Low cost antiviral activity of Plodia interpunctella haemolymph in vivo demonstrated by dose dependent infection

Pathogen infection routes and host innate immunity: Lessons from insects

Recent advances in insect-pathogen interactions have started to reveal the role of insect tissues and organs as natural infection routes for parasites and microbial pathogens. Here we summarize this information highlighting the micro- and macro-parasites that enter insects through distinct infection routes and link them to innate immune activity. We also examine whether the infection route determines the insect immune response and if the resulting immunological and physiological processes underpinning these different routes of infection are clearly distinct. Understanding how the infection route is associated with the robustness in insect host defense will help us identify conserved evolutionary and ecological patterns in order to design novel strategies for the management of destructive agricultural pests and disease vectors.

The target of selection matters: An established resistance-development-time negative genetic trade-off is not found when selecting on development time

Trade-offs are fundamental to evolutionary outcomes and play a central role in eco-evolutionary theory. They are often examined by experimentally selecting on one life-history trait and looking for negative correlations in other traits. For example, populations of the moth Plodia interpunctella selected to resist viral infection show a life-history cost with longer development times. However, we rarely examine whether the detection of such negative genetic correlations depends on the trait on which we select. Here, we examine a well-characterized negative genotypic trade-off between development time and resistance to viral infection in the moth Plodia interpunctella and test whether selection on a phenotype known to be a cost of resistance (longer development time) leads to the predicted correlated increase in resistance. If there is tight pleiotropic relationship between genes that determine development time and resistance underpinning this trade-off, we might expect increased resistance when we select on longer development time. However, we show that selecting for longer development time in this system selects for reduced resistance when compared to selection for shorter development time. This shows how phenotypes typically characterized by a trade-off can deviate from that trade-off relationship, and suggests little genetic linkage between the genes governing viral resistance and those that determine response to selection on the key life-history trait. Our results are important for both selection strategies in applied biological systems and for evolutionary modelling of host-parasite interactions.

A genotypic trade-off between constitutive resistance to viral infection and host growth rate

Genotypic trade‐offs are fundamental to the understanding of the evolution of life‐history traits. In particular, the evolution of optimal host defense and the maintenance of variation in defense against infectious disease is thought to be underpinned by such evolutionary trade‐offs. However, empirical demonstrations of these trade‐offs that satisfy the strict assumptions made by theoretical models are rare. Additionally, none of these trade‐offs have yet been shown to be robustly replicable using a variety of different experimental approaches to rule out confounding issues with particular experimental designs. Here, we use inbred isolines as a novel experimental approach to test whether a trade‐off between viral resistance and growth rate in Plodia interpunctella, previously demonstrated by multiple selection experiments, is robust and meets the strict criteria required to underpin theoretical work in this field. Critically, we demonstrate that this trade‐off is both genetic and constitutive. This finding helps support the large body of theory that relies on these assumptions, and makes this trade‐off for resistance unique in being replicated through multiple experimental approaches and definitively shown to be genetic and constitutive.

Responses to a warming world: Integrating life history, immune investment, and pathogen resistance in a model insect species

Environmental temperature has important effects on the physiology and life history of ectothermic animals, including investment in the immune system and the infectious capacity of pathogens. Numerous studies have examined individual components of these complex systems, but little is known about how they integrate when animals are exposed to different temperatures. Here, we use the Indian meal moth (Plodia interpunctella) to understand how immune investment and disease resistance react and potentially trade‐off with other life‐history traits. We recorded life‐history (development time, survival, fecundity, and body size) and immunity (hemocyte counts, phenoloxidase activity) measures and tested resistance to bacterial (E. coli) and viral (Plodia interpunctella granulosis virus) infection at five temperatures (20–30°C). While development time, lifespan, and size decreased with temperature as expected, moths exhibited different reproductive strategies in response to small changes in temperature. At cooler temperatures, oviposition rates were low but tended to increase toward the end of life, whereas warmer temperatures promoted initially high oviposition rates that rapidly declined after the first few days of adult life. Although warmer temperatures were associated with strong investment in early reproduction, there was no evidence of an associated trade‐off with immune investment. Phenoloxidase activity increased most at cooler temperatures before plateauing, while hemocyte counts increased linearly with temperature. Resistance to bacterial challenge displayed a complex pattern, whereas survival after a viral challenge increased with rearing temperature. These results demonstrate that different immune system components and different pathogens can respond in distinct ways to changes in temperature. Overall, these data highlight the scope for significant changes in immunity, disease resistance, and host–parasite population dynamics to arise from small, biologically relevant changes to environmental temperature. In light of global warming, understanding these complex interactions is vital for predicting the potential impact of insect disease vectors and crop pests on public health and food security.

The route of infection determines Wolbachia antibacterial protection in Drosophila

Bacterial symbionts are widespread among metazoans and provide a range of beneficial functions. Wolbachia-mediated protection against viral infection has been extensively demonstrated in Drosophila. In mosquitoes that are artificially transinfected with Drosophila melanogaster Wolbachia (wMel), protection from both viral and bacterial infections has been demonstrated. However, no evidence for Wolbachia-mediated antibacterial protection has been demonstrated in Drosophila to date. Here, we show that the route of infection is key for Wolbachia-mediated antibacterial protection. Drosophila melanogaster carrying Wolbachia showed reduced mortality during enteric-but not systemic-infection with the opportunist pathogen Pseudomonas aeruginosaWolbachia-mediated protection was more pronounced in male flies and is associated with increased early expression of the antimicrobial peptide Attacin A, and also increased expression of a reactive oxygen species detoxification gene (Gst D8). These results highlight that the route of infection is important for symbiont-mediated protection from infection, that Wolbachia can protect hosts by eliciting a combination of resistance and disease tolerance mechanisms, and that these effects are sexually dimorphic. We discuss the importance of using ecologically relevant routes of infection to gain a better understanding of symbiont-mediated protection.

The Complete Genome Sequence of Plodia Interpunctella Granulovirus: Evidence for Horizontal Gene Transfer and Discovery of an Unusual Inhibitor-of-Apoptosis Gene

The Indianmeal moth, Plodia interpunctella (Lepidoptera: Pyralidae), is a common pest of stored goods with a worldwide distribution. The complete genome sequence for a larval pathogen of this moth, the baculovirus Plodia interpunctella granulovirus (PiGV), was determined by next-generation sequencing. The PiGV genome was found to be 112, 536 bp in length with a 44.2% G+C nucleotide distribution. A total of 123 open reading frames (ORFs) and seven homologous regions (hrs) were identified and annotated. Phylogenetic inference using concatenated alignments of 36 baculovirus core genes placed PiGV in the “b” clade of viruses from genus Betabaculovirus with a branch length suggesting that PiGV represents a distinct betabaculovirus species. In addition to the baculovirus core genes and orthologues of other genes found in other betabaculovirus genomes, the PiGV genome sequence contained orthologues of the bidensovirus NS3 gene, as well as ORFs that occur in alphabaculoviruses but not betabaculoviruses. While PiGV contained an orthologue of inhibitor of apoptosis-5 (iap-5), an orthologue of inhibitor of apoptosis-3 (iap-3) was not present. Instead, the PiGV sequence contained an ORF (PiGV ORF81) encoding an IAP homologue with sequence similarity to insect cellular IAPs, but not to viral IAPs. Phylogenetic analysis of baculovirus and insect IAP amino acid sequences suggested that the baculovirus IAP-3 genes and the PiGV ORF81 IAP homologue represent different lineages arising from more than one acquisition event. The presence of genes from other sources in the PiGV genome highlights the extent to which baculovirus gene content is shaped by horizontal gene transfer.