Silk properties and overwinter survival in gregarious butterfly larvae

Complex plant quality-microbiota-population interactions modulate the response of a specialist herbivore to the defence of its host plant

Many specialist herbivores have evolved strategies to cope with plant defences, with gut microbiota potentially participating to such adaptations.In this study, we assessed whether the history of plant use (population origin) and microbiota may interact with plant defence adaptation.We tested whether microbiota enhance the performance of Melitaea cinxia larvae on their host plant, Plantago lanceolata and increase their ability to cope the defensive compounds, iridoid glycosides (IGs).The gut microbiota were significantly affected by both larval population origin and host plant IG level. Contrary to our prediction, impoverishing the microbiota with antibiotic treatment did not reduce larval performance.As expected for this specialized insect herbivore, sequestration of one of IGs was higher in larvae fed with plants producing higher concentration of IGs. These larvae also showed metabolic signature of intoxication (i.e. decrease in Lysine levels). However, intoxication on highly defended plants was only observed when larvae with a history of poorly defended plants were simultaneously treated with antibiotics.Our results suggest that both adaptation and microbiota contribute to the metabolic response of herbivores to plant defence though complex interactions. Read the free Plain Language Summary for this article on the Journal blog.

Long-term spatiotemporal genetic structure of an accidental parasitoid introduction, and local changes in prevalence of its associated Wolbachia symbiont

Population bottlenecks associated with founder events strongly impact the establishment and genetic makeup of populations. In addition to their genotype, founding individuals also bring along parasites, as well as symbionts that can manipulate the phenotype of their host, affecting the host population establishment, dynamics and evolution. Thus, to understand introduction, invasion, and spread, we should identify the roles played by accompanying symbionts. In 1991, the parasitoid wasp, Hyposoter horticola, and its associated hyperparasitoid were accidentally introduced from the main Åland islands, Finland, to an isolated island in the archipelago, along with their host, the Glanville fritillary butterfly. Though the receiving island was unoccupied, the butterfly was present on some of the small islands in the vicinity. The three introduced species have persisted locally ever since. A strain of the endosymbiotic bacterium Wolbachia has an intermediate prevalence in the parasitoid H. horticola across the main Åland population. The infection increases its susceptibility of to hyperparasitism. We investigated the establishment and spread of the parasitoid, along with patterns of prevalence of its symbiont using 323 specimens collected between 1992 and 2013, from five localities across Åland, including the source and introduced populations. Using 14 microsatellites and one mitochondrial marker, we suggest that the relatively diverse founding population and occasional migration between islands might have facilitated the persistence of all isolated populations, despite multiple local population crashes. We also show that where the hyperparasitoid is absent, and thus selection against infected wasp genotypes is relaxed, there is near-fixation of Wolbachia.