Effects of fertilizer, fungal endophytes and plant cultivar on the performance of insect herbivores and their natural enemies

1. Endophytic fungi are associates of most species of plants and may modify insect community structures through the production of toxic alkaloids. Fertilization is known to increase food plant quality for herbivores, but it is also conceivable that additional nitrogen could increase the production of the insect toxic alkaloid, peramine, in endophyte-infected plants. 2. The relative importance of soil fertility and endophyte infection on herbivores and their natural enemies is unknown. As performance of the host plant is often affected by an interaction between endophyte infection and genetic background, four different plant cultivars were tested. The main questions addressed in this study were whether plant cultivar and fertilizer addition to endophyte-infected and endophyte-free Lolium perenne affect alkaloid concentrations, plant life-history traits and the abundances of aphid species and their parasitoids. 3. In a full factorial outdoor experiment we found a strong positive effect of fertilizer on plant biomass and on the abundance of aphids and parasitoids. While plant traits differed between cultivars, there was little effect of cultivar on either aphid or parasitoid abundance. Only endophyte-infected plants contained alkaloids, and the concentration of peramine was enhanced in fertilized plants. However, endophyte infection had no negative effect on aphid or parasitoid abundances. Plant traits were only weakly influenced by endophyte infection in the field, which contrasts with plant growth room studies, where both germination rate and plant height were influenced by endophyte–cultivar interactions. 4. The generally weak effects of endophytes in the outdoor experiment could be explained by various additional constraints under field conditions and the relatively low peramine concentration that we observed

Drought stress differentially affects leaf-mining species

1. The impact of climate change on phytophages is difficult to predict, due in part to variation between species in their responses to factors such as drought stress. Here, the hypothesis that several species within the leaf-mining feeding guild will respond in a consistent way to changes in rainfall patterns is tested, using a manipulative field experiment. 2. Summer drought, enhanced summer rainfall, and control treatments were imposed on a calcareous grassland community, and the responses of five leaf-mining species were assessed. 3. One leaf-mining species was more abundant under enhanced rainfall, one was more abundant under drought, and the other three species showed no consistent response to the rainfall treatments. Higher parasitism levels under drought may partly explain the response of one species (Stephensia brunnichella) to the treatments. 4. These results show that generalisations relating to drought stress impacts cannot be drawn at the feeding guild level for leaf-mining insects

Forest type interacts with milkweed invasion to affect spider communities

Abstract Non-native tree plantations constitute a large part of forestation worldwide. Plantations are prone to invasion by exotic herbaceous plant species due to habitat properties, including understory vegetation structure. We established 40 sampling sites in 10 plantation forests. Sites were selected according to tree species (native poplar forests and exotic pine plantations) and common milkweed (Asclepias syriaca) density (invaded and non-invaded sites) in a full factorial design. We collected spiders with pitfall traps. We found a significant effect of A. syriaca invasion on spider functional diversity (Rao's quadratic entropy), with invaded sites having a lower functional diversity than non-invaded sites. A larger effect of invasion with A. syriaca on the RaoQ of spiders was observed in pine compared to poplar plantations. Spider species were larger, and web-building spiders were more frequent in poplar forests than in pine plantations. We found no effect of A. syriaca invasion on species richness or abundance of spiders. Species composition of spider assemblages in the two forest types was clearly separated according to non-metric multidimensional scaling. We identified seven species associated with pine plantations and six species associated with poplar plantations. The similar species richness and the higher functional diversity of non-invaded sites suggested that these trait states were less similar than invaded sites and that functionally different species were present. In contrast, the invaded sites had lower functional diversities and thus more uniform trait state compositions, suggesting that environmental filtering played an important role in species sorting, making invaded plantations low-quality secondary habitats for the original spider fauna