Submitted to: Texas Aquatic Plant Management Society
Publication Type: Abstract Only
Publication Acceptance Date: July 10, 2005
Publication Date: July 10, 2005
Citation: Moran, P.J. 2005. Potential for insect vectoring of a plant pathogenic fungus to improve biological control of waterhyacinth. Aquatic Plant Management Society Meeting Program. p.57.
Biological control of floating waterhyacinth (Eichhornia crassipes) worldwide has been aided by the introduction of two weevils, Neochetina eichhorniae and N. bruchi. In the U.S., several native plant pathogens have developed host associations with waterhyacinth, including the fungus Cercospora piaropi, which causes necrotic spotting on leaves. Applications of small amounts of spores of C. piaropi to weevils, followed by field releases of inoculated weevils, could lead to additive or synergistic biological control and avoid the need for costly large-scale foliar applications of fungi. Field site sampling in 2004 confirmed our earlier reports of a positive correlation between leaf scarring by waterhyacinth weevils and leaf coverage with spots indicative of C. piaropi infection. In laboratory trials, Neochetina spp. weevils readily transferred inoculum to culture plates by walking on inoculated plates, or by being sprayed with spore suspensions and allowed to dry. Weevils remained capable of infecting plates for at least two weeks after spray inoculation. Plants in greenhouse tanks and field tanks infested with pre-inoculated weevils developed C. piaropi symptom levels equal to the levels produced by simultaneous infestation with non-inoculated weevils and foliar application of the fungal suspension. Plants in tanks receiving inoculated weevils had lower numbers of leaves and reduced biomass than did plants receiving non-inoculated weevils. Formulation technology and another pathogenic fungus (Acremonium zonatum) will be used to further improve weevil-fungus vectoring relationships, and to increase their role in biocontrol of waterhyacinth.