ABSTRACT Neochetina eichhorniae Warner and N. bruchi Hustache, biological control agents of Eichhornia crassipes (Martius) Solms-Laubach, are usually incapable of flight but occasionally develop indirect flight muscles enabling dispersal. This reportedly alternates with oogenesis and is reversible. We examined host quality as a possible explanation for the transitions between these 2 states by allowing populations of the 2 species to develop on plants differing in nutritive quality and then examining the status of their ovaries and flight muscle development. The leaf nitrogen content of the plants increased directly with fertilizer treatment levels but herbivory by the weevils changed the pattern of variation. Neochetina eichhorniae suppressed overall nutritive quality while still enabling tissue nitrogen levels to increase with fertilizer treatments. Neochetina bruchi, however, negated these effects and tissue nitrogen levels failed to correlate with fertilizer treatments. As a result, herbivore intensit...