Feeding of the panphytophagous oribatid mite Scheloribates laevigatus (Acari : Oribatida) on cyanobacterial and algal diets in laboratory experiments

The feeding of Scheloribates laevigatus on green algae and cyanobacteria wa s observed under laboratory conditions using food preference tests, microan atomy of the digestive tract and epifluorescence microscopy. The level of c onsumption of the algal species studied - Klebsormidium flaccidum, Protosip hon botryoides, Chlorella ellipsoidea and Desmococcus vulgaris - differed. The cyanobacterium Trichormus variabilis was rejected by the mite. The most preferred alga D. vulgaris (syn. Protococcus viridis) was digested only pa rtly, in a manner similar to C. ellipsoidea. Probably, only the contents of cells mechanically damaged by chelicerae were digested, as living cells we re observed in faecal pellets on both diets. On the other hand, no living c ells of K. flaccidum and P. botryoides were detected after gut passage. Int act cell walls of ruptured cells of P. botryoides, C. ellipsoidea and D. vu lgaris were found in the faecal pellets in the rectum. K. flaccidum cell wa ils were observed in the food boli in the mesenteron, but they were more fr agmented in comparison with Tt botryoides cell walls. This indicates that t he observed algal cell walls were not digested, while the contents were. Th e starch inside the algal cells seems to be the main energy source for the mites. Extrapolation to natural conditions is discussed. Although S. laevig atus is regarded as a fungivorous grazer, its feeding on algae indicates an alternative feeding guild for this species - algivorous browser. (C) 2001 Elsevier Science B.V. All rights reserved.