Explore the vast range of titles available.

Biological control of Cryphonectria parasitica fungus, causal agent of chestnut blight, by virus infection (hypovirulence) has been shown to be an effective control strategy against chestnut blight in Europe and some parts of North America. The most studied mycovirus is the Cryphonectria hypovirus 1 (CHV-1) type species of the Hypoviridae family. To efficiently provide biocontrol, the virus must be able to induce hypovirulence in its fungal host in chestnut trees. Here, two different CHV-1 subtype I virus strains (E-5 and L-18), gained by transmissions, were tested for their hypovirulence induction, biocontrol potential, and transmission between vegetatively compatible (VCG) and incompatible fungal isolate groups in sweet chestnut seedlings and branches. Both strains of CHV-1 showed great biocontrol potential and could protect trees by efficiently transmitting CHV-1 by hyphal anastomosis between fungal isolates of the same VCG and converting virulent to hypovirulent cankers. The hypovirulent effect was positively correlated with the virus concentration, tested by four different reverse-transcription PCRs, two end-point and two real-time methods, one of which represents a newly developed real-time PCR for the detection and quantification of CHV-1.

Camouflage, and in particular background-matching, is one of the most common anti-predator strategies observed in nature. Animals can improve their match to the colour/pattern of their surroundings through background selection, and/or by plastic colour change. Colour change can occur rapidly (a few seconds), or it may be slow, taking hours to days. Many studies have explored the cues and mechanisms behind rapid colour change, but there is a considerable lack of information about slow colour change in the context of predation: the cues that initiate it, and the range of phenotypes that are produced. Here we show that peppered moth ( Biston betularia ) larvae respond to colour and luminance of the twigs they rest on, and exhibit a continuous reaction norm of phenotypes. When presented with a heterogeneous environment of mixed twig colours, individual larvae specialise crypsis towards one colour rather than developing an intermediate colour. Flexible colour change in this species has likely evolved in association with wind dispersal and polyphagy, which result in caterpillars settling and feeding in a diverse range of visual environments. This is the first example of visually induced slow colour change in Lepidoptera that has been objectively quantified and measured from the visual perspective of natural predators.

Light sensing by tissues distinct from the eye occurs in diverse animal groups, enabling circadian control and phototactic behaviour. Extraocular photoreceptors may also facilitate rapid colour change in cephalopods and lizards, but little is known about the sensory system that mediates slow colour change in arthropods. We previously reported that slow colour change in twig-mimicking caterpillars of the peppered moth ( Biston betularia ) is a response to achromatic and chromatic visual cues. Here we show that the perception of these cues, and the resulting phenotypic responses, does not require ocular vision. Caterpillars with completely obscured ocelli remained capable of enhancing their crypsis by changing colour and choosing to rest on colour-matching twigs. A suite of visual genes, expressed across the larval integument, likely plays a key role in the mechanism. To our knowledge, this is the first evidence that extraocular colour sensing can mediate pigment-based colour change and behaviour in an arthropod. Amy Eacock et al. examine the sensory input mechanism for slow colour change in the twig-mimicking caterpillars of the peppered moth. They find that this camouflage process does not require the use of eyes, relying instead on extraocular colour sensing.

In England, Cryphonectria parasitica was detected for the first time in 2011 in a nursery and in 2016 in the wider environment. Surveys between 2017 and 2020 identified the disease at different sites in Berkshire, Buckinghamshire, Cornwall, Derbyshire, Devon, Dorset, London, West Sussex, and the island of Jersey, while the present study comprises the results of the 2020–2023 survey with findings in Derbyshire, Devon, Kent, Nottinghamshire, Herefordshire, Leicestershire, London, West Sussex, and the islands of Jersey and Guernsey. A total of 226 suspected samples were collected from 72 surveyed sites, as far north as Edinburgh and as far west as Plymouth (both of which were negative), and 112 samples tested positive by real-time PCR and isolation from 35 sites. The 112 isolates were tested for the vegetative compatibility group (VCG), mating type, and Cryphonectria hypovirus 1 (CHV1). Twelve VCGs were identified, with two of them (EU-5 and EU-22) being the first records in the UK. Both mating types were present (37% MAT-1 and 63% MAT-2), but only one mating type was present per site and VCG, and perithecia were never observed. Cryphonectria hypovirus 1 (CHV1), consistently subtype-I haplotype E-5, was detected in three isolates at a low concentration (5.9, 21.1, and 33.0 ng/µL) from locations in London, Nottinghamshire, and Devon.

