First report of a member of the family Mermithidae parasitizing the sandhopper Orchestoidea tuberculata (Amphipoda, Talitridae) in Chile

Specimens of the sandhopper Orchestoidea tuberculata (Amphipoda; Talitridae) collected from sandy beaches in south-central Chile, were found to be parasitized by juvenile mermithids, constituting the first record of a mermithid infecting a marine amphipod in Chile. A morphological description of juveniles is provided. Sequence analyses based on mitochondrial COI and nuclear 18S rDNA of the mermithids showed extremely low genetic variation. Phylogenetic analyses indicate that the mermithid is more closely related to Hexamermis agrotis, which parasitize Coleoptera, than to Thaumamermis zealandica, which parasitizes New Zealand confamilial talitrid amphipods.

Three Aedes species infested by mermithids in France

Mermithid nematodes (Nematoda, Mermithidae) parasitising mosquitoes could be useful as biological agents for the control of host populations. Nine female mosquitoes belonging to the species Aedes cantans, Ae. communis, and Ae. rusticus were found parasitised by mermithids in Northern France. Sequencing of partial 18S rDNA showed 100% sequence homology for all processed specimens. The mermithid sequences were closely related to specimens previously recorded from Anopheles gambiae in Senegal. However, 18S sequences do not allow for identification of nematodes at the genus or species level. Our specimens could also be related to Strelkovimermis spiculatus, or belong to other genera not yet sequenced such as Empidomermis, the only mermithid genus recorded from mosquitoes in France.

Is the morphology of Culicoides intersexes parasitized by mermithid nematodes a parasite adaptation? A morphometric approach to Culicoides circumscriptus (Diptera: Ceratopogonidae)

Mermithidae is a family of endoparasitic nematodes known to cause intersexuality in arthropods. Intersexes of the genus Culicoides parasitized by mermithids have been the object of several studies aiming to describe their particular morphology. Culicoides intersexes are specimens with male genitalia and feminized sexually dimorphic structures, i.e. antennae, mouthparts and wings. To date, these specimens have only been described qualitatively and a quantitative approach supported by statistical analysis is lacking. Here we conduct morphometric analyses of sexually dimorphic structures in a sample of Culicoides circumscriptus that includes 34 intersexes with the aim of describing precisely the intersexual morphology. The morphology of antennae and the mouthparts was studied by multivariate statistical analysis of linear measures, and wing form by implementing geometric morphometrics techniques. While intersex wings proved to have a similar size to male wings, their shape was intermediate between males and females. However, when allometric shape variation was removed, the wing shape of intersexes was almost identical to that of females. The intersex antennae were morphometrically of the female type, especially when size variation was considered. In contrast, the measured mouthparts (the labrum and the third palpal segment) were halfway between males and females, even when body size was considered. Overall, the antennae and the wings showed a higher degree of feminization than the mouthparts. These findings indicate that the degree of feminization depends both on the morphological structure and on body size. Moreover, we propose that the feminization of the wings and antennae has an adaptive meaning for the parasite, which would favor female-like traits in order to access more easily its breeding sites, where the parasite has plenty of new hosts to infect. Female-like antennae would be beneficial to detect these sites, while having female-like wings would favor the host's capacity of dispersal to these sites.