Mud-puddling in the yellow-spined bamboo locust, Ceracris kiangsu (Oedipodidae: Orthoptera): Does it detect and prefer salts or nitrogenous compounds from human urine?

C. kiangsu adults were observed visiting human urine, especially on hot summer days. The main chemicals in fresh human urine include inorganic salts and CO(NH2)2. When human urine was incubated, NH4HCO3 became the richest nitrogenous compound. The phagostimulants, repellents and attractants in urine were identified here. On the filter papers treated with fresh or incubated urine samples, the 5th instar nymphs and the adults started and continued gnawing around the edges, in contrast to the 3rd and the 4th instar nymphs. The consumed areas were dramatically greater on the filters treated with the urine samples incubated for 3–6 days. The feedings of both male and female adults were also stimulated by several urine-borne components such as NaCl, NaH2PO4, Na2SO4, KCl, NH4Cl and NH4HCO3 but not by CO(NH2)2. Among them NaCl was the most powerful phagostimulant. The repelling, or attractive/arresting effects of CO(NH2)2 and NH4HCO3 were also evaluated by a two-choice test. When exposed to water- and CO(NH2)2 solution-immersed filters simultaneously, the adults prefer to stay on water-immersed filter. In contrast, when provided water- and NH4HCO3 solution-treated filters, the adults prefer to stay on NH4HCO3 solution-treated filter. This demonstrated that CO(NH2)2 acted as a repellent and NH4HCO3 as an attractant/arrestant. In the bamboo forest, similar feeding behavior was also elicited by NaCl, NH4HCO3 but not by CO(NH2)2. Comparing to NaCl solution, a mixed solution of NaCl and CO(NH2)2 (1:1) significantly decreased the consumed area of the treated filters whereas a mixed solution of NaCl and NH4HCO3 (1:1) dramatically increased the consumed area. These results demonstrated that the phagostimulatory effect by NaCl was reduced by CO(NH2)2 in fresh urine and was enhanced by NH4HCO3 in incubated urine.