Host specialisation and competition asymmetry in coleopteran parasitoids.

When specialists and generalists compete for a limited resource, specialists are more constrained because they are less likely to find an alternative resource. In parasitoids with overlapping host ranges, asymmetric competition should therefore exist where specialists are more likely to win the host in a contest. Competition between parasitoids has been studied mostly in hymenopterans. In hymenopteran parasitoid wasps, females must reach the host to lay their eggs and can thus strongly influence the outcome of competition between future offspring by killing eggs or larvae of competitors. We studied competition between the free-ranging larvae of two sympatric coleopteran parasitoid rove beetles (one specialist, Aleochara bilineata and a generalist, Aleochara bipustulata) with overlapping host ranges competing in agricultural fields for pupae of the cabbage root fly. In these species, females lay their eggs in the soil, then first instars find the host where they will develop as solitary parasitoids and deal with potential competitors. Because adult longevity and fecundity favour the generalist, we postulated that first instars of the specialist would be superior larval competitors. Accordingly, we studied the outcome of encounters between first instars of the two species provided with a single host. Irrespective of its release prior to or simultaneously with its generalist competitor, the larva of the specialist most often won. Moreover, specialist larvae still won half of the encounters when generalist larvae were given a 24-h advantage. This might explain the coexistence of the two species in the field.

Permanent genetic resources added to molecular ecology resources database 1 April 2013-31 May 2013.

This article documents the addition of 234 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Acipenser sinensis, Aleochara bilineata, Aleochara bipustulata, Barbus meridionalis, Colossoma macropomum, Delia radicum, Drosophila nigrosparsa, Fontainea picrosperma, Helianthemum cinereum, Liomys pictus, Megabalanus azoricus, Pelteobagrus vachelli, Pleuragramma antarcticum, Podarcis hispanica type 1A, Sardinella brasiliensis and Sclerotinia homoeocarpa. These loci were cross-tested on the following species: Acipenser dabryanus, Barbus balcanicus, Barbus barbus, Barbus cyclolepis, Drosophila hydei, Drosophila melanogaster, Drosophila obscura, Drosophila subobscura, Fontainea australis, Fontainea fugax, Fontainea oraria, Fontainea rostrata, Fontainea venosa, Podarcis bocagei, Podarcis carbonelli, Podarcis liolepis, Podarcis muralis and Podarcis vaucheri.

Short- and long-range cues used by ground-dwelling parasitoids to find their host.

Parasitoids of phytophagous insects face a detectability-reliability dilemma when foraging for hosts. Plant-related cues are easily detectable, but do not guarantee the presence of the host. Host-related cues are very reliable, but much harder to detect from a distance. Little is known in particular about the way coleopteran parasitoid females use these cues when foraging for a suitable place to lay their eggs. The question is of interest because, unlike hymenopteran larvae, coleopteran parasitoid larvae are highly mobile and able to forage for hosts on their own. We assessed whether females of the parasitoid rove beetle Aleochara bipustulata (L.) (Coleoptera: Staphylinidae) are attracted to plant (Swede roots, Brassica napus) and host-related cues [pupae of the cabbage root fly Delia radicum (L.) (Diptera: Anthomyiidae)]. In the field, A. bipustulata adult females were captured in selective pitfall traps containing pieces of roots damaged by D. radicum larvae, but not in traps containing pieces of healthy roots or D. radicum pupae. However, in the laboratory, the odour of D. radicum pupae attracted A. bipustulata females to mini-pitfalls. Video monitoring in the laboratory showed that foraging A. bipustulata females preferred a zone containing D. radicum pupae and larval tracks rather than one containing an extract of D. radicum-infested roots. Our results suggest a behavioural sequence where A. bipustulata females use plant-related cues at a distance, but then switch their preference to host-related cues at a close range. This would be the first observation of this behaviour in coleopteran parasitoids.

Wolbachia segregation rate in Drosophila simulans naturally bi-infected cytoplasmic lineages.

Wolbachia are maternally transmitted endocellular bacteria infecting several arthropod species. In order to study Wolbachia segregation rate, Drosophila simulans females from an Indo-Pacific population (Seychelles) bi-infected by the two Wolbachia variants wHa and wNo were backcrossed to uninfected males in two conditions. In the first case, Seychelles males from a stock cured from its Wolbachia by tetracycline treatment were used. In the second case, the males came from a naturally uninfected Tunisian population. It was found that (i) the two Wolbachia variants can segregate, so that bi-infected females can produce a few offspring infected only by wHa or wNo. This occurs in both backcross conditions. (ii) Segregation leads more frequently to wHa than to wNo mono-infection. (iii) Wolbachia transmission is lower when the Seychelles genome is introgressed by the Tunisian genome, suggesting that host genomic factors might influence infection fate.

Wolbachia transfer from Drosophila melanogaster into D. simulans: Host effect and cytoplasmic incompatibility relationships.

Wolbachia are maternally transmitted endocellular bacteria causing a reproductive incompatibility called cytoplasmic incompatibility (CI) in several arthropod species, including Drosophila. CI results in embryonic mortality in incompatible crosses. The only bacterial strain known to infect Drosophila melanogaster (wDm) was transferred from a D. melanogaster isofemale line into uninfected D. simulans isofemale lines by embryo microinjections. Males from the resulting transinfected lines induce >98% embryonic mortality when crossed with uninfected D. simulans females. In contrast, males from the donor D. melanogaster line induce only 18-32% CI on average when crossed with uninfected D. melanogaster females. Transinfected D. simulans lines do not differ from the D. melanogaster donor line in the Wolbachia load found in the embryo or in the total bacterial load of young males. However, >80% of cysts are infected by Wolbachia in the testes of young transinfected males, whereas only 8% of cysts are infected in young males from the D. melanogaster donor isofemale line. This difference might be caused by physiological differences between hosts, but it might also involve tissue-specific control of Wolbachia density by D. melanogaster. The wDm-transinfected D. simulans lines are unidirectionally incompatible with strains infected by the non-CI expressor Wolbachia strains wKi, wMau, or wAu, and they are bidirectionally incompatible with strains infected by the CI-expressor Wolbachia strains wHa or wNo. However, wDm-infected males do not induce CI toward females infected by the CI-expressor strain wRi, which is found in D. simulans continental populations, while wRi-infected males induce partial CI toward wDm-infected females. This peculiar asymmetrical pattern could reflect an ongoing divergence between the CI mechanisms of wRi and wDm. It would also confirm other results indicating that the factor responsible for CI induction in males is distinct from the factor responsible for CI rescue in females.

Diffusion properties of an artificial membrane used for Langerhans islets encapsulation: an in vitro test.

Glucose and insulin permeability of an artificial membrane (AN69, HOSPAL, Sweden) used for Langerhans islets encapsulation were investigated. In vivo, a 1 and 7 d intraperitoneal implantation of the AN69 membrane in rats induced a loss of permeability towards glucose and insulin probably due to a protein-coating performed after implantation. In vitro, a protein-coating of the AN69 membrane with fetal calf serum solution reproduced similar results. Thus this in vitro test which mimicks in vivo conditions should be proposed to evaluate rapidly the physicochemical properties of a membrane suitable for pancreatic islets encapsulation.