Parasitic wasp responses to symbiont-based defense in aphids

BACKGROUND: Recent findings indicate that several insect lineages receive protection against particular natural enemies through infection with heritable symbionts, but little is yet known about whether enemies are able to discriminate and respond to symbiont-based defense. The pea aphid, Acyrthosiphon pisum, receives protection against the parasitic wasp, Aphidius ervi, when infected with the bacterial symbiont Hamiltonella defensa and its associated bacteriophage APSE (Acyrthosiphon pisum secondary endosymbiont). Internally developing parasitoid wasps, such as A. ervi, use maternal and embryonic factors to create an environment suitable for developing wasps. If more than one parasitoid egg is deposited into a single aphid host (superparasitism), then additional complements of these factors may contribute to the successful development of the single parasitoid that emerges. RESULTS: We performed experiments to determine if superparasitism is a tactic allowing wasps to overcome symbiont-mediated defense. We found that the deposition of two eggs into symbiont-protected aphids significantly increased rates of successful parasitism relative to singly parasitized aphids. We then conducted behavioral assays to determine whether A. ervi selectively superparasitizes H. defensa-infected aphids. In choice tests, we found that A. ervi tends to deposit a single egg in uninfected aphids, but two or more eggs in H. defensa-infected aphids, indicating that oviposition choices may be largely determined by infection status. Finally, we identified differences in the quantity of the trans-β-farnesene, the major component of aphid alarm pheromone, between H. defensa-infected and uninfected aphids, which may form the basis for discrimination. CONCLUSIONS: Here we show that the parasitic wasp A. ervi discriminates among symbiont-infected and uninfected aphids, and changes its oviposition behavior in a way that increases the likelihood of overcoming symbiont-based defense. More generally, our results indicate that natural enemies are not passive victims of defensive symbionts, and that an evolutionary arms race between A. pisum and the parasitoid A. ervi may be mediated by a bacterial symbiosis

Tree diversity and species identity effects on soil fungi, protists and animals are context dependent

Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se

Effects of different water percentages in non-surfactant water-in-diesel emulsion fuel on the performance and exhaust emissions of a small-scale industrial burner

In a previous study, a device that combined two existing mixing methods to produce water-in-diesel emulsion fuel (W/D) without surfactant had been developed and tested on a small-scale engine by Ithnin et al. However, it is inapplicable for industrial burners with high fuel flow rate. Therefore, a device with a similar concept was developed in this study. W/D has been proven to improve combustion, but it was unknown if non-surfactant W/D made by the device can improve burner performance and exhaust emissions. The aim of this study is to analyse the fuel consumption, flame temperature and emissions of the industrial burner utilising Malaysian Diesel grade 2 (D2M) labelled as D2, surfactant-added W/D and non-surfactant W/D produced by the device. Both emulsion fuels tested contained 5%, 10% and 15% water by volume. Based on the comparative evaluation, the performance of non-surfactant W/D was comparable to surfactant-added W/D. Compared to D2, non-surfactant W/D reduced fuel consumption, nitrogen oxides, particulate matter, carbon monoxides and hydrocarbons emissions by up to 17%, 53%, 34%, 24% and 44%, respectively. Although the increase in water content decreased the flame temperature, W/D with 5% water had higher flame temperature and had better fuel consumption than D2