Biological control of Cryphonectria parasitica fungus, causal agent of chestnut blight, by virus infection (hypovirulence) has been shown to be an effective control strategy against chestnut blight in Europe and some parts of North America. The most studied mycovirus is the Cryphonectria hypovirus 1 (CHV-1) type species of the Hypoviridae family. To efficiently provide biocontrol, the virus must be able to induce hypovirulence in its fungal host in chestnut trees. Here, two different CHV-1 subtype I virus strains (E-5 and L-18), gained by transmissions, were tested for their hypovirulence induction, biocontrol potential, and transmission between vegetatively compatible (VCG) and incompatible fungal isolate groups in sweet chestnut seedlings and branches. Both strains of CHV-1 showed great biocontrol potential and could protect trees by efficiently transmitting CHV-1 by hyphal anastomosis between fungal isolates of the same VCG and converting virulent to hypovirulent cankers. The hypovirulent effect was positively correlated with the virus concentration, tested by four different reverse-transcription PCRs, two end-point and two real-time methods, one of which represents a newly developed real-time PCR for the detection and quantification of CHV-1.

In England, Cryphonectria parasitica was detected for the first time in 2011 in a nursery and in 2016 in the wider environment. Surveys between 2017 and 2020 identified the disease at different sites in Berkshire, Buckinghamshire, Cornwall, Derbyshire, Devon, Dorset, London, West Sussex, and the island of Jersey, while the present study comprises the results of the 2020–2023 survey with findings in Derbyshire, Devon, Kent, Nottinghamshire, Herefordshire, Leicestershire, London, West Sussex, and the islands of Jersey and Guernsey. A total of 226 suspected samples were collected from 72 surveyed sites, as far north as Edinburgh and as far west as Plymouth (both of which were negative), and 112 samples tested positive by real-time PCR and isolation from 35 sites. The 112 isolates were tested for the vegetative compatibility group (VCG), mating type, and Cryphonectria hypovirus 1 (CHV1). Twelve VCGs were identified, with two of them (EU-5 and EU-22) being the first records in the UK. Both mating types were present (37% MAT-1 and 63% MAT-2), but only one mating type was present per site and VCG, and perithecia were never observed. Cryphonectria hypovirus 1 (CHV1), consistently subtype-I haplotype E-5, was detected in three isolates at a low concentration (5.9, 21.1, and 33.0 ng/µL) from locations in London, Nottinghamshire, and Devon.

