Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Proceedings
Publication Acceptance Date: November 1, 2003
Publication Date: April 1, 2004
Citation: Moran, P.J. 2004. Opportunistic and plant-mediated interactions between neochetina spp weevils and the fungal pathogen cercospora piaropi fungi on waterhyacinth (eichhornia crassipes). International Symposium on Biological Control of Weeds. (Proceedings) Interpretive Summary: Waterhyacinth is a non-native floating plant imported from South America over 100 years ago that is now causing serious weed problems in the Rio Grande, irrigation canals and reservoirs in the Lower Rio Grande Valley of Texas and throughout the southeastern U.S. USDA scientists released two waterhyacinth weevils as biological control agents in the 1970s. The weevils feed on the leaves and can reduce plant growth, flowering and reproduction. A fungal disease native to the U.S. causes brown spotting on leaves and also reduces the ability of waterhyacinth to cause problems. How do the weevils and the disease interact when they attack the plant at the same time? This study found that high levels of spotting on old leaves lead to more beetles feeding scars on tender young leaves. However, levels of spotting and scarring vary a lot between four field sites and within sites. Might there be an explanation inside the plant? This study found that waterhyacinth plants with high levels of spotting also had high levels of peroxidase, an antioxidant enzyme in the plant, and higher levels of the mineral, potassium. Phenolics, a type of chemical the plant makes that reacts with peroxidase, were lso higher in concentration in plants with lots of spots. A properly timed human release or a natural infestation with a combination of the fungus that causes spotting and the weevils will likely improve biological control of waterhyacinth.