occurrence of ‘geographic dialects’, with plants from different ranges having distinct volatile profiles and responding strongly to VOCs emitted by others in the same geographical area22. This evidence invites the question if native plants can detect and respond to the VOCs of invasive plants.
Here, in a semi-field experiment, we explored the VOC emissions of the New Zealand native plant, mānuka, in the presence of two exotic invasive species, heather and broom (without physical above- or below-ground contact). The results reveal significantly lower VOC emissions by mānuka neighouring invasives than conspecifics, particularly when paired with heather, supporting previous field observations where mānuka was observed to have lower VOC emissions in invaded sites33, and suggest that above-ground volatiles alone are at least partly accountable for this response.
Increasingly, reports show that the species composition of neighbouring vegetation strongly influences VOC emissions. For instance, Trifolium pratense reduced its volatile emissions when growing with conspecifics, possibly to avoid herbivore attraction and reduce nearby heterospecifics’ ability to eavesdrop on herbivore information shared between conspecifics21,45. Contrary, lower emissions have been reported for Pinus halepensis46, Rosmarinus officinalis, and Cistus albidus47 under interspecific interactions, showing that responses to neighbouring plants may vary depending on the species involved.
We hypothesise that changes in VOC emissions by native plants can occur via two non-exclusive mechanisms (a) as a direct response to the cues of a competing plant, e.g., volatile and non-volatile compounds or (b) as an indirect response to environmental changes caused by invasive species, e.g., changes in light or soil nutrients. The contribution of these direct and indirect factors is difficult to disentangle under field conditions, but previous studies21,45 show that aboveground VOCs alone are sufficient to elicit changes in the emissions of receiving plants and that responses will vary depending on the neighbour’s identity. We also acknowledge the possibility of ‘chemical camouflage’ (i.e., the adsorbance and re-release of neighbouring plants’ chemical compounds) as a potential factor that could contribute to higher emissions in some plots48,49,50. Therefore, further studies are required to elucidate the mechanisms behind the observed phenomenon.
The exact mechanism of plant “olfaction” (i.e., perception of volatile cues by a plant) is still not well-understood. Questions like whether plants have VOC-sensing receptors and other transporters or VOCs are perceived through direct modification of cell membranes, remain unanswered51,52. Nevertheless, receiving plants use volatile cues to establish their neighbours’ identity and state, informing their decisions about imminent threats such as competition and herbivory19,20,39,53. Therefore, upon deciphering neighbours’ volatile cues, it is plausible that plants alter their emissions for a number of purposes (a) to benefit conspecifics (e.g., increased emission to attract pollinator and herbivores’ natural enemies), (b) to harm competitors (e.g., increased emission for VOC-mediated allelopathy), (c) to reduce plant apparency to antagonists (i.e., reduced emission to avoid herbivores), or (d) as preparedness for competition (e.g., reduce emissions to reallocate resources to growth and reproduction).
In the case of mānuka, the reduced emissions when exposed to the cues of aggressive neighbours could be preparedness for competition39,54. Thus, the plant lowers its emission to reallocate much-needed resources to compete with the invaders, since VOC production comes at a cost55. Alternatively (or simultaneously) reduced emissions in response to an invader’s cues could be a means to minimise apparency to avoid nectar robbers or herbivores that can negatively affect its fitness44. Testing these hypotheses would be another step toward understanding the impact of invasive species on natives’ chemical communication in this and similar systems.
Herbivores’ response to host and non-host cues
Plant volatiles play a vital role in host plant selection by phytophagous insects16. Most insects appear to distinguish host and non-host plants based on specific blends of ubiquitous volatiles, although some specialists are known to use taxonomically restricted compounds (such as isothiocyanates in cruciferous plants) to find their hosts16. However, responses to plant volatiles are not entirely fixed, since early feeding experience and learning can play a role in determining future choices56,57,58,59, allowing for some behavioural plasticity. During plant invasions, native insects are confronted with new olfactory cues from plants they did not co-evolve with. Likewise, introduced biocontrol agents will experience a similar challenge when faced with native plants. Exploring if these new cues affect native insects’ host-selection process is essential to understanding the ecological impacts of invasive plants (i.e., potential disruption of native plant–insect communication), and to ensure the safety of introduced biocontrol agents.
