First record of a mermithid nematode (Nematoda: Mermithidae) parasitizing winged females of gall-forming aphids (Hemiptera: Aphididae: Eriosomatinae)

Juvenile mermithid nematodes were found to parasitize winged females (sexuparae) of Eriosoma auratum and Tetraneura radicicola. The morphological characteristics of mermithid nematodes are briefly described. The 18S rDNA and 28S rDNA extracted from one nematode were sequenced and used to construct a Bayesian phylogenetic tree, on which the host ranges of mermithid nematodes were represented. Our study indicated that mermithid parasitism of sexuparae led to fewer and smaller sexual female embryos. This is the first record of a mermithid in relation to eriosomatine aphids and the fourth record with respect to Aphididae.

Mermithid nematode (Nematoda: Mermithidae) parasites of a fossil black fly (Diptera: Simuliidae) in Baltic amber

Summary A new species of fossil mermithid, Heydenius simulphilus sp. n. (Nematoda: Mermithidae), is described from two parasitic juvenile specimens adjacent to a male black fly (Diptera: Simuliidae) in Baltic amber. It is proposed that the nematodes emerged from their developmental sites in the haemocoel of the black fly host through a wound in the abdomen of the latter, as indicated by the release of a droplet of haemolymph and damaged cuticle. Various internal structures of the nematodes are identified and related to those found on extant developing mermithids. This is the first fossil record of mermithid parasitism of a black fly.

Let's go swimming: mermithid-infected earwigs exhibit positive hydrotaxis

Certain species of parasites have the apparent ability to alter the behaviour of their host in order to facilitate the completion of their own life cycle. While documented in hairworms (phylum Nematomorpha), the ability for mermithid parasites (from the sister phylum Nematoda) to force hosts to enter water remains more enigmatic. Here, we present the first experimental evidence in a laboratory setting that an insect which normally never enters open water (the European earwig Forficula auricularia) will readily enter the water when infected with a mermithid nematode (Mermis nigrescens). Only adult mermithids appear capable of inducing this polarising shift in behaviour, with mermithid length being a very strong predictor of whether their host enters water. However, mermithid length was only weakly associated with how long it took an earwig to enter water following the beginning of a trial. Considering the evidence presented here and its alignment with a proteomic investigation on the same host–parasite system, this study provides strong evidence for adaptive behavioural manipulation and a foundational system for further behavioural and mechanistic exploration.

A mermithid nematode, Cretacimermis aphidophilus sp. n. (Nematoda: Mermithidae), parasitising an aphid (Hemiptera: Burmitaphididae) in Myanmar amber: a 100 million year association

A new species of fossil mermithid,Cretacimermis aphidophilussp. n. (Nematoda: Mermithidae), is described from the primitive extinct aphid,Caulinus burmitis(Hemiptera: Burmitaphididae), in mid-Cretaceous Myanmar amber. Aphid parasitism by mermithid nematodes is rare today with only two known cases involving root-feeding aphids. Based on the habits of the parasitised extant aphid hosts, it is likely that the fossil aphid was also a root parasite and encountered the infective stage mermithid in the soil. Such fossils provide rare glimpses of nematode-host associations from the distant past and provide minimum dates for the appearance of specific mermithid clades.