Ian Denholm

The aphid Myzus persicae is a destructive agricultural pest that displays an exceptional ability to develop resistance to both natural and synthetic insecticides. To investigate the evolution of resistance in this species we generated a chromosome-scale genome assembly and living panel of >110 fully sequenced globally sampled clonal lines. Our analyses reveal a remarkable diversity of resistance mutations segregating in global populations of M. persicae. We show that the emergence and spread of these mechanisms is influenced by host–plant associations, uncovering the widespread co‐option of a host-plant adaptation that also offers resistance against synthetic insecticides. We identify both the repeated evolution of independent resistance mutations at the same locus, and multiple instances of the evolution of novel resistance mechanisms against key insecticides. Our findings provide fundamental insights into the genomic responses of global insect populations to strong selective forces, and hold practical relevance for the control of pests and parasites.

Soils and plant root rhizospheres have diverse microorganism profiles. Components of this naturally occurring microbiome, arbuscular mycorrhizal (AM) fungi and plant growth promoting rhizobacteria (PGPR), may be beneficial to plant growth. Supplementary application to host plants of AM fungi and PGPR either as single species or multiple species inoculants has the potential to enhance this symbiotic relationship further. Single species interactions have been described; the nature of multi-species tripartite relationships between AM fungi, PGPR and the host plant require further scrutiny. The impact of select Bacilli spp. rhizobacteria and the AM fungus Rhizophagus intraradices as both single and combined inoculations (PGPR_[i] and AMF_[i]) within field extracted arable soils of two tillage treatments, conventional soil inversion (CT) and zero tillage (ZT) at winter wheat growth stages GS30 and GS39 have been conducted. The naturally occurring soil borne species (PGPR_[s] and AMF_[s]) have been determined by qPCR analysis. Significant differences (p < 0.05) were evident between inocula treatments and the method of seedbed preparation. A positive impact on wheat plant growth was noted for B. amyloliquefaciens applied as both a single inoculant (PGPR_[i]) and in combination with R. intraradices (PGPR_[i] + AMF_[i]); however, the two treatments did not differ significantly from each other. The findings are discussed in the context of the inocula applied and the naturally occurring soil borne PGPR_[s] present in the field extracted soil under each method of tillage.

Circumscriptions of both the genus Gymnadenia and the 11–27 species that it contains are highly controversial. These Eurasian terrestrial orchids are nectar-rewarding and pollinated primarily by Lepidoptera. Opinions expressed on the number of species occurring in the British Isles range from one to four, though there exists broad agreement that at least three recognizable, ecologically differentiated taxa are widespread. Here, we use a large-scale morphometric survey of these supposedly ‘cryptic’ taxa to determine whether phenotypic differentiation exists alongside their documented genotypic and ecological differentiation, seeking the most diagnostic morphological characters. Ten Gymnadenia plants were measured in each of 29 populations that encompassed the entire taxonomic range and geographic distribution of the genus within the British Isles. Results were subjected to detailed multivariate and univariate analyses, and interpreted in the context of molecular phylogenies, including a bespoke Europe-wide nrITS phylogeny that includes 17 plants sampled across Britain and Ireland. Floral micromorphology was investigated through scanning electron microscopy. Ecotypes occurring respectively in calcareous grasslands (G. conopsea s.s.), acid heaths (G. borealis) and calcareous to neutral marshes (G. densiflora) are subtly but reliably distinct, both morphologically and molecularly, though locally their morphological distinctiveness is somewhat weakened by the occurrence of infrequent populations in dune slacks and chalk downs that are intermediate in phenotype between the grassland and marsh ecotypes ('subsp. cf. friesica'). A polythetic taxonomic key emphasizes the characters and character-state ranges that are demonstrably the most diagnostic. Given that they are reliably genetically differentiable, and individuals can be distinguished with ∼85% confidence using morphological characters such as flower dimensions, depth of flower colour, and leaf number and size, we uphold our previous arguments that the three ecotypes merit species-level recognition. In the continued absence of field sequencing devices, identification is best attempted through quantitative examination of morphology focused at the population level, rejecting records of isolated plants. Despite their strong morphological similarity, genus-wide molecular data show that the British species are not each other's closest relatives. Gymnadenia borealis remains one of only three orchid species putatively endemic to the British Isles.