In this work, we explored the behavioural responses of the native mānuka beetle (P. festiva) and the introduced heather beetle (L. suturalis) towards volatiles of their host and non-host plants and their combination in a Y tube olfactometer. Our results showed a strong attraction response by the native mānuka beetle towards its host-plant’s volatile cues, when plant volatiles were presented against clean air, but no preference when host and non-host cues were presented simultaneously. In contrast, the introduced heather biocontrol agent showed an interest in the non-host plant (mānuka) when presented against clean air, but showed a much stronger preference for its host’s volatile cues irrespective of when presented alone or in combination with non-host cues.
Host-searching and selection by adult phytophagous insects involves complex decisions like prioritising their own diet versus choosing plants that would be best for their offspring16,60. This may be a challenge for species like P. festiva where adults and juveniles feed on different plants or organs, with grubs feeding on roots of different species, whereas adults feed mainly on the foliage of mānuka plants61,62,63.
The host range for P. festiva includes pasture, Leptospermum scoparium (mānuka), Kunzea ericoides (kānuka), Discaria toumatou (matagouri) and even invasive Rosa rubiginosa (briar)61,62,63. Considering this, the beetle is probably either attracted by ‘signatory compounds’ shared by common hosts or simply avoids cues from non-hosts64. Analyses of the volatile profiles of P. festiva’s host (mānuka) and non-host plant (heather) reveal that they share many compounds, while some other compounds differ between species33,35. Further studies involving electroantennography could be useful in identifying the compounds (attractants or deterrents) that are relevant in the host selection of P. festiva.
We found that P. festiva was not significantly attracted to heather’s volatile cues when offered in the no-choice test but was equally attracted to mānuka and heather cues when provided simultaneously in the Y-tube, suggesting that the presence of heather may interfere with the beetle’s host searching behaviour. However, in the Petri dish trial, where other cues (i.e., visual, gustatory, and tactile) were present, P. festiva did not feed on heather when offered simultaneously with mānuka in the Petri dish, suggesting that visual, gustatory or tactile cues play an important role in host acceptance for this species.
Lochmaea suturalis, on the other hand, is a monophagous insect and was selected as a biocontrol agent for heather on the Central Plateau because of the high levels of damage it causes to its host plant in Europe65. L. suturalis was first released on the Central Plateau in 1996, following years of host-range testing but initially established poorly, attributed to adverse weather conditions31 and possibly low foliar nitrogen levels66 and the consequences of genetic bottlenecking67. Subsequent releases have been more successful, with beetle outbreaks causing significant damage to heather in many areas26. Recent evidence also shows that heather produces many volatile compounds, including green leaf volatiles, terpenes and aldehydes35,68, which may be crucial in communicating with its natural enemy, L. suturalis.
Our laboratory assays show that L. suturalis is significantly attracted to its host-plant volatile cues when offered alone or simultaneously with that of a non-host plant in the Y-tube. Nevertheless, the beetle was significantly attracted to non-host volatile cues when presented against a blank, raising questions about its foraging behaviour in areas with low heather densities. The Petri dish trials somewhat answered this. The beetle chose its host plant exclusively over mānuka when both were offered simultaneously. Although the beetle selected mānuka when given no other choice, this was not often significant, and only a few (26.7%) of the tested beetles attempted to feed on mānuka in the absence of its host plant.
Host-switching or host-range expansion by biocontrol agents is rare in contemporary biocontrol programmes partly because of sufficient pre-release tests to ensure high host specificity, but it may sometimes occur69. For instance, a study in Nebraska, USA, showed that the introduced biocontrol agent Rhinocyllus conicus attacks native Cirsium undulatum significantly more in landscapes invaded by the exotic Carduus nutans than in agriculture landscapes and other areas without Carduus nutans, highlighting the risk of native plants serving as secondary hosts70. In our trials, we did not find substantial evidence of L. suturalis feeding on mānuka, suggesting that it retains its high host-specificity, and that host switch or host range expansion is unlikely to occur.
Since both beetle species were collected in the field as adults and non-sexed, we cannot provide further detail regarding their previous feeding experience or whether sexes differ in their behaviour and preferences. We, therefore, encourage future studies to explore these interactions using laboratory-reared beetles and test separately for larvae, adults, and different sexes.
