Ecological impact of entomopathogenic nematodes used to control the large pine weevil, Hylobius abietis (Coleoptera: Curculionidae)

The large pine weevil (Hylobius abietis; Coleoptera: Curculionidae) is one of the most economically damaging pests in forestry across Northern Europe. Its larvae develop in coniferous tree stumps on clearfell sites and adult weevils feed on seedlings that are replanted on these sites, causing substantial mortality. As the drive towards achieving the sustainable management of natural resources increases, biological control agents are being considered as an alternative to chemical pesticides. Though such agents have great potential for contributing towards a reduction in the ecological impact of pest insect control, they must also be investigated for any potentially damaging effects they may have in whichever context they are being employed. Entomopathogenic nematodes (EPN; Steinernema carpocapsae and Heterorhabditis downesi) are currently being inundatively applied to tree stumps on coniferous clearfell sites in the UK and Ireland as biological control agents against the large pine weevil. The aim of the laboratory and field-based experiments and field sampling of clearfell sites that were carried out for this thesis was to investigate the risks associated with this use of EPN in this setting. To this end, the persistence of EPN in soil and bark after application to clearfell sites was recorded and attempts were made to investigate the possibility of hybridisation occurring between an exotic and a native Steinernema strain. Effects of EPN on some important non-target insects on clearfell sites, the service-providing wood decomposer Rhagium bifasciatum and the pine weevil parasitoid Bracon hylobii were also assessed in laboratory and field experiments. EPN presence in soil samples collected around tree stumps on clearfell sites five months, one year and two years after application of EPN decreased significantly from year one to year two. EPN presence on all sites sampled two years post EPN application was relatively low (less than 7 % positive soil samples). A similar trend was observed for EPN persistence under the bark of stumps. No EPN at all were detected two years after application on those sites treated on a small scale by manually applying nematodes. EPN persistence appeared to be better predicted by tree stump species (which in turn is indicative of the number of pine weevils developing within them) compared to soil type. Spread of nematodes was limited mostly to a 40 cm radius around stumps and little evidence of EPN presence in untreated areas was found on any of the investigated sites. While some spread of EPN to areas adjoining two of the sites occurred, there was no evidence of establishment off-site. (Chapter III). Attempts to distinguish between an indigenous and an exotic strain of S. feltiae and their hybrid using two molecular methods (Amplified Fragment Length Polymorphism or AFLP and Restriction Fragment Length Polymorphism or RFLP) were confounded by methodological obstacles. However, RFLP analysis of the strains did indicate a high rate of intraspecific and even intrastrain variation for S. feltiae. Using this method it was also possible to tentatively identify a field-isolated Steinernema sp. as Steinernema kraussei, though two other unidentified isolates could not be assigned to a particular species (Chapter IV). The saproxylic beetle community in deadwood other than tree stumps on Irish clearfell sites appears to be dominated by the longhorn beetle Rhagium bifasciatum (Coleoptera: Cerambycidae; Fabricius 1775). Both S. carpocapsae and H. downesi invaded decomposing logs and infected all stages of this species within logs when applied directly to them. However, infection only occurred to a large extent (> 50 % of insects) if the applied dose of EPN was half that applied to tree stumps (1.8 million IJs) to control the pine weevil and infection was also significantly lower when such logs were incubated in the field rather than the laboratory. R. bifasciatum individuals were infected in all regions of logs and baiting of wood samples revealed that IJs were penetrating logs to their very centre, indicating high mobility and infectivity of IJs within this substrate. S. carpocapsae emerged in numbers of 1,000 IJs or more per week for up to eight weeks after first emergence while H. downesi emergence had effectively ceased by the fifth week. A substantial number of live S. carpocapsae IJs remained in host cadavers even after eight weeks of emergence. Infection of R. bifasciatum was also recorded on three clearfell sites to which EPN had been applied around tree stumps previously (only a single infected larva found on one of the sites). Wood samples from some of these logs contained high numbers of EPN IJs (> 6,000), suggesting that EPN were recycling within logs. However, since infection of R. bifasciatum decreased significantly as the distance between a log and treated tree stumps increased it appears that the risk to this serviceproviding non-target insect can be minimised by being as accurate as possible when applying nematodes. (Chapter V). The ectoparasitoid wasp Bracon hylobii Ratz. (Hymenoptera: Braconidae) is closely associated with the large pine weevil and may therefore be at risk if EPN are applied against the latter (eggs laid on EPN-infected host larvae do not develop to adulthood). Female wasps did not parasitise dead hosts in standard trials (small bark patch [2.25 cm2]; host either freeze-killed or killed by EPN). However, naive wasps parasitised hosts that were moribund (i.e. those that died of EPN-infection within the 24 h period they were offered to wasps) significantly less frequently than either healthy control hosts or infected hosts that survived the 24 h trial period. Experienced wasps (one egg laying experience) parasitised all of these host types with similar frequency. Behavioural observations provided no evidence of wasps locating heavily infected or dead hosts and then rejecting them. Heavily infected hosts that died within the 24 h trial period during which they were offered to wasps tended to move less than their surviving counterparts and wasp oviposition was significantly correlated with host movement and host feeding during trials. NaЇve wasps were significantly less likely to parasitise hosts that had their mandibles glued shut than those that did not (this had no effect on parasitism by experienced wasps). Thus, it is suggested that vibrations caused by these host activities were the most important cue driving host location and/or host acceptance in B. hylobii. In continuous 30 minute observation of trials in which wasps were offered a host at the centre of a large bark patch (20.25 cm2), experienced wasps spent more time close to the host when it was moving and were also significantly more likely to approach the host when it was moving, indicating a vibrotaxic response. Moreover, they only were attracted to dead hosts (freeze-killed or killed by EPN) when the bark covering them was being scratched manually from below to simulate host movement. Some experienced wasps parasitised freeze-killed and EPN-killed hosts when an artificial vibrational stimulus was added in this way and the dead host was moved about inside its chamber. B. hylobii also parasitised hosts the species is not known to be associated with, including larvae of longhorn beetle R. bifasciatum and waxmoth larvae (Galleria mellonella). These results suggest that wasp foraging behaviour, host acceptance and oviposition success is most affected by vibrational cues and that naïve wasps are less likely to locate moribund hosts that move and feed less due to infection with EPN. The risk is expected to be further mediated in a field situation where wasps are likely to encounter several hosts in one host patch and more likely to be attracted to those hosts that are healthy and producing more or stronger vibrational and volatile cues compared to moribund hosts (Chapter VI). In summary, persistence and spread of EPN after application to tree stumps on clearfell sites was low and there was no evidence of a substantial impact on non-target insects. It can therefore be concluded that the overall risks associated with the use of EPN as an inundative biological control agent against the large pine weevil are low

