Abstract

Typically, females of eriophyoid mites of the large conifer-associated genus Trisetacus Keifer 1952 have long spermathecal tubes, which are at least twice as long as the spermathecae. In this paper, we report on four Trisetacus species collected in the USA from Cupressaceae that possess atypical short spermathecal tubes and demonstrate a distinct reduction trend in leg chaetotaxy when setae lʹ and/or bv II may be absent, and setae ftʹ II are very short. They are: 1) Trisetacus virginianus n. sp. and 2) T. thujae (Garman 1883, = T. thujivagrans Smith 1977a syn. nov.) from indigenous North American conifers Juniperus virginianus and Thuja occidentalis, respectively, and 3) Trisetacus maculatus n. sp. and 4) T. morgantownensis n. sp. from Japanese endemics, Chamaecyparis pisifera and C. obtusa, respectively, introduced to the USA. In these four Trisetacus species, the spermathecal apparatus consists of two drop-shaped segments, each about 2.5‒3 µm long and about 2‒2.5 µm wide, and resembles that of Boczekella, a nalepellid genus restricted to pinacean genera Larix and Pseudolarix. A new subgenus, Brevithecus n. subgen., is erected within the genus Trisetacus to accommodate the four Trisetacus species from Cupressaceae. Future molecular phylogenetic studies are needed to test whether Brevithecus is nested within Trisetacus or represents a separate genus, which may be a sister to either Trisetacus or Boczekella.