Visual camouflage is a textbook example of natural selection, and a widespread strategy used by both predators and prey to avoid detection. Background matching, where the animal resembles the colour, brightness, and/ or pattern of the surrounding visual background is a common form of visual camouflage, and can occur through genetic polymorphism, behavioural background choice, or dynamic colour change. Dynamic colour change can occur very rapidly (milliseconds) or gradually, sometimes taking weeks to complete. Visual cues such as colour, brightness, and pattern, have been shown to elicit colour change, and in some colour-changing animals visual cues are sensed outside of the eye using extraocular photoreceptors (EOPs). Colour change research has been focused predominantly on rapid, chromatophore-based colour change, as observed in cephalopods. In contrast, little is known about the physiology and evolutionary origins of gradual colour change.To avoid predation in a wide range of environments, caterpillars of the peppered moth (Biston betularia) masquerade as twigs and gradually change colour to match them. This thesis investigates the colour-changing response in B. betularia larvae: the shape of the reaction norm to colour and brightness gradients; the use and molecular basis of extraocular photoreception; and whether B. betularia alter resting behaviour to maximise concealment. Through a series of artificial twig experiments, I found that B. betularia larvae respond to both colour and luminance cues to produce a continuous range of phenotypes, rather than being restricted to a brown/green polyphenism as previously reported. To test for the possibility of extraocular photoreception, I occluded the eyes (ocelli) of groups of larvae and compared responses to colour and luminance with non-blindfolded control larvae. There was no difference in the colour-changing response of blindfolded larvae compared to controls, and blindfolded larvae also rested on colours that better matched their own colour to the same extent as non-blindfolded controls. I next examined the potential for visual machinery in the larval dermis, finding expression of a suite of visual genes throughout dermal tissue in B. betularia larvae and adults. In larvae, this expression was generally much higher relative to head tissue than found for adults. This finding corroborates the morphological and behavioural evidence for dermal photoreceptors in B. betularia larvae.The final chapter is an attempt to examine the exclusivity of extraocular photoreception in B. betularia, and its evolutionary origins, through tissue-specific measurement of opsin expression in larvae and adults of a phylogenetically broad sample of Lepidoptera. Dermal opsin expression was found in other species, but depended on the gene (UV, blue, LW1, LW2) and developmental stage. Phylogenetic signal was found only for expression of LW1 in larvae, and LW2 in adults. Larval colouration strategy between species also appears to affect dermal opsin expression.The thesis provides strong evidence for a novel physiological phenomenon: extraocular colour photoreception in the dermis of an insect, used to mediate colour change and behavioural background choice. The observation that dermal opsin expression occurs in several other species suggests that EOPs may be widespread in the Lepidoptera. Future work should be directed at the challenging task of understanding the mechanism underlying this class of EOPs, and characterising their functional roles in other species.

Light sensing by tissues distinct from the eye occurs in diverse animal groups, enabling circadian control and phototactic behaviour. Extraocular photoreceptors may also facilitate rapid colour change in cephalopods and lizards, but little is known about the sensory system that mediates slow colour change in arthropods. We previously reported that slow colour change in twig-mimicking caterpillars of the peppered moth (Biston betularia) is a response to achromatic and chromatic visual cues. Here we show that the perception of these cues, and the resulting phenotypic responses, does not require ocular vision. Caterpillars with completely obscured ocelli remained capable of enhancing their crypsis by changing colour and choosing to rest on colour-matching twigs. A suite of visual genes, expressed across the larval integument, likely plays a key role in the mechanism. To our knowledge, this is the first evidence that extraocular colour sensing can mediate pigment-based colour change and behaviour in an arthropod.

Phytophthora pluvialis is a forest tree pathogen present in the USA, New Zealand, UK and Belgium. Reported hosts include Douglas-fir in the USA, New Zealand, UK and Belgium, as well as tanoak in the USA, radiata pine in New Zealand, Japanese larch and western hemlock in the UK. Disease symptoms range from needle lesions and casting on radiata pine through to twig and stem cankers, and crown dieback on western hemlock, Douglas-fir and Japanese larch. Current detection methods rely on isolation and culture, or PCR using a single-copy gene target with limited sensitivity at low pathogen titre. A qPCR assay targeting a multiple-copy mitochondrial gene was designed to increase sensitivity of P. pluvialis detection in forest samples, critical for informing biosecurity, long term disease management and ongoing research. The resulting assay has a detection limit of 12.8 fg mycelial DNA and can detect the pathogen on average 6.12 qPCR cycles before the single-copy target assay. In New Zealand forest samples, the assay was found to consistently detect P. pluvialis in all stages of radiata pine needle disease symptoms from early asymptomatic infection through to fully cast needles. The new assay allowed for asymptomatic detection of P. pluvialis in radiata pine needle samples four weeks before visual symptoms of disease were observed. The availability of a highly sensitive assay has also enabled rapid and confident diagnostic support of the biosecurity response in the UK during recent detection of P. pluvialis. The assay has been used in applications requiring detection at low pathogen titre levels including asymptomatic infection, stream baiting, cast needles and during biosecurity responses, making it a useful tool for effective early detection and management of P. pluvialis in affected forests.Competing Interest StatementThe authors have declared no competing interest.