Cognitive deficits and functional outcome in schizophrenia

Cognitive dysfunction is a core feature of schizophrenia. Deficits are moderate to severe across several domains, including attention, working memory, verbal learning and memory, and executive functions. These deficits pre-date the onset of frank psychosis and are stable throughout the course of the illness in most patients. Over the past decade, the focus on these deficits has increased dramatically with the recognition that they are consistently the best predictor of functional outcomes across outcome domains and patient samples. Recent treatment studies, both pharmacological and behavioral, suggest that cognitive deficits are malleable. Other research calls into question the meaningfulness of cognitive change in schizophrenia. In this article, we review cognitive deficits in schizophrenia and focus on their treatment and relationship to functional outcome

Causes and consequences of representational drift.

The nervous system learns new associations while maintaining memories over long periods, exhibiting a balance between flexibility and stability. Recent experiments reveal that neuronal representations of learned sensorimotor tasks continually change over days and weeks, even after animals have achieved expert behavioral performance. How is learned information stored to allow consistent behavior despite ongoing changes in neuronal activity? What functions could ongoing reconfiguration serve? We highlight recent experimental evidence for such representational drift in sensorimotor systems, and discuss how this fits into a framework of distributed population codes. We identify recent theoretical work that suggests computational roles for drift and argue that the recurrent and distributed nature of sensorimotor representations permits drift while limiting disruptive effects. We propose that representational drift may create error signals between interconnected brain regions that can be used to keep neural codes consistent in the presence of continual change. These concepts suggest experimental and theoretical approaches to studying both learning and maintenance of distributed and adaptive population codes.This work is supported by the Human Frontier Science Program, ERC grant StG 716643 FLEXNEURO, and NIH grants (NS108410, NS089521, MH107620)

Overlapping functionality of the Pht proteins in zinc homeostasis of streptococcus pneumoniae

