Biomedical subjects

Glen Powell

Publications and source records attributed to Glen Powell.

6 recordsLinked to original sources

PubMed2006

The effects of kaolin particle film on Plutella xylostella behaviour and development.

Studies were conducted to evaluate the effect of a kaolin-based particle film against the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The effect of the particle film on development, survival and host plant selection was tested on calabrese seedlings, Brassica oleracea italica Plenck cv. Fiesta F(1), under controlled environmental conditions in the laboratory. Survival to adulthood was significantly reduced and development time increased on kaolin-treated compared with water-treated host plants. The hatch rate of neonate P. xylostella larvae from eggs laid on an artificial substrate was unaffected by the particle film applied after oviposition. Experiments showed that, when given the choice, significantly fewer larvae first made contact with the kaolin-treated compared with the water-treated plant material and that after 24 h there were still significantly fewer larvae present on kaolin-treated leaves. Adult females, however, deposited more eggs on host plants coated with the kaolin particle film. As part of this series of experiments the water control treatment was compared with plant material which had been sprayed with kaolin on the upper surface only and on both leaf surfaces. In general, any observed treatment effect was enhanced with an increase in the particle film coverage. The results warrant the extension of investigations of kaolin-based particle films to field-based P. xylostella management strategies.

Animals↗

PubMed2006

Host plant selection by aphids: behavioral, evolutionary, and applied perspectives.

As phloem feeders and major vectors of plant viruses, aphids are important pests of agricultural and horticultural crops worldwide. The processes of aphid settling and reproduction on plants therefore have a direct economic impact, and a better understanding of these events may lead to improved management strategies. Aphids are also important model organisms in the analysis of population differentiation and speciation in animals, and new ideas on plant utilization influence our understanding of the mechanisms generating biological diversity. Recent research suggests that the dominant cues controlling plant preference and initiation of reproduction are detected early during the stylet penetration process, well before the nutrient supply (phloem) is contacted. Aphids regularly puncture cells along the stylet pathway and ingest cytosolic samples, and the cues stimulating settling and parturition likely are metabolites present in peripheral (nonvascular) plant cells. We discuss these findings and their implications for aphid evolution and management.

Animals↗

PubMed2005

Intracellular salivation is the aphid activity associated with inoculation of non-persistently transmitted viruses.

Approximately 75 % of aphid-vectored viruses are transmitted in a non-persistent (non-circulative) manner. Localization studies indicate that such viruses are acquired via ingestion and retained in the food canal of the maxillary stylets, but the inoculation mechanism has remained unresolved. Electrical recording of stylet penetration activities reveals that inoculation is associated with the first intracellular activity (subphase II-1) following maxillary puncture of an epidermal cell. Subphase II-1 may represent virus inoculation via egestion (regurgitation of virions with food-canal contents) or salivation (saliva-mediated release of virions from the common food-salivary duct at the tips of the maxillary stylets). Here, inoculation of the circulatively transmitted Pea enation mosaic virus was used as a marker for intracellular salivation during epidermal cell punctures. The results confirmed that inoculation of non-persistently transmitted viruses (subphase II-1) is associated with active injection of saliva directly into the cytoplasm.

Animals↗

PubMed2003

Reproductive response of generalist and specialist aphid morphs with the same genotype to plant secondary compounds and amino acids.

Many studies have paid particular attention to the role of either secondary plant compounds or amino acids as determinants of host-plant range in phytophagous insects. Here we examine the relative importance of both of these classes of compound in host acceptance by generalist and specialist morphs of the black bean aphid, Aphis fabae, that are morphologically similar and genetically identical. Eleven secondary plant compounds and six amino acids with known biological activity in aphids are presented to insects within an artificial membrane system as single compounds, mixtures of same-class compounds and combined mixtures of the two classes of compound. It is found that 1) when specific single secondary compounds and amino acids are presented to generalist and specialist morphs of A. fabae, differential responses are exclusively consistent with plant-use strategy for amino acids but not for secondary compounds, 2) neither secondary compound nor amino acid mixtures give reproductive responses entirely consistent with plant range, but the response to secondary compounds is broadly consistent with plant range whereas the response to amino acids is not, 3) when secondary compounds and amino acid mixtures are combined, the response to secondary compounds generally dominates that to amino acids. Some scenarios of plant-range determination by secondary plant compounds and amino acids, suggested by results, are discussed.

