Barley/cereal yellow dwarf viruses (YDVs) cause yellow dwarf disease (YDD), which is a continuous risk to cereals production worldwide. These viruses cause leaf yellowing and stunting, resulting in yield reductions of up to 80%. YDVs have been a consistent but low-level problem in European cereal cultivation for the last three decades, mostly due to the availability of several effective insecticides (largely pyrethroids and more recently neonicotinoids) against aphid vectors. However, this has changed recently, with many insecticides being lost, culminating in a recent European Union (EU) regulation prohibiting outdoor use of the neonicotinoid-insecticide compounds. This change is coupled with the growing challenge of insecticide-resistant aphids, the lack of genetic resources against YDVs, and a knowledge deficit around the parameters responsible for the emergence and spread of YDD. This means that economic sustainability of cereal cultivation in several European countries including France and United Kingdom is now again threatened by this aphid-vectored viral disease. In this review, we summarize the current knowledge on the YDV pathosystem, describe management options against YDD, analyse the impacts of the neonicotinoid ban in Europe, and consider future strategies to control YDV.
Results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rose-grain aphid (Metopholophium dirhodum) and the bird-cherry – oat aphid (Rhopalosiphum padi), are used to measure levels of pyrethroid resistance. Aphid pests on cereals in the British Isles are predominantly controlled by pyrethroid insecticides, especially since the implementation of the recent ban on neonicotinoid seed treatments on all outdoor crops. Resistance to pyrethroids has been detected in one of the main aphid pests, the grain aphid (Sitobion avenae), probably brought on by the sustained use of these pyrethroid sprays to control cereal aphids, which can transmit plant viruses, especially Barley Yellow Dwarf Virus (BYDV). The withdrawal of several insecticide compounds (e.g. pirimicarb, dimethoate, chlorpyrifos and the aforesaid neonicotinoids) for cereal aphid control will probably increase the selection pressure, leading to increased levels of resistance in S. avenae, and, potentially, the evolution of resistance in other cereal aphid species. In this article we present the results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rosegrain aphid (Metopholophium dirhodum) and the bird-cherry– oat aphid (Rhopalosiphum padi), in order to measure levels of pyrethroid resistance. At present, little is known about the extent of pyrethroid resistance in S. avenae beyond the UK and in other cereal aphids. It therefore becomes increasingly important to monitor these pests to inform crop management decisions in light of the recent loss of other insecticides. The unintended consequences of the rapid withdrawal of insecticides, together with a failure to prepare and install alternative products and control approaches in advance, will probably ultimately lead to the loss of effectiveness of insecticidal compounds like pyrethroids.
The grain aphid Sitobion avenae is a prolific pest of cereal crops worldwide, controlled effectively with pyrethroid insecticides. However, the classic knock down resistance (kdr) mutation, L1014F on the S. avenae sodium channel gene, has been identified as the cause of the recently observed heterozygous (kdr-SR) resistance in the SA3 grain aphid super-clone. Results indicate that the kdr-SR SA3 clone can survive pyrethroid exposure above twice the normal field rate, continuing to reproduce thereafter. Additionally, the SA3 clone was found to be capable of producing sexual oviparous morphs, able to lay eggs following pyrethroid exposure. This demonstrates that possession of the L1014F mutation does not preclude the capacity to produce sexual morphs. This makes the adoption of an effective resistance management strategy imperative, within a wider integrated pest management (IPM) approach to control grain aphid.
Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is an economically important insect pest of horticultural crops. To identify an effective and reliable monitoring system for adult vine weevil, this study investigated the influence of colour, height and entrance position on the efficacy of a model monitoring tool using modified paper cups as refuges. Vine weevil preferences were determined by the number of individuals recorded within a refuge. When provided with a binary choice between black or white refuges, vine weevil adults showed a preference for black refuges. Vine weevils provided with a range of coloured refuges (blue, green, red and yellow) in addition to black and white refuges showed a preference for black and blue over the other colours and white refuges in group choice experiments. Refuge height and entrance position also influenced vine weevil behaviour with individuals exhibiting a preference for taller refuges and those with entrance openings around the refuge base. These results provide insights into refuge selection by adult vine weevils, which can be exploited to improve monitoring tool design. The importance of developing an effective monitoring tool for vine weevil adults as part of an integrated pest management programme is discussed.
As urban areas and land-use constraints grow, there is increasing interest in utilizing urban spaces for food production. Several studies have uncovered significant potential for urban growing to supplement production of fruit and vegetables, focusing on one or two cities as case studies, whilst others have assessed the global scale potential. Here, we provide a national-scale analysis of the horticultural production potential of urban green spaces, which is a relevant scale for agri-food and urban development policy making using Great Britain (GB) as a case study. Urban green spaces available for horticultural production across GB are identified and potential yields quantified based on three production options. The distribution of urban green spaces within 26 urban towns and cities across GB are then examined to understand the productive potential compared to their total extent and populations. Urban green spaces in GB, at their upper limit, have the capacity to support production that is 8x greater than current domestic production of fruit and vegetables. This amounts to 38% of current domestic production and imports combined, or >400% if exotic fruits and vegetables less suited to GB growing conditions are excluded. Most urban green spaces nationally are found to fall within a small number of categories, with private residential gardens and amenity spaces making up the majority of space. By examining towns and cities across GB in further detail, we find that the area of green space does not vary greatly between urban conurbations of different sizes, and all are found to have substantial potential to meet the dietary needs of the local urban population. This study highlights that national policies can be suitably developed to support urban agriculture and that making use of urban green spaces for food production could help to enhance the resilience of the national-scale food system to shocks in import pathways, or disruptions to domestic production and distribution.
Resistance to insecticides used to control pests is an issue of increasing concern for agriculture. The grain aphid, Sitobion avenae, is a pest of cereals and grasses worldwide, and one of growing concern due to the evolution of resistance to certain insecticides.Resistance confers benefits to insects by enabling them to survive exposure to insecticide compounds; however, the mutations conferring resistance may also penalise the insect in pesticide-free environments due to fitness costs associated with the new phenotype. Here we tested the hypothesis of a reproductive penalty linked to the knockdown resistance mutation (kdr) to pyrethroid insecticides. The mutation occurs predominantly in a single SA3 clone. To date, only heterozygous-resistant forms (kdr-SR) have been detected in populations in Ireland and the UK, and this suggests that a fitness penalty may preclude the formation of both male and female heterozygousresistant sexual forms. By designing an experiment which included a resistant and a non-resistant clone, we were able to simulate reduced daylight and temperature conditions which, in nature, trigger sexual reproduction and therefore study the responses of each clone. This allowed us to detect the switch from asexual females to sexual females and males and report on the conditions associated with the production of sexual forms. The results showed that both aphid clones were able to produce sexual forms with no difference in the onset of sexual reproduction, although reproductive strategies differed between clones. The later onset of male forms in the SA3 clone may decrease the likelihood of mating interactions to create fully resistant (kdr-RR) genotypes and this may constitute a fitness penalty due to pyrethroid resistance.
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