Variation of success of Leptopilina boulardi in Drosophila yakuba: the mechanisms explored.

Despite an increasing knowledge of insect immune defences and virulence strategies used by parasitoids to escape them, the mechanisms underlying variation of success between parasitoid strains are still poorly understood. We have investigated this point using two lines of the parasitoid wasp Leptopilina boulardi that differ in virulence towards Drosophila yakuba. By injecting oil drops in D. yakuba larvae parasitized by virulent IS(y) females and then dissecting the larvae at different times following injection, we demonstrate that the IS(y) line alters host encapsulation ability but only during the early parasitism period. This effect is mimicked by injecting venom gland extracts, indicating that venom proteins are likely involved in immunosuppression. By contrast, the IS(m) line, unsuccessful on D. yakuba, has no immunosuppressive effect. This variation in virulence may be explained by the striking difference we report in haemocytic profiles between IS(m)- and IS(y)-parasitized larvae. We discuss our results in the light of our knowledge of the strategies evolved by Leptopilina species to counteract the D. melanogaster immune system as well as the role of parasitoid venoms in intra-specific variation of parasitoid virulence.

Developmental study of the Proboscis Extension Response to heat in Rhodnius prolixus along the life cycle.

Triatominae are blood-sucking insects that localise their hosts using a range of sensory signals to find food, and among them, the heat emitted by the hosts. Heat is one of the main short-range cues in vertebrate hosts, able to trigger alone the Proboscis Extension Response (PER) that precedes the bite. Previous studies demonstrated that heat responsiveness of fifth-instar nymphs is maximum to moderate temperatures (30-35°C) compatible with those of their vertebrate host's body surface. This study investigated whether this thermal preference for biting is maintained along the life cycle of R. prolixus, from the first larval instar to male and female adults. The results showed that PER rates were at maximum around 30-35°C and decreased for a warmer temperature. The same thermal preference was maintained all along the life cycle, despite the increase in the size of the antennae linked to the growth. Interestingly, a decreased thermal responsiveness was stated in males as compared with larval instars and females. This decrease might reveal a lower motivation for host-seeking and might have an impact on males's vectorial competence.

Ultra Deep Sequencing of a Baculovirus Population Reveals Widespread Genomic Variations.

Viruses rely on widespread genetic variation and large population size for adaptation. Large DNA virus populations are thought to harbor little variation though natural populations may be polymorphic. To measure the genetic variation present in a dsDNA virus population, we deep sequenced a natural strain of the baculovirus Autographa californica multiple nucleopolyhedrovirus. With 124,221X average genome coverage of our 133,926 bp long consensus, we could detect low frequency mutations (0.025%). K-means clustering was used to classify the mutations in four categories according to their frequency in the population. We found 60 high frequency non-synonymous mutations under balancing selection distributed in all functional classes. These mutants could alter viral adaptation dynamics, either through competitive or synergistic processes. Lastly, we developed a technique for the delimitation of large deletions in next generation sequencing data. We found that large deletions occur along the entire viral genome, with hotspots located in homologous repeat regions (hrs). Present in 25.4% of the genomes, these deletion mutants presumably require functional complementation to complete their infection cycle. They might thus have a large impact on the fitness of the baculovirus population. Altogether, we found a wide breadth of genomic variation in the baculovirus population, suggesting it has high adaptive potential.