Feeding impact and bionomics of the grasshopper Cornops aquaticum on the water hyacinth Eichhornia crassipes in Central Amazonian floodplains

Cornops aquaticum (juveniles, adults) was monitored on 5 m(2) of floating Eichhornia crassipes in a whitewater floodplain near Manaus during one year. Its abundance and biomass varied as a consequence of changing host plant densities caused by the flood pulse of the Solimoes/Amazon River. During rising waters C. aquaticum usually exhibited five nymphal instars, while during falling waters there were six instars. Average development from oviposition to adult took 71 or 81 days, respectively, the nymphal phase lasting 41 or 54 days. Longevity was 3.2 months in males and 5.8 months in females. The average food intake per g dry weight (dw) grasshopper (five nymphal instars) per day was approximately 0.9 g dw of Eichhornia leaves. Given a daily net primary production of 15 g m(-2)dw of E. crassipes, estimated food intake was 16.7%. This feeding impact could not prevent mass development of floating Eichhornia stocks.