ABSTRACT
One insect considered to be most promising from the standpoint of host specificity and potential for control of water hyacinth is the weevil Neochetina bruchi Hustache. During the course of study it was discovered that two species of weevils were involved, N. bruchi and a new species, N. eichhorniae Warner. A third species of Neochetina was found associated with Eichhornia azurea, N. affinis Hustache. Plant quality is an important factor in the growth and development of Neochetina. In this regard, competitors can change plant quality to the point that the plants no longer provide suitable shelter for the adult weevils, although the leaves may still be acceptable as food. Among the competitors which produce this effect are two genera of scarab beetles, Cyclocephala and Dyscinetus. There is considerable variation among the populations of Neochetina in Argentina. The variation depends on time of year and location. During the summer in Tigre the population increased to more than one insect per plant.
