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Papers by Robert Glinwood

Research paper thumbnail of The interaction between bird cherry-oat aphid and barley in a changing climate

South African Journal of Botany

Research paper thumbnail of Landing Preference and Reproduction of Rhopalosiphum padi (Hemiptera: Aphididae) in the Laboratory on Three Maize, Potato, and Wheat Cultivars

Journal of insect science (Online), 2015

The bird cherry-oat aphid Rhopalosiphum padi (L.) transmits the nonpersistent Potato virus Y (PVY... more The bird cherry-oat aphid Rhopalosiphum padi (L.) transmits the nonpersistent Potato virus Y (PVY) to seed potatoes. Planting a nonvirus host plant around the main crop can reduce PVY incidence, because aphids tend to land in high numbers at the edge of a field and the crop border acts as a virus sink. This study determined R. padi landing and settling preferences and reproductive rates on three cultivars each of maize and wheat compared with potato in the laboratory as a basis for identifying an attractive crop border plant. Aphids were reared on maize and wheat to control for bias due to previous experience. Irrespective of origin, alates preferred to land almost exclusively on maize and wheat rather than on potato cultivars in choice experiments. Aphid settling on the maize and wheat cultivars depended on aphid origin. In no-choice experiments, R. padi produced the highest number of offspring on the wheat cultivars, irrespective of origin. Plant nitrogen content and trichome dens...

Research paper thumbnail of Red:far-red light conditions affect the emission of volatile organic compounds from barley (Hordeum vulgare), leading to altered biomass allocation in neighbouring plants

Annals of botany, Jan 7, 2015

Volatile organic compounds (VOCs) play various roles in plant-plant interactions, and constitutiv... more Volatile organic compounds (VOCs) play various roles in plant-plant interactions, and constitutively produced VOCs might act as a cue to sense neighbouring plants. Previous studies have shown that VOCs emitted from the barley (Hordeum vulgare) cultivar 'Alva' cause changes in biomass allocation in plants of the cultivar 'Kara'. Other studies have shown that shading and the low red:far-red (R:FR) conditions that prevail at high plant densities can reduce the quantity and alter the composition of the VOCs emitted by Arabidopsis thaliana, but whether this affects plant-plant signalling remains unknown. This study therefore examines the effects of far-red light enrichment on VOC emissions and plant-plant signalling between 'Alva' and 'Kara'. The proximity of neighbouring plants was mimicked by supplemental far-red light treatment of VOC emitter plants of barley grown in growth chambers. Volatiles emitted by 'Alva' under control and far-red light-e...

Research paper thumbnail of Brassicaceae cover crops reduce Aphanomyces pea root rot without suppressing genetic potential of microbial nitrogen cycling

Plant and Soil, 2015

Aims Brassicaceae cover crops can be used to suppress soil-borne pathogens. The aim was to invest... more Aims Brassicaceae cover crops can be used to suppress soil-borne pathogens. The aim was to investigate the effect of different brassicas with different glucosinolate profiles on the development of Aphanomyces pea root rot in subsequent pea plants, and the genetic potential of free-living N 2 -fixing bacteria and ammonia oxidising bacteria (AOB) and archaea (AOA) performing key soil ecosystem services. Methods The Brassicaceae species Brassica juncea and Sinapis alba and non-Brassicaceae species Secale cereale were grown for 11-weeks in Aphanomyces euteiches infested soil at low and high nitrogen (N) fertiliser doses. After removing both shoots and roots of the cover crops, peas were grown as a bioassay to evaluate Aphanomyces pea root rot development. Soil was sampled before harvesting the cover crops and at the end of the bioassay. Volatile compounds were collected in the root-soil environment before harvesting the Brassicaceae cover crops to determine the concentration of isothiocyanates. The abundance of genes involved in N 2 -fixing bacteria and ammonia oxidation in AOA and AOB were assessed. Results Pea root rot disease severity was reduced in Brassicaceae grown soil at the high N fertiliser dose. This was associated with increased growth of the cover crops. The growth of Brassicaceae did not suppress the abundance of N-cycling microbial communities, but rather increased the AOB at the end of the bioassay, most likely due to increased N availability. The disease suppressive effect was higher with S. alba than with B. juncea, and this coincided with a more diverse composition and higher concentration of aliphatic ITCs released from S. alba roots. Fewer nodules were formed after the Brassicaceae crops, especially Sinapis alba. Conclusions Brassicaceae cover crops, particularly S. alba, can be used to control soil-borne pathogens without major side effects on the genetic potential of beneficial soil microorganisms involved in N cycling. However, less nodule formation after brassicas indicates an effect on rhizobium activity.

