Search

Abstract: Food webs in agricultural systems are complex and trophic linkages are difficult to track using conventional methodologies. Here, we review three alternative approaches that allow empirical assessment of feeding interactions: DNA-based techniques, and stable isotope and fatty acid analyses. DNA-based methods, namely multiplex PCR and next-generation sequencing, allow identification of food types and host–parasitoid linkages, resulting in taxonomically highly resolved feeding networks. Stable isotopes and fatty acids reflect the assimilation of broader categories of resources, as metabolised into the consumers’ tissue, together with the associated energy and nutrient fluxes in the food web. We discuss the strengths of the approaches but also highlight their limitations, providing practical advice on which technique is best suited to answer specific questions in examining food web interactions in agroecosystems. Future refinements of these techniques, especially when used in combination, could herald a new era in agricultural food web ecology, enabling management and environmental impact to be placed in the mechanistic context of trophic networks. [Copyright &y& Elsevier]

Abstract: The use of diagnostic polymerase chain reaction (PCR) is a valuable approach to study host–parasitoid interactions. It circumvents problems inherent to rearing parasitoids from field-collected hosts or host dissection. Here, we present a PCR-based detection method for Diadegma semiclausum, Cotesia glomerata, and Cotesia rubecula, which are key-parasitoids of the three lepidopteran cabbage pests Plutella xylostella, Pieris brassicae, and Pieris rapae, respectively. Primer pairs for the three parasitoid species and Pl. xylostella were developed: they were used either separately in singleplex PCR or combined in multiplex PCR to (1) screen simultaneously for the two Cotesia species or to (2) detect the parasitoid D. semiclausum and identify its host Pl. xylostella in one PCR. The new idea to simultaneously identify parasitoid and host by molecular markers is useful when the host, in our case early-instar larvae of Pl. xylostella, is morphologically difficult to distinguish from other host species also occurring in the same habitat. Concentration–response trials revealed comparable detection sensitivity of singleplex and multiplex PCR, with detection limits ranging from 0.03 to 2.2pg of parasitoid DNA/μl PCR. Furthermore, the different developmental time of immature D. semiclausum and C. glomerata did not influence parasitoid detection success in either assay type. Based on multiplex PCR screening of field-collected caterpillars, we found in Pl. xylostella, P. brassicae, and P. rapae parasitism rates of 33.4% by D. semiclausum, 52% by C. glomerata, and 53.4% by C. rubecula, respectively. [Copyright &y& Elsevier]

Abstract: Non-target effects of the entomopathogenic fungus Beauveria brongniartii (Ascomycota: Clavicipitaceae) on Poecilus versicolor (Coleoptera: Carabidae), a potential antagonist of the European cockchafer Melolontha melolontha, were studied with three different B. brongniartii formulations, Melocont-Pilzgerste, Melocont-WP, and Melocont-WG. All formulations induced significantly enhanced mortality rates among third instar larvae of the target pest M. melolontha, but no negative effects on the non-target organism were observed. However, small but statistically significant differences were observed for P. versicolor when the fungus was applied: larval development time from first instar to adult stage was decreased by 6.8% (4 days) and the biomass of teneral beetles increased by 8.4% (3.7mg) compared to that of the control groups. Additionally, third instar larvae of P. versicolor were exposed to B. brongniartii-infected M. melolontha cadavers to either consume material from the mycosed carcasses or come in contact with them while searching for food. Again, no significant negative effects on P. versicolor could be observed. The results suggest that under field conditions B. brongniartii would be a negligible risk for P. versicolor. [Copyright &y& Elsevier]

• Intraguild predation within beetle communities was analysed in cereal fields. • Organic fertilization increased non-pest prey and lowered intraguild predation. • Lower intraguild predation correlated with lower pest spread, but not density. • No effect of organic fertilization was found on pest density or consumption. • Fertilization effects may offset pest predation from lower predator interference. Intraguild predation is an extreme form of competition, that depends on resource availability, niche overlap, behaviour and diversity. However, despite modelling and mesocosm experiments, field studies are scarce, and we know nothing of its temporal dynamics within real-world food webs, particularly in the context of biological control. To address this, we added manure to cereal fields to increase decomposer prey, and analysed the diet of over 6000 predators over the entire cropping season during two consecutive years. Our results show that manure increased available prey temporarily and reduced intraguild predation. With this organic fertilization, a reduction in pest spread between tillers within fields correlated with lower intraguild predation, while pest density remained unchanged across treatments, making the net effect on biological control unclear. We hypothesize that the mechanism responsible for why lowering intraguild predation reduces pest spread are changes in predator behaviour, that allow predators to exert more pressure on pests. Conversely, the absence of an effect on pest density may be linked to other effects of fertilization, such as increased pest and plant growth counteracting any increase in predation pressure. The high temporal resolution of our data showed how dynamic IGP is throughout the season, which stresses the importance of studying food webs over time, to generate a mechanistic understanding of biological control. [ABSTRACT FROM AUTHOR]

The arrival of electronic voting has generated considerable controversy, mostly about its vulnerability to fraud. By comparison, virtually no attention has been given to its usability, i.e., voters’ ability to vote as they intend, which was central to the controversy surrounding the 2000 US presidential election. Yet it is hard to imagine a domain of human–computer interaction where usability has more impact on how democracy works. This article reports a laboratory investigation of the usability of six electronic voting systems chosen to represent the features of systems in current use and potentially in future use. The primary question was whether e-voting systems are sufficiently hard to use that voting accuracy and satisfaction are compromised. We observed that voters often seemed quite lost taking far more than the required number of actions to cast individual votes, especially when they ultimately voted inaccurately. Their satisfaction went down as their effort went up. And accuracy with some systems was disturbingly low. While many of these problems are easy to fix, manufacturers will need to adopt usability engineering practices that have vastly improved user interfaces throughout the software industry. [Copyright &y& Elsevier]