Conclusion
Our results demonstrate that invasive plants can influence native plants’ volatile emissions. In this case, we found reduced VOC emissions in a native plant (Leptospermum scoparium) neighbouring the invasive weed Calluna vulgaris. Alterations in VOC emission could be the result of responses to environmental changes induced by invaders or to their chemical cues. Alternatively, native plants could passively adsorb and re-release neighbouring plants’ VOCs. Regardless of the mechanism, changes in native plants’ volatile profiles could interfere with their chemical communication and interactions. Our data also show that native insects’ chemical interactions with their host can be disrupted by invasive plants. We found that a native insect (Pyronota festiva) was not successful in discriminating between its host plant and an invasive non-host when their volatiles were presented simultaneously, suggesting that native insects may face challenges finding their host in invasive plant-dominated landscapes. However, the native insect showed a clear preference for its host plant in feeding assays where other cues were present, highlighting the importance of non-volatile cues. Our results also reinforce that the introduced biocontrol agent against heather (Lochmaea suturalis) is highly host-specific and does not pose any serious threat to mānuka and possibly other non-target plants. Together, these results contribute to filling the knowledge gap on the role of plant volatiles in interactions between native and introduced species, however, multiple questions remain open for future exploration.
Data availability
All relevant data supporting the findings of this study are available from the corresponding author upon reasonable request.
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Acknowledgements
The authors appreciate the help of Kyaw Min Tun during VOC data collection. We are also grateful to Shaun Nielson, Tracy Harris and Cleland Wallace for their technical support.
Funding
The College of Sciences, Massey University, supported this study through a research fund granted to ACM. The Royal Society of New Zealand also supported the work through a Fast Start Marsden Grant to ACM (MFP-MAU2004).
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A.C.M. and E.E. conceived and designed the experiment. E.E. and D.P.B. set up the experimental plots for Experiment one. E.E. collected and analysed the data for Experiment one. E.E., L.S. and D.P.B. collected and maintained beetles for Experiment two. E.E. and L.S. collected and analysed the data for Experiment two. E.E., L.S. and A.C.M. led the writing of the manuscript. D.P.B. was involved in editing and providing comments on the manuscript. All authors approved the manuscript for publication.
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Effah, E., Svendsen, L., Barrett, D.P. et al. Exploring plant volatile-mediated interactions between native and introduced plants and insects.
Sci Rep 12, 15450 (2022). https://doi.org/10.1038/s41598-022-18479-z
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Received: 04 May 2022
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Accepted: 12 August 2022
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Published: 14 September 2022
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DOI: https://doi.org/10.1038/s41598-022-18479-z
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Science
The total solar eclipse in North America could shed light on a persistent puzzle about the sun – Phys.org
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A total solar eclipse takes place on April 8 across North America. These events occur when the moon passes between the sun and Earth, completely blocking the sun’s face. This plunges observers into a darkness similar to dawn or dusk.
During the upcoming eclipse, the path of totality, where observers experience the darkest part of the moon’s shadow (the umbra), crosses Mexico, arcing north-east through Texas, the Midwest and briefly entering Canada before ending in Maine.
Total solar eclipses occur roughly every 18 months at some location on Earth. The last total solar eclipse that crossed the US took place on August 21 2017.
An international team of scientists, led by Aberystwyth University, will be conducting experiments from near Dallas, at a location in the path of totality. The team consists of Ph.D. students and researchers from Aberystwyth University, Nasa Goddard Space Flight Center in Maryland, and Caltech (California Institute of Technology) in Pasadena.
There is valuable science to be done during eclipses that is comparable to or better than what we can achieve via space-based missions. Our experiments may also shed light on a longstanding puzzle about the outermost part of the sun’s atmosphere—its corona.
The sun’s intense light is blocked by the moon during a total solar eclipse. This means that we can observe the sun’s faint corona with incredible clarity, from distances very close to the sun, out to several solar radii. One radius is the distance equivalent to half the sun’s diameter, about 696,000km (432,000 miles).
Measuring the corona is extremely difficult without an eclipse. It requires a special telescope called a coronagraph that is designed to block out direct light from the sun. This allows fainter light from the corona to be resolved. The clarity of eclipse measurements surpasses even coronagraphs based in space.
We can also observe the corona on a relatively small budget, compared to, for example, spacecraft missions. A persistent puzzle about the corona is the observation that it is much hotter than the photosphere (the visible surface of the sun). As we move away from a hot object, the surrounding temperature should decrease, not increase. How the corona is heated to such high temperatures is one question we will investigate.