Research paper thumbnail of Cycle-characteristic odour of cow urine can be detected by the female face fly (Musca autumnalis)

Reproduction in domestic animals = Zuchthygiene, 2014

Due to declining dairy cow fertility rates, there is great interest in developing tools for oestr... more Due to declining dairy cow fertility rates, there is great interest in developing tools for oestrus detection. Compounds in the volatile profile of oestrous cows are suggested as oestrus-specific, but consistent results have not been presented. Certain haematophagous arthropods can discriminate stages of the mammalian reproductive cycle based on host volatiles. This study investigated whether the face fly, Musca autumnalis de Geer (Diptera: Muscidae), can discriminate between urine from cows in oestrus and urine collected during the luteal phase. Individual flies were tested in a two-choice behavioural assay with choice between odour of oestrous or luteal urine and water (control). Flies chose the control arm significantly more when exposed to oestrous urine than when exposed to luteal urine. Analysis of volatiles showed that 1-hexadecanol (cetyl alcohol) was released in greater amounts from oestrous urine than from urine collected during the luteal phase. In a dose response assay, ...

Research paper thumbnail of arthropod pests

Plant volatiles provide herbivorous arthropods with information that allows them to discriminate ... more Plant volatiles provide herbivorous arthropods with information that allows them to discriminate between host and non-host plants. Volatiles may also indicate plant stress status, and natural enemies can use herbivore-induced plant volatiles as cues for prey location. Neighbouring plants may also make use of volatile cues to prepare for herbivore attack. Since both constitutive and inducible plant volatile emissions can

Research paper thumbnail of Aphid acceptance of barley exposed to volatile phytochemicals differs between plants exposed in daylight and darkness

Plant signaling & behavior, 2007

It is well known that volatile cues from damaged plants may induce resistance in neighboring plan... more It is well known that volatile cues from damaged plants may induce resistance in neighboring plants. Much less is known about the effects of volatile interaction between undamaged plants. In this study, barley plants, Hordeum vulgare cv. Kara, were exposed to volatiles from undamaged plants of barley cv. Alva or thistle Cirsium vulgare, and to the volatile phytochemicals, methyl salicylate or methyl jasmonate. Exposures were made either during natural daylight or darkness. Acceptance of exposed plants by the aphid Rhopalosiphum padi was assessed, as well as the expression of putative marker genes for the different treatments. Aphid acceptance of plants exposed to either barley or C. vulgare was significantly reduced, and an effect of the volatiles from undamaged plants was confirmed by the induction of pathogenesis-related protein, PR1a in exposed plants. However the effect on aphid acceptance was seen only when plants were exposed during darkness, whereas PR1a was induced only afte...

Research paper thumbnail of Volatile interaction between undamaged plants affects tritrophic interactions through changed plant volatile emission

Plant Signaling & Behavior, 2014

Volatile interactions between unattacked plants can lead to changes in their volatile emissions. ... more Volatile interactions between unattacked plants can lead to changes in their volatile emissions. Exposure of potato plants to onion plant volatiles results in increased emission of 2 terpenoids, (E)-nerolidol and tmtt. We investigated whether this is detectable by the ladybird Coccinella septempunctata. the odor of onion-exposed potato was significantly more attractive to ladybirds than that of unexposed potato. Further, a synthetic blend mimicking the volatile profile of onion-exposed potato was more attractive than a blend mimicking that of unexposed potato. When presented individually, tmtt was attractive to ladybirds whereas (E)-nerolidol was repellent. Volatile exchange between unattacked plants and the consequent increased attractiveness for ladybirds may be a mechanism that contributes to the increased abundance of natural enemies in complex plant habitats.

Research paper thumbnail of Change in acceptability of barley plants to aphids after exposure to allelochemicals from couch-grass (Elytrigia repens)

Journal of Chemical Ecology, 2003

The response of the bird cherry-oat aphid, Rhopalosiphum padi, to barley plants was investigated ... more The response of the bird cherry-oat aphid, Rhopalosiphum padi, to barley plants was investigated following exposure of the plants to root allelochemicals from the aggressive weed couch-grass, Elytrigia (Agropyron) repens. Plants were treated either with root exudates from living couch-grass plants or with previously identified couch-grass root compounds 15-hydroxyindole-3-acetic acid, DL-5-hydroxytryptophan, L-5-hydroxytryptophan hydrate, and 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (carboline)] either separately or in mixtures. In choice and no-choice settling tests, aphid acceptance of barley plants was significantly reduced following treatment with root exudates, and the carboline when tested alone or in combination with the other compounds. In contrast, the other compounds without the carboline were less active in reducing aphid acceptance. In a probing bioassay, individual substances were either neutral or stimulatory to aphids, indicating that the reduced settling was probably not due to direct effects on aphids, but rather due to effects on the plant. This was confirmed in olfactometer assays, in which aphids were repelled by odors from barley plants following treatment with a mixture containing all four chemicals.

Research paper thumbnail of The potential for modifying plant volatile composition to enhance resistance to arthropod pests

CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2010

... aphid parasitoid Diaeretiella rapae spent more time on Arabidopsis producing elevated levels ... more ... aphid parasitoid Diaeretiella rapae spent more time on Arabidopsis producing elevated levels ... reducing risks for plant self-toxicity [cf. ... Additive and synergistic integration of multimodal cues of both hosts and non-hosts during host selection by woodboring insects. ...

