Biological agents which accelerate winter decay of Eichhornia crassipes in the northeastern of Argentina.

POI DENEIFF, ALICIA SUSANA GUADALUPE; CASO SYLVINA LORENA

Eologia e Manejo de Macrófitas Aquáticas

Editora da Universidade Estadual de Maringá

Lugar: Maringá, Brasil; Año: 2003; p. 127 - 144

In this paper we listed the species that feed on aquatic plants in the northeast of Argentina, and we put the emphasis on the effect caused by herbivorous insects on Eichhornia crassipes which is dominant in many Paraná River floodplain lakes. The studies were carried out between March 1997 and March 1998 in two lakes and in an artificial reservoir which plants presented differences in their vigour (proportion of dry leaves and nutritional quality) and density (number of leaves per area). At each site, 3 monthly samples were taken at a distance of 5 m from the edge along a transect, with a ring of 3,000 cm2. The vigour of E. crassipes populations was evaluated by counting the total number of leaves by m2 and the percentage of green, standing dead and wilt leaves. From the comparison among sites, it is observed that in the natural lakes, linked to the hydrodynamics of the Paraná river, there was a higher proportion of leaves attacked by herbivores. Two species of Neochetina (N. bruchi and N. eichhorniae) produced damage throughout the year, affecting 81 to 98 % of the total leaf number while the number of tunnels bores by Thrypticus sp. was low in September, when the annual outbreak of the host population began. The larvae of Thrypticus prefers the leaves of largest size (more mature) and the petiole base, until a height lower than 14% of the total height of the leaves.The highest population density of Neochetina spp, the highest number of tunnels of Thrypticus per leaf, and the highest damage index were recorded in the fall, when the decay in the annual biomass curve and the maximum detritus accumulation of E. crassipes. are produced.