Two New Species of Acariscus: A. pluvius and A. anous (Acarinida: Trombiculidae)

Abstract

Two species of chiggers were found on sea birds collected at Guam. A plover and a noddy from Bougainville were infested with one of the species. The presence of chiggers on sea birds whose migrations are extensive may explain in part the wide distribution of certain trombiculids. The hosts of the species under discussion, plover, tattler, and noddy, are noted for long flights over open sea. Both of these chiggers are typical of the genus Acariscus Ewing, 1943. The genera Acariscus, Trombicula, and Eutrombicula are closely related. Acariscus is more closely related to certain species of Trombicula than to Eutrombicula. However, since Trombicula has a three-pronged palpal claw, and Acariscus has a twopronged claw, they are readily distinguishable. The line of demarcation between Acariscus and Eutrombicula is not so well defined. Both genera have the twopronged palpal claw, but they are separated on the number of dorsal and ventral setae. Eutrombicula has 22 dorsal and 14 ventral setae. Acariscus has more than 22 dorsal setae and more than 14 ventral setae with at least two pairs posterior to the anus. The number of dorsal setae in some species is 22, while the number of ventral setae is more than 14. Womersley (1944), who has had more experience with Eastern chiggers than any other worker, does not accept Acariscus but includes it in his concept of Trombicula. The taxonomic system of the TROMBICULIDAE is still somewhat fluid even at the generic level. It is the author's opinion that additional genera will have to be raised, or sub-generic categories will have to be introduced so that relationships can be shown more exactly. It is for these reasons that the broad concept of Trombicula is not accepted and the present species are placed in Acariscus.