Two New Species of Larvicidal Nematodes (Mermithidae) from Larvae of Chironomus plumosus (Diptera: Chironomidae) in Minnesota, U.S.A.

Abstract

Telomermis amphiorchis n. gen., n. sp. and Gastromermis plumosus n. sp. are described from the larvae of Chironomus plumosus in the north arm of Lake Itasca, Clearwater County, Minnesota. Telomermis is distinguished from other mermithid genera in having a terminal mouth, four head papillae, a short S-shaped vagina, no visible cuticular cross-fibers, amphidal opening posterior to head papillae, two simple spicules, and a rounded posterior terminus. The post-parasitic juvenile lacks a larval horn. Gastromermis plumosus is distinguishable from most species of the genus by the mouth opening, amphidal opening and head papillae being at the same level. Four other adequately described species of Gastromermis have those characteristics. The length and shape of the spicule, amphids, and vagina is used to separate G. plumosus from the four species. Octomyomermis itascensis heavily infected the larvae of Chironomus plumosus from 1959 through 1962. In 1969-1970, it was replaced by the two new species. The 1969-1970 condition also existed