Research paper thumbnail of Herbivory by a Phloem-Feeding Insect Inhibits Floral Volatile Production

PLoS ONE, 2012

There is extensive knowledge on the effects of insect herbivory on volatile emission from vegetat... more There is extensive knowledge on the effects of insect herbivory on volatile emission from vegetative tissue, but little is known about its impact on floral volatiles. We show that herbivory by phloem-feeding aphids inhibits floral volatile emission in white mustard Sinapis alba measured by gas chromatographic analysis of headspace volatiles. The effect of the Brassica specialist aphid Lipaphis erysimi was stronger than the generalist aphid Myzus persicae and feeding by chewing larvae of the moth Plutella xylostella caused no reduction in floral volatile emission. Field observations showed no effect of L. erysimimediated floral volatile emission on the total number of flower visits by pollinators. Olfactory bioassays suggested that although two aphid natural enemies could detect aphid inhibition of floral volatiles, their olfactory orientation to infested plants was not disrupted. This is the first demonstration that phloem-feeding herbivory can affect floral volatile emission, and that the outcome of interaction between herbivory and floral chemistry may differ depending on the herbivore's feeding mode and degree of specialisation. The findings provide new insights into interactions between insect herbivores and plant chemistry.

Research paper thumbnail of Volatile Exchange between Undamaged Plants - a New Mechanism Affecting Insect Orientation in Intercropping

PLoS ONE, 2013

Changes in plant volatile emission can be induced by exposure to volatiles from neighbouring inse... more Changes in plant volatile emission can be induced by exposure to volatiles from neighbouring insect-attacked plants. However, plants are also exposed to volatiles from unattacked neighbours, and the consequences of this have not been explored. We investigated whether volatile exchange between undamaged plants affects volatile emission and plant-insect interaction. Consistently greater quantities of two terpenoids were found in the headspace of potato previously exposed to volatiles from undamaged onion plants identified by mass spectrometry. Using live plants and synthetic blends mimicking exposed and unexposed potato, we tested the olfactory response of winged aphids, Myzus persicae. The altered potato volatile profile deterred aphids in laboratory experiments. Further, we show that growing potato together with onion in the field reduces the abundance of winged, host-seeking aphids. Our study broadens the ecological significance of the phenomenon; volatiles carry not only information on whether or not neighbouring plants are under attack, but also information on the emitter plants themselves. In this way responding plants could obtain information on whether the neighbouring plant is a competitive threat and can accordingly adjust their growth towards it. We interpret this as a response in the process of adaptation towards neighbouring plants. Furthermore, these physiological changes in the responding plants have significant ecological impact, as behaviour of aphids was affected. Since herbivore host plants are potentially under constant exposure to these volatiles, our study has major implications for the understanding of how mechanisms within plant communities affect insects. This knowledge could be used to improve plant protection and increase scientific understanding of communication between plants and its impact on other organisms.

Research paper thumbnail of Aphid sex pheromones: manipulation of beneficial insects for aphid population control

Pesticide Science, 1999

ABSTRACT

Research paper thumbnail of Identification of mosquito repellent odours from Ocimum forskolei

Parasites & Vectors, 2011

Background: Native mosquito repellent plants have a good potential for integrated mosquito contro... more Background: Native mosquito repellent plants have a good potential for integrated mosquito control in local settings. Ocimum forskolei, Lamiaceae, is used in Eritrea as a spatial mosquito repellent inside houses, either through crushing fresh plants or burning dry plants. We verified whether active repellent compounds could be identified using gas-chromatography coupled electroantennogram recordings (GC-EAD) with headspace extracts of crushed plants.

Research paper thumbnail of Ant-aphid mutualism: the influence of ants on the aphid summer cycle

Oikos, 2012

Th ere are few longtime studies on the eff ects on aphids of being tended by ants. Th e aim of th... more Th ere are few longtime studies on the eff ects on aphids of being tended by ants. Th e aim of this study is to investigate how the presence of ants infl uences settling decisions by colonizing aphids and the post-settlement growth and survival of aphid colonies. We conducted a fi eld experiment using the facultative myrmecophile Aphis fabae and the ant Lasius niger . Th e experiment relied on natural aphid colonization of potted plants of scentless mayweed Tripleurospermum perforatum placed outdoors. Ants occurred naturally at the fi eld site and had access to half of the pots and were prevented from accessing the remainder. Th e presence of winged, dispersing aphids, the growth and survival of establishing aphid colonies, and the presence of parasitoids were measured in relation to presence or absence of ants, over a period of fi ve weeks. Th e presence of ants did not signifi cantly infl uence the pattern of initial host plant colonization or the initial colony growth, but ant-tended aphids were subject to higher parasitism by hymenopteran parasitoids. Th e net result over the experimental period was that the presence of ants decreased aphid colony productivity, measured as the number of winged summer migrants produced from the colonized host plants. Th is implies that aphids do not always benefi t from the presence of ants, but under some conditions rather pay a cost in the form of reduced dispersal.

