Technical Abstract: Insect biological control agents of weeds may aid infection by plant pathogens by generating wounds or vectoring. Pathogen infection may lead to plant biochemical changes that alter host suitability for insects. In waterhyacinth (Eichhornia crassipes), adult Neochetina bruchi and N. eichhorniae weevils feed mostly on immature leaves, while symptoms of infection by Cercospora piaropi, a fungal pathogen, occur mostly on old leaves. This study examined associations between weevil scarring and spotting (necrosis) on leaves, and determined if necrosis is associated with levels of biochemical factors that may influence weevil feeding. Scarring and necrosis scores were positively correlated across four field sites sampled at four times. Two of the four sites tended to have higher scarring and necrosis scores, but scores were not correlated at individual times. Total available carbohydrate (TAC), potassium and phenolic contents did not vary across sites in a manner consistent with necrosis scores. Peroxidase activities and potassium levels in furled leaves were positively correlated to necrosis scores in oldest nonsenescent leaves. Phenolic content in late-season samples was also correlated to necrosis. Prior C. piaropi symptom production on old leaves of cultivated plants did not influence weevil feeding on young leaves. Infection and symptom production does not alter the feeding of weevils by changing plant biochemical components.