Streptococcus pneumoniae is a globally significant pathogen that causes a range of diseases, including pneumonia, sepsis, meningitis, and otitis media. Its ability to cause disease depends upon the acquisition of nutrients from its environment, including transition metal ions such as zinc. The pneumococcus employs a number of surface proteins to achieve this, among which are four highly similar polyhistidine triad (Pht) proteins. It has previously been established that these proteins collectively aid in the delivery of zinc to the ABC transporter substrate-binding protein AdcAII. Here we have investigated the contribution of each individual Pht protein to pneumococcal zinc homeostasis by analyzing mutant strains expressing only one of the four pht genes. Under conditions of low zinc availability, each of these mutants showed superior growth and zinc accumulation profiles relative to a mutant strain lacking all four genes, indicating that any of the four Pht proteins are able to facilitate delivery of zinc to AdcAII. However, optimal growth and zinc accumulation in vitro and pneumococcal survival and proliferation in vivo required production of all four Pht proteins, indicating that, despite their overlapping functionality, the proteins are not dispensable without incurring a fitness cost. We also show that surface-attached forms of the Pht proteins are required for zinc recruitment and that they do not contribute to defense against extracellular zinc stress

Partition of mixed-mode fractures in 2D elastic beams with through-thickness shear forces

Partition of mixed-mode fractures in 2D elastic beams with through-thickness shear force

Effect of Poisson’s ratio mismatch on brittle interfacial cracking between two dissimilar elastic layers

Previous work by the authors (Harvey et al., 2015) on brittle interfacial cracking between two dissimilar elastic layers is extended to accommodate Poisson’s ratio mismatch in addition to the existing capability for elastic modulus mismatch. Under crack tip bending moments and axial forces, it is now possible to use a completely analytical 2D elasticity-based theory to calculate the complex stress intensity factor (SIF) and the crack extension size-dependent energy release rates (ERRs). To achieve this, it is noted that for a given geometry and loading condition, the total ERR and bimaterial mismatch coefficient are the two main factors affecting the partitions of ERR. Based on this, equivalent material properties are derived for each layer, namely, an equivalent elastic modulus and an equivalent Poisson’s ratio, such that both the total ERR and the bimaterial mismatch coefficient are maintained in an alternative equivalent case. Cases for which no analytical solution for the SIFs and ERRs currently exist can therefore be ‘transformed’ into cases for which the analytical solution does exist. The approach is verified against results from 2D finite element method simulations in which excellent agreement is observed for cases of plane stress and plane strain with a variety of loading conditions

The mechanics of interface fracture:(1) brittle homogenous and bi-material interfaces

A powerful analytical methodology is discovered and is used to partition the total energy release rate of mixed-mode 1D fractures on brittle homogeneous or bi-material interfaces into its mode I and II components based on the classical and shear-deformable plate theories and 2D elasticity. Previously unsolvable problems are solved and confusions explained

The mechanics of interface fracture in layered composite materials: (1) brittle homogenous and bi-material interfaces

A powerful analytical methodology is discovered and is used to partition the total energy release rate of one dimensional (1D) interface fractures on brittle homogeneous or bi-material interfaces into its mode I and II components based on the classical and shear-deformable plate theories and 2D elasticity. Previously unsolvable problems are solved and confusions explained

The first histidine triad motif of phtd is critical for zinc homeostasis in Streptococcus pneumoniae

Streptococcus pneumoniae is the world's foremost human pathogen. Acquisition of the first row transition metal ion zinc is essential for pneumococcal colonization and disease. Zinc is acquired via the ATP-binding cassette transporter AdcCB and two zinc-binding proteins, AdcA and AdcAII. We have previously shown that AdcAII is reliant upon the polyhistidine triad (Pht) proteins to aid in zinc recruitment. Pht proteins generally contain five histidine (His) triad motifs that are believed to facilitate zinc binding and therefore play a significant role in pneumococcal metal ion homeostasis. However, the importance and potential redundancy of these motifs have not been addressed. We examined the effects of mutating each of the five His triad motifs of PhtD. The combination of in vitro growth assays, active zinc uptake, and PhtD expression studies show that the His triad closest to the protein's amino terminus is the most important for zinc acquisition. Intriguingly, in vivo competitive infection studies investigating the amino- and carboxyl-terminal His triad mutants indicate that the motifs have similar importance in colonization. Collectively, our new insights into the contributions of the individual His triad motifs of PhtD, and by extension the other Pht proteins, highlight the crucial role of the first His triad site in zinc acquisition. This study also suggests that the Pht proteins likely play a role beyond zinc acquisition in pneumococcal virulence