Gudbjorg I. Aradottir

The first crop plant genetically engineered to release an insect pheromone for defence.

Insect pheromones offer potential for managing pests of crop plants. Volatility and instability are problems for deployment in agriculture but could be solved by expressing genes for the biosynthesis of pheromones in the crop plants. This has now been achieved by genetically engineering a hexaploid variety of wheat to release (E)-β-farnesene (Eβf), the alarm pheromone for many pest aphids, using a synthetic gene based on a sequence from peppermint with a plastid targeting amino acid sequence, with or without a gene for biosynthesis of the precursor farnesyl diphosphate. Pure Eβf was produced in stably transformed wheat lines with no other detectable phenotype but requiring targeting of the gene produced to the plastid. In laboratory behavioural assays, three species of cereal aphids were repelled and foraging was increased for a parasitic natural enemy. Although these studies show considerable potential for aphid control, field trials employing the single and double constructs showed no reduction in aphids or increase in parasitism. Insect numbers were low and climatic conditions erratic suggesting the need for further trials or a closer imitation, in the plant, of alarm pheromone release.

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 June 2010 - 31 July 2010.

This article documents the addition of 205 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Bagassa guianensis, Bulweria bulwerii, Camelus bactrianus, Chaenogobius annularis, Creontiades dilutus, Diachasmimorpha tryoni, Dioscorea alata, Euhrychiopsis lecontei, Gmelina arborea, Haliotis discus hannai, Hirtella physophora, Melanaphis sacchari, Munida isos, Thaumastocoris peregrinus and Tuberolachnus salignus. These loci were cross‐tested on the following species: Halobaena caerulea, Procellaria aequinoctialis, Oceanodroma monteiroi, Camelus ferus, Creontiades pacificus, Dioscorea rotundata, Dioscorea praehensilis, Dioscorea abyssinica, Dioscorea nummularia, Dioscorea transversa, Dioscorea esculenta, Dioscorea pentaphylla, Dioscorea trifida, Hirtella bicornis, Hirtella glandulosa, Licania alba, Licania canescens, Licania membranaceae, Couepia guianensis and 7 undescribed Thaumastocoris species.

Aspects of insect chemical ecology: exploitation of reception and detection as tools for deception of pests and beneficial insects

Empirical exploitation of insect reception and detection at the peripheral neurosensory level has been extremely valuable for identifying pheromones and other semiochemicals, mainly by electroantennogram or single cell preparations coupled with capillary gas chromatography. Differential sensitivity to semiochemicals at the single‐cell level has allowed the identification of some of the most active semiochemicals relating to host location and, more importantly, to the avoidance of nonhosts. However, in terms of molecular recognition, there is still a considerable gap in understanding the detection of particular molecules and their discrimination from closely‐related chemical structures. New approaches will be needed to understand the processes of molecular recognition more precisely. Nevertheless, from electrophysiological studies to the most advanced molecular techniques, it has been possible to identify semiochemicals for the deception of pests in their quest to find plant and animal hosts, as well as mates. Even the deception of insects antagonistic to pests, particularly parasitoids, can now be exploited for managing pests in more sustainable systems. Successes in exploiting insect semiochemicals in the interests of better agriculture and animal husbandry are exemplified, and potential new ways of learning more about reception and detection for deception are discussed. This takes the subject beyond the management of pest and beneficial insects to wider commercial and social opportunities.

Delivering sustainable crop protection systems via the seed: exploiting natural constitutive and inducible defence pathways

To reduce the need for seasonal inputs, crop protection will have to be delivered via the seed and other planting material. Plant secondary metabolism can be harnessed for this purpose by new breeding technologies, genetic modification and companion cropping, the latter already on-farm in sub-Saharan Africa. Secondary metabolites offer the prospect of pest management as robust as that provided by current pesticides, for which many lead compounds were, or are currently deployed as, natural products. Evidence of success and promise is given for pest management in industrial and developing agriculture. Additionally, opportunities for solving wider problems of sustainable crop protection, and also production, are discussed.

Triticum monococcum lines with distinct metabolic phenotypes and phloem‐based partial resistance to the bird cherry–oat aphid Rhopalosiphum padi

Abstract Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry–oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.

