Persistence of Biological Control Agents in Waterhyacinth Following Herbicide Application

Authors: Goode, Ashley; Tipping, Philip; GETTYS, LYN - University Of Florida; Knowles, Brittany; VALMONTE, RYANN - University Of Central Florida; Pokorny, Eileen

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2019
Publication Date: 4/15/2020
Citation: Goode, A.B., Tipping, P.W., Gettys, L., Knowles, B.K., Valmonte, R., Pokorny, E.N. 2020. Effect of refuges on the fate of biocontrol agent populations. Florida Entomologist. 103(1):132-135. https://doi.org/10.1653/024.103.0423.
DOI: https://doi.org/10.1653/024.103.0423

Interpretive Summary: In Florida, waterhyacinth (Pontederia [Eichhornia] crassipes) (Martius) Solms Laubach (Liliales: Pontederiaceae) is primarily controlled by herbicides but overall control is enhanced by biological control agents that decrease growth and reproduction and increase herbicide efficacy. However, herbicide applications disrupt the populations of these insects when applied indiscriminately. Previous studies identified the utility of preserving populations of biological control agents in the vicinity of herbicide treated areas using refuges for the insects. The objective of this experiment was to see how refuges of untreated P. crassipes affect the populations of biological control agents and subsequently, how those populations impact the regrowth of the new weed mat post-treatment. Pontederia crassipes mats were grown with and without biological control insects then treated with two concentrations of herbicide. Plant growth metrics and insect densities were monitored pre- and post-treatment and compared using t-tests, ANOVA, and non-parametric tests. Results indicated that insect populations rebounded in tanks post-herbicide treatment without additional insect releases and those treatments with biocontrol agents produced less dense P. crassipes mats with lower MRGR than the control treatments. This type of refuge system could easily be integrated into the current management regime of P. crassipes.

Technical Abstract: In Florida, waterhyacinth (Pontederia [Eichhornia] crassipes) (Martius) Solms Laubach (Liliales: Pontederiaceae) is primarily controlled by herbicides but overall control is enhanced by biological control agents that decrease growth and reproduction and increase herbicide efficacy. However, herbicide applications disrupt the populations of these insects when applied indiscriminately. Previous studies identified the utility of preserving populations of biological control agents in the vicinity of herbicide treated areas using refuges for the insects. The objective of this experiment was to see how refuges of untreated P. crassipes affect the populations of biological control agents and subsequently, how those populations impact the regrowth of the new weed mat post-treatment. Pontederia crassipes mats were grown with and without biological control insects then treated with two concentrations of herbicide. Plant growth metrics and insect densities were monitored pre- and post-treatment and compared using t-tests, ANOVA, and non-parametric tests. Results indicated that insect populations rebounded in tanks post-herbicide treatment without additional insect releases and those treatments with biocontrol agents produced less dense P. crassipes mats with lower MRGR than the control treatments. This type of refuge system could easily be integrated into the current management regime of P. crassipes.