Research paper thumbnail of Movement by mating females of a host alternating aphid: a response to leaf fall

Oikos, 2000

. Movement by mating females of a host alternating aphid: a response to leaf fall. -Oikos 90: 43 ... more . Movement by mating females of a host alternating aphid: a response to leaf fall. -Oikos 90: 43 -49. Autumn remigrants of the host alternating bird cherry-oat aphid, Rhopalosiphum padi, colonise individual plants of the winter host, Prunus padus. However, they do not select leaves at different stages of senescence, which is surprising as leaf fall is a definitive deadline for production and development of mating females. For successful development mating females should be mobile and have the capacity to evaluate leaf senescence. Although remigrants do not selectively colonise leaves at different stages of senescence, mating females were found in very low numbers on leaves that were about to be shed. In choice test and olfactometer bioassays, abscising leaves were avoided by mating females. In the field mature leaves were available for colonisation during the period of leaf fall of P. padus. We conclude that mating females abandon abscising leaves in favour of leaves at an earlier stage of senescence, increasing the time available for mating. Our results support the role of remigrants as pioneers which identify good winter host plants, and of mating females as mobile searchers for optimal feeding and mating sites.

Research paper thumbnail of Olfactory learning of plant genotypes by a polyphagous insect predator

Oecologia, 2011

Olfactory learning may allow insects to forage optimally by more efficiently finding and using fa... more Olfactory learning may allow insects to forage optimally by more efficiently finding and using favourable food sources. Although olfactory learning has been shown in bees, insect herbivores and parasitoids, there are fewer examples from polyphagous predators. In this study, olfactory learning by a predatory coccinellid beetle is reported for the first time. In laboratory trials, adults of the aphidophagous ladybird Coccinella septempunctata did not prefer the odour of one aphid-infested barley cultivar over another. However, after feeding on aphids for 24 h on a cultivar, they preferred the odour of that particular cultivar. The mechanism appeared to be associative learning rather than sensitisation. Although inexperienced ladybirds preferred the odour of an aphid-infested barley cultivar over uninfested plants of the same cultivar, after feeding experience on a different cultivar this preference disappeared. This may indicate the acquisition and replacement of olfactory templates. The odour blends of the different aphid-infested barley cultivars varied qualitatively and quantitatively, providing a potential basis for olfactory discrimination by the ladybird. The results show that predatory coccinellids can learn to associate the odour of aphid-infested plants with the presence of prey, and that this olfactory learning ability is sensitive enough to discriminate variability between different genotypes of the same plant.

Research paper thumbnail of Effect of within-species plant genotype mixing on habitat preference of a polyphagous insect predator

Oecologia, 2011

The effects of within-species plant genotype mixing on the habitat preference of a polyphagous la... more The effects of within-species plant genotype mixing on the habitat preference of a polyphagous ladybird were studied. Plant species diversity is often claimed to positively affect habitat preferences of insect predators, but the effects of within-species genotype diversity have not been extensively studied. In a field experiment with different barley (Hordeum vulgare) genotypes in mixed and pure stands, adult seven-spot ladybird Coccinella septempunctata, a polyphagous predator, preferred a specific combination of genotypes over the single genotypes alone before aphids had arrived in the crop, and again when aphids were emigrating. In laboratory experiments on adult ladybird orientation to odour from barley, ladybirds were attracted/arrested by the mixed odour of the same barley genotype mixture that was preferred in the field. Exposure of one barley genotype to volatiles from the other also caused the odour of the exposed plants to become more attractive to ladybirds. The results support the hypothesis that plant volatiles may attract or arrest foraging adult ladybirds, contributing to the selection of favourable habitats, and they show that within-species plant genotype mixing can shape interactions within multitrophic communities.

Research paper thumbnail of The effect of repellents Ocimum forskolei and deet on the response of Anopheles stephensi to host odours

Medical and Veterinary Entomology, 2006

The behavioural response of Anopheles stephensi Liston (Diptera: Culicidae) to incubated host odo... more The behavioural response of Anopheles stephensi Liston (Diptera: Culicidae) to incubated host odours (from human and goat) and to human odour in combination with a repellent plant, Ocimum forskolei (Labiatae), or deet (N, N, diethyl-toluamide) (20%) was tested in a dual-port olfactometer. An. stephensi was significantly attracted to both host odours compared with air alone, but showed no preference when given a choice between both host odours simultaneously. In choice tests, the addition of deet to human odour did not significantly divert mosquitoes to human odour alone, but did divert them to goat odour. O. forskolei combined with human odour diverted mosquitoes to goat or human odour alone. Combinations of human odour and O. forskolei, and human odour and deet were both as unattractive as air alone, and attracted mosquitoes equally when offered simultaneously. The results indicate that use of O. forskolei as a repellent would be beneficial in reducing vector biting if used in communities in areas with partially zoophilic mosquito species such as An. stephensi, and where animals are present.

