Studies on the life history ofRiccardoella limacum(Schrank) (Acari-Trombidiformes)

Abstract

Summary R. limacum is associated with pulmonate molluscs and is commonly called the slug mite. It belongs to a family of Trombidiform mites referred to as the Ereynetidae. Previous work on life cycle studies in this family is briefly reviewed. In the present study the life cycle of this mite has been studied from the following aspects: (A) The use of the genital region as a criterion in distinguishing the various stages in the life cycle, (B) results of studies on the life cycle in the laboratory, and (C) the occurrence and frequency of the various life cycle stages collected from slugs. Adult females lay eggs which hatch to larvae in up to 3 days at 25°C. Three nymphal stages are recognized in the life cycle namely protonymph, deutonymph and tritonymph followed by adult males or females, all separable on the basis of the number and type of genital and aggenital setae. Adults occur in by far the largest numbers in populations collected from slugs at different times of the year. There is no evidence that the deutonymph contains the eggs, that it is neotenous or that the adult stage is disappearing from the life cycle. Adult females normally contain the eggs and are oviparous only. The life cycle and structure of the various stages appears closely to resemble those described by Grandjean (1939) for other ereynetids and by Brickhill (1958) for two species from a closely related family of tydeid mites.