Insect damage to and mortality of seedlings of Chenopodium album L. and Fallopia convolvulus (L.) Á.Löve

During 1997-1999, the damage and mortality caused by insect herbivores to pigweed (Chenopodium album) and wild buckwheat (Fallopia convolvulus) were studied in an early fallow field at Prague-Ruzyně. The highest abundances of Ch. Album and F. convolvulus (83 and 3.5 plants/m2, resp.) were recorded in 1999, the lowest (11.6 and 0.3 plants/m2, resp.) in 1998. Mortality was low in 1997 (9.6% and 1.4%, resp.) and 1999 (4.0% and 2.5%, resp.), but high in 1998 (25% and 10%, resp.) due to concurrent drought. In accordance with previous studies on Thlaspi arvense, herbivory and concurrent drought may increase the mortality of Ch. Album and F. convolvulus seedlings, and thereby alter the species composition of the weed community during secondary succession.