Dave Chandler

A Virulent Strain of Deformed Wing Virus (DWV) of Honeybees (Apis mellifera) Prevails after Varroa destructor-Mediated, or In Vitro, Transmission

The globally distributed ectoparasite Varroa destructor is a vector for viral pathogens of the Western honeybee (Apis mellifera), in particular the Iflavirus Deformed Wing Virus (DWV). In the absence of Varroa low levels DWV occur, generally causing asymptomatic infections. Conversely, Varroa-infested colonies show markedly elevated virus levels, increased overwintering colony losses, with impairment of pupal development and symptomatic workers. To determine whether changes in the virus population were due Varroa amplifying and introducing virulent virus strains and/or suppressing the host immune responses, we exposed Varroa-naïve larvae to oral and Varroa-transmitted DWV. We monitored virus levels and diversity in developing pupae and associated Varroa, the resulting RNAi response and transcriptome changes in the host. Exposed pupae were stratified by Varroa association (presence/absence) and virus levels (low/high) into three groups. Varroa-free pupae all exhibited low levels of a highly diverse DWV population, with those exposed per os (group NV) exhibiting changes in the population composition. Varroa-associated pupae exhibited either low levels of a diverse DWV population (group VL) or high levels of a near-clonal virulent variant of DWV (group VH). These groups and unexposed controls (C) could be also discriminated by principal component analysis of the transcriptome changes observed, which included several genes involved in development and the immune response. All Varroa tested contained a diverse replicating DWV population implying the virulent variant present in group VH, and predominating in RNA-seq analysis of temporally and geographically separate Varroa-infested colonies, was selected upon transmission from Varroa, a conclusion supported by direct injection of pupae in vitro with mixed virus populations. Identification of a virulent variant of DWV, the role of Varroa in its transmission and the resulting host transcriptome changes furthers our understanding of this important viral pathogen of honeybees.

Sampling and occurrence of entomopathogenic fungi and nematodes in UK soils

Abstract The occurrence of entomopathogenic fungi and nematodes was measured in samples of soil collected from cultivated and uncultivated habitats in Warwickshire, UK. Fungi and nematodes were isolated from the samples of soil by “baiting” with larvae of the wax moth, Galleria mellonella (Lepidoptera: Pyralidae). Following two pilot experiments, a main study was done using soil collected from an arable field, a network of hawthorn hedges and four mature woodlands. 70 isolates of entomopathogenic fungi were obtained from 400 samples of soil. Hyphomycete fungi (15.8% occurrence) were isolated from significantly more samples of soil than entomophthoralean fungi (1.8% occurrence, P

A Strong Immune Response in Young Adult Honeybees Masks Their Increased Susceptibility to Infection Compared to Older Bees

Honeybees, Apis mellifera, show age-related division of labor in which young adults perform maintenance (“housekeeping”) tasks inside the colony before switching to outside foraging at approximately 23 days old. Disease resistance is an important feature of honeybee biology, but little is known about the interaction of pathogens and age-related division of labor. We tested a hypothesis that older forager bees and younger “house” bees differ in susceptibility to infection. We coupled an infection bioassay with a functional analysis of gene expression in individual bees using a whole genome microarray. Forager bees treated with the entomopathogenic fungus Metarhizium anisopliae s.l. survived for significantly longer than house bees. This was concomitant with substantial differences in gene expression including genes associated with immune function. In house bees, infection was associated with differential expression of 35 candidate immune genes contrasted with differential expression of only two candidate immune genes in forager bees. For control bees (i.e. not treated with M. anisopliae) the development from the house to the forager stage was associated with differential expression of 49 candidate immune genes, including up-regulation of the antimicrobial peptide gene abaecin, plus major components of the Toll pathway, serine proteases, and serpins. We infer that reduced pathogen susceptibility in forager bees was associated with age-related activation of specific immune system pathways. Our findings contrast with the view that the immunocompetence in social insects declines with the onset of foraging as a result of a trade-off in the allocation of resources for foraging. The up-regulation of immune-related genes in young adult bees in response to M. anisopliae infection was an indicator of disease susceptibility; this also challenges previous research in social insects, in which an elevated immune status has been used as a marker of increased disease resistance and fitness without considering the effects of age-related development.

Biopesticides: pest management and regulation.

Biological controls that utilize natural predation, parasitism or other natural mechanisms, is an environmentally friendly alternative to chemical pesticides. Chemical pesticide methods are becoming less readily available due to increasing resistance problems and the prohibition of some substances. This book addresses the challenges of insufficient information and imperfectly understood regulatory processes in using biopesticides. It takes an interdisciplinary approach providing internationally comparative analyses on the registration of biopesticides and debates future biopesticide practices.