We have two main scientific instruments. The first of these is Cip (coronal imaging polarimeter). Cip is also the Welsh word for “glance,” or “quick look.” The instrument takes images of the sun’s corona with a polariser.
The light we want to measure from the corona is highly polarized, which means it is made up of waves that vibrate in a single geometric plane. A polarizer is a filter that lets light with a particular polarization pass through it, while blocking light with other polarizations.
The Cip images will allow us to measure fundamental properties of the corona, such as its density. It will also shed light on phenomena such as the solar wind. This is a stream of sub-atomic particles in the form of plasma—superheated matter—flowing continuously outward from the sun. Cip could help us identify sources in the sun’s atmosphere for certain solar wind streams.
Direct measurements of the magnetic field in the sun’s atmosphere are difficult. But the eclipse data should allow us to study its fine-scale structure and trace the field’s direction. We’ll be able to see how far magnetic structures called large “closed” magnetic loops extend from the sun. This in turn will give us information about large-scale magnetic conditions in the corona.
The second instrument is Chils (coronal high-resolution line spectrometer). It collects high-resolution spectra, where light is separated into its component colors. Here, we are looking for a particular spectral signature of iron emitted from the corona.
It comprises three spectral lines, where light is emitted or absorbed in a narrow frequency range. These are each generated at a different range of temperatures (in the millions of degrees), so their relative brightness tells us about the coronal temperature in different regions.
Mapping the corona‘s temperature informs advanced, computer-based models of its behavior. These models must include mechanisms for how the coronal plasma is heated to such high temperatures. Such mechanisms might include the conversion of magnetic waves to thermal plasma energy, for example. If we show that some regions are hotter than others, this can be replicated in models.
This year’s eclipse also occurs during a time of heightened solar activity, so we could observe a coronal mass ejection (CME). These are huge clouds of magnetized plasma that are ejected from the sun’s atmosphere into space. They can affect infrastructure near Earth, causing problems for vital satellites.
Many aspects of CMEs are poorly understood, including their early evolution near the sun. Spectral information on CMEs will allow us to gain information on their thermodynamics, and their velocity and expansion near the sun.
Our eclipse instruments have recently been proposed for a space mission called moon-enabled solar occultation mission (Mesom). The plan is to orbit the moon to gain more frequent and extended eclipse observations. It is being planned as a UK Space Agency mission involving several countries, but led by University College London, the University of Surrey and Aberystwyth University.
We will also have an advanced commercial 360-degree camera to collect video of the April 8 eclipse and the observing site. The video is valuable for public outreach events, where we highlight the work we do, and helps to generate public interest in our local star, the sun.
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Science
Mar 30: An Australian Atlantis and other lost landscapes, and more… – CBC.ca
Quirks and Quarks54:00An Australian Atlantis and other lost landscapes, and more…
On this week’s episode of Quirks & Quarks with Bob McDonald:
Archaeologists identify a medieval war-horse graveyard near Buckingham Palace
Quirks and Quarks9:04Archaeologists identify a medieval war-horse graveyard near Buckingham Palace
We know knights in shining armour rode powerful horses, but remains of those horses are rare. Now, researchers studying equine remains from a site near Buckingham Palace have built a case, based on evidence from their bones, that these animals were likely used in jousting tournaments and battle. Archaeologist Katherine Kanne says the bone analysis also revealed a complex, continent-crossing medieval horse trading network that supplied the British elite with sturdy stallions. This paper was published in Science Advances.
In an ice-free Arctic, polar bears are dining on duck eggs — and gulls are taking advantage
Quirks and Quarks9:22In an ice-free Arctic, Polar bears are dining on duck eggs — and gulls are taking advantage
Researchers using drones to study ground-nesting birds in the Arctic have observed entire colonies being devastated by marauding polar bears that would normally be out on the ice hunting seals, except the ice isn’t there. What’s more, now they’re enabling a second predator — hungry gulls that raid the nests in the bears’ wake. Andrew Barnas made the observations of this “gull tornado” by following around polar bears in East Bay Island in Nunavut. The research was published in the journal Ecology and Evolution.
A NASA mission might have the tools to detect life on Europa from space
Quirks and Quarks8:05A NASA mission might have the tools to detect life on Europa from space
NASA’s Europa Clipper mission, due to launch this fall, is set to explore the jewel of our solar system: Jupiter’s moon, Europa. The mission’s focus is to determine if the icy moon, thought to harbour an ocean with more water than all of the water on Earth, is amenable to life. However, postdoctoral researcher Fabian Klenner, now at the University of Washington, demonstrated how the spacecraft may be able to detect fragments of bacterial life in a single grain of ice ejected from the surface of the moon. The study was published in the journal Science Advances.
