Sagamiscintilla thalassemicola (Bivalvia: Galeommatoidea: Galeommatidae) is a rare ectocommensal bivalve that lives on the proboscis of echiuran worms, Anelassorhynchus spp. (Annelida: Thalassematidae: Thalassematinae: Thalassematini), and has been known only from the temperate zones of Japan. In this study, we found S. thalassemicola on the proboscis of the large echiuran Ochetostoma sp. (Thalassematidae: Thalassematinae: Thalassematini) on intertidal flats of three islands of the Ryukyu Archipelago, southern Japan. These are the first records of S. thalassemicola on non-Anelassorhynchus hosts and also from the subtropical regions. Additionally, we also collected S. thalassemicola from an intertidal flat of Kushimoto, Wakayama, Kii Peninsula, Japan, which is an update of the easternmost record of this species. The genetic differences in the mitochondrial cytochrome c oxidase subunit I and nuclear internal transcribed spacer 2 genes among S. thalassemicola, including those with Ochetostoma sp. from the subtropical region and with Anelassorhynchus spp. from the temperate region, can be considered within the intraspecific variation. These suggest that S. thalassemicola uses different echiuran hosts in the temperate and subtropical regions, respectively.

Parasites sometimes expand their host range and cause new disease aetiologies. Genetic changes can then occur due to host-specific adaptive alterations, particularly when parasites cross between evolutionarily distant hosts. Characterizing genetic variation in Cryptosporidium from humans and other animals may have important implications for understanding disease dynamics and transmission. We analyse sequences from four loci (gp60, HSP-70, COWP and actin) representing multiple Cryptosporidium species reported in humans. We predicted low genetic diversity in species that present unusual human infections due to founder events and bottlenecks. High genetic diversity was observed in isolates from humans of Cryptosporidium meleagridis, Cryptosporidium cuniculus, Cryptosporidium hominis and Cryptosporidium parvum. A deviation of expected values of neutrality using Tajima's D was observed in C. cuniculus and C. meleagridis. The high genetic diversity in C. meleagridis and C. cuniculus did not match our expectations but deviations from neutrality indicate a recent decrease in genetic variability through a population bottleneck after an expansion event. Cryptosporidium hominis was also found with a significant Tajima's D positive value likely caused by recent population expansion of unusual genotypes in humans. These insights indicate that changes in genetic diversity can help us to understand host-parasite adaptation and evolution.

The insect cuticle is covered by a thin layer of hydrocarbons not only preventing desiccation but also playing an important role in the sexual communication of several species. In the pteromalid wasp Lariophagus distinguendus, a parasitoid of grain infesting beetles, female cuticular hydrocarbons (CHCs) elicit male courtship behaviour. We analyzed the CHC profiles of male and female L. distinguendus wasps reared on different beetle hosts by coupled gas chromatography- mass spectrometry (GC-MS). Statistical analysis of the data revealed significant differences between strains reared on different hosts, while spatially isolated strains reared on the same host produced similar profiles. CHC profiles of parasitoids reared on Stegobium paniceum were statistically distinguishable from those of wasps reared on all other hosts. A host shift from Sitophilus granarius to S. paniceum resulted in distinguishable CHC profiles of L. distinguendus females after only one generation. Considering the role of CHCs as contact sex pheromones, our data suggest that host shifts in parasitic wasps might lead to reproductive isolation of host races due to the modification of the cuticular semiochemistry.

The diamondback moth (DBM, Plutella xylostella L. (Lepidoptera: Plutellidae)) consumes a wide variety of brassicaceous host plants and is a common pest of crucifer crops worldwide. A highly unusual infestation of a sugar pea crop was recorded in Kenya in 1999, which persisted for two consecutive years. A strain (DBM-P) from this population was established in the laboratory and is the only one of several strains tested that can complete larval development on sugar peas. The oviposition acceptance and preference of the DBM-P strain was assessed in the presence of cabbage plants, sugar pea plants or both, in comparison to another strain (DBM-Cj) that was collected from cabbage and is unable to grow on pea plants. As expected, DBM-Cj females preferred to oviposit on cabbage plants. Surprisingly, DBM-P females also laid most eggs on cabbage and very few on peas. However, they laid significantly more eggs on the cabbage plant when pea plants were present. Our findings suggest that DBM-P manifested the initial stages of an evolutionary host range expansion, which is incomplete due to lack of oviposition fidelity on pea plants.

Host shifts in herbivorous insects are thought to sometimes provide enemy-free space on the novel host plant. A population of the diamondback moth Plutella xylostella (Linnaeus), an oligophagous pest on crucifers, recently shifted to sugar snap- and snowpeas (Pisum sativum) in Kenya, resulting in heavy damage to these crops. The impact of this host shift on the interaction with Diadegma mollipla (Holmgren), one of the most frequent parasitoid species attacking P. xylostella in this area, was investigated. Parasitism rates and development of two strains of D. mollipla, one reared from a cabbage-feeding strain of P. xylostella and the second from the new pea-feeding strain, changed based on the host-plant that P. xylostella fed upon, with both parasitoid strains more effective on the novel host plant. Parasitism by the cabbage-D. mollipla strain on P. xylostella infesting peas was four times higher than on P. xylostella infesting cabbage when a single plant species was present. However, when both crops were offered together, the level of parasitism dropped to the level seen when cabbage was offered alone. Diadegma mollipla developed on both hosts, but cabbage-D. mollipla had a longer total development time. Pupae of cabbage-feeding P. xylostella were significantly heavier than pupae of pea-feeding P. xylostella and parasitism had no influence on these differences. Diadegma mollipla preferred to parasitize the pea-feeding P. xylostella. Thus, the host shift by P. xylostella to a novel host plant did not necessarily provide enemy-free space, with the parasitoid species tested. The implications of these findings for the host–parasitoid relationship are discussed.