Arbuscular Mycorrhizal (AM) fungi form mutualistic symbiotic relationships with approximately 80% of terrestrial plant species, while producing the glycoprotein glomalin as a structural support molecule along their mycelial network. Glomalin confers two benefits for soils: (1) acting as a carbon and nitrogen storage molecule; (2) the binding of soil microaggregates (<250 µm) to form larger, more stable structures. The present study aimed to test the hypothesis that a correlation between glomalin and soil aggregation exists and that this is influenced by the method of seedbed preparation. The soils from two crops of winter wheat in Hertfordshire, UK, practising either conventional (20 cm soil inversion) or zero tillage exclusively, were sampled in a 50 m grid arrangement over a 12 month period. Glomalin and water stable aggregates (WSA) were quantified for each soil sample and found to be significantly greater in zero tillage soils compared to those of conventional tillage. A stronger correlation between WSA and glomalin was observed in zero tillage (Pearson’s coeffect 0.85) throughout the cropping year compared to conventional tillage (Pearson’s coeffect 0.07). The present study was able to conclude that zero tillage systems are beneficial for AM fungi, the enhancement of soil glomalin and soil erosion mitigation.

Arbuscular mycorrhizal (AM) fungi are one of the most common fungal organisms to exist in symbiosis with terrestrial plants, facilitating the growth and maintenance of arable crops. Wheat has been studied extensively for AM fungal symbiosis using the carcinogen trypan blue as the identifying stain for fungal components, namely arbuscles, vesicles and hyphal structures. The present study uses Sheaffer blue ink with a lower risk as an alternative to this carcinogenic stain. Justification for this is determined by stained wheat root sections (n=120), with statistically significant increases in the observed abundance of intracellular root cortical fungal structures stained with Sheaffer blue ink compared to trypan blue for both Zulu (P=0.003) and Siskin (P=0.0003) varieties of winter wheat. This new alternative combines an improved quantification of intracellular fungal components with a lower hazard risk at a lower cost.

BACKGROUND: The R81T mutation conferring target‐site resistance to neonicotinoid insecticides in Myzus persicae was first detected in France and has since spread across much of southern Europe. In response to recent claims of control failure with neonicotinoids in Tunisia, we have used a molecular assay to investigate the presence and distribution of this target‐site mutation in samples collected from six locations and six crops attacked by M. persicae.RESULTS: The resistance allele containing R81T was present at substantial frequencies (32–55%) in aphids collected between 2014 and 2016 from northern Tunisia but was much rarer further south. It occurred in aphids collected from the aphid's primary host (peach) and four secondary crop hosts (potato, pepper, tomato and melon). Its absence in aphids from tobacco highlights complexities in the systematics of M. persicae that require further investigation.CONCLUSION: This first report of R81T from North Africa reflects a continuing expansion of its range around the Mediterranean Basin, although it remains unrecorded elsewhere in the world. Loss of efficacy of neonicotinoids presents a serious threat to the sustainability of aphid control. © 2017 Society of Chemical Industry

Although the majority of taxonomic studies of European orchids treat Pseudorchis as a monotypic genus, some observers have argued that the apparently circumboreal segregate P. straminea should also be treated as a full species. Here, we compare detailed in vivo measurements of 55 plants from nine populations of P. albida in Britain with ten plants from three populations of P. straminea in Iceland, We apply morphometric statistics to data for 31 morphometric characters, culled from an original set of 36. We also review current (limited) DNA-based evidence of their evolutionary divergence. Of the 31 variable morphometric characters, 14 help to distinguish the two species, including labellum dimensions, spur length, flower colour, bract and leaf lengths, leaf colour and apical hooding. Molecular divergence (notably in ITS) approximates the lowest level needed for acceptance of species-level distinction, but thus far, the molecular information is typological and does not encompass seemingly intermediate populations of ‘P. tricuspis’ occurring in the mountains of central Europe. Pseudorchis has the potential to become a valuable model system for the study of speciation and subsequent inter-/post-glacial migration. Despite persistent rumours, we found no evidence that P. straminea (or ‘P. tricuspis’) occurs in the British Isles; nonetheless, this species should continue to be sought in suitable habitats in northern Scotland. Morphological variation within P. albida is comparatively low, though the most exposed of our study populations exhibits (presumably ecophenotypic) dwarfing.

BACKGROUND: Tools with the potential to predict risks of insecticide resistance and aid the evaluation and design of resistance management tactics are of value to all sectors of the pest management community. Here we describe use of a versatile individual‐based model of resistance evolution to simulate how strategies employing single and multiple insecticides influence resistance development in the pollen beetle, Meligethes aeneus.RESULTS: Under repeated exposure to a single insecticide, resistance evolved faster to a pyrethroid (lambda‐cyhalothrin) than to a pyridine azomethane (pymetrozine), due to difference in initial efficacy. A mixture of these compounds delayed resistance compared to use of single products. The effectiveness of rotations depended on the sequence in which compounds were applied in response to pest density thresholds. Effectiveness of a mixture strategy declined with reductions in grower compliance. At least 50% compliance was needed to cause some delay in resistance development.CONCLUSION: No single strategy meets all requirements for managing resistance. It is important to evaluate factors that prevail under particular pest management scenarios. The model used here provides operators with a valuable means for evaluating and extending sound resistance management advice, as well as understanding needs and opportunities offered by new control techniques. © 2016 Society of Chemical Industry