DOI: 10.5061/dryad.td0j2r8
title: Data from: A plant pathogen modulates the effects of secondary metabolites on the performance and immune function of an insect herbivore

description: Host plant chemical composition critically shapes the performance of
 insect herbivores feeding on them. Some insects have become specialized on
 plant secondary metabolites, and even use them to their own advantage such
 as defense against predators. However, infection by plant pathogens can
 seriously alter the interaction between herbivores and their host plants.
 We tested whether the effects of the plant secondary metabolites, iridoid
 glycosides (IGs), on the performance and immune response of an insect
 herbivore are modulated by a plant pathogen. We used the IG-specialized
 Glanville fritillary butterfly (Melitaea cinxia), its host plant Plantago
 lanceolata, and the naturally occurring plant pathogen, powdery mildew
 (Phodosphaera plantaginis), as model system. Pre-diapause larvae were fed
 on P. lanceolata host plants selected to contain either high or low IGs,
 in the presence or absence of powdery mildew. Larval performance was
 measured by growth rate, survival until diapause, and by investment in
 immunity. We assessed immunity after a bacterial challenge in terms of
 phenoloxidase (PO) activity and the expression of seven pre-selected
 insect immune genes (qPCR). We found that the beneficial effects of
 constitutive leaf IGs, that improved larval growth, were significantly
 reduced by mildew infection. Moreover, mildew presence downregulated one
 component of larval immune response (PO activity), suggesting a
 physiological cost of investment in immunity under suboptimal conditions.
 Yet, feeding on mildew infected leaves caused an upregulation of two
 immune genes, lysozyme and prophenoloxidase. Our findings indicate that a
 plant pathogen can significantly modulate the effects of secondary
 metabolites on the growth of an insect herbivore. Furthermore, we show
 that a plant pathogen can induce contrasting effects on insect immune
 function. We suspect that the activation of the immune system toward a
 plant pathogen infection may be maladaptive, but the actual infectivity on
 the larvae should be tested.
description: Developmental
 traitsData file including the
 treatments, families and all the traits measured during development, such
 as molting dates, average duration of each larval instar in days, average
 final body mass and standard error, growth rate, number of dead larvae per
 petri dish. Model response variables are highlighted in red
 color.Main_file.xlsxBody massRaw data including final larval body mass of single individuals, from which the average body mass used in the paper was calculated.qPCR_dataqPCR raw data and calculations to obtain the log2 expression used in the paper (highlighted in red color). Different sheets include the calculations calibrated for the different treatment groups..PO_activityPhenoloxidase activity data by larval family and treatment. The response variable used in the paper is highlighted in red color.NMR_dataMedian and square root transformed NMR quantification data for aucubin, catalpol and aucubin+catalpol in the plant treatments (low and high IG, healthy and mildew infected). Response variable used in the paper are highlighted in red color. Raw data for individual samples is presented on a separate data sheet.