The effects of high concentrations of sodium in the drinking medium of the American cockroach Periplaneta americana (L.)

Abstract

1. 1. The concentration of sodium in the haemolymph of the American cockroach increased as the concentration of sodium in the experimental drinking solution increased. It was highest in the 700 mOsmole maintained animals. 2. 2. Over a 7-day period, the osmolality of the haemolymph increased in animals maintained on experimental solutions hyperosmotic to their blood. The cockroaches maintained their haemolymph hyposmotic to the experimental medium when drinking at all concentrations hyperosmotic to their blood. 3. 3. Cockroaches maintained on experimental solutions of less than 700 mOsmoles were found to survive for at least 10 days. Those at 700 mOsmoles perished before 10 days. 4. 4. Animals maintained on 700 mOsmoles experimental solution imbibed significantly more experimental fluid than those which drank more dilute solutions. 5. 5. The cockroaches' ability to hyporegulate their blood is discussed with relation to possible mechanisms of salt and water balance in insects.