Matching control options to a pest complex: the integrated pest management of aphids in sequentially-planted crops of outdoor lettuce

Abstract Sequentially planted short-season vegetable crops grown in temperate climates offer the opportunity to use known variations in pest phenology through the season to develop a strategic way of matching control options on different plantings to predicted levels of pest risk. To test this approach in the UK, five field experiments were done over two years to test integrated pest management (IPM) programmes for four aphid pest species ( Nasonovia ribisnigri, Macrosiphum euphorbiae, Pemphigus bursarius and Myzus persicae ) on outdoor lettuce crops. Crops were planted to coincide with different periods of forecast aphid risk. The results suggested that acceptable levels of aphid control could be achieved, provided a full range of treatment options (resistant cultivars, selective insecticides, biocontrol agents and validated pest forecasts) could be utilised. Commercial and technical constraints to the commercial adoption of this approach are discussed.

Deep space and hidden depths: understanding the evolution and ecology of fungal entomopathogens

Entomopathogens are important natural enemies of many insect and mite species and as such have been recognised as providing an important ecosystem service. Indeed, fungal entomopathogens have been widely investigated as biological control agents of pest insects in attempts to improve the sustainability of crop protection. However, even though our understanding of the ecology of fungal entomopathogens has vastly increased since the early 1800s, we still require in-depth ecological research that can expand our scientific horizons in a manner that facilitates widespread adoption of these organisms as efficient biological control agents. Fungal entomopathogens have evolved some intricate interactions with arthropods, plants and other microorganisms. The full importance and complexity of these relationships is only just becoming apparent. It is important to shift our thinking from conventional biological control, to an understanding of an as yet unknown “deep space”. The use of molecular techniques and phylogenetic analyses have helped us move in this direction, and have provided important insights on fungal relationships. Nevertheless, new techniques such as the PhyloChip and pyrosequencing might help us see beyond the familiar fields, into areas that could help us forge a new understanding of the ecology of fungal entomopathogens.

The ecology of fungal entomopathogens

Deep space and hidden depths: understanding the evolution and ecology of fungal entomopathogens.- Fungal evolution and taxonomy.- Molecular ecology of fungal entomopathogens: molecular genetic tools and their applications in population and fate studies.- Principles from community and metapopulation ecology: application to fungal entomopathogens.- Challenges in modelling complexity of fungal entomopathogens in semi-natural populations of insects.- Fungal entomopathogens in a tritrophic context.- Entomopathogenic fungi and insect behaviour: from unsuspecting hosts to targeted vectors.- Fungal entomopathogens in the rhizosphere.- Endophytic fungal entomopathogens with activity against plant pathogens: ecology and evolution.- Ecological considerations in producing and formulating fungal entomopathogens for use in insect biocontrol.- Fungal pathogens as classical biological control agents against arthropods.- Ecological factors in the inundative use of fungal entomopathogens.- Conservation biological control using fungal entomopathogens.

Effect of different Agaricus species on the development of the mushroom sciarid fly Lycoriella ingenua

Isolates from eight species of Agaricus were investigated in laboratory experiments for their effect on the development of the mushroom sciarid fly, Lycoriella ingenua (Dufour) (Diptera: Sciaridae), which is an important pest of the white mushroom Agaricus bisporus (Lange) Imbach (Agaricaceae). The population levels of L. ingenua developing in compost inoculated with Agaricus mycelium varied with the Agaricus isolate used, with some isolates causing high levels of inhibition. The development of L. ingenua populations and the survival of larval instars were inversely proportional to the amount of Agaricus inoculum applied. There was also a negative relationship between L. ingenua survival and the extension rate of the Agaricus isolate in compost. The results suggest that inhibition of L. ingenua population development by Agaricus is linked to the rate at which compost is colonized by fungal mycelium. Therefore, on mushroom farms, sciarid fly control should focus on protection of the compost before it has become colonized by mycelium, as this is when it is most vulnerable to the pest.

Differential effect of Agaricus host species on the population development of Megaselia halterata (Diptera: Phoridae).

Twelve isolates from the genus Agaricus (Fungi, Basidiomycota) were investigated for their ability to support development of the phorid fly, Megaselia halterata (Wood), which is an important pest of the commercial white button mushroom Agaricus bisporus. Combined effects of oviposition of adult female M. halterata and larval development in mushroom compost inoculated with Agaricus mycelium were determined using bioassays. The numbers of M. halterata offspring that developed were affected by the Agaricus isolate used, and there was a significant separation between resistant and susceptible isolates. In a bioassay where the female phorids had a choice of all 12 isolates for oviposition, three isolates produced >200 adults per 100 g compost pot while the remaining nine isolates had <20 adults per pot. Where there was no choice of Agaricus isolate for oviposition, five isolates resulted in >100 adults per 100 g compost pot while the remainder resulted in <4 adults per pot. With the susceptible isolates, there was a positive correlation between increasing concentration of mycelium in the substrate and phorid development until the concentration exceeded 40% after which numbers of emerging phorids declined. Genetic identity of Agaricus isolates was determined using ITS sequencing and phylogenetic methods, which revealed two major cluster groups. Isolates supporting the development of large populations of M. halterata were located in one of these clusters (group I), and were either Agaricus bisporus or other species from the same Agaricus section Duploannulatae. Isolates that did not support the development of M. halterata populations were located in a different cluster (group II) and were more genetically distant from A. bisporus, e.g. Agaricus sections Arvenses, Minores and Xanthodermatei. Species of Agaricus with resistance to M. halterata could have significant potential for the breeding and cultivation of phorid-free mushrooms.