Research paper thumbnail of An improved detection method for the Rhopalosiphum padi virus (RhPV) allows monitoring of its presence in aphids and movement within plants

Journal of Virological Methods, 2007

Research paper thumbnail of The interaction between bird cherry-oat aphid and barley in a changing climate

South African Journal of Botany

Research paper thumbnail of Landing Preference and Reproduction of Rhopalosiphum padi (Hemiptera: Aphididae) in the Laboratory on Three Maize, Potato, and Wheat Cultivars

Journal of insect science (Online), 2015

The bird cherry-oat aphid Rhopalosiphum padi (L.) transmits the nonpersistent Potato virus Y (PVY... more The bird cherry-oat aphid Rhopalosiphum padi (L.) transmits the nonpersistent Potato virus Y (PVY) to seed potatoes. Planting a nonvirus host plant around the main crop can reduce PVY incidence, because aphids tend to land in high numbers at the edge of a field and the crop border acts as a virus sink. This study determined R. padi landing and settling preferences and reproductive rates on three cultivars each of maize and wheat compared with potato in the laboratory as a basis for identifying an attractive crop border plant. Aphids were reared on maize and wheat to control for bias due to previous experience. Irrespective of origin, alates preferred to land almost exclusively on maize and wheat rather than on potato cultivars in choice experiments. Aphid settling on the maize and wheat cultivars depended on aphid origin. In no-choice experiments, R. padi produced the highest number of offspring on the wheat cultivars, irrespective of origin. Plant nitrogen content and trichome dens...

Research paper thumbnail of Red:far-red light conditions affect the emission of volatile organic compounds from barley (Hordeum vulgare), leading to altered biomass allocation in neighbouring plants

Annals of botany, Jan 7, 2015

Volatile organic compounds (VOCs) play various roles in plant-plant interactions, and constitutiv... more Volatile organic compounds (VOCs) play various roles in plant-plant interactions, and constitutively produced VOCs might act as a cue to sense neighbouring plants. Previous studies have shown that VOCs emitted from the barley (Hordeum vulgare) cultivar 'Alva' cause changes in biomass allocation in plants of the cultivar 'Kara'. Other studies have shown that shading and the low red:far-red (R:FR) conditions that prevail at high plant densities can reduce the quantity and alter the composition of the VOCs emitted by Arabidopsis thaliana, but whether this affects plant-plant signalling remains unknown. This study therefore examines the effects of far-red light enrichment on VOC emissions and plant-plant signalling between 'Alva' and 'Kara'. The proximity of neighbouring plants was mimicked by supplemental far-red light treatment of VOC emitter plants of barley grown in growth chambers. Volatiles emitted by 'Alva' under control and far-red light-e...

Research paper thumbnail of Brassicaceae cover crops reduce Aphanomyces pea root rot without suppressing genetic potential of microbial nitrogen cycling

Plant and Soil, 2015

Aims Brassicaceae cover crops can be used to suppress soil-borne pathogens. The aim was to invest... more Aims Brassicaceae cover crops can be used to suppress soil-borne pathogens. The aim was to investigate the effect of different brassicas with different glucosinolate profiles on the development of Aphanomyces pea root rot in subsequent pea plants, and the genetic potential of free-living N 2 -fixing bacteria and ammonia oxidising bacteria (AOB) and archaea (AOA) performing key soil ecosystem services. Methods The Brassicaceae species Brassica juncea and Sinapis alba and non-Brassicaceae species Secale cereale were grown for 11-weeks in Aphanomyces euteiches infested soil at low and high nitrogen (N) fertiliser doses. After removing both shoots and roots of the cover crops, peas were grown as a bioassay to evaluate Aphanomyces pea root rot development. Soil was sampled before harvesting the cover crops and at the end of the bioassay. Volatile compounds were collected in the root-soil environment before harvesting the Brassicaceae cover crops to determine the concentration of isothiocyanates. The abundance of genes involved in N 2 -fixing bacteria and ammonia oxidation in AOA and AOB were assessed. Results Pea root rot disease severity was reduced in Brassicaceae grown soil at the high N fertiliser dose. This was associated with increased growth of the cover crops. The growth of Brassicaceae did not suppress the abundance of N-cycling microbial communities, but rather increased the AOB at the end of the bioassay, most likely due to increased N availability. The disease suppressive effect was higher with S. alba than with B. juncea, and this coincided with a more diverse composition and higher concentration of aliphatic ITCs released from S. alba roots. Fewer nodules were formed after the Brassicaceae crops, especially Sinapis alba. Conclusions Brassicaceae cover crops, particularly S. alba, can be used to control soil-borne pathogens without major side effects on the genetic potential of beneficial soil microorganisms involved in N cycling. However, less nodule formation after brassicas indicates an effect on rhizobium activity.

