Differential detachment from resting hosts of replete larval and nymphal Ixodes ticks

To determine whether replete subadult Ixodes ticks detach more frequently from resting than from active hosts, diverse rodents and lizards were caged in an apparatus designed to record the ticks' sites of detachment relative to the resting site of the host. Replete larval Ixodes ricinus and Ixodes dammini accumulated mainly beneath the resting places of the mice (Apodemus agrarius and Peromyscus leucopus) most frequently parasitized in nature. Although nymphal I. ricinus similarly detached where these mice rested, nymphal I. dammini detached more randomly. When lizards were used as hosts, both subadult stages of I. ricinus tended to detach away from their main resting sites; these ticks detached from squirrels more randomly. Detachment ratios for other rodent hosts, that are abundantly infested by the larvae of these ticks in nature (Apodemus flavicollis and Clethrionomys glareolus), could not be derived because nymphs generally failed to attach. Our observations are consistent with reports that both subadult stages of I. dammini, but not the adult, feed on the same kind of nest-dwelling hosts and that the host range of I. ricinus is less focused. Detachment of mouse-feeding larvae from resting mice promotes subsequent nymphal attachment to conspecific hosts, and the absence of such behavior among nymphs facilitates access of the resulting adults to deer.     

The irradiated cercariae vaccine model: looking on the bright side of radiation

Schistosomes infect between 200 and 300 million people at any one time. A major strategy to reduce the impact of schistosomiasis on human health is the development of a defined antigen vaccine. Protective immunity induced in mice by irradiated cercariae may serve as a model for the development of a vaccine. In such vaccinated mice, worm burdens resulting from challenge infection can be reduced by more than 90% compared to non-vaccinated mice. During the past three decades, the irradiated-carcariae vaccine model has been dissected in the detail in order to determine factors that may be relevant to vaccination, such as the participating immune compartments, the site and kinetics of the immune response, and the antigens recognized. In this review, Dania Richter, Donald A. Harn and Franz-Rainer Matuschka highlight the research on the vaccine model, focusing on the murine model using gamma-irradiated cercariae of Schistosoma mansoni.     

Dispersal and dormancy strategies among insect species competing for a pulsed resource

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Peribacteroid space acidification: a marker of mature bacteroid functioning in Medicago truncatula nodules

Legumes form a symbiotic interaction with Rhizobiaceae bacteria, which differentiate into nitrogen‐fixing bacteroids within nodules. Here, we investigated in vivo the pH of the peribacteroid space (PBS) surrounding the bacteroid and pH variation throughout symbiosis. In vivo confocal microscopy investigations, using acidotropic probes, demonstrated the acidic state of the PBS. In planta analysis of nodule senescence induced by distinct biological processes drastically increased PBS pH in the N₂‐fixing zone (zone III). Therefore, the PBS acidification observed in mature bacteroids can be considered as a marker of bacteroid N₂ fixation. Using a pH‐sensitive ratiometric probe, PBS pH was measured in vivo during the whole symbiotic process. We showed a progressive acidification of the PBS from the bacteroid release up to the onset of N₂ fixation. Genetic and pharmacological approaches were conducted and led to disruption of the PBS acidification. Altogether, our findings shed light on the role of PBS pH of mature bacteroids in nodule functioning, providing new tools to monitor in vivo bacteroid physiology.     

Cold‐induced expression of diapause in Praon volucre: fitness cost and morpho‐physiological characterization

Cold exposure (2°C for 7 days) in constant darkness at mummy stage induces diapause expression in 9% of the Praon volucre Haliday population. Diapausing parasitoids show a significant delay in emergence time compared with nondiapausing counterparts. A diapause‐mediated polyphenism is observed in mummy colour, with diapausing mummies being clearly darker than nondiapausing ones. The diapause status of dark mummies is confirmed by a significant reduction in metabolic rate. Diapausing parasitoids also display specific morphological characteristics: they are heavier (fresh and dry mass) and accumulate larger fat reserves than nondiapausing counterparts. The diapause status is associated with a fitness cost in terms of adult longevity. There is no evidence of diapause‐related change in supercooling ability.     

One hundred years of instability in ensiferan relationships

Although Ensifera is a major insect model group, its phylogenetic relationships have been understudied so far. Few phylogenetic hypotheses have been proposed, either with morphological or molecular data. The largest dataset ever used for phylogeny reconstruction on this group is molecular (16S rRNA, 18S rRNA and 28S rRNA sequences for 51 ensiferan species), which has been used twice with different resultant topologies. However, only one of these hypotheses has been adopted commonly as a reference classification. Here we re‐analyse this molecular dataset with different methods and parameters to test the robustness and the stability of the adopted phylogeny. Our study reveals the instability of phylogenetic relationships derived from this dataset, especially for the deepest nodes of the group, and suggests some guidelines for future studies. The comparison between the different classifications proposed in the past 70 years for Ensifera and our results allows the identification of potential monophyletic clades (katydids, mole crickets, scaly crickets + Malgasia, true crickets, leaf roller crickets, cave crickets) and the remaining unresolved clades (wetas, Jerusalem crickets and most of the highest rank clades) in Ensifera phylogeny.     

Effect of Prior Exposure to Noninfected Ticks on Susceptibility of Mice to Lyme Disease Spirochetes

To determine whether prior exposure to Nearctic Ixodes vector ticks protects native reservoir mice from tick-borne infection by Lyme disease spirochetes, we compared their infectivities for white-footed mice and laboratory mice that had been repeatedly infested by noninfected deer ticks. Nymphal ticks readily engorged on tick-exposed laboratory mice, but their feeding success on white-footed mice progressively declined. Tick-borne spirochetes readily infected previously tick-infested mice. Thus, prior infestation by Nearctic ticks does not protect sympatric reservoir mice or Palearctic laboratory mice from infection by sympatric tick-borne spirochetes.     

Experimental investigations on the host range of Sarcocystis podarcicolubris

Lizards experimentally infected with S. podarcicolubris sarcocysts were fed to different species of the family Colubridae. Only species of the genus Coluber proved to be suitable definitive hosts and passed sporocysts in their feces. No sporo- cysts were shed by the species of the genus Elaphe, Coronella and Malpolon that were tested. Fecal sporocysts from different species of the genus Coluber were orally administered to numerous lizards of the genera Lacerta, Podarcis and Algyroides. In all experimental lizards, except the controls, sarcocysts of S. podarcicolubris developed.