Recording the movement of adult vine weevil within strawberry crops using radio frequency identification tags

BACKGROUND:Vine weevil (Otiorhynchus sulcatus) is a major pest of soft fruit and ornamental crops. There is an urgent need to improve control of vine weevil and in particular to provide growers with effective Integrated Pest Management-compatible controls with which to target the adult stage of this pest. One approach would be to exploit the behaviour of adult vine weevil to disseminate spores of an entomopathogenic fungus placed within the crop environment in artificial refuges. To be effective this approach requires that the weevils move through the crop environment and in doing so spread the pathogen from the artificial refuges. OBJECTIVE:Use passive radio frequency identification (RFID) tags to study the movement of adult vine weevil within crop environments. METHOD:A series of laboratory bioassays were completed in which the effect of attaching RFID tags using a thermoplastic or a cyanoacrylate adhesive on survival and movement, on both horizontal and vertical surfaces, of adult vine weevil was determined. An outdoor field experiment was then completed at Harper Adams University in order to test the potential of this technique for studying vine weevil movement within crop environments. RESULTS:Attaching RFID tags using the thermoplastic adhesive did not result in any weevil deaths over a 21 day period. In contrast, just over half (53%) of the weevils to which the RFID tag was attached using the cyanoacrylate adhesive died over the same period. The mean of weevil horizontal movement speed was significantly slower when an RFID tag was attached using a thermoplastic (1.01 cm/s) or a cyanoacrylate (0.29 cm/s) adhesive compared with untagged weevils (1.83 cm/s). However, weevils that were tagged using the thermoplastic adhesive were significantly faster than weevils tagged using the cyanoacrylate adhesive. Mean vertical movement speed was also significantly slower when weevils were tagged using the thermoplastic adhesive (0.18 cm/s) compared with untagged weevils (0.37 cm/s). Weevils tagged using the cyanoacrylate adhesive were unable to climb vertical surfaces.In the field experiment, weevils moved away from their release points. Nine days after the start of the experiment weevils were on average 3.38 m from their release points indicating a speed of movement of 0.38 m/day. The mean distance of movement from their release points did not increase further during the rest of the experimental period, but remained relatively constant at between 2.50 and 3.28 m. As such, for weevils that remained within the crop environment, there is no evidence of dispersal behaviour,with movement behaviour observed more likely to be driven by resource utilisation. However, not all weevils remained within the crop area. Indeed, 15 (38%) of released weevils and/or RFID tags left the crop area, indicating possible long range dispersal by these individuals or evidence of predation of the weevils.A total of 11 (28%) of the RFID tagged weevils released into the crop were recovered alive and with the tag still attached after 35 days. These weevils were estimated to have moved a distances of between 2.65 and 17.30 m (average distance moved 7.50 m) during this period. These distances are likely to underestimate the distance moved by each weevil as they assume that each weevil took the most direct route between each point and did not move other than this. In total eight of the RFID-tagged weevils moved both along and between rows of strawberry grow-bags. At the start of the experiment the 11 RFID tagged weevils occupied 11 (14%) of the strawberry grow-bags. If these weevils took the most direct route between each position within the crop where they were detected these weevils would have crossed, and potentially laid eggs in, 44 (58%) of the grow-bags during the 35 days of the experiment. If they had taken a more indirect route the weevils could have potentially laid eggs in a higher number of the grow-bags. CONCLUSIONS:Results presented here indicate that RFID tags can be used to study the movement of vine weevil adults within crop environments. However, the weight and size of currently available tags significantly slows the movement of weevils under laboratory conditions and frequency of detection may affect estimates of actual distance moved. Despite this, the rate at which vine weevil dispersed through the strawberry crop was comparable to the speed of movement recorded previously by others when weevils were released into an urban environment. Use of RFID tags also resulted in detection rates far higher than those reported in studies by others using traditional mark-release-recapture techniques. Use of RFID tags in the present study indicates that adult vine weevil have the potential to disperse spores of a suitable entomopathogenic fungus from artificial refuges throughout the crop environment. Use of this technique could also be applied to investigate the effect of other plant protection products as well as the impact of different cropping systems on vine weevil movement and survival.