Research paper thumbnail of Cycle-characteristic odour of cow urine can be detected by the female face fly (Musca autumnalis)

Reproduction in domestic animals = Zuchthygiene, 2014

Due to declining dairy cow fertility rates, there is great interest in developing tools for oestr... more Due to declining dairy cow fertility rates, there is great interest in developing tools for oestrus detection. Compounds in the volatile profile of oestrous cows are suggested as oestrus-specific, but consistent results have not been presented. Certain haematophagous arthropods can discriminate stages of the mammalian reproductive cycle based on host volatiles. This study investigated whether the face fly, Musca autumnalis de Geer (Diptera: Muscidae), can discriminate between urine from cows in oestrus and urine collected during the luteal phase. Individual flies were tested in a two-choice behavioural assay with choice between odour of oestrous or luteal urine and water (control). Flies chose the control arm significantly more when exposed to oestrous urine than when exposed to luteal urine. Analysis of volatiles showed that 1-hexadecanol (cetyl alcohol) was released in greater amounts from oestrous urine than from urine collected during the luteal phase. In a dose response assay, ...

Research paper thumbnail of arthropod pests

Plant volatiles provide herbivorous arthropods with information that allows them to discriminate ... more Plant volatiles provide herbivorous arthropods with information that allows them to discriminate between host and non-host plants. Volatiles may also indicate plant stress status, and natural enemies can use herbivore-induced plant volatiles as cues for prey location. Neighbouring plants may also make use of volatile cues to prepare for herbivore attack. Since both constitutive and inducible plant volatile emissions can

Research paper thumbnail of Aphid acceptance of barley exposed to volatile phytochemicals differs between plants exposed in daylight and darkness

Plant signaling & behavior, 2007

It is well known that volatile cues from damaged plants may induce resistance in neighboring plan... more It is well known that volatile cues from damaged plants may induce resistance in neighboring plants. Much less is known about the effects of volatile interaction between undamaged plants. In this study, barley plants, Hordeum vulgare cv. Kara, were exposed to volatiles from undamaged plants of barley cv. Alva or thistle Cirsium vulgare, and to the volatile phytochemicals, methyl salicylate or methyl jasmonate. Exposures were made either during natural daylight or darkness. Acceptance of exposed plants by the aphid Rhopalosiphum padi was assessed, as well as the expression of putative marker genes for the different treatments. Aphid acceptance of plants exposed to either barley or C. vulgare was significantly reduced, and an effect of the volatiles from undamaged plants was confirmed by the induction of pathogenesis-related protein, PR1a in exposed plants. However the effect on aphid acceptance was seen only when plants were exposed during darkness, whereas PR1a was induced only afte...

Research paper thumbnail of Volatile interaction between undamaged plants affects tritrophic interactions through changed plant volatile emission

Plant Signaling & Behavior, 2014

Volatile interactions between unattacked plants can lead to changes in their volatile emissions. ... more Volatile interactions between unattacked plants can lead to changes in their volatile emissions. Exposure of potato plants to onion plant volatiles results in increased emission of 2 terpenoids, (E)-nerolidol and tmtt. We investigated whether this is detectable by the ladybird Coccinella septempunctata. the odor of onion-exposed potato was significantly more attractive to ladybirds than that of unexposed potato. Further, a synthetic blend mimicking the volatile profile of onion-exposed potato was more attractive than a blend mimicking that of unexposed potato. When presented individually, tmtt was attractive to ladybirds whereas (E)-nerolidol was repellent. Volatile exchange between unattacked plants and the consequent increased attractiveness for ladybirds may be a mechanism that contributes to the increased abundance of natural enemies in complex plant habitats.

Research paper thumbnail of Change in acceptability of barley plants to aphids after exposure to allelochemicals from couch-grass (Elytrigia repens)

Journal of Chemical Ecology, 2003

The response of the bird cherry-oat aphid, Rhopalosiphum padi, to barley plants was investigated ... more The response of the bird cherry-oat aphid, Rhopalosiphum padi, to barley plants was investigated following exposure of the plants to root allelochemicals from the aggressive weed couch-grass, Elytrigia (Agropyron) repens. Plants were treated either with root exudates from living couch-grass plants or with previously identified couch-grass root compounds 15-hydroxyindole-3-acetic acid, DL-5-hydroxytryptophan, L-5-hydroxytryptophan hydrate, and 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (carboline)] either separately or in mixtures. In choice and no-choice settling tests, aphid acceptance of barley plants was significantly reduced following treatment with root exudates, and the carboline when tested alone or in combination with the other compounds. In contrast, the other compounds without the carboline were less active in reducing aphid acceptance. In a probing bioassay, individual substances were either neutral or stimulatory to aphids, indicating that the reduced settling was probably not due to direct effects on aphids, but rather due to effects on the plant. This was confirmed in olfactometer assays, in which aphids were repelled by odors from barley plants following treatment with a mixture containing all four chemicals.

Research paper thumbnail of The potential for modifying plant volatile composition to enhance resistance to arthropod pests

CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2010

... aphid parasitoid Diaeretiella rapae spent more time on Arabidopsis producing elevated levels ... more ... aphid parasitoid Diaeretiella rapae spent more time on Arabidopsis producing elevated levels ... reducing risks for plant self-toxicity [cf. ... Additive and synergistic integration of multimodal cues of both hosts and non-hosts during host selection by woodboring insects. ...