Population genetics of Tuberolachnus salignus, an obligate parthenogenetic aphid

1 This study reports the results obtained in an investigation of the putatively parthenogenetic aphid species Tuberolachnus salignus Gmelin. Tuberolachnus salignus is one of the largest aphid species in the world but where and how it overwinters is not known. It has recently become noteworthy because it is increasingly found on commercially grown willows used in bioenergy production. 2 Seven newly‐developed polymorphic microsatellite markers were used to investigate the genetic diversity of the species, and also to confirm its reproduction strategy. 3 Tuberolachnus salignus shows very low clonal diversity; only 16 genotypes were found in 660 specimens from 27 populations in five countries. 4 There was limited geographical structuring in the samples, although the two most common genotypes, which comprised more than half of the specimens collected, had a very wide distribution. 5 Furthermore, we determined that these aphids, which live in very dense colonies, can consist of more than one genotype, suggesting aggregation of colonizing T. salignus. These results confirm the parthenogenetic nature of T. salignus and demonstrate the presence of common genotypes that are widespread in time and space.

Unravelling mycorrhiza-induced wheat susceptibility to the English grain aphid Sitobion avenae

Arbuscular mycorrhizal (AM) fungi are root symbionts that can increase or decrease aphid growth rates and reproduction, but the reason by which this happens is unknown. To investigate the underlying mechanisms of this interaction, we examined the effect of AM fungi on the English Grain aphid (Sitobion avenae) development, reproduction, attraction, settlement and feeding behaviour on two naturally susceptible varieties Triticum aestivum (L.) variety Solstice and T. monococcum MDR037, and two naturally resistant lines, T. monococcum MDR045 and MDR049. Mycorrhizal colonisation increased the attractiveness of T. aestivum var. Solstice to aphids, but there was no effect on aphid development on this variety. Using the Electrical Penetration Graph (EPG) technique, we found that mycorrhizal colonisation increased aphid phloem feeding on T. monococcum MDR037 and MDR045, colonisation also increased growth rate and reproductive success of S. avenae on these varieties. Mycorrhizas increased vascular bundle size, demonstrating that these fungi can influence plant anatomy. We discuss if and how this could be related to an enhanced success rate in phloem feeding in two varieties. Overall, we present and discuss how mycorrhizal fungi can affect the feeding behaviour of S. avenae in wheat, inducing susceptibility in a resistant variety.

Role of Semiochemicals in Integrated Pest Management

Semiochemicals are signalling chemicals used to carry information between living organisms and which cause changes in their behaviour. They are emitted by one individual and cause a response in another. Most invertebrates rely on olfaction as the principal sensory modality for sensing their external environment. Attraction of insects to plants and other host organisms involves detection of specific semiochemicals or specific ratios of semiochemicals. Avoidance of unsuitable hosts can involve the detection of specific semiochemicals, or mixtures of semiochemicals, associated with non-host taxa. For integrated pest management, there is an opportunity to develop non-toxic interventions using semiochemicals that influence the behaviour of pest insects. Attractants can be used in baited traps to monitor pest populations. Furthermore, semiochemicals that repel pests or attract their natural enemies could be used to keep pest populations below damaging levels.

Searching for wheat resistance to aphids and wheat bulb fly in the historical Watkins and Gediflux wheat collections: Wheat resistance to aphids and wheat bulb fly

Abstract Insect pests can reduce wheat yield by direct feeding and transmission of plant viruses. Here we report results from laboratory and field phenotyping studies on a wide range of wheat, including landraces from the Watkins collection deriving from before the green revolution, more modern cultivars from the Gediflux collection (north‐western Europe) and modern UK Elite varieties, for resistance to the bird cherry‐oat aphid, Rhopalosiphum padi (Homoptera: Aphididae) and the English grain aphid, Sitobion avenae (Homoptera: Aphididae). A total of 338 lines were screened for R. padi and 340 lines for S. avenae. Field trials were also conducted on 122 Watkins lines to identify wheat bulb fly, Delia coarctata, preference on these landraces. Considerable variation was shown in insect performance among and within different wheat collections, with reduced susceptibility in a number of varieties, but phenotyping did not identify strong resistance to aphids or wheat bulb fly. Field trials showed within collection differences in aphid performance, with fewer aphids populating lines from the Watkins collection. This differs from development data in laboratory bioassays and suggests that there is a pre‐alighting cue deterring aphid settlement and demonstrates differences in aphid preference and performance on older plants in the field compared with seedlings in the laboratory, highlighting the need for phenotyping for aphid resistance at different plant growth stages. No association was identified between performance of the different insect species on individual varieties, potentially suggesting different nutritional requirements or resistance mechanisms.