Amino Acids↗

PubMed2003

Decision making by generalist and specialist aphids with the same genotype.

One idea to explain the high incidence of specialisation in phytophagous insects is that their nervous systems are simple and unable to efficiently recognise multiple host plants. Here this 'neural limitations' hypothesis is tested using a generalist (the summer winged virginopara) and specialist (the autumn gynopara) morph of a single clone of the black bean aphid, Aphis fabae, that are almost identical morphologically and have the same genotype. Electrical monitoring of stylet behaviour and non-invasive behavioural observations are used to compare initial plant recognition, first reproduction, 'first registered phloem contact' and 'phloem acceptance' of the generalist and specialist on their specific host plants (generalist--herbaceous hosts, Beta vulgaris, Papaver dubium, Rumex obtusifolius, Vicia faba; specialist--woody host, Euonymus europaeus) and on the same host (E. europaeus). Additional analyses of behaviour over the first few minutes of plant contact are carried out for three mutual non-host plants: Euonymus alatus, Prunus padus and Brassica pekinensis. Few examples are found where the host-selection behaviour of the specialist on its host plant is more efficient than the generalist across its hosts and there is little difference in the behaviour of the different forms on the same host. Indeed there are several instances where the generalist is behaviourally more efficient than the specialist. These include absolute time to first reproduction by the generalist on various herbaceous hosts and the same host, E. europaeus, absolute time to first registered phloem contact by the generalist on P. dubium, and incidence of phloem acceptance by the generalist on several of its herbaceous hosts. Rejection of non-hosts is carried out more efficiently by the specialist gynopara on P. padus and B. pekinensis but not on E. alatus. For generalist and specialist morphs of the same A. fabae genotype, therefore, broad host range does not appear to be associated with a reduced ability to make plant-use decisions.

Animals↗

PubMed2002

Maternal reproductive decisions are independent of feeding in the black bean aphid, Aphis fabae.

Aphids are phloem feeders and an important assumption has been that reproduction is initiated only after phloem ingestion. Here we investigate the plant tissue location of parturition cues in winged and wingless, summer virginoparae and autumn migrants (gynoparae) of the black bean aphid, Aphis fabae. These seasonal forms have different host preferences. Using electrical penetration graph (EPG: to observe activity of the mouthparts) and video-monitoring procedures we demonstrate that the time to first parturition after host-plant contact is significantly shorter than the time to first registered phloem contact in the summer winged form. In gynoparae, the time to first parturition does not significantly differ from time to first phloem contact but is shorter than time to first phloem ingestion. Times to first parturition, first registered phloem contact and first phloem ingestion do not differ significantly in the summer wingless form. Simultaneous EPG and video recording procedures show that a high proportion of individuals of all morphs (45-70%) initiate reproduction before sustained phloem activities (salivation/ingestion). The only behaviours that all individuals demonstrate before first parturition are 'non-penetration' (aphid on plant surface with mouthparts outside plant) and stylet 'pathway activity', including secretion of gelling saliva and penetration of the non-vascular (epidermis and mesophyll) cells. A short period of penetration of the peripheral plant tissues (five cell punctures per individual) by aphids tethered and monitored by EPG decreases the time to first parturition of the winged summer form when subsequently placed on a Parafilm sachet containing 15% sucrose solution. This treatment also significantly increases the incidence of reproduction and individual reproductive output of gynoparae over a 24-h period. No detectable effects of tissue penetration on subsequent reproductive output are observed in the wingless summer form. Additionally, EPGs reveal that a number of aphids of all morphs display xylem ingestion, which occurs predominantly before initiation of phloem feeding but is not necessary to initiate parturition. It is concluded that aphids are likely to detect parturition cues during stylet punctures of cells within peripheral tissue layers, before reaching the phloem vessels.

Journal Article↗