Research paper thumbnail of Herbivory by a Phloem-Feeding Insect Inhibits Floral Volatile Production

PLoS ONE, 2012

There is extensive knowledge on the effects of insect herbivory on volatile emission from vegetat... more There is extensive knowledge on the effects of insect herbivory on volatile emission from vegetative tissue, but little is known about its impact on floral volatiles. We show that herbivory by phloem-feeding aphids inhibits floral volatile emission in white mustard Sinapis alba measured by gas chromatographic analysis of headspace volatiles. The effect of the Brassica specialist aphid Lipaphis erysimi was stronger than the generalist aphid Myzus persicae and feeding by chewing larvae of the moth Plutella xylostella caused no reduction in floral volatile emission. Field observations showed no effect of L. erysimimediated floral volatile emission on the total number of flower visits by pollinators. Olfactory bioassays suggested that although two aphid natural enemies could detect aphid inhibition of floral volatiles, their olfactory orientation to infested plants was not disrupted. This is the first demonstration that phloem-feeding herbivory can affect floral volatile emission, and that the outcome of interaction between herbivory and floral chemistry may differ depending on the herbivore's feeding mode and degree of specialisation. The findings provide new insights into interactions between insect herbivores and plant chemistry.

Research paper thumbnail of Volatile Exchange between Undamaged Plants - a New Mechanism Affecting Insect Orientation in Intercropping

PLoS ONE, 2013

Changes in plant volatile emission can be induced by exposure to volatiles from neighbouring inse... more Changes in plant volatile emission can be induced by exposure to volatiles from neighbouring insect-attacked plants. However, plants are also exposed to volatiles from unattacked neighbours, and the consequences of this have not been explored. We investigated whether volatile exchange between undamaged plants affects volatile emission and plant-insect interaction. Consistently greater quantities of two terpenoids were found in the headspace of potato previously exposed to volatiles from undamaged onion plants identified by mass spectrometry. Using live plants and synthetic blends mimicking exposed and unexposed potato, we tested the olfactory response of winged aphids, Myzus persicae. The altered potato volatile profile deterred aphids in laboratory experiments. Further, we show that growing potato together with onion in the field reduces the abundance of winged, host-seeking aphids. Our study broadens the ecological significance of the phenomenon; volatiles carry not only information on whether or not neighbouring plants are under attack, but also information on the emitter plants themselves. In this way responding plants could obtain information on whether the neighbouring plant is a competitive threat and can accordingly adjust their growth towards it. We interpret this as a response in the process of adaptation towards neighbouring plants. Furthermore, these physiological changes in the responding plants have significant ecological impact, as behaviour of aphids was affected. Since herbivore host plants are potentially under constant exposure to these volatiles, our study has major implications for the understanding of how mechanisms within plant communities affect insects. This knowledge could be used to improve plant protection and increase scientific understanding of communication between plants and its impact on other organisms.

Research paper thumbnail of Aphid sex pheromones: manipulation of beneficial insects for aphid population control

Pesticide Science, 1999

ABSTRACT

Research paper thumbnail of Identification of mosquito repellent odours from Ocimum forskolei

Parasites & Vectors, 2011

Background: Native mosquito repellent plants have a good potential for integrated mosquito contro... more Background: Native mosquito repellent plants have a good potential for integrated mosquito control in local settings. Ocimum forskolei, Lamiaceae, is used in Eritrea as a spatial mosquito repellent inside houses, either through crushing fresh plants or burning dry plants. We verified whether active repellent compounds could be identified using gas-chromatography coupled electroantennogram recordings (GC-EAD) with headspace extracts of crushed plants.

Research paper thumbnail of Ant-aphid mutualism: the influence of ants on the aphid summer cycle

Oikos, 2012

Th ere are few longtime studies on the eff ects on aphids of being tended by ants. Th e aim of th... more Th ere are few longtime studies on the eff ects on aphids of being tended by ants. Th e aim of this study is to investigate how the presence of ants infl uences settling decisions by colonizing aphids and the post-settlement growth and survival of aphid colonies. We conducted a fi eld experiment using the facultative myrmecophile Aphis fabae and the ant Lasius niger . Th e experiment relied on natural aphid colonization of potted plants of scentless mayweed Tripleurospermum perforatum placed outdoors. Ants occurred naturally at the fi eld site and had access to half of the pots and were prevented from accessing the remainder. Th e presence of winged, dispersing aphids, the growth and survival of establishing aphid colonies, and the presence of parasitoids were measured in relation to presence or absence of ants, over a period of fi ve weeks. Th e presence of ants did not signifi cantly infl uence the pattern of initial host plant colonization or the initial colony growth, but ant-tended aphids were subject to higher parasitism by hymenopteran parasitoids. Th e net result over the experimental period was that the presence of ants decreased aphid colony productivity, measured as the number of winged summer migrants produced from the colonized host plants. Th is implies that aphids do not always benefi t from the presence of ants, but under some conditions rather pay a cost in the form of reduced dispersal.