Pollution is preventing pollinators from recognizing floral plants by scent
Quirks and Quarks7:50Pollution is preventing pollinators from finding plants by scent
Our polluted air is transforming floral scents so pollinators that spread their pollen can no longer recognize them. In a new study in the journal Science, researchers found that a certain compound in air pollution reacts with the flower’s scent molecules so pollinators — like the hummingbird hawk-moths that pollinate at night — fail to recognize them. Jeremy Chan, a postdoctoral researcher at the University of Naples, said the change in scent made the flowers smell “less fruity and less fresh.”
An Australian Atlantis and underwater archeological remains in the Baltic
Quirks and Quarks17:14An Australian Atlantis and underwater archeological remains in the Baltic
During the last ice age, sea levels were more than 100 metres lower than they are today, which means vast tracts of what are currently coastal seafloor were dry land back then. Geologists and archaeologists are searching for these lost landscapes to identify places prehistoric humans might have occupied. These included a country-sized area of Australia that could have been home to half a million people. Archaeologist Kasih Norman and her colleagues published their study of this now-drowned landscape in Quaternary Science Reviews.
Another example is an undersea wall off the coast of Northern Germany that preserves an underwater reindeer hunting ground, described in research led by Jacob Geersen, published in the journal PNAS.
Science
Solar eclipse April 8 – South Grey News
March 28, 2024
Graphic: Appalachian Mtn Club
Grey Bruce Public Health is urging residents to resist the temptation to look directly at the sun during the upcoming solar eclipse and take steps to safeguard their visual health during this relatively rare celestial event.
On April 8, 2024, parts of southern and eastern Ontario will experience a total solar eclipse for the first time since 1925. Grey-Bruce will be outside of the so-called Path of Totality — a narrow area where the moon will completely block out the sun — but will still experience a partial eclipse.
The eclipse is expected to begin at about 2 pm and continue until 4:30 pm The eclipse will peak around 3:20 pm.
It is never safe to stare directly at the sun, but it may be tempting to do so during a solar eclipse.
Looking directly at the sun during an eclipse can cause retinal burns, blurred vision, and/or temporary or permanent loss of visual function, according to the Ontario Association of Optometrists. Damage to the eyes can occur without any sensation of pain.
Grey Bruce Public Health advises the following:
- Do not look directly at the sun without proper eye protection during the solar eclipse. Looking at even a small sliver of the sun before or after the eclipse without proper eye protection can harm vision.
- Keep a close eye on children and other vulnerable family members during the eclipse to ensure they do not inadvertently look up at the sun without proper eye protection.
- To safely view the eclipse, ISO-certified eclipse glasses that meet the ISO 12312-2 international safety standard must be worn. Ensure these glasses are in good condition, without any wrinkles or scratches, and that they fully cover the entire field of vision. Put on the glasses when looking away from the sun, then look at the eclipse. Look away from the sun before taking the glasses off.
- Regular sunglasses or homemade filters will not protect the eyes.
- It is not safe to view the eclipse through a camera/phone lens, telescope, binoculars, or any other optical device.
Other ways to safely experience the solar eclipse include watching a livestream of the event or creating and using an eclipse box or pinhole projector.
Anyone experiencing temporary vision loss or blurred vision during or after the eclipse should speak with their eye care professional or healthcare provider as soon as possible.
Anyone experiencing blindness (immediate or delayed) after viewing the eclipse must seek emergency care immediately.
More information on the upcoming eclipse is available on the GBPH website.
At South Grey News, we endeavour to bring you truthful and factual, up-to-date local community news in a quick and easy-to-digest format that’s free of political bias. We believe this service is more important today than ever before, as social media has given rise to misinformation, largely unchecked by big corporations who put profits ahead of their responsibilities.
South Grey News does not have the resources of a big corporation. We are a small, locally owned-and-operated organization. Research, analysis and physical attendance at public meetings and community events requires considerable effort. But contributions from readers and advertisers, however big or small, go a long way to helping us deliver positive, open and honest journalism for this community.
Please consider supporting South Grey News with a donation in lieu of a subscription fee and let us know that our efforts are appreciated. Thank you.
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