SPECIFICITY OF THE HOST-INDUCED NEGATIVE PHOTOTAXIS OF THE SYMBIOTIC WATER MITE, UNIONICOLA FORMOSA

The water mite Unionicola formosa (Acarina: Unionicolidae) exhibits positive phototaxis when free of any chemical influence of its molluscan host, Anodonta imbecilis. When mites are exposed either to water from the host's mantle cavity or to an homogenate of host mantle tissue, the sign of their phototaxis reverses to negative. The behavioral threshold concentration of mantle homogenate that induces negative phototaxis to monochromatic light is approximately 0.7 µg protein/ ml. Negative phototaxis does not occur in the presence of any chemical influence of the bivalves Elliptio complanata or Anodonta cataracta, neither of which species harbors this symbiont at the study site. A component of mantle tissue from Anodonta imbecilis that elicits the negative phototaxis is heat labile, sensitive to trypsin, and has a molecular weight in excess of 10,000 daltons.