Research paper thumbnail of Movement by mating females of a host alternating aphid: a response to leaf fall

Oikos, 2000

. Movement by mating females of a host alternating aphid: a response to leaf fall. -Oikos 90: 43 ... more . Movement by mating females of a host alternating aphid: a response to leaf fall. -Oikos 90: 43 -49. Autumn remigrants of the host alternating bird cherry-oat aphid, Rhopalosiphum padi, colonise individual plants of the winter host, Prunus padus. However, they do not select leaves at different stages of senescence, which is surprising as leaf fall is a definitive deadline for production and development of mating females. For successful development mating females should be mobile and have the capacity to evaluate leaf senescence. Although remigrants do not selectively colonise leaves at different stages of senescence, mating females were found in very low numbers on leaves that were about to be shed. In choice test and olfactometer bioassays, abscising leaves were avoided by mating females. In the field mature leaves were available for colonisation during the period of leaf fall of P. padus. We conclude that mating females abandon abscising leaves in favour of leaves at an earlier stage of senescence, increasing the time available for mating. Our results support the role of remigrants as pioneers which identify good winter host plants, and of mating females as mobile searchers for optimal feeding and mating sites.

Research paper thumbnail of Olfactory learning of plant genotypes by a polyphagous insect predator

Oecologia, 2011

Olfactory learning may allow insects to forage optimally by more efficiently finding and using fa... more Olfactory learning may allow insects to forage optimally by more efficiently finding and using favourable food sources. Although olfactory learning has been shown in bees, insect herbivores and parasitoids, there are fewer examples from polyphagous predators. In this study, olfactory learning by a predatory coccinellid beetle is reported for the first time. In laboratory trials, adults of the aphidophagous ladybird Coccinella septempunctata did not prefer the odour of one aphid-infested barley cultivar over another. However, after feeding on aphids for 24 h on a cultivar, they preferred the odour of that particular cultivar. The mechanism appeared to be associative learning rather than sensitisation. Although inexperienced ladybirds preferred the odour of an aphid-infested barley cultivar over uninfested plants of the same cultivar, after feeding experience on a different cultivar this preference disappeared. This may indicate the acquisition and replacement of olfactory templates. The odour blends of the different aphid-infested barley cultivars varied qualitatively and quantitatively, providing a potential basis for olfactory discrimination by the ladybird. The results show that predatory coccinellids can learn to associate the odour of aphid-infested plants with the presence of prey, and that this olfactory learning ability is sensitive enough to discriminate variability between different genotypes of the same plant.

Research paper thumbnail of Effect of within-species plant genotype mixing on habitat preference of a polyphagous insect predator

Oecologia, 2011

The effects of within-species plant genotype mixing on the habitat preference of a polyphagous la... more The effects of within-species plant genotype mixing on the habitat preference of a polyphagous ladybird were studied. Plant species diversity is often claimed to positively affect habitat preferences of insect predators, but the effects of within-species genotype diversity have not been extensively studied. In a field experiment with different barley (Hordeum vulgare) genotypes in mixed and pure stands, adult seven-spot ladybird Coccinella septempunctata, a polyphagous predator, preferred a specific combination of genotypes over the single genotypes alone before aphids had arrived in the crop, and again when aphids were emigrating. In laboratory experiments on adult ladybird orientation to odour from barley, ladybirds were attracted/arrested by the mixed odour of the same barley genotype mixture that was preferred in the field. Exposure of one barley genotype to volatiles from the other also caused the odour of the exposed plants to become more attractive to ladybirds. The results support the hypothesis that plant volatiles may attract or arrest foraging adult ladybirds, contributing to the selection of favourable habitats, and they show that within-species plant genotype mixing can shape interactions within multitrophic communities.

Research paper thumbnail of The effect of repellents Ocimum forskolei and deet on the response of Anopheles stephensi to host odours

Medical and Veterinary Entomology, 2006

The behavioural response of Anopheles stephensi Liston (Diptera: Culicidae) to incubated host odo... more The behavioural response of Anopheles stephensi Liston (Diptera: Culicidae) to incubated host odours (from human and goat) and to human odour in combination with a repellent plant, Ocimum forskolei (Labiatae), or deet (N, N, diethyl-toluamide) (20%) was tested in a dual-port olfactometer. An. stephensi was significantly attracted to both host odours compared with air alone, but showed no preference when given a choice between both host odours simultaneously. In choice tests, the addition of deet to human odour did not significantly divert mosquitoes to human odour alone, but did divert them to goat odour. O. forskolei combined with human odour diverted mosquitoes to goat or human odour alone. Combinations of human odour and O. forskolei, and human odour and deet were both as unattractive as air alone, and attracted mosquitoes equally when offered simultaneously. The results indicate that use of O. forskolei as a repellent would be beneficial in reducing vector biting if used in communities in areas with partially zoophilic mosquito species such as An. stephensi, and where animals are present.

Research paper thumbnail of An improved detection method for the Rhopalosiphum padi virus (RhPV) allows monitoring of its presence in aphids and movement within plants

Journal of Virological Methods, 2007